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Extreme Waves 11 Davy Jones’s Locker The origin of the term Davy Jones’s locker is not known with certainty. One speculation is that Jones ran a waterfront tavern frequented by sailors. He supposedly drugged them and confined them in his ale locker so they could be pressed into service by the British navy. Even if the origin of the term is obscure, the meaning is not. Davy Jones’s locker connotes a cold, watery grave, eternal rest at an unknown location at the bottom of the ocean. Many a person has suffered this fate when violent storms and huge waves overtook them. Some were famous, but most were sailors or passengers or coastal dwellers known only to their families and relatives. It is even fair to say that extreme waves and storms have changed the course of history, as in the case of the typhoon—“Divine Winds”—that devastated a Chinese fleet sailing to invade Japan in 1291, or the big waves that destroyed the Spanish Armada in 1588 and ultimately led to the ascendancy of British naval power. Civilization is in shock over the tragedy of the December 26, 2004, tsunami in Southeast Asia. The magnitude of suffering beggars understanding. Parents who experienced the unspeakable terror of their infants being ripped from their arms by the fury of the waves will live
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Extreme Waves with that horror forever. Families torn apart will always wonder what happened to missing loved ones. As I worked on this book in the days following the disaster, the estimate of deaths, first 20,000, doubled each day, eventually reaching 280,000. Sadly, we recognize that the true toll in human lives will never be known. Scientists will agonize as they ask themselves: “Could this catastrophe have been predicted?” Governments will be challenged by angry citizens: “Could warnings have been given, could aid have arrived faster, could more victims have been pulled from the sea or otherwise rescued?” The reality is that earthquakes cannot be prevented and some earthquakes will cause tsunami. What is preventable is needless loss of life. The knowledge exists to build earthquake-resistant and flood-resistant buildings; for economic and other reasons it is not always employed. Warning systems can be deployed—satellite communication technology today makes such systems a bargain compared to the cost of just one day of international aid to tsunami victims. There are conditions besides tsunami that can give rise to extreme waves—waves that can cause appalling property loss and loss of human lives in ships at sea. Extreme waves are likewise not preventable, but again, needless loss of life is preventable through the design of better vessels and improved weather forecasting models. Pressures due to economics and competition need to be examined to see if they are placing ships and crews at excessive risk. The research program currently under way within the European community is a much needed first step. Hopefully, this work will lead to better predictive tools and new design criteria for both seagoing vessels and offshore structures that will better enable them to withstand extreme waves. We can never quiet the stirrings of Ruau-Moko in the womb of the earth, nor can we still the restless waters raised by Poseidon. But through awareness, and better science and engineering, we could certainly improve the odds for survival. The keys are better design, forecasting and prediction, and warning systems. DESIGN OF PORT AND COASTAL FACILITIES Today, more people than ever before live along the shorelines of every country touching upon an ocean. Over the ages, the oceans have risen
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Extreme Waves and receded. Vast parts of the world that are today dry land were once ocean bottoms. Today there is clear evidence that the oceans are advancing; scientists dispute the causes—is it global warming due to human activities, or is it an inevitable cycling of global temperatures? To islanders such as those living on the coral islands of Tuvalu and Kiribati, it does not matter; they just know their land is disappearing. So, it is not just the risk of a tsunami that makes the design of port and coastal facilities so important; if the mean sea level rises, some coastal facilities will have a reduced margin of safety; others will simply disappear. Just what is the margin of safety? Elsewhere I’ve mentioned that the elevation of the Balboa Peninsula where I live is 10 feet above mean sea level—not much comfort there. The same is true of large sections of the Pacific and Atlantic coasts of the United States, as it is of countries ringing the Indian Ocean and of many Pacific Islands. There are two piers, about a mile apart, that are an integral part of our beachfront community. The southerly one, called the Balboa Pier, has a deck that rises 20 feet above mean sea level, while the Newport Pier, a little farther north, is 22 feet above mean sea level. Both piers have restaurants overlooking the ocean, and during daylight hours visitors or people fishing will be on the piers enjoying the view. Would they be safe in a tsunami? About 15 miles farther north is the giant port complex of the combined Los Angeles–Long Beach harbors. This seaport is the largest in the United States in terms of container ships; every day dozens of giant vessels enter the port from all over the world to discharge goods or to load materials for shipment overseas. There is a long breakwater that protects the harbor; it is 14 feet above mean sea level. I met with Tony Gioiello, the chief engineer of the Port of Los Angeles, to discuss port design. He told me that the port had contracted with the U.S. Army Corps of Engineers to construct a large-scale hydraulic model of the port, along with its breakwater, various piers, and other features. This model can be used to study tidal effects within the port, seiching, currents, and any other aspects that might affect its operation. To comply with California’s strict seismic design codes, the cranes and other critical port facilities are designed to withstand a major
