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Extreme Waves 10 When the Big Wave Comes: Are Ships Safe Enough? For various economic reasons, today’s commercial vessels are becoming larger and larger. Meanwhile, increased shipyard competition has created intense pressure to reduce shipbuilding costs. To reduce the amount of steel required—and thereby reduce labor costs—designers are making use of more sophisticated analytical tools for ship design and are specifying higher strength steel, so that less steel is required and therefore less shipyard labor. The net result is a substantial reduction of structural safety margins. There is also less material to resist the weakening effects of corrosion, so maintenance and frequent inspection are even more important and may not always occur as frequently as needed. Several of the shipmasters I interviewed expressed this concern. They said, in so many words, “Ships are not being built as well as they used to be.” This fact has been known about tankers since 1991, when a select committee of ship design experts was convened under the auspices of the U.S. National Research Council to review tanker designs in the wake of the Exxon Valdez disaster. Among their findings was the following: As newer design techniques were introduced, “safety factors” (design al-
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Extreme Waves lowances for unknown factors) were reduced, in the desire to keep costs down and to get maximum deadweight for minimum draft.”1 Now that we know that waves as high as 100 feet exist and occur more frequently than previously thought, what can be done to reduce the number of vessels breaking up or foundering and to reduce the number of crew lives lost every year? A wave of such height, with its steep towering face, could deliver an enormous impact—enough to break the back of the best-designed modern ship built in accordance with today’s standards. Even though such waves occur infrequently, are vessels safe enough? EVOLUTION OF MARITIME TRANSPORT In 2005 the world’s merchant fleet comprised 39,932 vessels of 300 gross tons or more with a total deadweight tonnage (dwt) of 909 million tons.2 (See Table 6.) New and larger vessels, especially tankers and container ships, are being built in record numbers. One of the determinants of vessel size is the depth and width of the Panama and Suez canals. The maximum beam allowed through the Panama Canal is 105.5 feet. This corresponds to a container ship carrying around 4,500 containers, or 4,500 TEUs (20-foot equivalent units), meaning a container nominally 20 feet long. Ships that can traverse the Panama Canal are referred to as “under Panamax” vessels. In the Suez Canal, vessels with a beam of up TABLE 6 Distribution of Vessels in the World Merchant Fleet Vessel Type Number of Ships Million Deadweight Tons Percentage of Merchant Fleet Capacity Tankers 10,126 368 40 Bulk carriers 6,347 319 36 General cargo 16,263 95 10 Container 3,220 99 11 Passenger 3,976 28 3 Totals 39,932 909 100
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Extreme Waves to 243 feet are allowed, but the allowable draft depends on the beam and ranges from 52.5 feet to 36 feet for a wider vessel. Currently, tankers as large as 200,000 deadweight tons can pass through the Suez Canal. The size of crude oil carriers (tankers) evolved from 10,000 to 20,000 deadweight tons in the 1940s to 1950s to 100,000 deadweight tons in the 1960s and 1970s. At first, size was somewhat dictated by the dimensions of the Suez Canal and the depth of major ports. However, recurring crises in the Middle East spurred the development of larger vessels. In the 1990s and 2000 very large crude carriers (VLCCs) with deadweight tonnage of 200,000 to 319,999 tons and ultra large crude carriers (ULCCs) with deadweight tonnage of 320,000 tons and more entered the fleet. These tankers can transport crude oil from the Persian Gulf around the Cape of Good Hope to deep-water ports in Europe and the U.S. East Coast, or across the Indian and Pacific oceans to the West Coast of North and South America. At the beginning of 2005 there were 10,126 vessels in the tanker fleet, 7,650 of which were engaged in transporting crude oil. The average age of these vessels is 17.5 years, but it is dropping as the new double-hulled vessels enter the fleet and the older ones are retired. In 2003, the tanker fleet transported 1.7 billion metric tons of crude oil—the equivalent of roughly 12 billion barrels of oil, or nearly two-thirds of the oil consumed each year.3 The largest tankers are too big for most U.S. ports, so oil is off-loaded at sea through a process known as lightering. For example, the TI Europe, a 442,470-deadweight-ton ULCC, 1,246 feet long, picked up 3 million barrels of crude oil in the Persian Gulf, crossed the Arabian Sea, then traveled southeast through the Indian Ocean, past tsunami-ravaged Sri Lanka and the coast of Sumatra, along Java, through the Lombok Strait (between Bali and Lombok islands), northwest through Makassar Strait between Borneo and Celebes, past Mindanao, and into the Pacific Ocean. This route follows or crosses the Philippine Trench and the Mariana Trench—some of the deepest waters in the world’s oceans. A ship lost at these depths will never be found. Beyond Guam, the course is past Hawaii and on to Southern California—a journey equivalent to more than halfway around the world.
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Extreme Waves Accompanying Captain Jan Jannsen—on board the Cygnus Voyager, a double-hulled tanker with a capacity for 1 million barrels of oil—I observed a typical lightering operation.4 The Cygnus Voyager was launched in 1994, is 900 feet long, and has a 160-foot beam—too large for the Panama Canal. She carries a crew of 30. On the bridge we were about 90 feet above the waterline. Looking toward the bow, the deck of the vessel stretched out—as long as two football fields laid end to end (but wider)—and was covered with a maze of pipes and valves for filling and emptying the various oil tanks. There were also a number of winches for mooring, two cranes, and four large sets of davits for lowering huge rubber fenders to protect the vessel when it came alongside TI Europe. Jannsen, as lightering master, assisted the masters of both vessels in bringing them together. Using a handheld radio to communicate with both helms, he stood on the port bridge wing of the Cygnus Voyager and guided the two tankers onto the same heading at the same speed. Then he patiently brought the two huge vessels closer and closer together until the crew was able to shoot the first mooring line across. Finally, 12 mooring lines connected the two vessels. The mooring process took four hours. All night long the two vessels crept along at slow speed, while 1 million barrels of crude oil were transferred. At 3:00 P.M. the next day, Captain Jannsen gave the order to drop the mooring lines, and the Cygnus Voyager separated from TI Europe and headed north for the refinery. This process had to be repeated two more times before TI Europe could finally turn west and begin the 30-day trip back to the Gulf. Bulk carriers carry coal, iron ore, grain, bauxite (aluminum ore), and other bulk products. Current vessels have capacities of 200,000 deadweight tons or more, and lengths of 900 to 1,100 feet. They have long, flat decks, hatches opening into the holds or storage spaces belowdecks, and an elevated bridge near the stern of the ship. Bulk carriers and combination carriers (OBOs) have had a high loss rate since first introduced in the 1970s. In round numbers, from 1970 to 2000 at least 100 bulk and combination carriers have been lost, and more than 1,000 crew members have been killed. Some sinkings are due to human error or collisions, but a number seem to be due to
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Extreme Waves preventable causes. It is estimated that 10 to 20 bulk carriers are lost annually due to structural failures.5 This is clearly an unacceptable rate of loss and, presumably, something that can be remedied, as evidenced by a postmortem of the Derbyshire disaster discussed later in this chapter. General cargo ships are the third most numerous type of vessels in the global fleet, but their numbers are declining and more are being sent to the ship breakers (scrap yards) each year than are being built each year. The decline in their numbers is due to the fact that greater volumes of goods are being carried by bulk carriers and container ships. Container ships are among the largest vessels sailing the seas today, second only to the largest tankers. They also constitute the fastest-growing segment of marine transport. From 2000 to 2005, nearly 900 new vessels were added to the fleet. More than 300 vessels have a capacity of 5,000 TEUs and 15 vessels have 8,000-TEU or greater capacity.6 The largest container ships in service in 2005—such as CSCL Asia and the P&O Nedlloyd Mondrian carry 8,500 TEUs. Thanks to Captains Jon Harrison and Mark Remijan, I was able to visit APL China on one of her stops in the Port of Los Angeles. She has a rating of 4,832 TEUs and is 905 feet long with a beam of 132 feet. Harrison and Remijan alternate as masters of APL China, working a shift of 70 days—the time it takes for the vessel to make two roundtrips between ports on the West Coast of the United States and ports in Asia. Harrison and Remijan took me on a tour of the vessel, from the engine room to the bridge. Containers are stored below deck in a series of bays with racks, nine layers high. The containers are attached to each other and to the racks by a latching mechanism at each corner called an interbox connector (IBC). On deck are seven layers—the first three layers secured by lashings in addition to the interbox connectors. It takes roughly three days to unload and reload the ship. In the captain’s cabin are several computers with satellite links for downloading the latest weather information. On my visit, one computer screen displayed the ship’s most recent track across the Pacific—a smooth crossing, no rough weather.
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Extreme Waves The trend toward larger vessels also applies to passenger and cruise ships—examples being Cunard’s Queen Elizabeth 2, 963 feet long, and the even newer Queen Mary 2, 1,131 feet long. Royal Caribbean Cruises Ltd. and the Carnival Group are reportedly planning new cruise ships that are even larger. So what do these trends imply for the safety of the world’s merchant fleet? Today’s vessels are larger and longer and of necessity traverse such hazardous seas as the treacherous waters of the Agulhas Current with greater frequency. Because of design economies, it appears that vessels are less able to withstand the impact of an extreme wave. At the same time, a large part of the global fleet is 20 years old or older. How will new and old vessels fare in encounters with extreme waves? Only time will tell. Building double-hulled tankers should improve safety, as long as the interior spaces between hulls can be inspected and maintained. Access to some portions is confined and difficult, and if care is not taken, corrosion or structural problems could go undetected. Heavy seas have been known to shake loose and claim the containers on container ships or damage them. One problem is a phenomenon known as parametric rolling, which occurs in heavy seas when the length of the ship is close to the wavelength. Depending on the speed of the vessel relative to the wave, the vessel will sometimes be in a trough and sometimes be supported on a crest. Container ships feature streamlined hulls designed for speed. Because of the load they carry, these ships have a wide flare on the bow and the stern to provide maximum deck surface. Consequently, the hull area presented to the sea varies, depending on whether the vessel is on a crest (where its broad, flat hull gives maximum stability and restoring force) or in a trough (where the restoring force is less). Then, if the vessel starts encountering waves at about twice its natural roll frequency, it will tend to roll. The restoring force brings the vessel back, but on a crest it over-compensates in effect. In the next trough, the restoring force is less, so the vessel rolls even more, and the rolls become larger and larger. It takes a drastic maneuver—an abrupt turn and speed change—to break this vicious cycle of dangerous rolling. The shipmaster must be quick to recognize the problem and take action, or the ship motion can
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Extreme Waves quickly get out of control.7 Warning systems have been developed to alert the crew to impending problems. Passenger ships have been disabled when large waves broke windows and flooded the bridge, rendering electronic systems inoperable. Design criteria for critical ship control areas may need to be revisited. POSTMORTEM: LOSS OF THE DERBYSHIRE Bulk and combination carriers appear to be the most problematic of vessels at risk, hull and hatch cover design being critical for safety. The loss of the Derbyshire (discussed in Chapter 3) illustrates the importance of these ship design details for large vessels that may encounter extreme waves. The disaster has been reviewed extensively, and we can hope that if insights gained can provide for safer ship design, the loss of the Derbyshire crew and the agony their family members have endured these many years will not have been entirely in vain. The question is: Should the combination carrier Derbyshire have been able to survive an extreme wave incident? In order to answer this question it is necessary to evaluate the strength of the hatch covers, since they are the vulnerable points of this type of vessel. If they fail, and water floods two compartments or more, there is a high likelihood the vessel will sink. Several postmortems of the Derbyshire disaster have been made, with the results indicating that the hatch covers would collapse if the vessel was hit by a wave around 47 feet high. Based on estimates made following the storm, Typhoon Orchid produced waves 70 to 85 feet high.8 These results suggest that the design of the Derbyshire was inadequate. The vessel did not have the ability to withstand the storm and therefore was doomed from its onset. The technical standards related to the design, construction, and surveying of ships are established by organizations known as classification societies. Classification originated in England in the 1700s, when marine insurers developed a system for independent inspection of the vessels they intended to insure. Those in excellent shape were classified “A,” while other vowels were assigned for less than excellent condition. Pioneered by Lloyds of London, the concept of ship classification was embraced by other seafaring nations—today there are approximately
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Extreme Waves 50 organizations involved. In 1968, seven major classification societies formed the International Association of Classification Societies, which today has 10 members. They are the American Bureau of Shipping, Bureau Veritas (France), China Classification Society, Det Norske Veritas (Norway), Germanischer Lloyd, the Indian Register of Shipping, Korean Register of Shipping, Lloyd’s Register (England), Nippon Kaiji Kyokai (Japan), Registro Italiano Navale (Italy), and the Russian Maritime Register of Shipping. The International Association of Classification Societies (IACS) claims that more than 90 percent of the world’s cargo-carrying tonnage is covered by the classification design, construction, and periodic inspections carried out in conformance with the rules and standards of its member organizations, including 95 percent of the world fleet of bulk carriers.9 Today ships are not assigned grades: they are either “in class” or not. If the ship operator fails to maintain the vessel to the required standards of care, or fails to submit the vessel for timely periodic inspections, classification may be withdrawn. Vessels are subject to an array of standards promulgated by such international conventions as the International Maritime Organization, by the flag state wherein the vessel is registered, and by its classification society. The International Association of Classification Societies supports the member organizations in several ways. It issues resolutions on technical or procedural matters, makes unified interpretations of matters arising from international conventions, and makes technical recommendations to the members. With the exception of procedural requirements, the association’s recommendations do not have to be accepted by the members. One of the association’s long-term goals is to develop unified standards and procedures for its members and, of course, to increase maritime safety and reliability. Noting the high rate of loss of bulk carriers, the association and its members initiated investigations and research to improve vessel safety. A series of documents have been developed and made available to member societies and vessel operators.10 The International Maritime Organization has also issued structural survivability guidelines for new and existing bulk carriers and new requirements for surveying the ships.
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Extreme Waves The IACS states that the majority of bulk carriers lost were more than 15 years old, were carrying iron ore at the time, and failed as the result of corrosion and cracking of the structure within cargo spaces, and as a result of overstressing by incorrect cargo-loading and cargo-discharging operations.11 There is no mention of extreme waves or rough seas as a cause of failure. The IACS has issued standard wave data—called IACS Recommendation 34—for use in the design of cargo-carrying vessels in the North Atlantic. Table 1 in that document indicates that most of the waves will have periods of 8 to 14 seconds and significant heights of 36 feet or less. In fact, the table indicates that around 98 percent of the waves to be encountered will be in the range of 6.5 to 36 feet and only 2 percent will be in the range of 39 to 56 feet, the highest waves listed.12 In response to growing discontent by ship owners concerned about the fact that ships being built today are less robust, three classification societies announced in 2001 that they would work together to establish common design criteria for standard ship types, beginning with tankers. In 2004, the chairman of the IACS council, Ugo Salerno, issued a letter reporting on the status of common rules for oil tankers and bulk carriers.13 The letter stated that two project teams—one known as the Joint Tanker Project and the other the Joint Bulker Project—have been formed. The objective of these projects is to develop new ship design rules. Salerno stated that IACS’s objective is that the new rules will be adopted and applied uniformly by all IACS members. As part of the Joint Tanker Project work, a survey was made of defects found in existing tankers. It showed that fractures and cracking accounted for two-thirds of the defects. The new tanker rules are tentatively scheduled for release in April 2006 and will apply to tankers designed and constructed after that date. The design wave loads in the new rules will be based on IACS Recommendation 34, described previously. In view of the tragic loss of the Derbyshire and numerous other vessels, as well as the unacceptably high loss rate among bulk carriers in general, it is timely for ship classification societies and other organizations that establish ship design criteria to change the rules. Obviously, no vessel can be made absolutely safe. Design is always a
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Extreme Waves compromise between safety, economics, and risk. To give an extreme example, a vessel cannot be designed to withstand 300-foot-high waves; it would be impractical to build and not economical to operate. Moreover, the probability of encountering such a wave is virtually nil. On the other hand, there is sufficient evidence to conclude that 66-foot-high waves can be experienced in the 25-year lifetime of oceangoing vessels, and that 98-foot-high waves are less likely but not out of the question. Therefore, a design criterion based on 36-foot-high waves seems inadequate when the risk of losing crew and cargo is considered. IACS Recommendation 34 should be modified so that the minimum design wave height is at least 65 feet. The dynamic force of wave impacts should also be included in the structural analysis (as opposed to relying on static or quasi-dynamic analyses). Good vessel maintenance is equally important, particularly to prevent corrosion of hulls and vital structural elements. Saltwater corrosion eats away unprotected steel, reducing its strength—a phenomenon ship surveyors call “wastage.” In 1960, the tanker vessel Pine Ridge was surveyed and given clearance to sail, even though wastage in key structural members ranged from 25 to 60 percent, meaning that the thickness of vital parts of the ship was only 25 to 60 percent of the original design value. Today, with thinner sections and less steel in modern vessels, careful maintenance and inspection are vital to control wastage. Could a modern vessel with 60 percent wastage survive a gale, let alone a serious storm? In 1960, the tanker Pine Ridge could not; she broke in half, and seven crew members, including the master, lost their lives. In the coming decade the world’s shipyards will be busy fulfilling orders for new tankers to replace the old single-hull vessels that must be withdrawn from service, as well as building more bulk carriers, building more and larger container ships, and building even larger passenger vessels. With fewer vessels overall in the merchant fleet, and with replacement vessels being more costly but more economical to operate, there is a benefit to be gained by investing in more robust designs, better safety equipment, more extensive crew training, improved weather instrumentation and weather routing, and conducting inspection and maintenance to rigorous standards. This opportunity to improve the safety and reliability of merchant vessels should not be lost.
Representative terms from entire chapter: