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Books > Extreme Waves >
In the interests of
economy and to make the book more “Reader Friendly,” the publisher had me
delete certain sections of the manuscript. I include some of this material
for the benefit of the reader who would like to explore the subject more
deeply, or who is curious about the supporting data for some of the
conclusions drawn in the book
-Craig B. Smith
From the Preface:
First, a word about
units. Today the world standard is the International System of units,
referred to as SI, and based on the meter as the unit of length. For the
convenience of the reader I show both SI and American/British units. These
approximate equivalents will help in visualizing distances and dimensions.
One meter, roughly one yard or 3 feet. A nautical mile, roughly 2
kilometers, slightly greater (15 percent more) than a statute mile. A knot
(one nautical mile per hour), roughly 2 kilometers per hour. Most
important, a nautical mile is equivalent to one minute (60 minutes to the
degree) of latitude. Finally, conversion factors are found in the Appendix
2.
From Chapter 1
A Brief History of
Ocean Exploration
Despite the dangers, humans continued to
explore the oceans for a thousand years beyond the time of Homer, staying
close to shore at first, then gradually venturing farther and farther
offshore, seduced by the traditionally calm waters and idyllic weather of
the Mediterranean. In 1,000 B.C the Phoenicians took control of the
Mediterranean and made it a Phoenician lake. In their galleys, some 20
meters (57 feet) long, they explored the shores of the Mediterranean Sea,
established cities, and eventually made their way to the Atlantic Ocean.
If we believe Herodotus, a Phoenician crew was the first to circumnavigate
Africa, taking three years to pass from the Red Sea, down the east coast,
around the Cape of Good Hope, and back through the Straits of Gibraltar.[1]
The Greeks learned much about sailing and navigation from the Phoenicians,
who, having no compasses, navigated by the North Star. From 800 to 1000
A.D. another group of hardy oceanfaring adventurers emerged in northern
Europe. From Scandinavia, Viking raiders reached England, France, and
Spain, and traveled east to parts of Russia and coastal areas of the
Baltic Sea. Piloting sturdy but light oceangoing vessels 20 to 24 meters
(57 to 79 feet) long, they crossed the North Atlantic Ocean to Iceland and
Greenland, and reached North America (Newfoundland) around 1000 A.D. At
this same time, but half a world away, China was turning out the world’s
best sailors and navigators. The Chinese developed paper, produced
accurate nautical charts, used astronomy for navigation, and began to
explore the South China Sea. Chinese junks—some as long as 45 meters (148
feet) — were the most reliable oceangoing vessels built up to that time.[2]
When the Ming Dynasty emperor Zhu Di came to
power, he rewarded several servants who had served him well. One, named
Cheng Ho was put in charge of a shipbuilding program. At a shipyard in
Nanking, Ho saw to the building of hundreds of vessels—some as long as 150
meters (492 feet)—to create a Treasure Fleet that was to explore all of
the known oceans and develop trade with foreign nations. Cheng Ho led
seven expeditions between 1405 and 1433, traveling south to cross the Bay
of Bengal, the Arabian Sea, and the Indian Ocean and to the north, the
East China Sea and the Sea of Japan. In the west, he reached the east
coast of Africa, near the site of Mombassa, and in the northwest,
traversed the Red Sea as far as Mecca and into the Persian Gulf. He also
visited Sumatra, Indonesia, Thailand, and Borneo.
In 1424, the emperor (who had changed his
name to Yong Le) died. The emperor’s son, Zhu Gaozhi, discontinued the
voyages of the Treasure Fleet. But when he died, his son Zhu Zhanji (Zhu
Di’s grandson) came to power and gave the order to resume the trips. Cheng
Ho died on the way home following the seventh voyage, and the emperor
closed the shipyard and idled the fleet.[3]
The Chinese withdrew into isolation. Even the
construction of oceangoing vessels was eventually banned, and their great
seafaring abilities and traditions faded into oblivion. Arab traders took
the place of the Chinese, and by 1400 A.D. were in control of the trade
routes and principal ports in the Indian Ocean. Their range extended from
the Red Sea and Persian Gulf south to eastern Africa and the Spice
Islands, but they feared venturing into the unknown of the South Atlantic.
Meanwhile, the Portuguese were exploring
southward, establishing bases along the west coast of Africa, and in 1488
Bartolomeu Diaz rounded the Cape of Good Hope. This set the stage for
Vasco da Gama to round the Cape and finally reach India (1498), in an
effort to reduce dependence on Arab traders for the spices and other
valued products from the Orient. Portuguese success led to Spanish
concerns that the Portuguese would dominate the lucrative trade with east
Asia, and eventually prepared the way for Columbus to prevail in his quest
for royal approval of a voyage west—the ‘backdoor’ route to the Spice
Islands and the riches of the Orient.
Discoverers of New
Worlds—Columbus and Magellan
Contrary to popular belief, Columbus did not
simply sail west on the spur of the moment because he believed the earth
was round and everyone else thought it was flat. Educated people of
Columbus’s time knew that the earth is round. Moreover, Columbus had made
a number of trips south along the west African coast, becoming familiar
with the wind patterns and reasoning that the same winds that drove
vessels south could also drive them west. He lived on and sailed from the
islands of Madeira already nearly 500 nautical miles (900 kilometers) from
the mainland and had visited the Canary Islands and the Azores, still
farther out into the Atlantic. Columbus observed that the plants growing
on Madeira and the Azores had no counterpart on the mainland, and
concluded that they must have come from seeds carried by the prevailing
currents from islands or continents to the west.[4]
He had sailed north to England and Ireland and knew how the winds and
currents behaved in the North Atlantic. Columbus’s great achievement was
that he recognized that there was something different about the winds that
originated around the Canary Islands. Here were winds that were westerly,
and constant, as opposed to the variable winds encountered sailing down
the coast. Without realizing it, Columbus had discovered the northeast
trade winds.
Upon departing from Spain, Columbus first
sailed southwest along the coast of Africa until he reached the Canary
Islands, then turned west. He planned for a voyage of 28 days, thinking
that would suffice for the voyage to the Orient (Japan) that he
anticipated was a mere 2,400 nautical miles (4,444 kilometers) distant. He
arrived at this conclusion through a series of errors—using some incorrect
data to start with—and then reduced the numbers still further for what can
only be described as “marketing” purposes: to sell the voyage to his royal
sponsors. As it was, the distance Columbus estimated for Japan was almost
exactly the distance to the Bahamas, where he made his first landfall on
October 12, 1492.[5]
His passage across the Atlantic was
remarkable. His log shows days of steady sailing at speeds of 6, 8, even
10 knots through calm seas.[6]
No major storms were encountered. Columbus kept two logs: a private one,
in which he tracked his actual position, and a second one, which he shared
with the crew. In the latter, he deliberately reduced the distance they’d
traveled from Spain, fearing that if the crew believed the distance to be
too great they would become convinced there was no way for them to sail
home and would panic and mutiny. Columbus knew that they could return by
first sailing northeast to catch the westerlies—the winds that blew east
across the Atlantic, and that is exactly what they did.
Columbus’s accomplishment excited the world
and triggered an age of exploration. Others followed in his
footsteps—Cabral, to the coast of South America and then on to the
discovery of Brazil in 1500. Then, 19 years later, came Magellan’s epic
voyage. Fernão Magalhães was Portuguese, and like Columbus, sought the
support of Spain when Portugal refused to support his grand plan to go
east by sailing west. Eventually he secured the support needed, and on
September 20, 1519, sailed from Spain and into the Atlantic with an armada
of five vessels, known thereafter as the Armada de Molucca. Six months
later, battered by recurring storms that had nearly sunk the fleet, and
realizing he could not find the magical strait to the Spice Islands before
winter fell on the fleet in its full fury, he resolved to find a safe
place to spend the winter. This turned out to be a protected harbor near
the tip of Argentina, known today as Puerto San Julian.[7]
But Puerto San Julian provided only temporary
relief to Magellan; within days he faced mutiny on three of his five
ships. He successfully quelled the mutinies and regained control. Then,
during a break in the weather he sent one ship—the Santiago—south
to look for the strait; it lingered, got caught in a storm, and was lost.
Eventually, he recovered the crew and put everyone to work repairing and
refitting the remaining vessels as best they could. On August 24, the long
southern winter finally ending, he again set sail for the south, but could
continue for only two days before being forced to seek refuge from another
series of storms. Finally, in October he set sail again, and on October
21, 1520, discovered the strait that bears his name today.
Finding this strait was one thing; navigating
it was another. With no charts to guide him and facing tides running as
high as 7 meters (23 feet), fast-paced currents, and shifting winds,
navigation became an immense challenge for Magellan. Even worse, while
Magellan continued his struggle to find the way through the straits, his
largest vessel, the San Antonio, succumbed to a mutinous navigator,
and fled the straits to make its way back to Spain. When Magellan exited
the strait on November 28, 1520, he was down to three vessels and short on
rations. He worked his way north along the Chilean coast, finally catching
the southeast trade winds near the Juan Fernandez Islands. Next came days
of calm sailing that inspired Magellan to christen the Pacific mare
pacificum—in Latin, “peaceful sea”—as the three vessels moved forward
under the constant impulse of the trade winds.
By fluke or good fortune, Magellan avoided
the thousands of islands, reefs, and atolls that abound in the South
Pacific. But he did not make landfall until reaching the Marianas Islands
(Guam), 98 days after leaving the straits. Many of the crew had died, and
all suffered from scurvy and hunger. It was now March 6, 1521.
A year and a half later—on September 6,
1522—a heavily damaged vessel was observed approaching southern Spain. It
was the Victoria, the last of Magellan’s ships, his remaining crew
finally making it home to tell the story of his epoch voyage. The other
two ships had been lost in storms; Magellan himself had been killed and
buried in the Philippines, the victim of an ill-advised fight with
natives. The 18 surviving crewmen on the Victoria could claim the
first circumnavigation of the world. And not only that, as proof of
Magellan’s acumen, they unloaded a cargo of 381 sacks of cloves,
sufficient to make the trip profitable despite the loss of three vessels.[8]
From Chapter 2
Summary of Major
currents
Note: While reading the next nine paragraphs,
it is helpful to look at a world globe or map in order to visualize the
circulation paths of ocean waters as I describe them. Alternatively,
Figure 4 (See book) may help. In the Pacific, the Kuroshio Current (an
extension of the North Equatorial Current), curves northerly past Japan
and continues clockwise between the Aleutians and the Hawaiian Islands.
Kuroshio means “black stream” in Japanese. Similar to the Gulf Stream, it
is around 100 kilometers (62 miles) wide and transports large amounts of
warm tropical water north to colder zones. The Kuroshio Current can reach
speeds of 3 to 4 knots. The confrontation of this stream with storms
coming down from the north is one of the sources of giant waves.
Continuing the clockwise circulation, this current becomes the Northern
Pacific Current, which branches, a portion turning north along Canada and
Alaska, eventually forming the Alaska and Aleutian Currents, other sources
of giant waves. The southern portion becomes the California Current
flowing southeastward and down the coast of California and Baja California
at an average speed of 0.8 knots, eventually merging back into the North
Equatorial Current flowing west. During the winter, a weak countercurrent,
called the Davidson Current, flows northwestward from Baja California to
British Columbia.
The South Equatorial Current behaves
similarly, curving southward along Australia, where it is known as the
East Australia Current, past New Zealand, and eventually back toward the
tip of South America, where it divides, a portion flowing into the
Atlantic Ocean and the balance flowing northward along the west coast of
South America as the Humboldt Current.
In the Atlantic, that portion of the South
Equatorial Current that flows north along South America merges with the
North Equatorial Current and flows between the Windward Islands into the
Caribbean Sea, heading westerly toward the Yucatan Peninsula and then into
the Gulf of Mexico, where it creates a variable Loop Current that
circulates in the Gulf of Mexico. Near the Straits of Florida, this
current, the Antilles Current, and others merge to form the Gulf
Stream. The confluence of several powerful currents in the Gulf of Mexico
and their passage in the Gulf and around Cuba, then through the Straits of
Florida and the Bahamas, is often responsible for changeable and dangerous
weather conditions.
The Gulf Stream, first identified by Dampier
and later described by Benjamin Franklin, is remarkable for the volume of
warm water it carries northward and its distinctive deep blue color. It is
80 kilometers (50 miles) wide but can form eddies and snaking as it
meanders. Its speed is 2 to 4 knots off of the coast of Florida, but can
be as much as 4 to 5 knots. It moves northeasterly past the Grand Banks,
eventually becoming the North Atlantic Current. In the eastern Atlantic
this current divides, one portion branching northeast toward
Iceland and Norway (the Irminger Current and Norway Current), another
portion going north along the west coast of Greenland, and still another
portion moving east and then south toward the Canary Islands as it is
deflected by the coast of Europe. It eventually rejoins the North
Equatorial Current.
This pattern of clockwise circulating
currents in the Atlantic Ocean is remarkable in another respect. In the
central region bordered by the currents is a large eddy, bounding an area
with no significant currents. This is known as the Sargasso Sea because of
the large quantities of sargassum (a kind of seaweed) encountered there.
In the South Atlantic, the current moves
south along Brazil, encounters the Falklands Current, and then curves east
toward the Cape of Good Hope, where a portion turns north along the west
coast of Africa as the Benguela Current. The Benguela Current is further
strengthened by part of the Agulhas Current coming from the Indian Ocean
and around the tip of South Africa creating a strong current that flows at
speeds of around 0.33 knots.
In the Indian Ocean, the situation is similar
to that in the Pacific and Atlantic Oceans—two west-flowing equatorial
currents dominate. In the northern Indian Ocean (the Arabian Sea and Bay
of Bengal) some of the prevailing currents reverse direction from winter
to summer; for example, the Somali Current reverses direction in the
northern hemisphere summer and flows north at 5 knots or more. In the
southern Indian Ocean, the South Equatorial Current flows toward Africa,
divides as it flows south around Madagascar, then rejoins to form the
powerful Agulhas Current that flows south around the Cape of Good Hope at
speeds of 3 to 4 knots. Of this, we shall learn much more later.
The Southern Oceans of Antarctica are the
most desolate and foreboding of all. The Antarctic Circumpolar Current
flows west around the entire world, no continents obstructing its
movement, driven by the strong prevailing winds. It is fed by waters from
each of the oceans—the Brazil Current, the Agulhas Current, and others—and
transports waters between them.
In the Artic Ocean, on the Pacific side,
there is a weak current north through the Bering Strait and a southerly
flow along Siberia that becomes the Kamchatka Current. From the Atlantic,
a current flows northeasterly along the coast of Norway into the Arctic
Ocean, then turns north, crosses the North Pole, and emerges along the
east coast of Greenland as the East Greenland Current flowing back into
the North Atlantic.
Here I beg the reader’s indulgence for this
seemingly lengthy description of currents, which I have tried to make as
concise as possible. (For the seasoned sailor or navigator, please ignore
the omissions; they do not contribute materially to the purposes of this
book.)
From Chapter 2:
The Beaufort Wind
Scale
The Beaufort Wind Scale
|
Wind
force |
Wind
Description |
Wind
speed
m/sec knots |
Wind effect on the sea |
Probable wave
height meters
Average Max |
|
0 |
Calm |
0-0.2 <1 |
Sea
like a mirror |
-- -- |
|
1 |
Light air |
0.3-1.5 1-3 |
Scaly ripples without foam crests |
0.1 0.1 |
|
2 |
Light
breeze |
1.6-3.3 4-6 |
Small wavelets, glassy, non-
breaking crests |
0.2 0.3 |
|
3 |
Gentle
breeze |
3.4-5.4 7-10 |
Large wavelets, crests begin to
break, scattered white horses
(plumes of spray) |
0.6 1.0 |
|
4 |
Moderate breeze |
5.5-7.9 11-16 |
Small waves with frequent white
Horses |
1.0 1.5 |
|
5 |
Fresh
breeze |
8-10.7 17-21 |
Moderate waves, many white
Horses |
2.0 2.5 |
|
6 |
Strong
breeze |
10.8-13.8 22-27 |
Large waves, white foam crests,
some
spray |
3.0 4.0 |
|
7 |
Near
gale |
13.9-17.1 28-33 |
Mounting sea with foam blown
in
streaks down wind |
4.0 5.5 |
|
8 |
Gale |
17.2-20.7 34-40 |
Moderately high waves, crests
begin to break into spindrift |
5.5 7.5 |
|
9 |
Strong
gale |
20.8-24.4 41-47 |
High
waves, dense foam along
direction of wind; crests begin
to
topple over, spray can affect
visibility |
7.0 10 |
|
10 |
Storm |
24.5-28.4 48-55 |
Very
high waves with long over-
hanging crests. Heavy sea roll,
sea
surface white, limited visibility |
9.0 12.5 |
|
11 |
Violent
storm |
28.5-32.6 56-63 |
Exceptionally high waves. Other ships lost to view. Sea completely
covered with foam patches downwind. Poor visibility |
11.5 16.0 |
|
12 |
Hurricane |
>32.7 >64 |
Huge
waves. Air filled with foam
and
spray. Sea completely white with driving spray, visibility bad |
14.0
19
and greater |
Source: Based on Observer’s Handbook, UK
Meteorology Office
Today, the Beaufort Scale has been
supplemented by the Universal Sea State Code. Under this system, SS0 (sea
state zero) is described as “Sea like a mirror, wind less than one knot,
wave height zero; SS4 is “Rough sea; moderate waves, many crests break,
whitecaps, some wind-blown spray; winds moderate to strong breeze, 11-27
knots; wind whistles in rigging, average significant wave heights 1.2 to
2.4 meters (4 to 8 feet).” SS8 is “Mountainous seas; very high-rolling
breaking waves; sea surface foam-covered; very poor visibility; winds at
storm level, 55-63 knots; waves 9.1 to 13.7 meters (30 to 45 feet.)”
Excerpt from Chap 3
Probability of Large
Waves
If we consider waves as an example of a
stochastic process—a process that follows some form of a probability
distribution—wave behavior can be analyzed statistically but cannot be
predicted precisely. In other words, weather forecasters are unable to
say: “A 20-meter wave will occur at such and such a location at such and
such a time,” but they can say something like this: “There is likelihood
that 8 percent of the waves that occur in a year at this location will be
20 meters or higher.”
Now the question becomes, What kind of
probability distribution? Research has found that in deep water, the
height of small ocean waves obeys a Gaussian process, named after Karl
Friedrich Gauss (1777-1855), a German mathematician. In the Gaussian
process, the height of the waves follows a normal distribution.
While the term may seem intimidating, we’re
all familiar with a normal distribution, sometimes called a “bell curve”
due to its shape. A case in point: a teacher believing a class to be large
enough that the students’ abilities (or perhaps study habits) were a
Gaussian process, might grade “on the curve.” Another case in point: An
engineer cuts 1,000 samples from the same batch of steel reinforcing rod,
places them in a testing machine, and pulls on them until they snap. The
test results show that most break at a tensile force of 80,000 pounds per
square inch. However, some break as low as 70,000, others withstand
90,000. If the test results are graphed, a bell-shaped curve results. A
normal distribution has a mean value; in the example cited above,
this would be 80,000.
I stated earlier that weather forecasters
report wave heights as Hs, defined as the average of the
highest one-third measured (or predicted, in the case of forecasts) wave
heights. To estimate this value, a further assumption is needed—that is,
that the Gaussian process is narrow banded. This means that the wave
energy is grouped within a narrow band of periods. Waves produced by
moderate winds in deep water have this property. For this case, wave
amplitudes follow a Rayleigh probability law.[9]
Figure 8 (See book) shows a theoretical
Rayleigh Distribution. The vertical axis measures the probability
that a particular wave height will occur, while the horizontal axis is the
wave height. The figure shows the lowest 10 percent of the waves, the most
probable wave height Hp, the average wave height HA,
the significant wave height Hs, and the highest 10 percent of
the wave heights.
Figure 8: Rayleigh Distribution of Wave
Heights[10]
The significant wave height Hs
is marked on the graph and is equal to 1.6 HAve.[11]
The probability that a wave greater than Hs will occur
is shown by the shaded area under the curve to the right of Hs.
If the mathematics is carried out, this area is found to be 13.5 percent
of the total, meaning that there is a 13.5 percent chance that a wave
greater than Hs will occur, or that roughly one in seven waves
will be larger than Hs. This result is corroborated in a number
of cases (but not all) by buoy readings and measurements on offshore oil
platforms, where hundreds of measurements of Hs and the maximum
wave for a series can be compared. Compare this to surfer’s lore, as
described in Chapter 6. Young notes that this compares favorably with the
oft-stated mariner’s view that every seventh wave in a set is larger.[12]
A mathematician would recognize that the
Rayleigh distribution goes on forever. In other words, there is a
vanishingly small probability of very, very large waves. If we knew how
many wave records were represented in the Rayleigh distribution, we could
estimate Hmax . When the number of waves is not known, an
approximate relationship is Hmax = 1.77 Hs as stated
by Muga.[13]
If the wave height is much greater than this value, it falls outside of
the range we might reasonably expect. This is what has given rise to the
term “rogue” or “freak” wave. In a random sea, how many waves would it
take before you experienced Hmax? In 20 waves, there is about a
5 percent chance of reaching Hmax, and in 200 waves, a 5
percent chance of reaching 2.0Hs. An extreme wave—one greater
than 2.2 to 2.4 times Hs—has a 5 percent chance of occurring in
1,000 to 4,000 waves, assuming a constant sea.[14]
There would be 5 waves per minute, 300 waves per hour, if the waves had a
12 second period. Thus in traveling 3.3 to 13.3 hours in such a sea, a
vessel would have a 5 percent chance of experiencing an extreme wave.
During this time, at 10 knots, the vessel would have moved 33 to 133
nautical miles, hopefully to an area where Hs was smaller and
the consequences of encountering an extreme wave, less severe.
For larger waves, for variable wind
conditions, such as those associated with hurricanes, or for waves in
shallow water, more complex methods are required. As waves approach the
coast, they undergo a transition from a Gaussian to a non-Gaussian
process, and must be handled differently.[15]
Waves in shallow waters and very large waves are nonlinear and must be
analyzed by other means. Extreme waves have crests that are several times
higher than the distance from the center line to the bottom of the trough,
and they are steeper than other waves.
Figure 9 (See book) is an actual U.S.
Department of Commerce, National Oceanic and Atmospheric Administration
marine weather forecast for the North Pacific on March 7, 2005. Note the
storm centered at latitude 30 degrees north, longitude 150 degrees west,
northeast of the Hawaiian Islands. The forecast shows 40-knot winds and
waves with12.8 meter (42 foot) significant heights at the center of the
storm. These waves had a period of 12 seconds. Looks like a spot to avoid,
if you had the option. (See Chapter 5 for more about this particular
storm.)
Figure 9: Typical NOAA marine weather
wind/wave forecast
A new tool for measuring wave heights is the
satellite. As a satellite orbits the earth and passes over the oceans, it
collects a huge amount of data. Due to the sheer effort involved in
analyzing the data within a reasonable time, the data are averaged over a
period of days and a spatial grid of 2 degrees by 2 degrees (120 nautical
miles by 120 nautical miles or 222 by 222 kilometers).[16]
The practical implication of this is that individual, infrequent wave
events are not detected. Thus these data provide reliable estimates of the
significant wave height Hs on a global basis, but not the
extreme wave height, Hext. In Chapter 8 I describe more recent
research into satellite observations that have been designed to detect the
extreme wave height Hext, and the astonishing results that have
been obtained.
The satellites reveal two major bands
circling the world’s oceans where the greatest values of significant wave
height occur. These are areas where the significant
wave height is routinely almost 20 feet (6 meters.) As you might expect,
there is a distinct trend—there are more big waves in the winter. Figure
11 shows the situation in February—winter in the northern hemisphere. The
darkest area corresponds to a significant wave height of 6 meters, the
lighter shades, 4 and 5 meter heights. Note that they
encompasses a broad area of the North Atlantic, England to Newfoundland
and in the North Pacific, from the Gulf of Alaska to Japan, centered
around latitude 50 degrees north. Meanwhile, at this time—summer in the
southern hemisphere—the shaded area is centered along latitude 50 degrees
south.
Figure 10: Global significant wave heights Hs,
February
Next look at Figure 11, the same data for
August—winter in the southern hemisphere. The shaded band has broadened
into a swath of rough seas extending clear around the world, while in the
northern hemisphere the shaded areas are gone. In other words, conditions
in the Southern Ocean remain severe most of the year. Also note the
absence of large waves in the tropical zones near the equator. This area
is subject to a different condition, that of tropical cyclones. These
satellite observations are not programmed to detect such transient events
as hurricanes. (In Chapter 4 we will examine wave heights generated by
storms and hurricanes.)

Figure 11: Global significant wave heights Hs,
August
If the world’s major oceans are sliced along
a longitudinal meridian in their center, the variation of significant wave
height with latitude can be examined. If this is done, Hs
increases from around 4 meters at 60 degrees north, to 6 meters at 50
degrees north, and then declines to 2 to 3 meters (6 to 10 feet) at the
equator, again increasing to around 6.2 meters (20 feet) at 50 degrees
south latitude.
No wonder sailors call 50 degrees south “the
furious fifties.”
From Chapter 4
The Occurrence of
hurricanes
- North Atlantic and
Caribbean: from Venezuela on the south to the East Coast of the United
States and Central America on the west, Newfoundland on the north, and
eastward to Africa. Season: June 1 to November 30; peak: August to
October.
- Northeastern Pacific:
from Hawaii on the west to Mexico and Central America on the east,
between latitude 10 degrees and 30 degrees north. Season: May 15 to
November 30: peak; late August, early September.
- Northwestern Pacific:
Southeast Asia on the west, Japan and Siberia on the north, 160 degrees
west longitude as the eastern boundary, and latitude 10 degrees north as
the southern boundary. Season: July to November; peak: late August,
early September.
- North Indian Ocean:
Bay of Bengal. Season: April to December; double peak: May and November.
Severe tropical cyclones occur from April to June and late September to
early December.
- Southwestern Indian
Ocean and Australia-southeastern Indian Ocean: from the east coast of
southern Africa on the west to mid-Indian Ocean on the east, between 10
degrees and 35 degrees south latitude. Season: late October to May, with
a double peak, mid-January and mid-February to March.
- Southwest Pacific and
Australia: from Australia’s east coast and the Coral Sea , east to
longitude 180 degrees west, south to 35 degrees south latitude; also on
Australia’s west coast. Season: October to May, peak in late February,
early March.
[17]
From Chapter 4
The Saffir-Simpson
Hurricane Scale[18]
The strength of hurricanes is rated 1 to 5 on
the Saffir-Simpson Hurricane Scale based on the hurricane's intensity at
the time of reporting. The scale is used to give an estimate of the
potential property damage and flooding expected along the coast from a
hurricane landfall. Wind speed is the determining factor in the scale, as
storm surge values are highly dependent on the slope of the continental
shelf in the landfall region.
Category One Hurricane:
Winds 64-82 knots (74-95 miles per hour).
Storm surge generally 1.2 to 1.5 meters above normal. Central pressure
less than 980 millibars. No real damage to building structures. Damage
primarily to unanchored mobile homes, shrubbery, and trees. Some damage to
poorly constructed signs. Also, some coastal road flooding and minor pier
damage. Hurricanes Danny of 1997 and Gaston of 2004 were
category one hurricanes at peak intensity.
Category Two Hurricane:
Winds 83-95 knots (96-110 miles per hour).
Storm surge generally 1.8 to 2.4 meters above normal. Central pressure
975-965 millibars. Some roofing material, door, and window damage of
buildings. Considerable damage to shrubbery and trees, some trees blown
down. Considerable damage to mobile homes, poorly constructed signs, and
piers. Coastal and low-lying escape routes flood 2-4 hours before arrival
of the hurricane center. Small craft in unprotected anchorages break
moorings. Hurricane Bonnie of 1998 was a Category Two hurricane when it
hit the North Carolina coast, while Hurricane Frances was a
category two hurricane when it hit Florida.
Category Three Hurricane:
Winds 96-113 knots (111-130 miles per hour).
Storm surge generally 2.7 to 3.7 meters above normal. Central pressure
964-945 millibars. Some structural damage to small residences and utility
buildings and a minor amount of curtain wall failures. Damage to shrubbery
and trees, foliage blown off trees and large trees blown down. Mobile
homes and poorly constructed signs are destroyed. Low-lying escape routes
are cut by rising water 3-5 hours before arrival of the center of the
hurricane. Flooding near the coast destroys smaller structures, larger
structures damaged by battering from floating debris. Terrain lower than
1.5 meters (5 feet) above mean sea level may be flooded inland 13
kilometers (8 miles) or more. Evacuation of low-lying residences within
several blocks of the shoreline may be required. Hurricanes Roxanne of
1995 and hurricanes Ivan and Jeanne (2004) were category three
hurricanes at landfall on the Yucatan Peninsula of Mexico and in Alabama
and Florida, respectively.
Category Four Hurricane:
Winds 114-135 knots (131-155 mph). Storm
surge generally 4 to 5.5 meters (13-18 feet) above normal. Central
pressure 944-920 millibars. More extensive curtain wall failures with some
complete roof structure failures on small residences. Shrubs, trees, and
all signs are blown down. Complete destruction of mobile homes. Extensive
damage to doors and windows. Low-lying escape routes may be cut by rising
water 3-5 hours before arrival of the center of the hurricane. Major
damage to lower floors of structures near the shore. Terrain lower than 3
meters (10 feet) above sea level may be flooded requiring massive
evacuation of residential areas as far inland as 10 kilometers (6 miles).
Hurricane Luis of 1995 was a category four hurricane while moving
over the Leeward Islands. Hurricane Charley of 2004 also reached category
four status when it hit Florida, and most recently hurricane Katrina in
2005.
Category Five Hurricane:
Winds greater than 135
knots (155 miles per hour). Storm surge generally greater than 5.5 meters
(18 feet) above normal. Central pressure less than 920 millibars. Complete
roof failure on many residences and industrial buildings. Some complete
building failures with small utility buildings blown over or away. All
shrubs, trees, and signs blown down. Complete destruction of mobile homes.
Severe and extensive window and door damage. Low-lying escape routes are
cut by rising water 3-5 hours before arrival of the center of the
hurricane. Major damage to lower floors of all structures located less
than 4.6 meters (15 feet) above sea level and within 460 meters (1,500
feet) of the shoreline. Massive evacuation of residential areas on low
ground within 8 to 16 kilometers (5-10 miles) of the shoreline may be
required. Hurricane Mitch of 1998 was a category five hurricane at
peak intensity over the western Caribbean. Hurricane Andrew of 1992 was a
category five hurricane at peak intensity and is one of the strongest
tropical cyclones to hit Florida.
From Chapter 4
Hurricane-generated
wave heights
Stochastic methods similar to those described
in Chapter 3 can be used to forecast wave heights caused by hurricanes.[19]
Ochi suggests that hurricane-generated waves can be modeled as a Gaussian
random process, and therefore extreme wave heights can be calculated from
a known or estimated wave spectrum.[20]
The approach is to develop a wave spectrum that gives the time averaged
wave energy versus frequency. The spectra can then be correlated with the
expected wave height. The hurricane spectrum differs from an ordinary wind
spectrum because it has a sharp peak rather than being broad. If the
spectrum is measured by an ocean buoy in the path of the storm, it will
grow as the hurricane gets closer. (Figure 15).

Figure 15: Hurricane energy spectrum[21]
Note that from the initial point of
measurement, in 10 hours the significant wave height has doubled from 6.6
meters to 13.5 meters!
From Chapter 4
Wind speed change
from hurricane
Figure 16 shows the wind speed recorded at
Barrow Island, off the northwest coast of Australia, just below latitude
20 degrees south. The solid line is the mathematical prediction; the dots
are the recorded values for hurricane Ian in 1992. Note how the winds
begin to rise late on March 1, reach a maximum at 35 meters per second (66
knots) early on March 2, then drop to 5 meters per second (9.5 knots) as
the eye of the hurricane passes, and then increase again as the other side
of the storm passes over the island late on March 2.

Figure 16: Wind Speed as Eye of Hurricane
Passes[22]
From Chapter 4
Measured wave heights
during hurricanes
Figure 17 shows some of the data collected
from seven hurricanes in various stages of growth. Remember, the maximum
wave heights can be higher by as much as 30 percent or more than the
significant wave height!

Figure 17: Wave Height vs. Hurricane Wind
Speed[23]
The figure shows that
the significant wave height in meters is about one fourth (actually 24
percent) of the hurricane sustained wind speed expressed in meters per
second at the standard elevation of 10 meters above sea level.
From Chapter 4
Forecast Accuracy
National
weather services use several models for predicting the track and intensity
of hurricanes. Track forecasts are the latitude and longitude of the storm
center, while intensity refers to the maximum sustained surface wind.
Forecasts are typically issued for 12, 24, 36, 48, and 72 hours. Two main
types of mathematical models are used: one type predicts the storm track;
the second type is used to predict intensity. Some examples of models are
BAM, a computer model that tracks the early trajectory of storms; UKMET, a
global model developed by the United Kingdom Meteorological Office; and
NOGAPS, a global atmospheric model developed by the United States Navy.
For estimating intensity, the National Hurricane Center uses programs such
as the Statistical Hurricane Intensity Forecast (SHIFOR), the Geophysical
Fluid Dynamics laboratory (GFDL) model, or SHIPS. Ironically, the last
acronym stands for “Statistical Hurricane Intensity Prediction Scheme.”
Details of
these models are outside the purpose of this book; however, readers
interested in additional information are advised to consult the National
Hurricane Center Web site for an overview of the most recent models used
for forecasting. The Web site also provides references and links to more
detailed technical literature.[24]
From Chapter 5
Sources for Wave
information
There are a number of sources for wave and
weather information. Global weather forecasts for up to ten days are
provided by the European Center for Medium-Range Weather Forecasts at
http://www.ecmwf.int/. A general source for marine weather
information in the Atlantic and Pacific Oceans is http://www.nws.noaa.gov.
Another excellent source is a United States Navy Web site,
https://www.fnmoc.navy.mil/PUBLIC/WAM, commonly referred to as the
“WAM” site, features colored maps of the North and South Atlantic oceans,
the North and South Pacific oceans, and the Indian Ocean, showing wave
directions and significant wave heights. The color codes range from dark
blue for 0-1 meter, (0-3 feet) wave heights, up to dark brown 14.6 meters
(48 feet) wave heights. There is no scale to indicate 30.5 meter (100
feet) waves. The forecasts for each region extend out 6 days in 12-hour
intervals, so the movements of large waves can be anticipated. Plate 7
(See book) shows a WAM forecast for April 16, 2005, at 0 hours “Zulu”
(Greenwich) time. The biggest waves (about 11 meter or 36 feet) can be
seen at latitude 60 degrees south, off the coast of Antarctica. They can
be seen propagating north past Madagascar, in the opposite direction of
the Agulhas current, but no big waves are indicated in this region in the
forecast.
Plate 7: U.S. Navy Indian Ocean Wave Forecast
The United States National Oceanic and
Atmospheric Administration, as well as Canada, Scripps Institute, and
other entities operate a series of buoys in the northwest Pacific and
California coastal areas. These also can be accessed using the Internet.
For example, www.ndbc.noaa.gov will take you to the locations of
moored buoys scattered around the Pacific, as well as to the locations of
drifting buoys. To obtain the real time data from a buoy, click on its
image on the map. I did this for station 46006, which bears the name of
“SE PAPA.” It is a fixed buoy located 600 nautical miles west of Eureka,
California, at 40.8 north latitude and 137.5 degrees west longitude.
Reviewing the record for the last two days, I could see a clear pattern of
the wind speed building to 29 knots on March 7, with gusts to 35 knots, a
significant wave height of 5 meters, and a period of 14.3 seconds.
To see an example of a local conditions
report go to
http://facs.scripps.edu/surf/images, which will lead you to a series
of coastal buoys in the Southern California bight. On March 10, 2005, the
buoy at Goleta Point was showing the predominant swell arriving from the
west (around 260 degrees), with a dominant period of 18 seconds and a
significant wave height of 2.7 meters. Here again, the height was steadily
building.
In California, as in Hawaii, Australia,
Brazil, Tahiti, and other international surfing spots, there are
commercial services that provide surf forecasts. An example is
www.stormsurf.com. On March 8, 2005, this site predicted rising surf
on March 9 and 10. Farther south, near La Jolla, California, the forecast
indicated that select breaks with 100 percent exposure to the swell could
reach up to 1.8-2.1 meters at 17 to 20 second periods, and possibly 3-4.3
meters wave faces. For March 10, the forecast concluded with a final note:
Proceed with caution.
From Chap 7
What is the
significant wave height when multiple swells are present?
Trying to determine how
high the waves are in chaotic seas might seem to be nearly impossible, but
weather forecasters have devised methods, based on the randomness of
chaotic seas, that they use.[25]Assuming
that the significant heights of both the swell and the wind-driven sea are
known, the combined height can be approximated as the square root of the
sum of the squares, or:
Hcomb
= [(Hswell)2 + (Hsea)2]0.5
where Hcomb
is the significant height of the combined seas.
As an example, if wind
waves with Hs = 1 meter (3.3 feet) combine with a 2 meter (6.6
foot) high swell, the combined significant height would be:
Hcomb
= [(2)2 + (1)2]0.5 = [4+1]0.5
= 2.24 meters (7.33 feet)
The logic behind this
approach derives from the fact that the energy of waves is proportional to
the square of their height. This estimate is subject to the usual cautions
mentioned previously—that is, the wave heights are randomly distributed.
From Chapter 8:
Polynesian Navigation
by Wave Patterns
Any observer who spends time in the ocean
soon learns that wave patterns are more frequently complex than simple.
This fact was used to advantage by the early Polynesian navigators, who
discovered that there were repetitive patterns in the confused seas they
experienced as they ventured from island to island. The ancient
Polynesians knew that swell in the Pacific followed predictable paths,
depending on the time of year. When one of the prevailing swells struck an
island, certain wave patterns were established in a manner analogous to
the boulder in the center of a rapidly moving stream described above.
As early as the time of the first voyage of
Captain James Cook, the navigational capabilities of Polynesian sailors
became apparent. In his July 13, 1769 entry in his sea journal, Cook
relates that he was able to convince a priest and navigator named Tupia to
accompany him on the continuation of his voyage when he sailed away from
Matavai Bay, Tahiti.[26]
From his experiences with Tupia, Cook concluded that the Polynesians were
fully capable of sailing from one island to another, for a distance of
several hundred leagues (more than one thousand kilometers.) Over a period
of time, Polynesians populated a vast area of the Pacific Ocean, over 80
degrees of longitude (from 140 degrees east to 140 degrees west), or 4,800
nautical miles long, and over 60 degrees of latitude (30 degrees south to
30 degrees north, or 3,600 nautical miles wide. In most cases, they did it
on island-hopping journeys of 50 to 200 nautical miles.
How did they do it? How did they manage to
avoid deadly reefs and make accurate landfalls on remote islands without
benefit of compass, chart, or sextant?
In the 1900s it became apparent that some
navigators who knew the ancient techniques were still living, but they
were the last of a small group that was slowly dying off. In 1965, while
circumnavigating the world in a 40 foot catamaran, sailor David Lewis
learned the rudiments of their techniques, and then successfully sailed
from Tahiti to New Zealand, a distance of around 2,200 nautical miles,
without using navigation instruments. Convinced of the validity of the
methods, he returned in 1968-69 to study and document the ancient
navigation techniques, sailing in a 39 foot ketch to a number of South
Pacific islands. On these voyages he depended entirely on the skills of
several navigators whom he invited to guide him.[27]
About 15 years later after conducting some
preliminary research, a young sailor, Steve Thomas, took passage to
Satawal Island in the Caroline Island group, where he succeeded in
apprenticing himself to a navigator named Mau Piailug. Steve lived as a
member of Piailug’s family, and from him learned the navigational
techniques that had been handed down orally from generation to generation.[28]
Modern navigation uses the compass to
establish heading (direction of travel), charts to locate the position of
the vessel relative to its destination, and such instruments as
chronometers, sextants, loran, or global positioning satellites to “fix”
(determine) the position of the vessel.
In the Polynesian system, an initial heading
was established by back sighting landmarks on the departure island; from
this, an estimate of the set of the current could be made and the course
adjusted appropriately. Steering at night was done by observing the rising
or setting of known stars. During daylight or when stars were obscured by
clouds, swell patterns were used for navigation.
By lengthy training and memorization, the
navigator learned the positions of 30 or more prominent stars. During the
night the vessel was steered in the direction of a star known to rise over
the destination island. Once this star had risen too high above the
horizon to be useful for steering, the navigator steered to a second star
that rose in the same direction, or to an alternate star that was
“off-course” a known amount, for which the heading of the vessel was
adjusted.
This method is unique in another respect. In
the Polynesian navigator’s mental image, his vessel was fixed and the
destination island “moved” into position under various stars, until the
island reached a position under the star that told him he had arrived.
Contrast this to today’s navigation method whereby our vessel is moving
and the destination island is a fixed point that we seek to reach by
determining its distance and heading.
Polynesian navigators must retain a mental
image of the positions of 32 rising or setting stars, arranged in a manner
analogous to the points of a compass. Thus Polaris marks north, rising
Little Dipper (Ursae Minoris) marks roughly 15 degrees, rising Big Dipper
(Ursae Majoris), 27 degrees, rising Vega, 40 degrees. Similarly, setting
Little Dipper marks roughly 345 degrees, setting Big Dipper 333 degrees,
setting Vega, 320 degrees. Other stars fill out the remaining points on
the star map; the formal name for such a device is a sidereal compass.
Thomas describes a model of a sidereal
compass that Mau Piailug constructed on the beach with a central rock and
32 pieces of coral placed around it in a circle, each piece of coral
representing a particular star.[29]
During daylight, when no stars were visible,
the navigator made use of the ocean swell to judge the heading of the
vessel. Navigators were trained to recognize eight dominant swells. During
the winter months, dominant swells came from the northeast or east under
the influence of the trade winds. With a northerly heading and an east
swell, the navigator knew the heading was correct if the vessel rocked. On
an easterly course into an east swell, the vessel would pitch, bow rising
and then falling as the vessel rode over the swells. To maintain a
northwesterly heading, the navigator would adjust the sail and steering
oar positions until the vessel responded with a combined pitching and
rolling motion in the right proportions. The best way to do this, I’ve
been told, is to lie flat on your back on the deck and look up at a cloud
or star. The motion of the boat is easier to sense this way than staring
at the horizon.
Clearly this process required considerable
practice and skill, because, as we have seen, there are numerous waves in
a confused sea. Wind waves may ride on top of swell; there might be cross
swell from distant storms, and so on. The navigator had to discriminate to
find the dominant swell within this melee of ocean waves.
Polynesian navigators became familiar with
these patterns and in combination with the positions of the stars they
could observe overhead, used them to navigate from island to island over
long distances. The unique patterns established by the prevailing winds
and currents in the vicinity of each island enabled the navigators to
recognize where they were. To pass on the knowledge from generation to
generation, they constructed “charts” made of sticks laced together to
illustrate the wave patterns, using shells to mark the positions of
islands.[30]
Examples can be seen in the Bishop Museum, Honolulu and in the Nautical
Museum, Newport Beach, California. The most skilled navigators could sense
when they approached their destination by subtle shifts in the motion of
their vessels as the wave pattern changed.
Within 20 to 30 nautical miles of the
destination island, navigators relied on a number of different indicators.
First, waves reflected back from the island (if approaching from the
direction of the dominant swell) will cause the vessel to start a gentle
pitching motion. If not coming with the swell, the vessel will encounter
other wave patterns created by the refraction of the dominant swell as it
passes the island. Navigators were able to recognize a number of different
wave patterns; each had been given a specific name.
Other signs provide important indicators of
position. Certain seagoing birds, known to frequent specific islands,
would start appearing at distances of 20 to 30 nautical miles. Floating
vegetation and even certain species of fish could also provide positive
identification.
Once, while on a fishing trip out from Midway
Island, we’d left in the morning at dawn. Later in the day I happened to
look back in the direction of the island. The low-lying island was now
over the horizon and invisible, but its location was clearly evident by a
turquoise-green color in the clouds above it. This was caused by sunlight
reflecting the island and lagoon onto the clouds and could be seen at a
great distance. Clouds are formed by moisture-laden warm air rising over
islands. At other times, a bright column or glow can be seen on the
horizon, due to the reflection of sun or moon from shallow water or a
lagoon; this is known as the loom of land.
As the Polynesians had no means of
determining longitude, on longer voyages they usually sailed north or
south to the approximate latitude of their destination. They watched
zenith stars, or stars known to pass directly over the island to which
they were steering. Once they came abreast of that position, they would
tack and run downwind to their destination.
This is how the ancient Polynesians first
sailed from the Marquesas Islands to the big island of Hawaii. First they
sailed north to the Equator under the influence of the southeast trade
winds, struggled through the doldrums (and were probably driven west by
the Equatorial Counter Current), and then caught the northeast trades and
ran downwind to Hawaii, following the orange beacon of its zenith star,
Arcturus.
As for Thomas, he memorized the sailing
directions for various islands in the Carolines and accompanied the
Satawal navigators on several voyages to outlying islands. He carefully
documented their methods, noting the stars they used and how the wind and
swell patterns changed with the seasons. To accomplish this, he had to
become proficient in their language as well. There is, however, a certain
sadness to his book. In reading it, one senses the twilight of the ancient
skills that granted self-sufficiency to the islanders. Their sails and
canoes replaced by outboard motors, they must now hold jobs to pay for
fuel and supplies, and the old ways—those that had enabled them to
populate a vast region of Oceana—appear doomed.
In the 1970s, a group of Hawaiian researchers
constructed the Hokule‘a, a 60 foot-long replica of an ancient
Polynesian double voyaging canoe.[31]
The Hokule‘a was successfully sailed from Hawaii to Tahiti and
back.
Hokule’a departed from Honolua, Maui,
on May 1, 1976, and reached Papeete, Tahiti, 33 days later. The navigator
on that trip was Mau Piailug, whom Stephen Thomas was later to meet and
study under. Also on the crew were Ben Finney and Tommy Holmes, two of the
cofounders of the Polynesian Voyaging Society; David Lewis, who has
studied Polynesian navigation methods in the late 1960s; and 11 other crew
members. Under Piailug’s guidance, the 3,000 nautical mile trip was
accomplished without instruments. The voyage was significant because it
established beyond question that the Polynesians, using the ancient
methods of navigation, were able to explore and eventually settle vast
expanses of the Pacific Ocean.[32]
On the return trip a few weeks later, Piailug
remained behind and a different crew brought the boat back to Hawaii. In
July, this time navigating with instruments, it took 22 days to make the
trip north. The new crew included a young Hawaiian named Nainoa Thompson,
who subsequently studied navigation under Piailug and later became the
first Hawaiian navigator to guide Hokule’a on long voyages without
instruments.
With these two successful trips, there was
strong interest in further explorations, and in 1978, Hokule’a set
sail again. However, the vessel encountered rough weather almost
immediately, and before leaving Hawaiian waters, a tragedy occurred.
Through my brother, Ken Smith, a well-known water polo coach and educator
in Hawaii, I was introduced to Marion Lyman-Mersereau, who told me about
her experiences on Hokule’a.
Chapter 9: The
Pull of the Moon
(This chapter was
deleted from the original manuscript)
Imagine a wave that stretches halfway around
the world, has a period of 12 hours and 25 minutes, and is moving at
hundreds of miles per hour in the open sea.[33]
As surprising as it might seem, if you have spent any time on or near the
ocean, you’ve experienced such a wave. The crests of this wave are known
as high tides; its troughs, as low tides.
The rise and fall of tides along ocean
shores has been recognized since ancient times. When the first sailors
struck out tentatively in primitive vessels to cross bodies of water, they
knew that there were opportune moments to depart from and to return to
safe havens along the coast or in the mouths of rivers. The flow of water
caused by the tides could be a help or a hindrance to primitive craft that
depended on oars or sails for mobility. “To sail with the morning tide” is
more than an expression; it accurately states a pragmatic requirement for
moving a vessel out of many a harbor, particularly in the days before
boats were powered by engines.
Sometimes the obvious has to be relearned. In
Marina Del Rey, California, the rise and fall of the tides is noticeable
but the associated current is weak. When a sailor returns or departs from
a slip there, his concern is primarily with gauging the effect of whatever
wind might be blowing at the time. After several years of docking
Dreams at Deauville Marina in Marina Del Rey, I moved to Newport Beach
and had to find a new slip. The slip I eventually obtained was in a marina
along the main channel of the harbor. Newport Harbor is a long bay,
running roughly northwest-southeast, with the harbor mouth at the
southeast end (See Figure 23.) To the north of the main harbor is another
small boat harbor and beyond that an extensive but shallow lagoon and
wetlands known as the Back Bay. As the tide rises, water fills the main
harbor then flows into the Back Bay (a flood tide), and when the
tide falls, the process reverses and water flows out (an ebb tide).
The net effect of this is that a strong current of several knots can flow
in the main channel. The tidal range (maximum rise and fall of the water
level) is 1.2 to 2.4 meters (4 to 8 feet).
As I
approached my new slip for the first time on a Saturday, the slips on
either side of mine held boats full of people engaged in an afternoon
party. Entering the slip involved an approach from the southeast, followed
by a sharp turn to starboard. Meanwhile it was an ebb tide and a strong
current flowed down the main channel in a direction opposite to mine. As I
made the turn, the current carried Dreams sideways back in the
direction we’d just come, causing me to abort my docking operation in
close proximity to one of the parties. The spectators in that boat—now
almost close enough to step aboard Dreams—hastily grabbed their
drinks in the event of a collision, but made no effort to assist.
Fortunately, I avoided the other boats and on the third try I finally
managed to correct for wind and current and made it into the slip, where,
slightly embarrassed by my poor seamanship, I introduced myself to my new
neighbors and promised to do better next time.
Tidal Forces
The tides are caused by
balanced gravitational and centrifugal forces acting on large bodies of
water—the same forces that maintain the moon in its orbit around the earth
and the earth-moon system in its orbit around the sun. The tidal force can
be visualized by imagining that a point in the center of the Pacific Ocean
happens to lie directly beneath the moon. Here, at the point closest to
the moon, the gravitational force of the moon is strongest, and the ocean
surface will rise up, or “bulge” at this point, pulled by the moon’s
gravitational force. On the opposite side on the earth, somewhere in the
Indian Ocean, a similar bulge will be created. Since this point is more
distant from the moon, the moon’s gravitational pull is weaker and no
longer balances the centrifugal force. The unbalance allows water on the
opposite side of the earth to bulge also.
If the oceans rise up on the opposite sides
of the earth, it stands to reason that the ocean level will fall in other
locations. For example, if we imagined the moon to be directly above a
point on the equator at longitude zero degrees, and if the earth’s surface
was uniformly covered with water, the drop in water level would occur at
90 degrees west and 90 degrees east longitude. In reality, the earth is
not uniformly covered with water; the presence of the continents alters
how the tides actually flow.
We know the earth
rotates, and as it turns, the point closest to the moon also moves,
meaning the “bulge” in the ocean travels as the earth turns. Consequently,
an observer at a fixed point would see the ocean level first rise, then
fall, and then rise again. However, as the earth rotates toward the east,
the moon is also moving along in its orbit. Because of this, it takes
slightly more than 24 hours—actually, 24 hours, 50 minutes—before that
hypothetical spot in the Pacific Ocean is once again directly under the
moon. This is why the high tide arrives around 50 minutes later each day
at a given spot.
The sun also
affects the tides. However, even though it is much larger than the
moon—and therefore would be expected to exert a greater gravitational
force—it is much farther away and thus the moon exerts the dominant
effect. As the moon circles the earth every 29.5 days, it moves into and
out of alignment between the earth and sun. During a new moon, both the
moon and sun are on the same side of the earth and their tidal pulls
combine to create high tides. A week later, when the moon is in its first
quarter, it is 90 degrees out of alignment with the sun, and its maximum
tidal pull tends to offset the sun’s minimum. At a full moon, the earth,
moon, and sun are once again aligned on the same axis, with the earth in
the middle, and high tides are again produced. When the moon is new or
full, the tides are known as spring tides. Spring tides produce the
greatest range of tidal swing, ranging from low water to high water. The
careful observer, however, will note that there is a one to two day
difference between the day of the new or full moon and the day of the
highest tide; this is due to a phenomenon called the “age of the tide.” At
one-quarter and three-quarter moons, the crests of the moon tides and the
troughs of the sun tide tend to offset each other, and the swing between
high and low tides is less than it is with spring tides. These tides are
called neap tides.[34]
Finally, the
position of the sun relative to the equator varies from summer to winter.
At the summer solstice, the sun lies at an angle of 23.5 degrees north
relative to the equator, producing the northern hemisphere’s summer. At
the winter solstice, it lies at an angle of 23.5 degrees south. The angle
of the sun relative to the equatorial plane of the earth is called its
declination. Knowledge of declination is one of the tools used in
navigation. The moon likewise declines north and south relative to the
equator. It is inclined 5 degrees relative to the earth-sun orbit so its
declination varies between 28.5 degrees north and south. One effect of
declination is to shift the mix of diurnal and semidiurnal tides. Another
effect is the result of the fact that the orbits of the moon around the
earth and the earth around the sun are elliptical, not circular. This
means that at certain times the earth is closer to the moon and sun, while
at other times it is more distant and the tidal force is less.
Fortunately, all of
these movements—while difficult to visualize—are regular in nature due to
the constancy of planetary movements within the solar system, and can be
modeled and predicted years in advance by mathematical methods. Another
complication emerges, however, and that is the effect of local conditions.
Narrow inlets, shallow bays, irregular coastlines, the different sizes and
volumes of the oceans and seas all affect the ultimate height of the tides
at a given location. A good way to visualize this is to imagine the earth
turning and the moon-induced “bulge” remaining fixed in place. As a
shallow continental shelf is rotated under the bulge it acts as a wedge
and raises the wave front.[35]
Or, as the incoming tide enters a harbor or river that narrows, the level
rises. For these reasons local measurements of tides are combined with the
computer forecasts of planetary movements to construct accurate tide
tables. The moon makes a complete swing of north-south declination each
month, but requires 18.6 years to go through a complete cycle of its
maximum declination. For this reason, data must be collected for 19 years
to generate an accurate representation of the full range of tides at a
given location. Once this is done, the data can be averaged to determine
the mean tide level, sometimes called the mean sea level.
The mean sea level is defined as the average height of the surface of the
sea for all stages of the tides over a 19-year period. This becomes the
reference point for coastal or shore-based structures. For navigational
purposes, it is more important to know the low water mark (to avoid
running aground), so marine charts usually use the mean low water as a
reference, and the depths of harbors or reefs are referenced to this
level.
Types of Tides
Three types of tides can be observed:
diurnal—one high and low tide each day; semidiurnal—two equal highs and
lows each day; and a semidiurnal mixed tide. The last, as its name
suggests, is a combination of diurnal and semidiurnal tides and differs
from a straight semidiurnal tide in that the two highs are unequal as are
the two lows. The Gulf of Mexico, northern Alaska, and parts of north Asia
are examples of locations with diurnal tides. The East Coast of the United
States, the west coast of Africa, Europe, and the west coast of Central
America are predominantly semidiurnal. The U.S Pacific Coast, the
Caribbean, and the west coast of South America are examples of semidiurnal
mixed tides. All three types can occur in close proximity—as, for example,
around the Gulf of St. Lawrence, Prince Edward Island, Nova Scotia, and
the Bay of Fundy—although one type usually dominates.
The various crests and troughs of the tides
are given the names of high water (HW) and low water (LW) for the highest
and lowest points of diurnal and semidiurnal tides. In the case of
semidiurnal mixed tides the nomenclature becomes more complicated because
there are two crests and two troughs of different heights. They are
referred to as higher high water (HHW) and lower high water
(LHW), while lower low water (LLW) is used to distinguish the
lowest low tide, and the higher low tide is called higher low water,
abbreviated HLW. When the data are averaged as described in the preceding
paragraph, the terminology becomes mean lower low water (MLLW), mean
higher high water (MHHW), and so on.
Recall the grunion discussed in the preface.
Survival of this diminutive fish is predicated upon its ability to know
when the higher high water tide will occur. You might wonder how it does
this. Could it be that the grunion somehow senses the depth of the water
and knows when the lows and highs are occurring? Or, does it surface at
night to eye the size of the moon in anticipation of lovemaking on the
beach? If so, it is probably not alone in this regard; other beachgoers
have done this for ages.
Two examples
of MLLW and MHHW come to mind. One summer Nancy and I in Dreams and
our friends Tod and Linda White in Seascape (Refer to Chapter 5)
set sail for a week of cruising—the goal being to circumnavigate Catalina
Island, stopping and anchoring in various coves. One of the places I
wanted to visit was a cove called Little Harbor. I had gone into it once
briefly, just to see what it was like. The cove is divided into two parts
by a jutting promontory of stone. A reef extends across about half of the
opening to the cove. On the west side is the anchorage, with space for a
half dozen boats, and on the east side of the promontory is a beach with
breaking waves—the only spot on Catalina where surfing is possible. You
enter the cove on the starboard or east side and once past the reef, turns
to port for the anchorage, where the nominal depth is 2 to 3 fathoms (3.7
to 5.5 meters). The usual process is to swing in, drop a stern anchor in
shallow water, and a bow anchor forward but behind the reef. After
anchoring, I always dive the anchors to make certain they are set.
We accomplished this without incident and
settled in to enjoy ourselves. As I recall, it was our turn to cook, so
dinner was onboard Dreams. Before turning in, I checked the
position and the depth once again. The boat had not moved and the
fathometer read 2 fathoms. Dream’s draft is 1 fathom, so all was
well.
At 5:00 A.M. (or “oh dark five hundred” as my
navy friends like to say), I awoke instantly to the sound of a gentle
bump. What was that, I wondered, sitting up in the bunk. A moment later it
was repeated, this time a little more forcefully—enough to rattle the
stays and shake the mast. I leaped out of bed and flipped on the
fathometer. Sure enough, it read 1 fathom and we were hitting the bottom.
I raced to the cockpit and threw some slack in the stern anchor rode, and
used the windlass to pull the boat forward on the bow anchor. Fortunately
I had plenty of scope out and could do that without a problem. Once I had
1.5 fathoms on the fathometer and everything secure, I tried to figure out
what had happened. Then I realized the night before was MHHW—for the year.
Correspondingly, when the tide went out and we encountered MLLW, it was
negative, and the lowest depth of the year. At daybreak I dove under the
boat and checked the keel. Fortunately we’d been lying in a sandy spot so
no damage was done.
My memorable MHHW incident occurred about six
months later, when the next highest annual tide occurred. The winter of
2004-2005 was unusual in Southern California in terms of heavy and
continuous rainfall. Storm after storm rolled in from the Pacific or moved
down from the northwest. Newport’s beaches were littered with debris
washed down the Santa Ana River and other streams that empty into the
Pacific. At one point the beach was littered with large logs—where they
came from I could not imagine. Floating offshore, they were a considerable
hazard to any unwary fast-moving boat. The weather cleared briefly on New
Year’s Day to permit a sunny Rose Parade in Pasadena, then turned stormy
again. Rain fell more or less continuously during the second week in
January. From Friday to Sunday alone, more than 7.6 centimeters (3 inches)
of rain fell on Newport Beach. Beginning on Sunday, January 9, high tide
conditions prevailed. However, because of the unremitting rainfall,
continuous runoff into the bay, strong winds, and low pressure zone
hanging overhead, the bay rose even higher, coming over low spots in the
seawalls and flooding streets. On Monday, January 10, 2005, the tide
peaked at a higher high tide of 2.2 meters (7.2 feet) according to my tide
table. By Tuesday, January 11, the third day of the storm, the effective
level in the bay approximated 2.5 meters (8.3 feet) at high tide, and the
bay overflowed and flooded a good portion of the Balboa Peninsula, where I
live. On my street, water slowly rose to the level of the curbs and then
overflowed into the gardens and front yards of my house and neighboring
houses. Fortunately, the water did not enter the house, but it did remain
high for several hours before draining back into the bay. I interrupted my
writing on this book long enough to survey the scene and take some
photographs, wading barefoot in the river of saltwater that ran down the
street. One of my neighbors, Bob Wilson, interjected some humor in an
otherwise tense moment by launching a surf board down the street—his very
nervous dog onboard. Other neighbors joked about owning waterfront
property.
We were fortunate; other homes in Southern
California sustained major damage during the January storms. But the
experience brought home the significance of storm surges and the potential
for loss and damage they create, particularly when combined with an
unusually high tide.
Tide Waves
As I mentioned at the start of this chapter,
tidal changes act as a long wavelength wave. Since this wave has a long
period, its speed is determined by the depth of the water and can reach as
high as 370 knots. The tide wave can move across an ocean until it hits
the opposite shore, where it can be reflected or refracted or standing
waves can be established in ocean basins. Scientists have measured tidal
heights in the open ocean, although the change of tides is more easily
seen near shores. The position of the high tide moves in a known manner,
so if the tide is measured at one coastal location, it can be predicted
for nearby locations. For example, if the high tide on the west coast of
central Mexico occurs at midnight, it will be high tide near the tip of
Baja California two hours later, San Diego, about three hours later, Santa
Barbara, four hours later, and Alaska eight hours later. Yet, in the
western North Pacific Ocean, high tide occurs at the same hour along a
vast arc extending from Japan south to New Zealand. This can be seen from
lines of position where the high tide occurs at the same time in the major
oceans; these are known as cotidal lines.[36]
Why is this?
In a large ocean basin the tide wave moves
across the basin as a progressive tide. When the wave reaches the
shore, it is reflected back, but if the basin dimensions are large
compared to the wavelength, no standing wave is created. In a smaller
ocean basin, the dimensions can be such that the basin’s natural period
equals the tidal period of 12.42 hours (semidiurnal) or 24.83 hours
(diurnal). When this is the case, a standing wave can be produced. This is
the situation in the northeastern and southwestern Pacific and in the
North Atlantic Ocean. Because the standing wave travels a long distance,
the Coriolis force has an effect on the moving water, turning it slightly
in a clockwise direction (northern hemisphere) and counterclockwise in the
southern hemisphere. This is called a rotary tide wave. The
movement causes the high tide crest to rotate counterclockwise
around the basin while the tidal current itself rotates clockwise. Picture
a bicycle wheel lying flat on a map of the Pacific Ocean, its axle
(center) near the Hawaiian Islands and its rim touching the west coast of
North America. Imagine the wheel rotating counter clockwise; the movement
of the spokes will simulate the movement of the high tide crest.
In narrow bays, fiords, or channels open at
one end to the sea, it is possible for the natural period of the bay to
resonate with the tidal period. The classic case of this is the Bay of
Fundy between Nova Scotia and New Brunswick, some 90 nautical miles long.
At the entrance of the bay the tidal range is between plus and minus 1
meter (+/- 3.3 feet), but at the head of the bay it is between plus and
minus 7 meters (+/- 23 feet).
Seiching
Following
one of Southern California’s earthquakes, I noted that some of the water
had splashed out of a neighbor’s swimming pool. When I inquired as to how
this had happened, he described a series of waves created during the
earthquake. This phenomenon is known as seiching and can occur when
any external force disturbs an enclosed body of water. Waves move back and
forth from one end to the other. The period of the waves depends on the
size (length and depth) of the body of water. (See Appendix 1 for typical
calculations.) In this sense they can also be described as standing waves.
Seiches can be caused in bays and harbors by tidal currents, by the
arrival of a distant swell with just the right period, or by storms or a
tsunami. Sometimes these will oscillate for days.[37]
Seiches are generally not a problem and are detectable only by means of
careful measurements. However, in the case of harbor designs, one usually
studies the predominant wave periods in the area and ensures that the
harbor dimensions do not create a condition where large seiches can occur,
since this could cause excessive movement of floating docks and straining
of vessel mooring lines.
Hurricane
Katrina (August 29, 2005) caused an 8 meter (26 foot) storm surge. This
raised the level of Lake Pontchartrain enough to damage the levees and
flood New Orleans. It also caused a rotating seich that lasted for several
days.[38]
On a large
scale, seiches have proved dangerous, damaging boats at dock, and
occasionally killing people fishing near shores or on breakwaters. Such an
incident occurred on June 26, 1954, when a 3 meter (10 foot) high wave
suddenly rolled in from Lake Michigan and swept eight fishermen off of a
breakwater, drowning them.[39]
A seich requires some exciting force. On the
Great Lakes, seiches are caused by fast moving thunderstorms or squall
lines that move eastward across the lake. The combination of the wind
blowing toward a low pressure area enables a wave to form. In deep water,
the wave is not very high. With the right wind speed and direction, the
squall line can move as fast as the wave front, literally pushing it
ahead. As the wave approaches shallow water near the shore, its height
increases, governed by the same physics as any other wave. After hitting
the Michigan side of the lake, the wave is reflected back toward the
Illinois side. This is where its insidious nature becomes evident. If the
originating storm was fairly short-lived, the chances are that the lake
has returned to normal on the Illinois side; boaters and others may have
resumed their activities in the aftermath of the storm. Suddenly, out of
nowhere, a wave can appear and disrupt the scene. In 35 years, there have
been five major seiches that have caused damage along the Chicago
lakefront. During the summer of 1988 there were three noteworthy seiches
along the Chicago lakeshore. These were not as bad as the one in 1954, but
some damage resulted. They caused the water level to rise or fall by as
much as 0.3 to 1.2 meters (1 to 4 feet), in some cases with the change
occurring in less than 10 minutes. Boats can drop and hit bottom, or if
dock lines are snug, the lines can break or rip cleats out of the boat or
off the dock.
Tidal Bores
Tides in general do not create extreme waves.
Tidal currents in the open ocean are weak—say, 0.1 to 0.2 knots—but near
the coast or in bays and river mouths they can reach 5 knots or more. In
shallow rivers, when currents exceed a critical speed (c> (gD)0.5),
tidal bores appear.[40]
This is one tidal phenomenon that can create unusual if not large waves—a
wave that moves forward as a wall of water.
If large tides occur in narrow harbors or
river mouths, the rapidly changing height of the water is compressed into
a narrow channel, the current flowing much faster than the current of the
tide wave in the open ocean. This can cause a fast moving wave to sweep up
the channel, sometimes creating hazardous conditions for boats entering or
leaving the area. The wave can be a breaking wave or just an abrupt wave
front; it is called a tidal bore. Usually tidal bores are around 1
meter (3.3 feet) in height, but can be as high as 8 meters (26 feet) —for
example, on the Qiantang River in China. Plate 6 (See book) is a
photograph of the Qiantang bore taken in late August 1986, from a location
near the city of Hangzhou. The bore forms below the city and then travels
at the rate of 10 to 20 knots up stream for about 25 miles. In September
and October visitors arrive from all over China to watch the spectacle. A
number have ventured too close and have been swept to their deaths. Local
boatmen know to get their vessels out of the way!
Plate 6: The Qiantang River Tidal Bore
The Bay of Fundy, described above, was once
known for a tidal bore but has been modified by construction of a
causeway.[41]
Other notable tidal bores occur at Turnagain Arm of Cook Inlet, Alaska,
with a difference of 9.2 meters (30 feet), the Severn River, in England (a
series of waves about 0.3 meters (1 foot) high, the Seine River, and the
Amazon River.[42]
I had my first view of the Amazon River many
years ago, at Belem, a wonderful city near the mouth of the river. At the
time I was impressed with the Amazon’s tremendous size and the variety of
tropical plants and wildlife. I walked along the waterfront, where Indians
from upriver came to the feira (marketplace) to sell goods—wild
animals, snake skins, various herbs and remedies, bananas, and dozens of
tropical fruits totally unknown to me. I heard the stories about this
tremendous river—how it flowed out into the Atlantic with such force that
fresh water could be found 50 nautical miles or more distant from land. A
local legend told of shipwrecked sailors, on the verge of dying of thirst,
who, in their final hours of desperation started to drink saltwater—only
to discover it was fresh water. They were far from shore, but in the
outflow of the Amazon River.
Later I visited Manaus, 1,450 kilometers
upriver from the Atlantic Ocean. Flying west, the river was so wide that
looking down from the windows of the airplane, I could not see both banks
at once. There are floating docks in Manaus—designed for the huge rise and
fall of the river, from the rainy (flood) season to the dry season. If
memory serves me correctly, this fluctuation is 12 to 15 meters or more.
I’ve not seen the tidal bore on the Amazon. Bascom says it is spectacular
and attains a height of 7.6 meters in some locations. It travels upriver
at a speed of 12 knots for a distance 480 kilometers.[43]
Given what I know about
the river, it sounds plausible to me, and a good reason to return there
and check it out. Perhaps I could get Eric Akiskalian, Dan Moore, and some
of the other extreme surfers to join me; it would be the longest ride of
their lives!
From Chapter 10
Additional details
regarding the growth of container ships
There are three east-west principal trade
routes used by container vessels as well as a half a dozen secondary
routes. The main routes are the transpacific (Asia-North America),
Asia-Europe, and Europe-North America. The highest volume route is the
transpacific, where cargo volume has tripled between 1990 and 2004.[44]
During this time, the number of containers carried increased from 3
million to nearly 10 million TEUs. The Asia-Europe route has about
one-half as much traffic; the transatlantic, about one-fifth as much.
This increase in container transport volume
is the result of several factors: a doubling of the weekly sailings,
faster vessels, and an increase in the average vessel size. The average
speed has increased from around 19 knots in 1990, to 23 to 24 knots in
2004, and may reach 25 knots in the next decade.[45]
Also, electronic transfer of documents and payments has had an impact.
Industry practice is to measure capacity in
terms of an equivalent number of 6.1 meter (20 feet) long containers
transported. They have been the industry standard for years, but today
they are being supplanted by containers 12.2 meters (40 feet) long. There
are also refrigerated containers, typically 13.7 meters (45 feet) long.
Capacity of typical containers is shown below:
Type: 20
feet (1 TEU) 40 feet (2 TEU)
Length, meters
(feet) 6.1
(20) 12.2 (40)
Height, meters
(feet) 2.6
(8.5) 2.6 (8.5)*
Width, meters
(feet) 2.4
(8.0) 2.4 (8.0)
Gross weight, kilograms
(pounds) 30,480 (67,056) 30,480 (67,056)
Tare weight, kilograms
(pounds) 2,240 (4,928) 3,950 (8,690)
Volume, cubic meters
(cubic feet) 33.2 (1,173) 67.5
(2,383)*
* Some are 2.9 meters
(9.5 feet) high and have a volume of 76.4 cubic meters (2,695 cubic feet)
Loaded to capacity, a single container can
thus hold 30 metric tons (33.5 short tons) of goods. Even an empty
container weighs 2.2 to 4 metric tons (2.5 to 4.3 short tons). From these
dimensions, one can readily imagine the danger if a container is lost
overboard during a storm. Collisions between small vessels and a floating,
partially submerged container have resulted in the sinking of vessels
Average vessel capacity on the transpacific
route is expected to continue to increase, from 3,900 TEUs to around 5,800
TEUs by the year 2020. Within the next decade even larger vessels are
expected. New container ships will carry 6,000 to 8,000 TEUs or more. The
motivation for larger vessels is economic; the shipping cost per container
is expected to drop by $100 per TEU for an 8,000 TEU vessel and by $150
for a futuristic12,000 TEU vessel. Looking at new ship orders within the
next five years, 750 new container vessels will be procured. About 500 of
these will be Panamax size or smaller, typically 2,500 to 5,000 TEU
capacities, while 250 will be “post-Panamax,” with capacities of 5,000 to
more than 8,000 TEUs. Of the latter, nearly 50 percent are more than 8,000
TEUs and range in length from 900 to 1,150 feet.
From Chapter 10:
Analysis of the
Derbyshire Hatch Cover Failure
The hatch covers were apparently designed for
a uniform static wave load of 17,200 Pascals (1.75 metric tons per square
meter or 358 pounds per square foot).[46]
Since seawater has a density of 1.028 metric tons per cubic meter, this
design criterion is equivalent to the load imposed by a column of water
1.7 meters (5.6 feet) high on top of the hatch covers. The Derbyshire’s
freeboard was 6.9 meters and the coaming height was 2.0 meters, so the
total height of the hatch cover above the water line was 8.9 meters (29.2
feet). Hence, a wave 8.9 + 1.7 meters (5.6 + 29.2 feet) high, or 10.6
meters overall height, would be high enough to go over the rail, cover the
hatch, and cause the design loading to occur.
Recognizing that the design incorporates some
safety factor, the next question is: “At what load does total collapse
of a hatch cover occur?” When this analysis was carried out, the result
was a static loading 5.3 meters (17.4 feet) high.[47]
This corresponds to a wave 8.9 + 5.3 meters (29.2 + 17.4 feet), or 14.2
meters (46.6 feet) high.
In addition to failure caused by the dead
weight of tons of water on the hatch cover, it could also fail under
dynamic loading as well. In other words, as mountainous waves crash down
on the hatch cover, the impact causes a sharp pressure impulse, something
ship designers call a Gifle peak. This sudden pressure pulse
(analogous to the sudden rise in pressure caused by an explosion) can
produce stresses 11.6 times greater than those caused by the static load,
leading to brittle fracture of the steel. This type of fracture was
observed in the Derbyshire’s wreckage.[48]
Unfortunately, bulk carrier design standards have no requirement to
consider dynamic loading.
Finally, how high were the waves experienced
by Derbyshire? We do not know with certainty, although typhoon
Orchid’s reported wave heights in the vicinity were 18.3-plus
meters (60-plus feet). The height can be estimated on the basis of an
energy spectrum assumed for the storm depending on its duration. Assuming
the storm lasted 6 hours, this analysis indicates that the probability of
waves higher than 22 meters (72 feet) is 100 percent, higher than 24
meters (79 feet), 99 percent, and higher than 26 meters (85 feet), 80
percent.[49]
Appendix 1: Wave
Mathematics and Ship Design
(This is the complete
version of the Appendix)
The purpose of this
appendix is to provide additional details for readers who are interested
in understanding some of the theory behind extreme waves and how they
affect ships. It can be safely ignored by the general reader who has
already suffered through enough mathematics in the text.
Mathematics of the
Simple Wave
First, recall the
admonition first expressed in chapter 1—namely, that the actual sea
surface is a complex of many waves of varying sizes, coming from different
directions and having different periods. Only in the case of a calm sea,
with a single low swell, do the waves even remotely resemble the ideal
wave shown in figure A-1. The speed of waves depends on the depth of the
water in comparison to the wavelength. In the open ocean, the size of
waves depends on the exciting force (usually the wind); water depth is not
a factor until the wave reaches shallow water. In attempting to deal with
the complications presented by the actual sea state, analysts have
developed various linear models, each having applicability over a certain
range of conditions. Recognizing the limitations that linear models have
in representing complex seas, statistical (probabilistic) models have been
developed.
In efforts to further improve analytical
models, analysts have developed nonlinear mathematical models with the
goal of better modeling realistic waves and ultimately forecasting their
occurrence. Each method offers certain advantages in comparison to the
others; none have proved to be completely satisfactory.
To better understand
some of the theory behind linear wave analysis, we begin with the sine
wave, a simple waveform that occurs frequently in nature and that is
common to many fields of physics, including electricity, light, and sound.
The most common everyday example of a sine wave is the alternating
electric current found in every household with electric power. The shape
of this wave is illustrated below. As can be seen, starting on the left
hand side the wave has a crest, then the amplitude gradually falls to zero
on the center line horizontal axis, decreases to a negative crest, or
trough, and then returns to a maximum value again after crossing the
center line. In the home, the frequency f of the sine wave is 60 cycles
per second (50 cycles per second in Europe and many countries), the period
T of the wave is 1/60 second or 16.7 milliseconds. Period is the
reciprocal of frequency, that is, T =1/f. With waves, the period, not the
frequency is the term normally used.

Figure A-1: Wave Nomenclature
For ocean waves, H is called the wave height
(the difference in surface elevation from the crest of one wave to the
successive trough). In addition, the time elapsed for one complete cycle
of a wave—that is, from one crest to the next—is called the period T. The
wavelength L of waves in deep water is related to the period T.
In deep water, defined as water in which the
water depth D is equal to or greater than one-half the length of the
wave—that is, where:
Depth D >
0.5L, where D is the water depth in meters and L the wavelength, both in
meters, the wavelength of the ideal wave is given by [1]:
[50]
Wavelength L
(meters) = (g/2π) T2 [1]
where g is the
acceleration due to gravity, 9.81 m/sec2, T is the period in
seconds, and π = 3.1416.
Also,
Wavelength L
(meters) = cT [2]
where c is wave speed in
meters per second.
Equations [1] and [2]
can be simplified to the following forms:
Wavelength L
(meters) = 1.56 T2 where T is the period in seconds
Speed c
(meters/second) = 1.25 L0.5 = 1.56 T
Period T
(seconds) = 1/f where f is the frequency in cycles per second
Making use of these formulas, we can compute
the following values for typical idealized waves (all numbers are
rounded):
Period, T,
seconds 2 4 6 8
10 15 20
Wavelength
L, meters 6 25 56 100 160 350 620
Speed c,
meters/second 3 6 9 12
16 23 31
The speed of the wave is independent of depth
and is determined only by the period, as noted above.
Conversely, in shallow water, defined as
water where the depth is 1/25th or less of the wavelength, or
where:
Depth D <
L/25, where D is the water depth in meters and L is the wavelength.
The speed of the wave
depends on the depth in accordance with the following relationship:
Speed c,
meters/second = (gD)0.5
[3]
where g is the
acceleration due to gravity, 9.81 meters/second squared and D is the depth
in meters, as noted before.
Wave steepness is another parameter of
interest to us. It is defined as the ratio of the height of the wave to
the wavelength:
S
(steepness) = wave height H/ wavelength L
Using [2], the equation
for wavelength, the steepness of an ideal wave can be calculated as
follows:
S
(steepness) = (2π H)/gT2
[4]
The theoretical upper limit on steepness is
that point at which the wave becomes so steep that it breaks. This has
been calculated to correspond to a steepness of 1/7 = 0.14.[51]
The typical range of steepness for waves in deep water is around 0.01 to
0.1. If the steepness of the Draupner extreme wave shown in figure 24 is
analyzed, it is about 0.059, whereas the steepness of the significant
waves in that same record is 0.027.
Extreme waves are not only very steep, but
typically they are asymmetrical. In a symmetrical wave, the height of the
crest from the center of the wave would be the same as the distance from
the center of the wave to the bottom of the trough. In other words, the
crest height would be equal to 0.5 times the wave height. In extreme waves
we find that this ratio can be 0.7 or higher. In the Draupner wave
mentioned above, the crest height was 18.5 meters and the overall height
was 25.59 meters, giving a ratio of 0.72.
How Did Ramapo
Determine the Wave Height?
Figure A-2 shows the geometry of the vessel as it
encountered heavy seas. (Refer also to chapter 8 for a discussion.) I
assume the officer on the bridge of the Ramapo had or could easily
measure the following distances: d1, d2, and d3,
the horizontal distances from the stern to the mast, from the mast to the
bridge, and from the bridge to the bow, respectively. Also recognize that
d1 + d2, + d3 = Ls,
the length of the ship, or 146 meters. The height of the crow’s nest hc
and the height of the bridge hb
were also known. The angle of the ship θ and the distance to the projected
line of sight “x,” and the wave height hw
are unknown.

Figure A-2: USS Ramapo Height
Measurement Model
The first step is to
solve for “x” using similar triangles. We find:
x = [hb(d2
+ d3) –hcd3]/(hc-hb).
Next, find θ by
trigonometry:
θ = sin-1[hc/(d2
+ d3 + x)]
Finally, find hw
by similar triangles and trigonometry:
hw
= (146 + x)sin θ = 34.2 meters (112 feet)
Tsunami
Since tsunami have very long wavelengths
relative to the ocean’s depth, the velocity of a theoretical, sinusoidal
tsunami wave is given by [3], that is:
Tsunami wave speed c (meters/second) = (gD)0.5
Using this formula and the average depth of
the ocean, or 4,000 meters (13,115 feet), we see that a tsunami travels at
around 198 meters per second (713 kilometers or 442 miles per hour). In
deep water, a tsunami can travel faster than the commercial jets carrying
passengers to Hawaii. The periods are typically 10 to 20 minutes but can
be as long as an hour. Since the wavelength is a function of wave speed
and period, (L = cT, equation [2]), we can estimate that wavelengths are
typically in the range of 120 to 240 kilometers (74 to 148 miles).
The above relations do not hold when the
tsunami moves into shallow water. In this case, for shallow water where
the depth is between 0.5L and 0.04L, the tsunami wave speed is given by:
Tsunami wave speed c meters/second) = {(gL/2π)[tanh(2πD/L)]}0.5
[5]
When the
wave reaches shore, it increases in height in shallow water and then runs
up on land as indicated in figure 18. The maximum height of the run-up can
be estimated as:[52]
Maximum
run-up height Hmax meters = k(cot α)0.5 Hs1.25
[6]
In this equation α is
the slope of the seabed in degrees as the wave approaches shore, Hs
is the wave height at shore or the toe of the beach, and k is a constant
depending on the wave type. For a continental shelf, α could be as small
as 0.1 degrees and 1 to 10 degrees for a beach. If the wave is a solitary
wave, k is 2.83 but if the wave is preceded by a trough, k is 3.86 and if
it is a double wave (a large wave preceded by a small wave, then a
trough), k is 4.55. For a beach sloping 1 degree, an incident double wave
of height 0.5 meters would experience a run-up of 14.4 meters (47 feet).
Tsunami can
cause seiches in harbors and bays if the wave period is close to the
natural period of the bay or an even fraction (1/2 or ¼) or an even
multiple of the period. It is this phenomenon that led to the name tsunami
(Japanese for harbor waves) when sailors observed that waves continued
rocking the harbor long after the earthquake had stopped. An approximate
equation for the period is given by:
Closed
harbor or bay, period T in seconds = 2Lh(gD)-0.5
[7]
Open harbor
or bay, period T in seconds = 4Lh(gD)-0.5
Here Lh is
the length of the harbor or bay in meters, D is the depth in meters, and g
is the acceleration due to gravity, 9.81 meters/second.[53]
A “closed” harbor is one surrounded by a breakwater and having a narrow
entrance. Real harbors and bays have complicated geometries and these
equations may not give accurate results. Newport Harbor (figure 23) is an
example of an open harbor. Assuming an average depth of 3 fathoms (5.5
meters), and a length of 5,100 meters, the period of Newport using [7] is
around 2,775 seconds or 46 minutes. The period of Hilo Bay is around 30
minutes; the predominant period of the April 1, 1946 tsunami was 15
minutes, which was one of the reasons it was so devastating at Hilo. The
period of the Bay of Fundy is 13.3 hours—very close to the period of the
semidiurnal tides. This explains why the tidal range is between plus and
minus 1 meter high (+/- 3.3 feet) at the entrance and yet between plus and
minus 7 meters (+/- 23 feet) at the head of the bay. Research has shown
that this period arises from the combined system of the Gulf of Maine with
its deep water and the shallow depth of the bay.[54]
The above relations are
chiefly useful in that they provide insight into the physical parameters
(wavelength, period, and ocean depth) and how they affect wave propagation
and height. As mentioned in chapter 1, realistic ocean conditions are more
complicated. For example, run-up calculations are actually more
complicated because realistic shore conditions are never uniform.
Likewise, the periods of bays are affected by their width and of course
the depth is not uniform. In an effort to better model real waves,
theoreticians have developed more complex nonlinear models, and then
turned to numerical methods using digital computers to simulate wave
motions. Entire books are available on this subject, and details are
beyond the scope of this book.[55]
In chapter 3 the topic
of wave probabilities was introduced. Probabilities are developed using a
statistical approach that assumes that the sea state satisfies certain
criteria for randomness. This approach has many practical applications and
is in wide use, even though it does not meet the requirements for
forecasting extreme waves. It is particularly useful for the design of
structures.
Researchers
have used recorded wave height and period data (using a large number of
records) to construct wave energy spectra. These are based on the
principle that the wave energy is proportional to the square of the wave
height. Typical spectra graphs have a parameter called the spectral
density (related to the wave energy) on the vertical axis and period
or frequency on the horizontal axis. Model spectra are for deep water
(fully developed seas) and one for fetch-limited seas, called the Joint
North Sea Wave Project (JONSWAP) spectrum. These spectra can be modified
for a given location or for a given sea condition to make them specific
for a given purpose. They can also be used for hindcasting, in
other words, back-tracking from a recorded wave spectrum to come up with
an estimate of wave heights, average period, and average wavelength.[56]
Earlier I stated that
the use of linear theory and Gaussian models requires a number of
assumptions that are invalid in realistic seas. For example, real waves
are slightly nonlinear in deep water and very definitely nonlinear in
shallow water. This can be seen by considering asymmetry (high crests,
shallow troughs) and the fact that crests can be steep and troughs flat.[57]
To better
represent extreme waves, the Weibull probability function has been used.
(The Rayleigh distribution is a special case of the Weibull distribution.)
The assumption is made that the wave data represent a stationary sea state
between measurements. The Weibull distribution provides a good fit to the
Draupner extreme wave shown in figure 24, and thus may be a useful tool
for understanding some aspects of sea conditions (such as sea state
duration) leading to the formation of extreme waves.[58]
Recent Research on
Extreme Wave Models
As awareness of extreme waves has grown,
researchers intensified efforts to understand the physics underlying their
formation. If the occurrence of extreme waves can be linked to certain
meteorological or sea state conditions, then it might be possible to
forecast when they will occur. Such information would be invaluable to
mariners and the marine insurance industry.
Much of what we know about extreme
waves—indeed, the emphasis to learn more about them—has come from
observations by shipmasters who have witnessed encounters between their
vessel and an extreme wave or from survivors of vessels that foundered as
a result of an extreme wave incident. Those observations are by their
nature imprecise; generally they occurred too suddenly or under extremely
stressful conditions where exact measurements were impossible.
In chapter 8, I grouped them by
characteristic probable cause, in the following order:
- Strong currents
- Storms
- Continental shelves
and shallow seas
- Constructive
interference (superposition)
To these we may add
several additional possible mechanisms for extreme wave formation that are
the subject of current research:
- Nonlinear effects
- Spatial or temporal
focusing effects
- Multidirectional
effects
- Modulation and
resonance
A comment or two about each of these
mechanisms is useful. The first category, strong currents, has
indisputably been the source of extreme waves. When swell or storm waves
encounter a fast-moving opposing current such as the Agulhas Current or
the Gulf Stream, they tend to “pile up” as their velocity is reduced.
Professor Garrett pointed out that a wave with a phase speed of c meters
per second can be stopped by an opposing current of only ¼ c.[59]
When this happens, steep, high waves result, proceeded or followed by deep
troughs. Thus the evidence is clear that the probability of encountering
an extreme wave is greater under these conditions and a prudent mariner
should avoid this situation if possible.
The increase in wave size as a function of
wind velocity, fetch, and wind duration is a well-known phenomenon in
storms. There are correlations that provide estimates of the significant
wave heights under varying storm conditions, but none that predict the
random occurrence of extreme waves. This suggests that some additional
mechanism, yet to be fully understood, is at work. It would be useful to
know if extreme wave formation is governed by a threshold effect; in other
words, do seas have to build to a certain point before extreme waves are
produced? Or, is it purely a statistical effect?
The evidence seems to indicate the latter
possibility, because many mariners (myself included) recall sailing in
relatively calm seas where the significant wave height was one meter (a
few feet) or less, but suddenly a wave two to three times as high struck
the vessel.
Likewise, shallow water, bottom effects, and
refraction, have the effect of slowing waves and causing wave heights to
increase. Thus areas where there is a sharp transition in the sea depth
are potential danger zones in rough seas. The question here is: “Are there
certain sea or wind conditions that combine to cause an extreme wave and
how can they be anticipated?”
Constructive interference, (sometimes called
superposition) is the fourth category mentioned in chapter 8. Here I
included incidents (to the best of my knowledge) in which an extreme wave
struck a vessel in the absence of the other conditions described above.
Superposition is a well-known phenomenon, observable in many areas of
physics, so its existence is not in doubt. The relevant research question
is whether or not it is capable of causing waves that are 2.2-2.4 times as
high as the significant wave. From the Rayleigh distribution, the answer
would seem to be yes. (A factor of two seems obvious.)
Turning to the new areas of research,
attempts to model nonlinear wave effects may shed light on how
superposition can produce extreme waves. Nonlinearity makes mathematical
modeling much more difficult, so scientists and engineers always try to
develop linear models first and then turn to nonlinear models as a last
resort.
In case you, the reader, are not a
mathematician, scientist, or engineer, but have bravely ventured into this
appendix to further your understanding, let me offer a simple example that
will hopefully ease the pain of wading through successive paragraphs of
this section.
Consider a steel bar—say, a familiar piece of
reinforcing steel. Imagine that it is put in a tensile test machine, a
machine that grasps both ends of the bar and pulls on them. Suppose the
machine is set to pull with a certain force, and as a result the bar
stretches a small distance we will call “x.” Now, if the force is doubled,
the bar elongates a greater distance, this time equal to twice x, or “2x.”
If the force is tripled, the elongation becomes 3x, and so on. In
technical terms, we have discovered that strain (elongation) is directly
proportional to stress (applied force).[60]
In other words, the bar is acting as a linear system—double one variable,
the effect doubles.
However, if we keep increasing the force
indefinitely we know that at some point the bar will break. If the force
is increased carefully and slowly, what we observe is that the bar reaches
a point at which elongation more than doubles when the force is
doubled. In technical terms, the steel has been stretched beyond the
elastic limit.
Up to the elastic limit, the bar behaves like
a tight rubber band—remove the force, and it shrinks back to its original
length. This is another characteristic of a linear system. Once beyond the
elastic limit, the bar is permanently deformed. There no longer is a
simple one-to-one relationship between stress and strain; the bar now
behaves as a nonlinear system. Mathematically we say that “higher order
terms” must be brought into the equation to give accurate results. Let me
next explain what this means.
In the linear (elastic) region, elongation is
proportional to the applied force, so we can write:
e = kf
[8]
where e is elongation,
in millimeters or inches, k is a constant, and f is the applied force.
Now, once the bar passes the yield point, the equation has to be written
differently, and might take a form like this:
e = kf + k1f2
[9]
Here, k1 is another constant. Note
the exponent “2” on the second term of the equation. This means that the
square of the force has come into the picture. Whenever one of the
variables is squared or cubed, or increased to the nth power, it is said
to be a “higher order” term in the equation. These higher order terms seem
to be simple in appearance, but they give mathematicians headaches when it
comes to solving equations.
Back to extreme waves. Some new research is
directed at examining the effects of second order and higher terms in
mathematical models of waves, to see if this is a better way of modeling
waves. Some researchers go so far as to say that if rogue waves exist,
they must inherently be nonlinear.[61]
Some of the features of extreme waves—their steepness and shape of the
wave crest—are modeled more accurately when second-order terms are
included.
Another interesting new approach is based on
spatial and temporal focusing. Spatial focusing is another way of
describing what happens when waves are refracted by the ocean bottom
topography in coastal waters or by current gradients.[62]Temporal
focusing may result when waves disperse. Some wave groups may contract to
a few wavelengths and then combine with others to produce short groups of
very large waves.[63]
Some theorists believe that nonlinear focusing may allow a wave to
“borrow” energy from its neighbors, becoming as much as 4.5 to 5 times as
large as the average wave height.[64]
Multidirectional and multidimensional effects
are also being studied to see if they can cause extreme waves. The idea is
to investigate if extreme waves result from wave trains interacting at an
angle, or due to three-dimensional interactions—effects that would not be
modeled by a one-dimensional analysis. When I spoke with Dr. Susanne
Lehner, she indicated that waves from crossing seas arriving from two
different storms can add and build to an extreme size due to the
continuous input of energy. Also, the Benjamin-Feir index, introduced in
chapter 11, measures a phenomenon called the Benjamin-Feir instability. It
is defined as the ratio of the mean square slope of the frequency spectrum
peak to its normalized width. Under the right conditions, instability
causes the wave train to break up into periodic groups. Within each group
a further focusing takes place, producing a very large and steep wave
having a height roughly three times the initial height of the wave train.[65]
Finally, other research is directed at seeing
whether frequency or amplitude modulation could be responsible for extreme
waves. Or, is it possible that certain wave periods and frequencies will
resonate with a given sea-state condition to create extreme waves. The
analogy to this is easily demonstrated in a bathtub. A bathtub, or a
harbor for that matter, has a series of resonant frequencies. See equation
[7] above. If you take a piece of wood (or possibly just your hand) and
get the water sloshing back and forth at just the right period, a large
wave will occur.
Given that waves as high as 30.5 meters (100
feet) exist and occur more frequently than previously known, what are the
implications for ship design? To answer this question, I consulted with
Captain Jerry Fee, USN (ret).
Waves and Ship Design
Captain Fee kindly gave me a short course on
the process the United States Navy uses to design ships. The approach used
in commercial shipping is similar, although some of the design criteria
differ. According to Captain Fee, the primary stresses in a ship are
determined by an analysis based on hogging or sagging, using
an assumed wave height (in feet) given by:
H = 1.1 (Ls)0.5
[10]
where Ls is
the length of the ship in feet. Thus, for a vessel 900 feet long, the
design wave height would be (1.1)(30) = 33 feet high. Note: Converting the
formula to metric units it becomes H = 0.61 (Ls)0.5,
where now H and Ls are in meters. Historically, the U.S. Navy
has taken the position that the largest wave likely to be encountered was
21.4 meters (70 feet.) Based on more recent experiences the navy now
believes that larger waves can occur, but that they are unstable and only
last for a brief period. The possibility of extreme waves that are steeper
and possibly do not have longer wavelengths is now recognized.
Powerful computer programs using a method
called finite element analysis calculate the primary stresses in the
ship’s ribs, longitudinals, and other main structural elements, to ensure
that the sizing of steel members is adequate for the expected loads. The
navy’s general criterion is built around a Sea State 8 condition. In Sea
State 8, the average 1/3 highest wave is about 14 meters (45 feet). This
is typical for most hurricanes. Hurricane Camille is one of the
best recorded hurricanes, and the navy uses a wave scenario based on this
hurricane in their ship models to check for dynamic stability and
survivability. On the basis of other analyses, the navy has not had to
make any fundamental changes in ship design as a result of the prospect of
a wave greater than 21.4 meters (70 feet). Naval vessels appear to already
have sufficient strength built into them to survive an encounter with a
larger wave using the existing criteria since maximum hogging and sagging
loads are encountered when a ship is caught between two large waves whose
wavelengths equals the length of the ship.
The energy carried by a wave is proportional
to the square of its height. For this reason, a 30.5 meter (100 foot) high
wave will hit a vessel with four times the force of a 15 meter (50
foot) high wave. If a high wave is traveling at 35 knots and a vessel
traveling at 20 knots runs into it bow first, the combined velocity of the
impact is 55 knots. The resulting slamming force can stress the bow
structure.
Consequently, other parts of the ship structure that may be subject to
wave forces are also examined to ensure that they are sufficiently strong
to resist the forces that will occur. The next step is the design of the
deck plate for “deck wetness.” Those areas subject to extreme deck wetness
are the bow area and parts of the superstructure that encounter extreme
wave loading due to wave slap and the dynamic load of large amounts of
water pouring onto the deck in an extreme wave encounter. The basic
design criterion is to assume a pressure of 24 kilopascal (500 pounds per
square foot) for any area that is prone to “green water” (wave slap). Most
navy vessels are designed for at least 71.9 kilopascal (1500 pounds per
square foot), and some unique parts of a structure, such as the sponsons
on an aircraft carrier, are designed for as high as 359 kilopascal (7,500
pounds per square foot). In addition, a static head equivalent to a column
of green water 2.4 to 3.1 meters (8 to 10 feet) high, is designed in the
forward part of the vessel that is likely to encounter waves. This is
reduced linearly as you move aft from the bow of the vessel where a value
of 30.6 kilopascal (640 pounds per square foot) is used to a minimum value
of 1.2 meters (4 feet) of head, equivalent to about 12.3 kilopascal (256
pounds per square foot). Military vessels include additional design
conservatism to account for the need to resist blast over pressure during
combat operations.
Both military and commercial vessels are
designed to stay afloat with one or more hull compartments flooded. In the
case of commercial vessels, one or two flooded compartments is the norm,
while for the navy it is three.
The military has progressed from using steel
with a yield strength of 207 to 276 megapascal (30,000 to 40,000 pounds
per square inch) called HTS or high strength steel to using high yield
strength steels (called HY steels) that have a yield strength of 551
megapascal (80,000 pounds per square inch). Submarines use 714 megapascal
(100,000 pounds per square inch) HY steel. The norm for commercial ships
is HTS at 276 megapascal (40,000 pounds per square inch). Further
verification of ship designs is accomplished by carrying out model tests
in wave tanks. Once the vessel is commissioned, it will undergo sea trials
to verify performance and operational characteristics.
As the navy’s top ship designer, Captain Fee
took part in numerous sea trials. When he served as the Aegis shipbuilding
program manager, he took part in an interesting one. It was an Aegis-Class
cruiser that went to sea in February 1986, at a time when a strong
northeast storm had been blowing for several days with 50 knot winds.
Waves were around 12 to 15 meters (40 to 50 feet) high. Fee ordered the
ship to head into the waves at 30 knots, as opposed to the normal practice
of slowing down. After several hours the experiment had to be terminated,
because the air intakes 26 meters (85 feet) above the water line were
being blocked by ice formation! Incidentally, the ship suffered only minor
damage.
Current maritime design practice for
commercial vessels varies with the classification societies and is based
on withstanding the impact of an idealized (symmetrical) wave 10 to 15
meters (32 to 49 feet) high. The water in such a wave exerts a static
pressure of 49 to 75 kilopascal (1,024 to 1,568 pounds per square foot) on
the side of a hull and twice this amount if the total weight is on a
horizontal surface. The dynamic pressure is greater and depends on the
wave velocity:
Pressure P in Pascal = ½ Ccρc2
[11]
Here Cc is a
load concentration factor, taken as 3 for global impacts and as 9 or 10
for local impacts where the wave force is concentrated, ρ is the density
of salt water and c is the velocity of the wave crest in meters per
second.[66]
Extreme waves with heights of 15 to 30 meters (49 to 98 feet) can achieve
speeds of 40 to 80 knots (21 to 41 meters per second). For example, in the
case of the USS Ramapo, described in chapter 8, the 342 meter long
wave it encountered had a period of 14.8 seconds and a velocity of 23
meters per second. Using equation [11] with Cc = 3 we obtain:
c
(meter/sec) = 23 33 40
P (Pascal)
= 816,000 1,680,000 2,467,000
P (Pound/sq.
ft.) = 17,000 35,100 51,500
In the case
of FPSO Schiehallion, (see Appendix 2), bow plates were bent in
under wave impacts that were estimated after the fact as:
750,000 to 1,000,000 Pascal locally,
and
200,000 Pascal globally.
Later the vessel was
instrumented with pressure transducers and returned to station. Peak
pressures of 300,000 to 600,000 Pascal due to wave impacts were recorded.[67]
To see what wave pressure is needed to shear
hull plates, assume a plate thickness t = 0.0127 meters (0.5 inch) and
steel plate with a shearing resistance of s = 689 megapascal (100,000
pounds per square inch) and an opening 5 meters by 5 meters (16.4 feet by
16.4 feet), area A = 25 square meters, with a perimeter p of 20 meters.
The shearing pressure P in Pascal = stp/A
[12]
This gives 7,010,000
Pascal or 146,000 pounds per square foot. For these assumptions, it
appears that a load concentration factor of Cc = 9 would be
required to punch a hole in the hull. As incredible as it may seem, waves
can rip steel hulls apart or punch holes in them. This has been amply
demonstrated in the case of the Wilstar, the Pittsburgh, and
several aircraft carriers.
From Appendix 3
MISCELANEOUS TECHNICAL
DATA
Specific gravity (grams
per cubic centimeter or metric tons per cubic meter):
Water @ 4 degrees C =1.000
Water at 15
degrees C = 0.99913
Sea water at
15 degrees C =1.025 (average)
Note: sea water depends on NaCl content; 1%
=1.0053, 2% = 1.0125, 4% = 1.026, 6% = 1.0413
Ice = 0.917
Mercury at
15 degrees C = 13.559
Crude oil at
60 degrees F = 0.813 to 0.921
Note: crude
oil is 6.77 to 7.67 pounds/gallon or 6.8 to 7.8 barrels per metric ton.
Source: Handbook of
Chemistry and Physics, 41st ed. 1959, 1923, 2044, 2121,
2130-2131. Cleveland, Ohio: Chemical Rubber Publishing Co.
One standard atmosphere
= 76 centimeter (29.92 inches) of mercury = 33.9 feet of water = 1,013
millibars.
Appendix 2:
Representative Ship Disasters
(Note: in the
interest of conciseness this important Appendix was deleted from the book.
It provides the supporting documentation for some of the book’s findings.)
The following list of
70-plus incidents is indicative of the disasters that resulted when ships
encounter extreme waves. I have attempted to include incidents where
extreme waves damaged a vessel or either caused or contributed to its
loss. In some cases there were additional complications, such as fire or
explosion. The list spans the time from World War II to the present, and
includes various types of vessels large and small, although most are large
enough that one would not expect them to have difficulty in rough weather.
It is a partial list that only contains a small fraction of the vessels
lost at sea during this period. Most, but not all, were lost as a result
of the encounter; the few that survived were fortunate to avoid more
serious consequences. Some of these incidents are described in greater
detail in the body of the chapter, because I wanted to illustrate a
particular sea condition. For completeness, their names are listed here
also. The bold numbers in parenthesis following the entry refer to the
source documents and page numbers that are listed at the end of this
appendix.
Oil Tankers and Combination Carriers
As a result of several notorious oil spills
(the Amoco Cadiz, in the Atlantic, off the coast of France, the
Exxon Valdez, in Alaska, and the Torrey Canyon, near the United
Kingdom), much public attention has been focused on the safety of oil
tankers. The industry has responded with ever-more stringent safety
practices and has taken steps to convert the global fleet from single hull
vessels to double hulls. Historically there has been an average of two
major spills per year for the years 1960 plus 1965 to 1989. The top 50
spills lost anywhere from 157,000 barrels of crude oil to as much as
1,890,000 barrels. The cause of the disaster is divided almost
equally between one of four categories, either (1) collisions, of which
there were 11; (2) grounding or stranding, 13; (3) fire/explosion, 12; or
(4) structure, hull, or machinery failure, 12. (1, p. 14-17)
Hull and structure failures were primarily
caused by weather and heavy seas. So, on the average, about every other
year a tanker has been lost, presumably due to weather. Some examples from
the National Research Council (1991) reference:
·
Castillo de Bellver
(1983) 271,540 dwt. Broke up off of South Africa, followed with
fire/explosion. Spilled 239,000 metric tons (1,760,000 barrels) of crude
oil. (1, p. 16)
·
T/V Captain W. Arvelo
(February 24, 1989) This tanker sank in high winds about 5 nautical miles
north of the northeast coast of the Dominican Republic. (7)
·
FPSO Schiehallion
(November 19, 1998) 152,360 metric tons. The Schiehallion is a
floating production, storage and offloading (FPSO) tanker that is anchored
in the North Atlantic Ocean, west of the Shetland Islands. Her length is
245 meters (803 feet), beam is 45 meters (148 feet), and she has a storage
capacity of 950,000 barrels of crude oil. On the night of November 19,
when the significant wave height was around 14 meters, the vessel was
struck on the bow by a high wave. The wave damaged the bow 20 meters (66
feet) above the water line, caving in the bow plating a distance of about
25 centimeters (nearly 10 inches), and causing the vessel to be removed
from station and taken to a shipyard for repairs. (2, p. 38)
·
Caribbean Sea (1977)
30,661 dwt. Broke up in east Pacific. (1, p. 16)
·
Athene (1977) 256,000
dwt. This very large crude carrier (VLCC) was sailing in the Agulhas
Current off of Port Elizabeth, South Africa, when it encountered an
extreme wave. When the wave hit, the foremast was completely submerged and
the reinforced windows 17.7 meters (58 feet) above the water line were
stove in. It was estimated that the wave was 30 meters (98 feet) high.
Faulkner notes that had this been a bulk carrier with a heavy cargo, “she
would not have survived.” (3, p. 5-6)
·
Grand Zenith (January
11, 1977) 29,930 dwt. This tanker with 212,000 barrels disappeared in the
North Atlantic off of Cape Cod, cause unknown. Bascom states thatwhen this
tanker disappeared off of Cape Sable, Nova Scotia, at that time it was the
largest ship to be declared “missing, presumed lost.” It carried a crew of
38. (4, p. 151 and 27, p. 273)
·
Golden Drake (1972)
30,000 dwt, Fire/explosion in Atlantic near Bermuda. (1, p. 16, and 5,
p. 171)
·
Texaco Oklahoma (March
27, 1971) This tanker with a crew of 44 broke in two while fully loaded at
a position about 120 miles northeast of Cape Hatteras, North Carolina. It
was proceeding at a slow speed in a severe winter storm (Note: Gulf Stream
area!) The forward half submerged the crew sleeping in the forward
deckhouse; none of those 13 crew members survived. Hours later a passing
ship rescued 13 survivors from the remaining 31 crew members. The coast
guard concluded that hull fracture was caused by heavy seas. (25:
“Structural Failure and sinking of the Texaco Oklahoma off Cape
Hatteras on 27 March 1971, with the loss of 31 lives.”)
·
Pine Ridge (December 21,
1960) Like the Texaco Oklahoma, the Pine Ridge was offshore
from Cape Hatteras (about 90 nautical miles, 167 kilometers) but traveling
in the opposite direction. Weather worsened and the vessel found itself in
a gale. Green water came over the bow and suddenly there was a loud crack
and the forward section of the ship tore lose, causing the death of the
master, the first, second and third mates, the quartermaster, radio
officer and chief steward. The other 29 crew members were rescued and the
stern section towed to salvage. The marine board determined that the hull
failed due to wastage (corrosion), excessive hogging and sagging stress
due to improper ballasting, and heavy seas. Principal members were reduced
anywhere from around 20 percent to as much as 65 percent of original
design thickness. (25: “MVI Pine Ridge.”)
·
Chryssi (December 26,
1970) 29,653 dwt. This 190 meter (624 feet) long tanker broke up in the
Atlantic Ocean near Bermuda. It was carrying 226,000 barrels of oil.
(5, p. 171)
·
Paco Ocean (1969) 30,016
dwt. Broke in two, Northwest Pacific. (1, p. 16)
·
Keo (1969) Hull failure
off of Massachusetts. (1, p. 16)
·
World Glory (June 14,
1968) Only 10 of 34 crew survived; 334,000 barrels of crude oil went into
the Indian Ocean. See Chapter 9. (7)
Others:
- Prestige
(November 13, 2002) This tanker was hit by high waves off of Galicia
coast, Spain. It developed a hole in its side, started leaking, was
towed to deep water, broke in two, and sank, releasing 77,000 tons of
oil (approximately 448,000 barrels). (6)
- Erika
(December 12, 1999) This tanker broke in two in heavy seas, gale
force winds near Brest, France. Corrosion suspected as part of the
problem, 71,400 barrels of oil spilled. (8, p. 1)
- Nakhoda
(January 7, 1997) This Russian tanker carrying 36,400 barrels of oil
broke in 2 pieces in heavy seas northwest of Japan. (28)
- Mimosa (August
1991) This 357,000 dwt tanker had her rudder badly damaged during a
storm. The vessel then drifted helplessly in the Agulhas Current, in
relatively shallow waters that were from 55 fathoms to 110 fathoms (100
to 200 meters) deep. She came dangerously close to going aground in
Algoa Bay, South Africa, but disaster was avoided by a marine salvage
company. Another report stated that a large wave punched a hole in the
side plating of the hull, large enough to “drive a bus through.” (11,
p. 28, and 12, p. 4)
- Atigun Pass
(1982 or 1983) See Chapter 9.
- Cretan Star
(July 28, 1976) This tanker had a load of 28,600 tons of crude oil.
After leaving the Persian Gulf she encountered a storm. The master
radioed that she’d been hit by a huge wave that caused some damage and
oil leakage. That was the last word from the vessel. A subsequent search
by aircraft found an oil slick not far from Bombay, India, near the
ship’s last reported position. (4, p. 61)
- Wilstar (May
17, 1974) 132,000 dwt. It fell into a huge trough off South Africa, then
was hit by a rogue wave in the Agulhas Current. The vessel was heavily
damaged, with a large section of the bow, fabricated of 2.54 centimeter
(1 inch) thick steel plates, literally ripped away as if grabbed by a
giant hand. (10, p. 16 and 4, p. 64)
- Wafra
(February 27, 1971) 70,000 dwt. A tanker damaged by an extreme wave in
the Agulhas Current. Engine room flooded, taken under tow, towline
broke, and the vessel drifted onto the Agulhas Reef. (7 and 4, p. 64)
- World Horizon
(1973?) Supertanker damaged by an extreme wave in the Agulhas Current.
(4, p. 64)
- Bridgewater
(January 30, 1962). This tanker broke in two in a storm 230 nautical
miles northwest of Fremantle, Australia. The stern half was eventually
towed in for salvage. (27, p. 28)
- Marine Sulphur
Queen (February 4, 1963). The Marine Sulphur Queen (169
meters, 554 feet) was a somewhat unusual tanker. It had been converted
to carry molten sulfur. The last known contact with the vessel occurred
when her position was estimated as 25 degrees, 45 minutes north, 86
degrees west. This would have placed her in the gulf of Mexico around
250 nautical miles (463 kilometers) due south of Panama City, Florida.
The vessel and crew disappeared without a Mayday or trace. After several
weeks of searching, a life preserver, fog horn, and trail board with the
vessel’s name were found. Weather was known to be rough along the
vessel’s route, winds 25 to 46 knots, seas at around 5 meters (16 feet.)
Originally, it was thought that the vessel might have been sunk by a
rogue wave. However, the coast guard inquiry revealed that the vessel
had a history of fires in the insulation surrounding the molten sulfur
tanks and had experienced damage in two previous storms. The Board of
Inquiry concluded that the vessel might have exploded, may have broken
in two due to a failure of the hull girder, or may have capsized in
synchronous rolling. (25, report 5943 and 27, p. 125)
General Cargo, Bulk Carriers and Combination
Carriers (OBOs)
Bulk carriers are the one vessel type that
appears to be most susceptible to break-up by large waves. An appalling
number of bulk carriers have been lost in the last several decades, along
with hundreds of crew.
- Fei Cui Hai
(February 7, 1998) The China Overseas Shipping Company bulk carrier was
lost in the South China Sea between southern Vietnam and Singapore with
31 of the crew of 34 dead. (18)
- Flare (January
16, 1998) This bulk carrier broke up and sank in the Gulf of St.
Lawrence; 4 crew were rescued by a Canadian helicopter but 21 were lost.
(18)
- Viking
(September 16, 1994) Viking, a collier, was hit by huge waves off the
coast of Norway, suffering 21 injured crew.
- Berge Istra
(December 1975) This 224,000 ton combination bulk carrier is the biggest
ship ever to simply disappear without a trace. It was 314 meters (1,030
feet) long, with a beam of 50 meters (164 feet). Lost after sailing from
Tubarão, Brazil on Nov. 29, 1975. Last reported southwest of Mindanao,
Philippines. For weeks no one knew what happened to the ship.
Originally, because of its sudden disappearance, it was thought to be
the victim of an extreme wave. Later, two survivors were rescued. They
reported that the ship had exploded without warning, broke up, and sank
before a Mayday call could be made. (13, p. 198 and 4 p. 153)
- Anita (March
1973) 13,000 dwt. This Norwegian bulk carrier sailed from Virginia with
Germany as its destination. In the North Atlantic it reported
encountering a severe gale—60 knot winds, 15 meter (49 foot) seas;
nothing was ever heard from the ship again. It thus became one of the
hundreds of vessels to be entered on Lloyd’s List as “missing, presumed
lost.” (4, p. 158 and 14, p. 19)
- Norse Variant
(March 1973) In the North Atlantic with a cargo of coal, this 165 meter
(542 foot) long vessel broke in two during the same storm as the
Anita and sank at a position about 114 nautical miles southeast of
Cape May, New Jersey. Waves broke a hatch cover and the ship sank
quickly. In this case, a single survivor was rescued and thus the story
of the ship’s disappearance became known. This vessel also served as a
car transporter for Volkswagen automobiles. (4, p. 158 and 14, p. 19)
- M/V Sinar Andelas
(December 26, 2004) This cement carrier was in the port of Lhok Na,
Indonesia, when the wave from the December 26, 2004 southeast Asia
tsunami hit. The vessel capsized; of 23 members, 19 were reported
missing. (18)
- Theodore AS
(1973) 13,900 dwt. This bulk carrier sailed from Norway headed for Spain
with a cargo of iron ore. She was struck by a gale in the North Sea and
disappeared, becoming another entry on Lloyd’s List of “missing,
presumed lost.” (4, p. 159)
- Neptune Sapphire
(1973) See Chapter 8.
- Atlas Pride
(Date unknown) This was another cargo ship hit in terrible weather. A
rogue wave appeared out of nowhere and destroyed the entire bow. (12
, p. 4)
- Apollo Sea
(June 20, 1994) A bulk ore carrier lost at the Cape of Good Hope after
foundering in heavy weather—36 crew lost, damage to endangered African
Penguin breeding grounds from oil spill. (9, p. 1)
- MV Treasure
(June 23, 2000) Another bulk ore carrier foundered near same location as
Apollo Sea—this time in fair weather, with the loss of 1,400
metric tons of oil. (9, p. 1)
- Edmund Fitzgerald
(November 19, 1975) See Chapter 9.
- Selendang Ayu
(December 10, 2004) This 226 meter (740 feet) long Malaysian freighter
with a cargo of soybeans lost power when hit by big waves in the Bering
Sea. Gale force winds continued to blow it toward Unalaska Island,
despite efforts to tow it or anchor it. The vessel went aground on the
island and broke in half, releasing 154,000 liters (40,000 gallons) of
fuel oil. Six evacuated crew members died in a helicopter crash. (15,
p. 1)
- Unnamed vessel
(1960s) This bulk carrier was carrying ore from North Africa to England.
Off the northwest coast of Spain, along the 100 fathom (183 meters deep)
line, the ship was making good progress in moderate weather. At 0520
hours (5:20 A.M.), the chief officer was surprised to see the moon
blotted out and the deck of the ship obscured. At first, he thought a
cloud had passed over the moon, but then to his horror realized that a
giant wave was bearing down on the port beam of the vessel. Just before
reaching the ship, the wave started to break, hitting it and sweeping
the full length of the vessel. Fortunately the hatch covers did not fail
and the ship survived, although with damage that indicated the enormous
force of the blow it received. The forecastle head deck was bashed in
about 7.6 centimeters (3 inches), with supporting deck beams (35.6
centimeter or 14 inch wide steel channel beams) being cracked through;
12.7 centimeter (5 inch) stanchions were buckled; timber supports and
shelving below decks completely wrecked; flood lights and ladders 15.3
meters (50 feet) above the sea ripped loose; glass on compasses 21.4
meters (70 feet) above the water line were cracked, even though they
were protected by brass helmets. Finally, it was determined from other
damage that the wave was higher than 26 meters (85 feet). Ironically the
chief officer had warned the master of the risk of extreme waves in
shallow waters along the Spanish coast, but the master elected to stay
on the course he’d laid out. (16, p. 35-37)
- Daniel J. Morrell
(November 29, 1966) This 183 meter (600 foot) long ore carrier embarked
to pick up another load of iron ore. Unfortunately it was caught in a
violent late fall storm on Lake Huron. The ship broke in two, stranding
some crew members in the bow section. The stern section drifted away.
Four men got a raft launched and abandoned the bow section which sank
first. After a day and a half when rescuers located the raft in freezing
weather, only one person remained alive. (17, p. 41)
- Carl D. Bradley
(November 18, 1958) See Chapter 9.
·
SS Pennsylvania (
January 9, 1952) The SS Pennsylvania departed Seattle for Yokohama,
Japan. The vessel was loaded with a cargo of wheat and barley and
additional army supplies, including army trailers and dump trucks. Some
cargo was stored on deck. En route the vessel encountered gale-force winds
and seas of 11 to 14 meters (35 to 45 feet). Early on the morning of
January 9, the vessel reported that there was a 4.3 meter (14 foot) long
fracture in the hull and the vessel was coming about to return to Seattle.
At that time she was at 51 degrees, 9 minutes north, 141 degrees 31
minutes west, in the North Pacific southwest of Queen Charlotte Islands.
Problems developed with the steering gear, and the vessel lost steering.
The vessel was taking on water forward and in the engine room. The gear
was repaired but then the vessel reported that she was having difficulty
steering because the rudder was too far out of the water. The last
message received was around 10 P.M. advising that the crew was abandoning
ship. Despite a search, nothing was ever found of the vessel or its 46
crew members. (25: “MVI Pennsylvania”)
Container Ships
Container
ships have been hit by extreme waves, with the result that some containers
were damaged or lost over board, as in the case of the Hansa Carrier
described in Chapter 2. Instances where a container ship has been broken
up or capsized by extreme waves are uncommon. I met with two masters of
container ships, Captain Jon Harrison and Captain Mark Remijan, and asked
them if they had ever experienced a rogue wave. Jon said that he had not
experienced anything he considered an extreme wave, just storm waves 12 to
15 meters (39 to 49 feet) high. Mark said that he thought he might have
experienced one. This was on the President Jackson. See below for a
description of that incident.
·
M/V Xin Qing Dao
(October 27, 2004) This brand new (built in 2003) 5,600 TEU container ship
is 279.9 meters (918 feet) long, has a beam of 40.3 meters (132 feet) and
a draft of 14 meters (46 feet). En route from Malta to Hamburg, she
encountered a Beaufort Force 11 storm off the coast of Brittany. Waves
reached 30 meters (98 feet) and the vessel experienced rolling of 30
degrees. A total of 31 12.2 meter (40 foot) long containers were lost
overboard and 29 more were damaged. The vessel was able to reach the port
of Felixstowe, United Kingdom, on October 30, 2004. (18)
·
M/V OOCL America
(January 31, 2000) En route from Long Beach to Kaohsiung, this vessel
encountered a severe North Pacific storm. A wave caused the vessel to roll
45 degrees, causing an estimated 350 containers to be lost overboard and
several more to be crushed. There was also flooding and damage to
container bays, but the vessel did not sink. Two other container ships
were damaged in the same storm: M/V Sea-Land Hawaii (lost 21
containers) and M/V Sea-Land Pacific (lost 20 containers). (18)
·
M/V Jaami (December 26,
2004) This container ship was entering Colombo as the southeast tsunami of
December 26, 2004 hit. The vessel was driven against the breakwater where
it was abandoned but later salvaged. (18)
·
M/V MSC Carla (November
25, 1997) This 40,912 dwt container ship was en route from LeHavre, France
to Boston carrying 2,400 containers when it encountered a gale and seas
of 9.2 meters (30 feet) or greater. Early on the morning of November 25,
about 100 nautical miles north of São Miguel Island, Portuguese Azores,
the ship broke in two pieces. Portuguese military helicopters rescued 34
crew members. The bow section sank on November 30, with about half of the
containers. The stern section, with another 1,000 containers, was towed to
Las Palmas, Canary Islands, for salvage. (18)
- Hanjin Inchon
(1997-1998) Container ship reportedly lost with all hands. No details
available.
- Poet (October
25, 1980) Poet was a converted Liberty Ship, originally launched
in 1944. It was carrying a cargo of grain to Egypt when it vanished
during a storm, leaving no trace. The Marine Inquiry Board listed a
number of possible reasons why the ship might have been lost, including
hatch failure, structural failure, or capsizing, but was unable to reach
any definite conclusion. The crew of 34 was lost. (25 and 27, p.
164-165)
- Badger State
(December 26, 1969) This vessel, like Poet, was a 135 meter (441
foot) long cargo vessel built in 1944. It suffered an unusual disaster.
The vessel was loaded with bombs and ammunition destined for Vietnam. It
encountered two successive storms in the North Pacific. One mountainous
wave rolled the vessel 52 degrees, destroyed one lifeboat, and under the
force of violent rolling, some of the cargo broke loose. An explosion
opened a hole in the side of the ship. The crew of 40 sent a Mayday and
prepared to abandon ship. While lowering a lifeboat, a 2,000 pound bomb
fell out of the hole and landed in the lifeboat, capsizing it. There
were 14 survivors. (25: “SS Badger State”)
- President Jackson
(1992) This was a C-10 class vessel, 1st generation Post-Panamax,
capacity around 4,300 TEUs, launched in 1988. The master told me that
they were in the Bering Sea, had been in a storm for about 6 hours with
7 to 8 meter high swells in a quartering sea. The vessel was rolling 15
to 18 degrees, occasionally 20 degrees. It was daylight; he happened to
look aft and saw a wave, much larger than the others, coming towards the
stern quarter. When it hit, the President Jackson rolled 32-33
degrees. As the wave passed under the ship, it seemed to just hang there
in space, you could feel a strong vibration or shudder run through the
ship. The master threw the rudder over 20 degrees to counteract the
roll. He was not sure of the height of the wave, it all happened too
fast, but stated that it was significantly different from the 7-8 meter
waves the ship had been experiencing. It only happened once. (19)
- Hansa Carrier
(May 27, 1990) See Chapter 2. While in the center of the North Pacific,
roughly midway between the Aleutian and Hawaiian Islands, the vessel
encountered a severe storm. Waves hitting the vessel caused 21
containers to fall into the sea, spilling their contents of athletic
shoes.
Passenger Liners/Cruise Ships
There have been a number of instances where
passenger liners caught fire and burned up. Most striking of these was the
Yarmouth Castle (Caribbean Sea, November 13, 1965), where the
captain was the first to leave, and was locked up on one of the rescue
vessels for failing to help save the passengers. Others include such
well-known vessels as Leonardo da Vinci, Cunard Ambassado,
Homeric, Caribia, Laconia, Morro Castle, and
Antilles. (27) Passenger liners have not been immune to
damage by extreme waves, as these examples indicate:
- Norwegian Dawn
(April 16, 2005) The “Ocean view” staterooms on the port and starboard
sides of the luxury cruise ship Norwegian Dawn command an
excellent view of the sea from the 10th deck. There is a
large bed, private bathroom, clothes closet, sitting area with couch,
small table, and a desk with a television. Floor to ceiling glass doors
open to a private balcony. The 294 meter (965 feet) long vessel sailed
from New York on Sunday, April 10, 2005, for a visit to Florida and the
Bahamas, and was due to return to New York on Sunday, April 17, 2005, to
load passengers for the next cruise. Upon leaving the Bahamas for New
York, the Norwegian Dawn ran into a gale. Seas and winds coming
down from the north were running in opposition to the northbound Gulf
Stream. Weather was rough for the next 48 hours after the Norwegian
Dawn left the Bahamas, with the vessel rolling in 12 meter (40 feet)
high swells. Early Saturday morning the vessel was hit by a single freak
wave 21.4 meters (70 feet) high that caved in the sliding glass doors in
several forward-facing cabins. A flood of sea water rushed into the
Norwegian Dawn, flooding 62 cabins. Passengers reported broken
glass, clothing, newspapers, magazines floating in sea water, furniture
overturned. Four passengers received minor injuries. The Norwegian
Dawn diverted to Charleston South Carolina for emergency repairs and
to allow passengers whose cabins had been flooded to fly back to New
York. In Charleston, the U.S. Coast Guard reported that the vessel had
experienced some hull damage but was not taking on any water. (20)
- M/V Explorer
(January 27 2004) See Chapter 9.
- Monique
(August 1, 1953). This French passenger ship vanished in the South
Pacific with 120 persons on board. (27, p. 271)
- Caledonian Star
(March 2, 2001) See Chapter 9.
- M/V Rotterdam
(September 24, 2004) This 237 meters (777 feet) long, 62,000 ton Holland
America cruise ship found itself on the edge of hurricane Karl. Battered
by waves in rough seas it lost all power to 4 engines, disabling the
stabilizers and allowing the vessel to list as much as 40 degrees in 10
to 15 meter (33 to 49 foot) swells. Passengers suffered numerous minor
injuries and fractures and reported furniture flying around, pianos
rolling, plates crashing to the floor, TV sets rocketing across
staterooms. (18)
- Bremen
(February 22, 2001) See Chapter 9.
- Oceanos
(August 3,1991) During a storm off of East London, South Africa, the
cruise ship Oceanos (150 meters, 492 feet long) was battered by
severe wind and wave conditions and hit by an extreme wave or waves.
There was a leak in the engine room, power failed and the vessel sank.
All passengers and crew (580 persons) were rescued. This was the same
storm that damaged the Mimosa. (11, p. 28)
- Queen Elizabeth 2
(September 11, 1995) See Chapter 9.
- Michelangelo
(April 12, 1966) See Chapter 9.
- Queen Elizabeth
(1943) See Chapter 9.
- Queen Mary
(1942) See Chapter 9.
- Waratah (July
27, 1909) See Chapter 9.
Other types of Vessels
- Polar Star
(October 25 1985) The U.S. Coast Guard icebreaker Polar Star was
the first single ship to circumnavigate the North American continent by
traversing the Northwest Passage. After successfully completing the
dangerous passage through ice-filled waters, the 122 meters (399 feet)
long vessel was not far from Vancouver Island and was traveling south
east to Seattle when it was hit on the starboard beam by a sequence of
extreme waves—the so-called “Three Sisters.” This was thought to be due
to the interaction of increasingly heavy seas the vessel was headed
into, combined with a storm that had been building to the west of the
vessel for over 36 hours across a fetch of 1,613 kilometers (1,000
miles). The waves came suddenly out of the darkness at 0200 (2:00 A.M.),
causing the vessel to roll violently back and forth 50 degrees. Three
crew were tossed the width of the 26 meter (85 feet) wide bridge,
killing one and injuring two others. Winds reached 60 knots with gusts
to 80. The significant wave height was around 3.5 meters (11.5 feet),
while the “Three Sister Waves” that struck the ship were estimated as
three times as high, or 10.7 meters (35 feet). (21, p. 190-196)
- Nepenthe
(1983) See Chapter 9.
- Leviathan
(June 8, 2001) Leviathan, a 9.8 meter (32 foot) Down East cutter
was less fortunate than Nepenthe. With a 2-person crew, the
vessel left the Chagos Archipelago (near Diego Garcia Island) headed for
Ile de Mayotte, a small island in the Comoros, in the dangerous waters
of the Mozambique Channel. On the evening of June 8, they reported
experiencing high winds and heavy seas. That was the last that was heard
from them until their EPIRB was detected about 6 hours later at latitude
10.17 degrees south, longitude 49.67 degrees east. At this time of year,
the South Equatorial Current branches to flow around Madagascar, joining
up again at the southern end of the island to form the Agulhas current.
They would have passed through this turbulent area, and were likely
overwhelmed by confused seas. (26, p. 64-65)
- Trawler Gaul
(1974) This modern, 1,500 ton “super” trawler went down in a storm with
36 crew and was never heard from. Rumors flew about that it had been
torpedoed by a Soviet submarine, pulled under by a nuclear submarine, or
sunk by a rogue wave. The wreck was finally located in 1997, surveyed a
few years later, and at an official hearing in 2004, it was determined
that the vessel capsized due to flooding through open duff and offal
chutes on the factory deck. (24)
- Lady Alice
(September 6, 1980) See Chapter 9.
- U.S.S. Grouper
See Chapter 9.
- The U.S.S. Valley
Forge, an aircraft carrier, was hit by an extreme wave during a
strong winter storm near Cape Hatteras in the Gulf Stream. The wave was
more than twice the significant wave height and crashed down on the
starboard side of the forward flight deck so hard that it ripped the
deck from the ship. Steel girders and the 15.2 centimeter (6 inch thick)
teak flight deck were broken off and lost overboard. Photographs show
sections of the junior officer’s quarters dangling off the side of the
ship; fortunately, the area was unoccupied at the time of the incident.
(22; 10, p. 17)
- Műnchen
(December 1978) This state-of-the-art German cargo ship sent a frantic
Mayday radio call from the middle of the Atlantic. Despite a massive
search effort by dozens of ships in the vicinity, neither the vessel nor
survivors were ever found. Searchers did find one of the vessel’s
lifeboats, normally stowed at a location 20 meters (66 feet) above the
water line. Damage to the lifeboat supports indicated that it had been
ripped off the boat by the force of a large wave. Twenty-seven crew were
lost. (12)
- The U.S.S.
Independence (April 7-8, 1977) This was another aircraft carrier
that was hit by several extreme waves during a North Atlantic Storm. The
captain was quoted as saying that he looked out and saw the wave coming
a mile or mile and a half away (1.6 to 2.4 kilometers), and it looked
like the wave in the “Poseidon Adventure” (a movie depicting a passenger
ship being capsized by a huge wave at sea). The significant wave height
at the time was 7.6 to 9.2 meters (25 to 30 feet); the wave that struck
the carrier was around 16.7 to 18.3 meters (55 to 60 feet). (23, p.
14)
- U.S.S. Milwaukee
(October 1975) See Chapter 9.
- Ob (circa
1955-56) This Soviet diesel/electric Antarctica supply ship, reported
being hit by a 25 meter (82 feet) wave in the Southern Ocean. (4)
- U.S.S. Pittsburgh
(February 1945) See Chapter 9.
_________________________
Sources for the above
incidents:
1.
Committee on Tank Vessel
Design. 1991. Tanker Spills—Prevention by Design. National Research
Council, National Academy of Sciences, Washington DC: National Academy
Press, 14-17.
2.
Gorf, Peter, et al. 2001. “FPSO Bow Damage in Steep Waves.” In Olagnon and
Athanassoulis, eds., 37-46.
3.
Faulkner, Douglas. 2001. “Rogue Waves—Defining their Characteristics for
Marine Design.” In Olagnon and Athanassoulis, eds., 5-6.
4.
Bascom, Willard. 1980. Waves and Beaches. New York: Anchor Press.
5.
Couper, Alistair, ed. 1983. The Times Atlas of the Oceans. New
York: Van Nostrand Rheinhold.
6.
www.CNN.com.world
. 2002. “Crippled Fuel Oil Tanker Sinks,” Wednesday, November 20.
7.
National Oceanic and Atmospheric Administration (NOAA). “Oil spill
incident reports.”
http://spills.incidentnews.gov. Accessed September 2005.
8.
International Oil Pollution Compensation Funds “The Erika
Incident.”
http://www.iopcfund.org/erika.htm. Accessed September 2005.
9.
International Bird Rescue Research Center. “IBRRCs Big Assist at Oil Spill
in South Africa,” http://www.ibrrc.org/treasure_spill.html.
Accessed September 2005.
10.
Nickerson, Jerome W. 1993. “Freak Waves.” Mariners Weather Log,
Vol. 37, No. 4.
11.
Shillington F.A. and E. H. Schumann. 1993. “High Waves in the Agulhas
Current.” Mariners Weather Log, Vol. 37, No. 4.
12.
B British Broadcasting Corporation. 2002. “Rogue Waves.” Transcript of a
BBC program on Freak Waves. First aired on BBC TWO, November 14, 2002.
13.
Hendrickson, Robert. 1984. The Ocean Almanac. New York: Doubleday
14.
Kjeldsen, Soren Peter. 2001. “Measurements of Freak Waves in Norway and
Related Ship Accidents.” In Olagnon and Athanassoulis, eds., 19-35.
15.
Milbury, Jim. 2005. “Bering Sea
Shipwreck Spill Threatens Alaskan Islands,” NOAA Report, Vol. XIV,
No.1, 1.
16.
Cameron, Captain T. Wilson. 1993. “The Treachery of Freak Waves”
Mariners Weather Log, Vol. 37, No. 4, 35-37.
17.
Gillham, Skip. 1993. “The Daniel J. Morrell.” Mariners Weather Log,
Vol. 37, No. 4, 41.
18.
The law firm of Countryman and McDaniel. “Marine Casualty Reports.” See
Http://www.cargolaw.com/presentation-casualties. Used with permission.
19.
Personal communication, Captain Mark Remijan, June 5, 2005.
20.
“Cruise Ship Damaged,
Flooded by 70-foot Wave During Storm.” Washington
Post, April 18, 2005, p. A18. Also articles
posted on www.CNN.com/2005/TRAVEL on April 17 and April 19, 2005,
and Abbott, Mary Lu, “Rogue Waves Surprisingly Common,” Los Angeles
Times, May 22, 2005, pg. L-5. In June, a group of passengers filed a
$100 million lawsuit, claiming the cruise line had needlessly endangered
their lives. See Los Angeles Times,
June 26, 2005, p. L3. Passengers allege that despite
knowing about the storm, the vessel attempted to return to New York to
take part in a television show.
21.
Nickerson, Jerome W. 1986. “Three Sisters Mar Historic Voyage.”
Mariners Weather Log, Vol. 30, No. 4, 190-196.
22.
Personal communication, Admiral Joe Barth, April 20, 2005.
23.
Nickerson, Jerome W. 1985. “Marine Observations Program,” Mariners
Weather Log, Vol. 29, No. 1, 14.
24.
“Inquiry Into the Loss of the “Gaul.” 2002. Mr. Justice David Steele
presiding, December 17, London:
UK Department of Transport.
25.
Marine Board of Investigation Reports (Marine Casualty Report), United
States Coast Guard, U.S.
Department of Transportation. See
http://www.uscg.mil/hq/g-m/moa/reportindexcas.htm. Accessed June 2005.
26.
Griffiths, Jenni. 2002. “Without a Trace.” Cruising World,
December, 64-81.
27.
Ritchie, David. 1996. Shipwrecks—An Encyclopedia of the World’s Worst
Disasters at Sea. New York: Checkmark Books.
28.
See the Cargo Letter, Edition 310, January 6, 1997 at http://www.interpool.com/cargoletter.
See also the National Maritime Research Institute (Japan) for a photograph
of the bow section just before sinking.
http://www.nmri.go.jp.
Annotated Bibliography
(This is the complete
list of references and source material for the book.)
Aebi , Tania (with
Bernadette Brennan). 1989. Maiden Voyage. New York: Ballantine
Books. Aebi left New York at age 18, returning two and one-half years
later as the youngest woman to sail around the world alone.
Ambraseys, N. N. 1962.
“Data for the Investigation of the Seismic Sea Waves in the Eastern
Mediterranean.” Bulletin of the Seismological Society of America,
895–913. Includes a description of the modified Sieberg Tsunami Intensity
Scale.
Antar, Elias. 1971.
“Earthquake!” Saudi Aramco World, May/June, Vol. 22, No. 3.
Descriptions of some ancient earthquakes in the Middle East.
Barker, Ernie. 1998.
Rogue Wave. Unpublished manuscript. A single-handed sailor’s journal
of wave adventures in the Tasman Sea.
Barr, Edward J. 1994.
“Freak Wave on a Submarine.” Mariners Weather Log, Vol. 38, No. 4.
Report describing a large wave overrunning a submarine as it was in the
process of diving to periscope depth and the consequences.
Bascom, Willard. 1980.
Waves and Beaches. New York: Anchor Press. A classic book, very
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IEEE 2002. Remote
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technologies for remote sensing of the environment of the oceans and
continents
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that might be conducive to extreme wave formation.
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Bergen, Norway. Technical report, part of the European Community MaxWave
research project, with more evidence for the existence of extreme waves.
Jenkins, Bruce. 1999.
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Berkeley: Frog Ltd. Some people even go looking for extreme waves; this
narrative tells the story of the world’s most accomplished surfers who
have had intimate contact with waves large enough to crush modern
ocean-going vessels.
Junger, Sebastian. 1997.
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W. Norton. The classic story of man trying to survive at sea in the
presence of giant waves, with an explanation of one set of conditions that
can unexpectedly produce extreme wave conditions.
Kane, Herb K. 1976.
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Interesting history of ancient Polynesian navigation by a man who
participated in the design, construction, and sailing of the Hokule’a from
Hawaii to Tahiti.
Kinsman, Blair. 1965.
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waves, and how waves are formed—some material dated, but extremely well
written and entertaining.
Kotsch, Rear Admiral
William J. and Richard Henderson. 1984. The Heavy Weather Guide. 2nd
ed. Annapolis: Naval Institute Press. A valuable reference book for
merchant vessels encountering gales and heavy weather.
Knecht, G. Bruce. 2001.
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disastrous 1998 Sydney-Hobart race.
Krieger, Michael. 2002.
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in History. New York: The Free Press. Hundreds of oil field
workers are on a barge in the Gulf of Mexico when it is hit by Hurricane
Roxanne in 1995.
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Galveston, Texas by storm surge and large waves.
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outdated but classic review of wave theory.
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Chinese navigators.
Lewis, David. 1979.
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ancient Polynesian navigation methods by a man who studied under one of
the best surviving navigators.
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sailors who have sailed around the world alone, or crossed the oceans in
the smallest boats, or otherwise have experienced the sea and its greatest
challenges.
Mariner’s Weather Log.
various issues. Stennis Space Center, Mississippi: U.S. Department of
Commerce National Oceanic and Atmospheric Administration. A wealth of
real-life experiences with extreme waves by the men and ships that
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April 2001.
Marriott, John. 1987.
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including a description of the grounding of the Memphis.
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shipwrecks in the Americas, with a description of how wrecks are located
and a section detailing the exploration of Port Royal, Jamaica
Massel, Stanislaw R.
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theories used to model wind-wave interaction.
MaxWave Project. 2003.
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technical objectives, work plan, selected technical reports, and a
description of the tasks planned in this ambitious and important new
research program aimed at improving our knowledge of extreme waves.
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excellent compendium of recent research on modeling, and forecasting
extreme waves.
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vessel La Conte.
Warshaw, Matt. 2003.
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Engineering methods for the dynamic analysis of offshore structures.
Winchester, Simon. 2004.
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dramatic story of the island that blew up, and the devastating tsunami
that followed.
World Meteorological
Organization. 1988. Guide to Wave Analysis and Forecasting. Geneva:
World Meteorological Organization, WMO-702. The classic guide to
forecasting sea conditions.
Young, Ian R. 1999.
Wind Generated Ocean Waves. Oxford: Elsevier. A comprehensive review
of wind-wave analytical methods and theory including wave measurements.
Zebrowski, Ernest, Jr.
1997. Perils of a Restless Planet—Scientific Perspectives on Natural
Disasters. London: Cambridge University Press. A review of natural
disasters (storms, earthquakes, tsunami, volcanoes, asteroid impacts) and
their potential or actual impact on life on earth.
End Notes for
the excerpts listed above.
Note: Refer to
the annotated bibliography for the complete citation.
[1]
Herodotus (1972), 283.
[3]
Bergreen (2004), 232–238.
[4]
Dyson (1991), 64. See also Taviani (1989) and Morrison, (1978),
351–548.
[5]
Morrison (1978), 370.
[6]
Cummins (1992), 79–133.
[7]
Bergreen (2004), 132–171. See also Louise Levathes (1994), When
China Ruled the Seas. New York: Simon & Schuster.
[8]
Bergreen (2004), 391–392.
[9]
Ochi (1998), 58; Young (1999), 25.
[10]
After Bruce J. Muga, “Statistical Descriptions of Ocean Waves” Chapter
6 in Wilson, ed. (1984), 159.
[11] Muga (1984), 159–161; Young (1999), 26.
[12]
Young (1999), 27. Note: be warned that in spite of this, the largest
wave can be the third, the ninth, the tenth, et cetera.
[14]
Van Dorn (1974), 192–199.
[15]
Ochi (1998), 255–280.
[17]
See Sheets and Williams (2001), 285-286.
[18]
Source: U.S. NOAA, National Weather Service, National Hurricane Center
web Site at:
www.nhc.noaa.gov.
[23]
Source: Adapted from Ochi (2003), 19.
[24]
See Sheets and Williams (2001), 203–221. For the National Hurricane
Center Web site, go to www.nhc.noaa.gov.
[25]
World Meteorological Organization (1988), 2–4.
[26]
Price, ed. (1960), 43.
[30]
Lewis (1979), 200–203.
[31]
This was accomplished under the auspices of the Polynesian Voyaging
Society, formed in 1973 by Ben Finney, Herb Kane, and Tommy Holmes.
See http://pvs.kcc.hawaii.edu.
[33] Bascom (1980), 95–111. Chapter 5, “Tides and
Seiches.” This small book has one of the clearest descriptions of
tidal behavior that I’ve encountered, and in other respects is a
remarkable book. It has been out of print for some time.
[34]
LeBlond (1978), 510.
[36] Sverdrup et al. (2005), 286–287.
[38]
Ralph Vartbedian and Peter Pae (2005), “A Barrier That could Have
Been,” Los Angeles Times, Friday September 9, A10.
[39]
Jane Hollingsworth (1989), “The Chicago Seiches” Mariners Weather
Log, Vol. 3, No. 2, spring, 16–19.
[40] LeBlond (1978), 512.
[41] Sverdup et al. (2005), 289–290.
[42] Bascom (1980), 103–104.
[43]
Ibid., 104.
Chapter 10 End
Notes
[44]Mercator
(2005). Forecast of Container Vessel Specifications and Port Calls
within San Pedro Bay. Bellevue, Washington: Mercator Transport
Group
[45] Mercator (2005), 5-10, op. cit.
[46] Tarman and Heitman (no date) 8.
[50] Sverdrup et al., (2005), 252.
[53] Sverdrup et al., (2005), 289.
[54]
Personal communication, Craig B. Smith with Professor Chris Garrett,
University of Victoria, British Columbia, October 5, 2005.
[55]
For those interested in more detail, Bruce J. Muga, “Deterministic
Descriptions of Ocean Waves,” Chapter 2 in Wilson ed. (1984), provides
an excellent overview.
[56]
Bruce J. Muga,. “Statistical Descriptions of Ocean Waves,” Chapter 6
in Wilson, ed. (1984).
[57] Bitner-Gregersen (2002), 95.
[59]
Personal communication, Craig B. Smith with Professor Chris Garrett,
University of Victoria, British Columbia, October 5, 2005. See also
Müller, Garrett, and Osborne (2005), 68-69.
[60]
This is known as Hooke’s Law. The constant of proportionality between
stress and strain is known as Young’s modulus.
[61]
Paul H Taylor and Christopher Swan, (2000) “New Waves, Solitons, and
Spreading,” in Olagnon and Athanassoulis, eds. (2001), 245-254.
[62] Kristian B. Dysthe, (2000) “Modeling a Rogue
Wave—Speculations or a Realistic Possibility?” in Olagnon and
Athanassoulis, eds. (2001), 255-264.
[63]Efim
Pelinovski, et al., (2000) “Nonlinear Wave focusing as a Mechanism of
the Freak Wave Generation in the Ocean,” in Olagnon and Athanassoulis,
eds. (2001), 193-204.
[64]
Peter Janssen “Nonlinear four-wave interaction and freak waves” in
Müller, ed. (2005), 85-90.
[65]
Kristian B. Dysthe, (2000) “Modeling a Rogue Wave—Speculations or a
Realistic Possibility?” in Olagnon and Athanassoulis, eds. (2001),
255-264; also in the same reference: Miguel Onorato, et al.,
“Occurrence of Freak Waves from Envelope Equations in Random Ocean
Wave Simulations,”181 and Efim Pelinovski, et al., “Nonlinear Wave
Focusing as a Mechanism of the Freak Wave Generation in the Ocean,”
193-204.
[66]
Douglas Faulkner, “Rogue Waves—Defining their Characteristics for
Marine Design,” in Olagnon and Athanassoulis, eds. (2001), 9.
[67]
Peter Gorf, et al., “Bow Damage in Steep Waves”
in Olagnon and Athanassoulis, eds. (2001), 38-39.
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