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Extreme Waves earthquake without collapse. They successfully withstood large earthquakes, including the disastrous 1994 Northridge earthquake. Gioiello told me that port officials are concerned about the possibility of a tsunami damaging the port or interrupting port traffic and about the resulting economic impact. He sent engineers from the port to inspect damage in Southeast Asia following the tsunami there, and they concluded that from the viewpoint of Port of Los Angeles operations, earthquake damage rather than flooding is the most serious concern.1 Ports all over the world are expanding to accommodate larger vessels. The port complex at Los Angeles–Long Beach is no exception. Courtesy of Daniel, Mann, Johnson and Mendenhall and affiliated companies—major participants in the design and construction management of port facilities—I got a firsthand look at the new Pier 400 terminal facilities in the Port of Los Angeles. It is the world’s largest proprietary container terminal, served by 12 huge post-Panamax cranes that tower over the giant container ships and transfer containers onto an extensive rail system that then takes them by rail to destinations throughout the United States. The facility is designed to withstand a major earthquake. Regulations concerning the design of coastal facilities are often the responsibility of several different agencies—there is no single entity. For example, in the United States, state and local codes apply onshore and in the coastal zone, while federal regulations apply outside the state boundaries. A comprehensive new regulation for the design of marine facilities (primarily marine oil terminals and related facilities) was recently developed in California.2 I reviewed this document; it is comprehensive, incorporates the latest research findings, and would serve as a good model for all types of coastal facilities anywhere in the world. It includes wind and wave loads, earthquake, and tsunami design guidance. The challenge of protecting beachfront homes and businesses is much more complex. In an effort to counter tsunami damage, Japan has erected tsunami walls at a number of coastal locations, including the city of Tsu on the island of Honshu. Tsu, situated on Ise Bay, about 37 miles south of Nagoya, has been hit by a number of tsunami. Some tsunami walls are nearly 15 feet high, but tsunami have been known to
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Extreme Waves overflow them. For example, the Hokkaido earthquake of July 12, 1993, produced one of the largest tsunami in Japanese history—extremely large waves resulting in a 98-foot-high run-up. The tsunami hit the port town of Aonae on the small island of Okushiri, near the west side of Hokkaido within minutes after the earthquake. The town was surrounded by a 14.75-foot-high tsunami wall. Despite the wall, major damage occurred—including the loss of 340 homes—and although the wall may have blunted the force of the waves to some extent, 114 people died in Aonae alone.3 States such as California and Florida have thousands of miles of unprotected coastline, much of it expensive beachfront property. The safe thing to do would be to restrict the beaches to swimmers and sunbathers, and build houses on higher ground. However, this has not happened and is not likely to happen; homeowners instead will play the odds and hope that the “100-year event” does not occur while they own the property. OFFSHORE STRUCTURE DESIGN Offshore structures are designed for one of the most hostile environments imaginable. Only structures designed for outer space face more severe material and engineering challenges. In the offshore environment, a structure must withstand not only the daily stress of wind and wave, but the rare extreme event as well as the long-term effect of fatigue and saltwater corrosion. Offshore structures are predominantly those used by the petroleum industry. They are typically designed to withstand the fatigue due to flexing caused by normal wind, wave, and current forces and to withstand extreme conditions, usually expressed in terms of an event that occurs only once in 100 years. The extreme design criteria differ from area to area—for example, from the Gulf of Mexico to the west coast of Africa or to the North Sea. The northern North Sea provides a good example of one of the more severe environments:4 100-year extreme wave height: 102 feet 1-year summer storm wave height 46 feet
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Extreme Waves Wind 80 knots Current 2.9 knots By comparison, in the Gulf of Mexico the 100-year extreme wave is 72 feet. Offshore platforms are constructed with steel legs or concrete columns, or may float and be held in place by an anchoring system. A common configuration is the steel jacket type, which resembles a bar stool, but typically has eight or more legs. In the North Sea, the typical water depth for such a platform is 328 feet. A number of platforms have been instrumented to measure incident wave heights and periods, movement of the platform decks, stresses, and related information. Measured data can then be compared with the values used to design the platform in an effort to assess the margin of safety. For example, a metal-jacketed platform in the Frigg field, northern North Sea, was analyzed using several years of recorded data.5 In a 1981 storm when the significant wave height was 45 feet, the maximum wave height was around 62 feet. This wave caused the deck to move approximately 3.5 inches. When these results were extrapolated to the case of the 100-year wave, the extreme displacements were found to be 90 percent or less of the design values, indicating that the structure would survive the extreme wave unless it was somehow weakened beforehand. What could weaken the structure? Shifting or settlement of the sea bottom could reduce the strength of the support legs, or corrosion could weaken them. Over time, the constant pounding of the sea could weaken or break some of the numerous cross members and braces of the support structure. Alternatively, marine life growing on the legs and underwater structure could increase its effective mass and the area presented to waves, causing the structure to experience greater forces and impacts than would occur in the clean condition. SHIP DESIGN To understand why ships sink, you need to know some basics of ship flotation and stability, and the implications for ship design. Throw a
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Extreme Waves piece of wood in a lake, a stream, or the ocean and it will be seen to roll and bob with the motion of the water. These motions resemble those of an airplane; likewise a ship can move in six different ways: Forward, sideways, vertically (up and down); as well as roll sideways, pitch up and down, and yaw about a vertical axis. Once a vessel has been designed for level floating in calm water, with sufficient freeboard (clearance above the waterline), when it is fully loaded and the load properly distributed so the decks stay high and dry, its roll and pitch are the two characteristics of greatest interest. The weight of a ship and its cargo may be thought of as a force acting downward through its center of gravity. Opposing this downward force is an upward force—the buoyancy force—that keeps the vessel afloat. When the ship is upright and level, the buoyancy force acts through a point called the center of buoyancy that is aligned with the center of gravity. As the ship rolls, the shape of that part of the hull presented to the water changes, and the buoyancy force now pushes upward at a point away from the center of the ship (more toward the side of the hull), causing the ship to return to an upright position. When the ship rolls, the buoyancy force is directed through a point above the center of gravity called the metacenter. The metacentric height is the distance from the center of gravity to the metacenter. It is usually abbreviated GM. A vessel with a large metacentric height and weight low in the vessel (a tanker or dry bulk ship) is very stable—that is, it can heel over a great deal and still return to an upright position. Such a vessel is also said to be “stiff,” meaning it responds quickly to sea motions and is uncomfortable to passengers. On the other hand, a vessel with a smaller metacentric height (a passenger ship) will be more comfortable to passengers because of its slower response to rolling. This type of vessel is said to be “tender.” (Remember reading about the SS Waratah elsewhere in this book?) The cargo in a bulk carrier, container ship, or tanker, when properly stored and evenly distributed, ensures that the vessel rides in the water as the designers intended—not too high, so as to be top heavy, and not too low, so as to be subject to breaking seas. In the empty state, vessels take on ballast to maintain stability.
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Extreme Waves In the old days of wooden sailing vessels, small stones often made up the ballast. In California’s early history, trading vessels would sail up from Mexico to collect cargos of hides and tallow from the cattle ranches and haciendas. A favorite loading spot was Catalina Harbor, on the back side of Catalina Island. The ships would drop anchor there and unload their load of ballast stones at one side of the harbor. Today these stones from old Mexico form a long finger of land that curls out into the harbor in the shape of the letter C. The California Yacht Club (Marina Del Rey, California) has its “Ballast Point Station” there. Ballasting is very important. Today, most vessels incorporate special tanks into which seawater can be pumped to ballast the vessel. Another approach is to pump water into an empty fuel tank. Some shipmasters are reluctant to do this unless absolutely necessary, because later the tank must be cleaned before it can be refilled with fuel—resulting in a possible delay. On occasion, this hesitancy has led to the loss of the vessel in a storm. Captain Jerry Fee was the director of ship design for the U.S. Navy and also served as the president of the American Society of Naval Engineers for a number of years.6 When discussing ship design with Fee, I asked him how he came to be a ship designer. He told me that in addition to being a graduate of the U.S. Naval Academy and spending three years at the Massachusetts Institute of Technology in postgraduate naval engineering training, he spent five years on active duty on destroyers and then a number of years in the Navy’s salvage and repair operations. From these experiences, he developed firsthand knowledge of the effects of heavy weather on naval vessels, as the following incident shows. “In February 1962, I was serving as junior officer of the deck on a Fletcher class destroyer—the USS Taylor—DD468,” said Fee. “We were involved in patrols and maneuvers about 100 nautical miles off of the east coast of Russia, west of the Aleutian islands and not far from Kamchatka in the Bering Sea. For four days the destroyer wallowed in extremely heavy seas so rough that the ward room was closed and the only meals were sandwiches grabbed at random. The Taylor rolled about 40 degrees in 30- to 40-foot-high waves during the storm, on occasion as much as 53 degrees—so much that from the flying bridge
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Extreme Waves 50 feet above the waterline it seemed as though you could reach out and touch the water. “The U.S. squadron was frequently overflown by Soviet aircraft monitoring us during the storm. On the bridge, officers braced themselves with one foot on the bulkhead (wall) and the other on the deck, due to the angle of the ship. A rogue wave—estimated to be 60 feet high—crashed over the bow of the ship, arched over the entire foredeck, and hit the top of the flying bridge, demolishing its cover. The flying bridge had an aluminum enclosure to protect the crew from the weather. As the roof collapsed around me, tons of water drove me to my knees and I had to grab a stanchion to avoid being washed off the bridge as the water poured off the ship.” There is no substitute for personal experience when it comes to designing ships to withstand heavy weather! As mentioned above, every vessel has a range of stability that depends on its design and load. If the vessel rolls beyond the range of stability, the vessel will no longer be able to right itself and will capsize. Fee told me that Navy destroyers are designed to be able to recover from extreme rolls approaching 90 degrees. In towing tank tests the Fletcher class (DD445) model recovers from rolls as great as 110 degrees; however, in a real situation, once the roll exceeds 90 degrees, the uptakes (air intake or engine exhausts) are likely to take on water, which would severely inhibit the ship’s recovery from a roll. Fee went on to explain that in addition to designing vessels for stability, ship designers must build into them sufficient strength to withstand the forces imposed by operations, normal seas, and storms. The “backbone” of a ship is its hull, a steel structure not unlike a steel building laid on its side. Key structural elements are defined by the scantlings, or design specifications. Hull design is examined from two perspectives: sagging, a condition whereby the vessel is supported fore and aft on two large waves and the center sags, and hogging, where the vessel is supported by a single large wave in the center and the bow and stern sections are unsupported. The hull is designed and reinforced to withstand the extreme loads imposed by whichever of these two conditions is most extreme. Next, the hull and deck plates are designed to withstand the impact of wave and water. This can take two forms: the
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Extreme Waves deadweight of tons of water that can result from a large wave washing over the deck, and the “slap” force or impact of a fast-moving wave striking the ship. Interestingly, this is more crucial for a large vessel than for a small ship; the small ship will more likely move with the wave, whereas the large vessel, possessing huge inertia, is more likely to be battered as an immovable object by the wave. (See Plates 14 and 15.) Typical maximum fetch for a local storm over the ocean is 500 nautical miles. If the wind blows for a long enough period of time—say, a day and a half to two days over this distance, waves with a significant wave height of 33 to 49 feet will be produced. Such waves have a wavelength of 300 to 600 feet, the length of a good-sized ship. This is one of the reasons they can be so damaging—if the vessel rides up on the crest of the wave with the bow and stern unsupported. Tankers and bulk carriers (vessels carrying coal, grain, ore, cement, etc.) are susceptible because of the design. If the vessel is partially supported on a large wave, hogging or sagging (bending) failure can occur.7 THE LOSS OF THE MARINE ELECTRIC The breakup of the Derbyshire in Typhoon Orchid near Okinawa is described in Chapters 3 and 10. Nearly 20 years passed from the time the vessel disappeared until the British government finally conducted a formal investigation into the loss of the ship. The hearings brought a sense of closure to the grieving relatives of the lost crew members, although that was slight consolation given their loss and the length of time that had passed. The two-decade-long ordeal of resolving the Derbyshire mystery has had an additional benefit—to focus attention on the appalling loss of bulk carriers and crew. It is unfortunate that this investigation did not take place earlier, because in the interim dozens of bulk carriers continued to fall victim to large waves. The loss of the Marine Electric occurred in stormy seas about 27 nautical miles off the coast of Virginia on Friday, February 11, 1983, during one of the worst storms to hit the East Coast in more than 40 years. The waves were not the highest ever experienced in that area, but at 40 feet they were certainly high enough. In other ways, the Marine Electric incident is representative of nearly all the elements involved in ship design and safety at sea in heavy weather.8
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Extreme Waves To start with, the Marine Electric was a reconditioned World War II ship. Originally built as a tanker, she was modified in 1961 to be a bulk carrier. This process included adding a new center section and extending the length of the vessel to 605 feet. Her normal run was to carry 24,000 tons of coal from Norfolk, Virginia, and deliver it to the Boston area, where it was used as fuel in electric power plants. The first and perhaps most elementary aspect of safety at sea is “don’t overload the vessel.” Cargo ships are marked with a set of load lines, called Plimsoll marks that are approved by regulatory bodies and insurance carriers. Plimsoll marks show where the waterline should be when the vessel is fully loaded. The correct level varies with salinity, water temperature, and service conditions. In tropical freshwater the load line (labeled TF) is higher, meaning the ship can ride lower in the water, whereas in cold, dense water, the load line is lower, meaning the ship has to ride higher. An example is the load line labeled WNA, for winter conditions in the North Atlantic. A ship loaded in a freshwater port will magically ride higher in the ocean because of the greater buoyancy of saltwater. Equally important is the distribution of the load throughout the ship. Obviously, it cannot all be on one side or the vessel will develop a dangerous list in that direction. To prevent this situation from occurring accidentally, cargo ships and tankers have baffles built into their holds or use other methods to keep the cargo from shifting. If the load is concentrated forward and aft, the vessel will have a tendency to “hog” and potentially break apart in the center. Equally problematic is concentrating the load amidships, so that the vessel could sag in the center when supported fore and aft by a large wave. Also important is the condition of hatches and ventilators—anything that could let water into the vessel during heavy seas. Flooding can obviously disrupt the balance of a fully loaded vessel. Pumps capable of pumping out water in the case of a leak somewhere are essential. The Marine Electric had a problem in this regard. The deck and many hatch covers were cracked. They had been crudely patched, but despite repeated requests in writing by the crew, they were not repaired. At midnight on February 10, 1983, Marine Electric sailed. Weather advisories were posted with gale warnings. As noted in Chapter 2, this
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Extreme Waves means winds in excess of 34 knots. By the afternoon of the next day, the weather had worsened to a Force 10 gale. Seas were heavier, and occasionally the Marine Electric plowed her way through a rogue wave estimated at 60 feet high. It was about this time that the crew spotted the Theodora, a 65-foot fishing boat. They passed each other in the storm. A short while later the Theodora was heard on the radio calling the coast guard. She was taking on water and in danger of sinking—and did not know her exact position. Marine Electric responded to the coast guard with an estimate of the Theodora’s last position. At this point, the coast guard asked Marine Electric to turn around, locate the other vessel, and stand by until help arrived. Once, I was sailing downwind from San Miguel Island back to Santa Rosa Island in Dreams. The seas were moderate, with waves about 6 feet high. Three of us were on a diving and fishing trip to the Channel Islands. I knew we were heading into rough water, so I’d advised the crew to lash all of the dive gear securely on deck. I happened to look back to see what kind of waves were chasing us when I spotted a black object in the water. It was a dive bag loaded with a regulator, wet suit, dive computer—at least a thousand dollars worth of gear. Retrieving it meant coming about and chasing it before it sank. In this maneuver, timing is important. You want to turn the boat (if possible) in the trough between waves, quickly enough that the next wave does not catch you broadside and roll you. This maneuver successfully executed, the dive bag was pulled aboard a few minutes later with a boat hook just before it sank and was lost forever. With this experience in mind, you have to admire the nerve of the captain of the Marine Electric. Reversing course with a vessel nearly 20 times longer than Dreams and in seas five times higher was no easy feat. Marine Electric successfully came about and headed back to the distressed vessel. Now Marine Electric was taking heavy seas on her stern. She stood by the Theodora for several hours until the coast guard arrived and managed to drop some pumps to the Theodora so she was able to control flooding and make her way to port. Then Marine Electric once again made the turn and resumed her former course, bow into the waves. By the evening of February 11, Marine Electric was in trouble her-
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Extreme Waves self. The vessel was no longer plowing through the big waves. She was down at the head, as they say, meaning the bow was riding too low in the water. By 3:00 A.M., the crew realized that Marine Electric was not going to make it. They radioed their position to the coast guard and requested immediate help, then changed course to try to make Delaware Bay. A few minutes later the large vessel was listing heavily. The crew tried to ready the lifeboats. While they were in the process, the boat rolled over and capsized. Some crew jumped; some were tossed into the frigid water. Some were trapped inside the foundering vessel and never had a chance. By luck, one man found a life raft with capacity for 15 men in the violent seas and hung on to it. He was joined by three others. After struggling for minutes the first man succeeded in getting into the raft. He tried to get the others into the raft as it was being pummeled by huge waves. Their hands were too cold to grip. Despite his efforts, he could not pull them in. One by one, they drifted away to certain death. Finally, a coast guard helicopter arrived on the scene; three men survived the ordeal; the rest of the crew—31 sailors—including the captain, were lost at sea. In the aftermath of the sinking, a marine board of inquiry found that the cause of sinking was “fracture of the vessel.” The coast guard’s report placed the blame on water leaking in through the cracks in the deck and failed hatch covers.9 The coast guard report stated that, in accordance with the International Convention on Load Lines of 1966, hatch covers were “to be designed for an assumed load of 358 pounds per square foot with a safety factor of 4.25 on the material ultimate strength.” Note that at 64 pounds per cubic foot seawater density, it would take just 5.6 feet of seawater on top of the hatches to reach this loading. There is little doubt that waves much larger than this slammed on top of the hatch covers. What can we learn from the loss of vessels such as the Marine Electric and the Derbyshire? An obvious conclusion is that design standards need to be reviewed in light of what is currently known concerning the size and occurrence of extreme waves. A wave 50 feet high carries four times as
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Extreme Waves much energy as a wave 25 feet high, and a wave 100 feet high has 16 times the energy. A vessel designed for 25-foot-high seas might not be able to withstand the tremendous forces imposed by extreme waves—forces that can collapse hatch covers, buckle hull plates, or even break the back of the vessel. There is no single, internationally accepted standard-making body for ship design, no uniform set of rules. Instead, rules are promulgated by various classification societies for each type of vessel, and each classification society has its own set of rules. Design loadings are generally expressed in engineering terms, and it is not clear what sea state they are based on. From the sample I’ve been able to review, it appears that a sea state with 35-foot-high waves is the norm.10 In light of current knowledge, this is inadequate. I would not want to serve on a 900-foot-long vessel built to these standards and routinely traversing the Gulf Stream, or the Agulhas or Kuroshio currents. A secondary conclusion is that the masters of vessels designed in accordance with the older standards need to know the capability of their ships and need to have the authority to avoid those waters where there is a higher probability of encountering extreme waves. Requiring a rigid adherence to schedule and route may cause the vessel and crew to be endangered needlessly. Finally, if the vessel is not properly maintained, there is no telling what kind of seas she will be able to withstand if put to the ultimate test. Normal practice is dry dock every five years, at which time the vessel is supposed to be inspected for cracks and damage due to corrosion. Older vessels frequently had hull plates that were 1 inch thick. Given today’s high-strength steels, the thickness has been reduced in many cases to 0.4 inches. In addition, new epoxy paints provide better corrosion protection.11 But if defects in the epoxy paint are not detected and repaired, the margin of safety for corrosion damage is less than it used to be. MARINE WEATHER FORECASTING AND ROUTING The first line of defense against extreme waves is never to encounter one. While there is no absolute guarantee that this can be done, mari-
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Extreme Waves ners can improve the odds in their favor by avoiding weather conditions known to give rise to extreme waves and by avoiding those parts of the oceans where their incidence is greatest. Marine weather charts provide sea state conditions (surface wind speed and direction, significant wave heights, swell period and direction, isobar lines, atmospheric pressure highs and lows, locations and movements of developing storms or gales). Refer back to Figure 9 for an example of a wind-wave forecast. Upper air (500-millibar) charts show the direction and strength of the upper air winds that have an important effect on surface conditions. Winds at the 500-millibar level generally blow from west to east. By examining the “troughs and ridges” of upper-air isobars, forecasters can anticipate where surface lows and highs will occur. Other charts show tropical cyclone danger areas, sea surface temperature, and satellite imagery.12 Weather analyses are issued once or twice per day, and forecasts typically are issued for 24, 48, and 96 hours, although other periods also may be used. Weather charts and text reports are available to ships at sea via shortwave (single sideband) radio or satellite links. Today, even small cruising yachts can access these reports. For example, on Dreams, using a laptop computer, a terminal node controller (a fancy name for a radio-frequency modem, a device that encodes or decodes text or graphics files transmitted by radio), and a high-frequency shortwave radio, I can download the latest marine weather charts. With this capability, a vessel can keep track of weather in its vicinity as well as distant weather trends. At present, the ability to forecast extreme waves does not exist. Researchers are working to identify sea state conditions that can be correlated with the occurrence of extreme waves. If the work is successful, it may be possible to provide warnings to vessels to avoid areas where such waves could occur. In particular, a parameter called the Benjamin-Feir instability index may correlate with sea conditions where extreme waves are more likely. European weather forecasters are experimenting with this approach.13 There are global ocean maps that indicate prevailing significant wave heights for each month of the year. This information, combined with knowledge of major currents such as the Agulhas or Gulf Stream, provides an indication of areas where extreme waves are more likely to occur.
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Extreme Waves While most of the marine weather data are in the public domain and free, there are also commercial services that provide specialized weather services on a subscription or fee basis. Captains Jon Harrison and Mark Remijan demonstrated this type of capability when I visited them on board APL China. They have access (via satellite and e-mail) to the latest NOAA and other weather reports to enable them to plot their own routes across the Pacific Ocean, or they can use a weather routing service. Harrison and Remijan said that generally they do their own routing using a program developed by Dr. Henry Chen. The program is very sophisticated and enables the ship master to program acceptance criteria for a route—that is, beam seas no higher than 5 meters, head seas no greater than 6 meters, no rolling greater than 20 degrees, no tropical storm approach (at 35-knot wind speed contour) closer than 50 nautical miles, etc. The program then takes the latest weather data and the ship’s parameters and computes a route that satisfies the input criteria or, if this is impossible, reports “no solution.” Different routes can be evaluated by simulating against forecast weather conditions. Subsequently, I visited Dr. Chen, the president of Ocean Systems, Inc., at his office in Alameda, California. He demonstrated how a shipboard computer would download forecast current, wind, and wave information for an ocean area of interest. The program he developed is called Vessel Optimization and Safety System (VOSS). A unique feature is that it has the ship response characteristics (such as fuel consumption versus speed, roll and pitch periods, etc.) generated for the ship’s actual loading condition (drafts and GM) and stored in memory. The ship’s master can input safe operating envelope parameters unique to the vessel. These can include such parameters as maximum wave, maximum wind speed, maximum roll angle, number of bow slams per hour, number of times green water hits on the deck per hour, and other conditions. With this information, the master can select a destination and the program will define the optimum route that avoids exceeding the safe operating envelope and minimizes the fuel consumption for the desired arrival time. Alternate routes can be evaluated in terms of total fuel consumption, average speed, and estimated time en route so the master can evaluate the consequences of one versus another. Glo-
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Extreme Waves bal wind and wave forecast data for VOSS are provided through a partnership with Oceanweather, Inc.14 Weather routers provide specialized forecasts for sailors and also will provide weather updates and suggested course changes during a voyage. They can supply a detailed weather outlook for the area to be sailed. For example, in 2001 I sailed in Dreams to Isla Guadalupe (Mexico), an island that is 150 nautical miles offshore from Baja California at 29 degrees north latitude. Since my two crew members (Russell Spencer and Erik Oistad) had been with me on a previous attempt when we altered our plans due to bad weather and never made it to the island, Erik suggested that this time we make use of a weather routing service. We were also concerned because two weeks earlier Hurricane Juliette had hammered Cabo San Lucas at the tip of Baja California. We selected weather router Rick Shema and told him our destination and expected departure date. A few days before we were ready to sail, he advised that the weather looked favorable and gave us a report on what we could expect to encounter. Periodically we advised him by e-mail (over the single sideband radio) of actual conditions, and he gave us an updated forecast halfway through the two-week trip. Also, as part of his service, he monitored conditions along our route and was prepared to contact us by e-mail if bad weather was headed our way. We had good weather during the entire trip, but it was reassuring to know that we had recourse to a second opinion if the weather deteriorated.15 While preparing this book I called Shema and asked him if he thought it possible to include extreme wave warnings in his forecasts. After some research he said: “It might be possible by incorporating some indices relating wave steepness to the wave spectrum, and then introducing additional wave parameters into wave forecast models, to identify ocean areas with greater probability of extreme wave formation. The marine forecaster routing ships could then alert the vessel to the possible risks and offer alternative routing to avoid high-risk areas. More research is necessary before this can be done routinely. Forecasting the timing and location of individual extreme waves is unlikely due to the randomness and complexity involved in their formation.” Knowing Shema, I suspect it is just a matter of time before he’ll come up with an extreme wave advisory service for his customers.
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Extreme Waves EXTREME WAVE PREDICTION If better vessel design and avoiding hazardous weather conditions are the first weapons in protecting against the dangers of extreme waves, providing warnings when they are about to occur has to be the next most important step we can take. Tsunami warning systems are described in Chapter 6. The technology exists and has been demonstrated; what remains is implementation and public awareness on a global scale. For other forms of extreme waves, scientists are working to develop ways of predicting what sea conditions could conceivably lead to extreme waves. The work is being pursued on a number of fronts: developing remote sensing technologies that permit the measurement of wave heights and direction using high-frequency, satellite-based radar systems; making improved sea state forecasting models; creating maps or atlases that advise mariners where extreme waves are most likely to occur; developing instrumentation systems including shipborne radar that can measure sea conditions; and carrying out research aimed at improving the design of vessels, offshore structures, and coastal facilities to withstand the impact of extreme waves. Dreams is equipped with radar having a 24-nautical-mile maximum range. This is very useful when I am attempting to avoid other vessels at night or in fog. One phenomenon that affects radar sensitivity is so-called backscatter. Backscatter is defined as radar waves that are reflected to the vessel by things other than the target vessel, including rain or signals reflected by the sea itself. Reflection from the sea surface is called sea clutter. Remarkably, scientists have found ways to use satellite radar measurements of sea clutter to detect extreme waves. In another development, wave detection systems using marine x-band radar (radar with a 3- to 6-centimeter wavelength) have been installed on offshore platforms as well as on ships.16 Researchers such as Dr. Susanne Lehner and others are working to increase the availability of measured data and to improve wave forecasting algorithms. Radar data have been compared to data obtained by wave-riding buoys that measure wave height and direction, good accuracy being reported. Dr. Lehner and her colleagues have done pioneering work in this field using data collected by synthetic aperture
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Extreme Waves radar on a remote sensing satellite operated by the European Space Agency.17 Using representative data collected during the summer and fall of 1996, Lehner found a number of waves characterized by extreme height, steepness, and asymmetry (crests higher than trough depth). Near Antarctica, waves as high as 97.7 feet were detected in an area where the sea state consisted of waves with a significant height of 33 feet, so the ratio was 2.9, indicative of rogue waves. Researchers also reconstructed waves in the storm track of Hurricane Fran in the Atlantic; there the waves reached heights of 50 to 60 feet. An extension of this work that Lehner has demonstrated is to provide global maps of the highest individual wave heights and maximum wave steepness; such information, if available routinely on a daily forecast basis, would be a godsend to mariners and represents a very exciting development in this field. CONCLUSIONS Humans have lived in a symbiotic relationship with the sea for millennia. In addition to serving as essential sources of food and providing important means of transportation, oceans have an enduring quality—a draw that does not fade with time. Thus it is unlikely that humans will abandon coastal areas because of the remote risk of a tsunami. Memories often fade following a disaster—a generation may pass, and then people move back to risky areas. With the growth of the world population, more and more people are likely live in coastal regions. Other than building mammoth seawalls, there is little that can be done to protect coastal areas within a few hundred kilometers of a tsunami origin. However, as noted in Chapter 6, tsunami education programs that teach people to evacuate coastal areas immediately on foot when a large earthquake is felt will save lives. Tsunami waves travel too fast to make a warning possible, and even if a warning is given, in densely populated coastal communities, evacuation by automobile on congested roads may become impossible. So tsunami may be a risk that has to be accepted in coastal communities. Fatalism should not be allowed to preclude the installation of ex-
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Extreme Waves tensive warning systems in coastal areas surrounding all oceans. Early warning systems are cheap compared to the cost of lives lost. The benefit of early warning systems has been amply demonstrated by the success of hurricane warnings and evacuations in the southeastern United States and other areas. Also, work continues on the science of earthquake prediction. While today it is not possible to predict the size and magnitude of impending earthquakes, it is reasonable to hope that at some future time this will be possible. Prediction could give a sufficient lead time to nearby communities if the time frame were measured in hours rather than minutes. ARE SHIPS’ CREWS BEING SENT TO SEA TO DIE NEEDLESSLY? Likewise, prediction and mapping of extreme wave risk areas as a routine part of weather forecasts will save hundreds of lives every year. With the current trend toward larger vessels and longer voyages, the risk to mariners is increasing and the ability to avoid rogue waves takes on an even greater importance. I get the impression that certain classes of vessels have overemphasized construction economies at the expense of crew safety. In conducting the research for this book, I was shocked at the shipping loss statistics I found—a major vessel, every day or two, somewhere in the world. Ironically, with the environmental sensitivity that exists today in most parts of the world, if an oil tanker spills a few hundred barrels of oil on someone’s beach, it is front-page news. But let a 650-foot-long bulk carrier suddenly disappear with 30,000 tons of cargo and its entire crew, and it may only be noted in passing in the newspapers. For the family members of the crew, it is a different matter, of course. They live with the terrible uncertainty of not knowing what really happened. They may live with this uncertainty for years, as in the case of the Derbyshire, until investigators in deep-water submersible vessels finally find the broken remains of the vessel on the ocean bottom and are able to piece together what happened or, as is the case in many such losses (the Waratah being a prime example), what happened is never known. There is just the terrible void caused by those who are never seen again.
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Extreme Waves I wonder if there isn’t a moral issue here. How can shipbuilders and owners countenance the thought that their ship crews are being placed in mortal danger by less than adequate ship design or poorly maintained vessels? Are merchant ship crews expendable? Are relatives and family members of lost crew the only people who care? For more than two centuries the phrase “Davy Jones’s locker” has been synonymous with death in the sea. Today, with an improved understanding of extreme waves, we have the potential to ensure that the loss of a vessel due to giant waves becomes a rare event. It is time to take the necessary steps, time to slam the door shut on Davy Jones’s locker.
Representative terms from entire chapter: