668 MARINE SPILLAGE—SOURCES AND HAZARDS INTRODUCTION Scope Pollution of navigable waterways resulting from operation of commercial and naval vessels may be a consequence of normal service or from casualties such as collisions and groundings. Propulsion system fuel oil and liquid cargoes may be involved in any case and will be considered in this chapter. Waste disposal from shipping is of comparatively small magnitude compared to waterway pollution from shoreside sources and will not be considered. Emphasis will be on description of the pollution problem and on means for prevention. The subject of spill collection and disposal is considered elsewhere in this text. Problem Definition Normal operations A decade ago, the primary source of pol- lution of the world’s waterways was the intentional discharge of oily ballast water during routine operations. At that time, for virtually all seagoing operations ballast water was taken aboard for a portion of the voyage in order to obtain sufficient draft and trim for propeller immersion, adequate steering abil- ity, acceptable conditions of seaworthiness; and to satisfy man- dated operational and regulatory requirements for intact and damaged stability. If assigned ballast tank capacity was inad- equate to meet these requirements, it was the general practice to ballast empty fuel oil tanks, or empty liquid cargo tanks in the case of tank vessels. This procedure resulted in the neces- sity for pumping overboard large quantities of contaminated ballast water before taking on fuel oil or liquid cargoes. These procedures have been largely outlawed by international agree- ments developed by the International Maritime Organization (IMO) of the United Nations, and enforced by the national regulatory agencies of the member countries. Casualties Spills resulting from casualties generally receive more attention in the world press than incidents involving operational discharges. Spills may occur from operational mishaps in the pumping of fuel oil bunkers and liquid cargoes. Incidents of spills that occur from collisions and groundings are accompanied by associated dangers to personnel and the environment and are likely to involve the largest quantities of pollutant discharged in a single incident. The magnitude of such spills is clearly far greater in the case of a loaded tank vessel than the grounding and rupture of the double bottom fuel tanks of a dry cargo vessel. SHIP CLASSIFICATION AND DESCRIPTION The arrangements and general characteristics of the various merchant ship types are well described in such standard texts as Reference (1) and in the technical literature, including the comprehensive discussion in Reference (2) covering U.S. shipbuilding during the 1936Ϫ1976 period. Accordingly, the following discussion will be restricted to characteristics pertinent to the pollution problem, for example, arrangement of tank spaces. The following standard abbreviations have been used throughout for convenience: DWT ϭ deadweight ϭ total displacement Ϫ light weight ϭ cargo ϩ consumables mld. ϭ molded fbd. ϭ freeboard B.P. ϭ between perpendiculars Break Bulk Vessels The greatest variety of seagoing vessels are in this category which includes the ordinary general cargo vessels carrying a great variety of dry products in raw material as well as finished and packaged form. An outline sketch of the cross- section through a typical cargo hold, showing hatchway, tween decks and fuel oil or ballast spaces, is shown in Figure 1. Fuel oil is commonly carried in the double bot- toms, as indicated, but may also be carried in deep tanks, particularly outboard of shafting and in the vicinity of the machinery spaces. Except for settling and daily service tanks, all bunker spaces are normally piped for fuel oil or ballast. The availability of cubic capacity for tankage assigned only to ballast service is limited in such vessels and frequent use of fuel tanks for ballasting is likely in most operations. Unitized Cargo Carriers Ships in this category are usually designed for the exclu- sive transport of standard containers or wheeled trailer vans, and, to a lesser extent as hybrid carriers to handle container, wheeled vehicles and general break-bulk cargo. In the case of container ships, as illustrated in the typical hold section, Figure 2. the cellular nature of the cargo stowage requires some “squaring off” of the hold spaces, with the result that considerable wing space is available for ballast tanks. As a C013_003_r03.indd 668C013_003_r03.indd 668 11/18/2005 10:40:56 AM11/18/2005 10:40:56 AM © 2006 by Taylor & Francis Group, LLC MARINE SPILLAGE—SOURCES AND HAZARDS 669 FUEL OIL OR BALLAST FUEL OIL OR BALLAST FUEL OIL OR BALLAST INNER BOTTOM THIRD DECK SECOND DECK MAIN DECK SHIP 16,000 DWT PARIA LIMPA, built in the 1940’s alongside the 326,000 DWT UNIVERSE PORTUGAL Courtesy, The Motor Ship. FIGURE 1 Outline midship section through cargo hold, typical break bulk dry cargo vessel. C013_003_r03.indd 669C013_003_r03.indd 669 11/18/2005 10:40:56 AM11/18/2005 10:40:56 AM © 2006 by Taylor & Francis Group, LLC 670 MARINE SPILLAGE—SOURCES AND HAZARDS result such vessels are able to operate with clean ballast only and no ballasting of fuel tankage is normally required. Roll-on/roll-off or trailer ships are similarly “squared off” internally and, in addition, may have extensive deep tank spaces available below the lowest vehicle deck. As with the container ships, tankage is likely to be available in suf- ficient quantity to permit full clean ballast operations. Dry Bulk Carriers Dry bulk carriers are engaged primarily in the transport of such commodities as coal, grain and ores. Two general con- figurations exist, as shown in Figure 3. For light weight, high cubic cargoes, such as coal and grains, the hold con- figuration is such that water ballast capacity, in the amount of 35 per cent to 40 per cent of cargo deadweight, is avail- able for clean ballast service, as shown in Figure 3a and 3b. Fuel oil bunkers are generally confined to deep tanks within the machinery spaces or to portions of the wing and double bottom tanks adjacent to the machinery spaces. Clean ballast operation is generally feasible. Vessels designed specifically for heavier cargoes such as ores are generally arranged with comparatively small cargo holds and large surrounding tank spaces as shown in Figure 3c. Clean ballast operation is readily accomplished under all loading conditions. Liquid Bulk Tank Vessels The modern tank vessel has evolved from the standard 16,000 deadweight ton (DWT) “T2” tanker of World War II to modern tank vessels exceeding 500,000 DWT capacity. The transport of liquid cargoes, predominantly petroleum crudes and refined petroleum products is the single largest category of waterborne commerce and represents the greatest potential pollution hazard with respect to normal operations as well as casualties. Accordingly, characteristics of vessels in the liquid bulk trades will be considered in somewhat greater detail than other ship types. Petroleum Crude and Products Carriers With the exception of the steam turbo-electric main propulsion machinery and electric drive cargo pumps, the World War II T2 tanker is, in general arrangement, a parent of the tanker designs devel- oped during the early post-war years. Typical characteristics of these vessels include: 1) Cargo section divided by a pair of longitudinal bulkheads into port, center and starboard tanks. 2) Relatively short cargo tanks independent of ship size. 3) Poop, bridge and forecastle superstructures with navigating bridge located amidships. 4) Forward and after fuel bunkers. 5) Forward and after pump rooms. 6) Relatively long, single screw, main propulsion machinery, with separate boiler and engine rooms. From the late 1950s until the present, tanker design evolved through the following changes, all directly related to reduced cost of construction and operation: 1) Increase in size to over 500,000 DWT capacity, with corresponding increases in dimensions and operating drafts. MAIN DECK INNER BOTTOM BALLAST BALLAST FUEL OIL OR BALLAST FUEL OIL OR BALLAST FIGURE 2 Outline midship section through container hold, typical container ship. C013_003_r03.indd 670C013_003_r03.indd 670 11/18/2005 10:40:58 AM11/18/2005 10:40:58 AM © 2006 by Taylor & Francis Group, LLC MARINE SPILLAGE—SOURCES AND HAZARDS 671 2) Simplification of arrangement, particularly by reduction in number and increased size of cargo tanks. Typical modern crude oil tankers are arranged with as few as five center tanks and ten wing tanks. Secondary arrangement changes have included elimination of superstructure and houses amidships, location of all accommodation and navigation spaces aft and elimination of forward pump room and fuel bunkers. 3) Speed has remained within the 14 to 16 knot range. 4) Crew size has been reduced substantially, averag- ing as low as 19 men on U.S. flag as well as for- eign tankers. 5) Propulsion system power levels have increased with size, approaching 40,000 SHP on a single screw. Centralized pilot house control of all propulsion machinery is a state-of-the-art development avail- able to operators of diesel and steam turbine machinery. 6) Cargo pumping systems are generally similar to those of the post World War II period, except for increase in pumping rate with ship size. Elimination of pump rooms and fitting of deep well pumps in each cargo tank is a recent trend, following the arrangements of special products carriers. Regulatory effects on tanker design, imposed since the 1973 MARPOL Convention for the Prevention of Pollution from Ships, have been significant. These regulations, imposed progressively from 1973 through 1985, include the follow- ing requirements and constraints: 1) Limitation on maximum cargo tank size to 30,000 cubic meters. 2) Segregated ballast tanks (SBT) on all new tankers larger than 20,000 DWT capacity. SBT capac- ity must be sufficient to obtain the following conditions: • Capacity to obtain minimum mean ballast draft of 0.02L ϩ 2 meters, where L ϭ length between perpendiculars • Trim by the stern no greater than 0.015L • Draft at the stern sufficient to submerge the propeller • SBT located to so as to protect 30% to 40% of the side shell in way of the cargo tanks. (Actual requirements vary with ship size and geometry.) Since the segregated ballast tanks are restricted to clean bal- last service only, the net effect of these requirements has been to increase the ship dimensions to accommodate the required SBT volume. As a result, modern tankers that meet the SBT requirements are volume rather than weight limited, and will only load to the assigned draft marks when carrying very dense cargoes. The SBT capacity requirements are considerable, amounting to about 25% to 40% of the deadweight. The optimum SBT and cargo tank arrangements, for minimum ship acquisition cost, vary with ship size and proportions. A common arrangement is to assign two pairs of wing tanks within the cargo tank section to SBT service. In some cases the preferred arrangement is the concentration of segregated ballast in double bottom tanks extending under the entire length of the cargo tank section of the ship. Table 1 include a summary of principal characteristics of U.S. flag tank vessels built since 1977. All meet the MARPOL SBT requirements. The SBT arrangements are reviewed later in connection with protection from collision and grounding. Special Products A great variety of liquid products are carried in specially constructed tankers. While the quanti- ties carried are small compared to the volume of petroleum FIGURE 3 Outline midship sections through cargo holds, typical dry bulk carriers. CARGO HOLD CARGO HOLD CARGO HOLD BALLAST (c) ORE CARRIER BALLAST BALLAST BALLAST BALLAST BALLAST BALLAST BALLAST BALLAST (b) DRY BULK CARRIER, DOUBLE SKIN SIDE SHELL (a) DRY BULK CARRIER, SINGLE SKIN SIDE SHELL GRAIN OR BALLAST GRAIN OR BALLAST GRAIN OR BALLAST GRAIN OR BALLAST C013_003_r03.indd 671C013_003_r03.indd 671 11/18/2005 10:40:59 AM11/18/2005 10:40:59 AM © 2006 by Taylor & Francis Group, LLC 672 MARINE SPILLAGE—SOURCES AND HAZARDS crudes and refined products, transport of these commodities may involve unique containment problems and associated hazards. Special products carriers may be classified in the following manner, according to nature of cargo: 1) Liquefied natural gasses (LNG) and liquefied petro- leum gasses (LPG). (a) Low temperature—ambient pressure contain- ment—The most exacting containment require- ments are in this category, with cargo carried at about −260ЊF for liquefied natural gas (LNG). The largest LNG carriers at this time have capacities of about 130,000 cubic meters. LPG transport includes the carriage of such gasses as propane, butane and ethylene, with propane, carried at about Ϫ50ЊF, the most common. In a typical LNG or LPG carrier, cargo is car- ried in an independent, insulated tank or membrane liner. Double bottom and wing tank spaces are nor- mally assigned to salt water ballast and fuel oil is carried in a relatively small portion of the double bottom and in deep tanks within the machinery spaces. Geometry is similar to that of a container ship and clean ballast operation is accomplished with no difficulty. (b) High pressure—ambient temperature—LPG may be carried in pressure vessels, designed to the A.S.M.E. Code for Unfired Pressure Vessels. While this mode of containment has been gen- erally superceded by low temperature transport for international trade, a considerable amount of LPG and similar cargoes is carried in this man- ner on the inland waterways of the United States and Europe and in smaller coastwise vessels and barges. The limiting design condition is usually for propane, in cylindrical tanks designed for 250 psig. In general, vessels carrying cargoes in pres- sure vessels have sufficient cubic capacity to per- mit clean ballast operation. 2) Miscellaneous liquefied gasses—Anhydrous ammo- nia is carried in significant quantities in U.S. inland and coastal waters. This commodity may be carried at low temperature or under pressure, in containment designed for the transport of propane. Chlorine gas is commonly transported by barges in U.S. waters, primarily in pressure vessel contain- ment. Other commodities of importance are primarily petro-chemicals, including butadiene, ethane, ethyl chloride, prophylene and vinyl chloride. 3) High temperature commodities—The transport of molten sulfur at about 275ЊF in heated independent insulated tanks has become the most common high TABLE 1 Representative modern U.S. flat tank vessels NAME EXXON CHARLESTON EXXON BAYTOWN ATIGUN PASS B.T. SAN DIEGO EXXON VALDEZ Length, B.P., m 185.93 229.82 263.35 278.90 288.04 Breadth, mld, m 32.26 32.26 52.74 50.60 50.60 Depth, mld, m 18.29 18.29 22.86 23.78 26.83 Draft, keel, m 12.80 11.73 17.47 18.08 19.66 Displacement, tonnes 56,970 73,700 200,400 220,800 244,145 Deadweight, tonnes 42,800 58,645 176,160 191,100 214,860 Cargo capacity, m 3 59,200 62,660 184,300 209,980 240,890 Ballast capacity, m 3 18,500 32,000 57,400 59,600 69,600 Cargo Chem. and prods. Crude Crude Crude Crude Number of cargo tanks 42 14 13 15 13 Propulsion machinery Dir. diesel Dir. diesel St. turbine St. turbine Dir. diesel Horsepower, max continuous 17,000 bhp 17,000 bhp 26,700 bhp 28,000 shp 32,240 bhp Service speed, knots 16 15.8 16.5 14.25 16.25 Year delivered 1983 1984 1977 1978 1986 Notes: 1) Segregated ballast yes yes yes yes yes 2) Double bottom yes yes no yes no 3) Double hull no no no no no C013_003_r03.indd 672C013_003_r03.indd 672 11/18/2005 10:40:59 AM11/18/2005 10:40:59 AM © 2006 by Taylor & Francis Group, LLC MARINE SPILLAGE—SOURCES AND HAZARDS 673 temperature commodity carried on international and inland waters. Internal hull geometry resembles that of the low temperature LPG or LNG vessel, with double bottom and wing tank spaces available for clean ballast. The transport of asphalt and bitumen in the molten state is less exacting than the case of molten sulfur transport and cargo is normally carried in con- ventional integrated tanks. Sulfur and bitumen cargoes are relatively dense and clean ballast operation should be expected. The use of cargo tanks for ballast services is not feasible, except for emergency situations. 4) Toxic and corrosive chemicals—A great variety of hazardous cargoes are carried in relatively small quan- tities in a variety of containment systems. References (3) and (4) contain a hazardous cargo classification and data for specific commodities, with particular respect to marine transportation. Virtually all hazardous cargo carriers will be built with sufficient ballast tank capacity, in the form of integral double bottom or wing tanks. It is unlikely that the use of cargo tanks for salt water ballast would be permitted, except for emergency conditions. Combination Bulk Carriers In order to improve the overall utilization of conventional dry or liquid bulk carriers, combination bulk carriers have been developed to permit transporting dry and liquid cargoes within the same cargo hold spaces. A typical voyage, for example, would involve carrying crude oil from the Persian Gulf to Maine, ballast from Maine to Hampton Roads, coal from Hampton Roads to Japan, Japan to Persian Gulf in bal- last, etc. Cargo operations of this type involve unique cargo handling and hold cleaning problems, with associated poten- tial pollution problems. Two general configurations exist, the ore-oil carrier and the more common ore-bulk-oil (OBO) carrier. These are analogous in function and similar in geometry to ore car- riers and general bulk carriers, respectively, illustrated in this section sketches in Figure 3. A common modification in the latter case is the provision of a double skin side shell to facilitate hold cleaning. Referring to Figure 3, the ore-oil carrier is equipped to carry cargo oil in the wing tanks as well as the center cargo hold. The double bottom space is normally reserved for clean ballast. The degree to which an ore-oil carrier can maintain a clean ballast operation, when operating as a tanker, will depend on the relation of cargo density to cargo volume available. The OBO will be operated with dry and liquid car- goes restricted to the main hold spaces, hence such vessels will normally operate with clean ballast, as a conventional bulk carrier. In both cases, however, hold cleaning between cargoes is a major operational problem that will be consid- ered in later discussions. The largest dry bulk carrier in existence is believed to be the 365,000 DWT ore carrier BERGE STAHL, delivered in 1986. The largest combination carrier is the 280,000 DWT ore/oil carrier SVEALAND, delivered in 1972. Miscellaneous Commercial Vessels The great variety of miscellaneous and floating craft that could be sources of pollution are too numerous to consider here. In general, all can be considered, with respect to pol- lution, in one of the categories considered earlier. One par- ticular case, of current interest, however, is the development of large, unmanned seagoing barges for the ocean transport of dry and liquid bulk commodities. Tank barges of 50,000 DWT are in service. The geometry of a tank barge resembles that of an austere crude oil tanker of comparable deadweight, with five center tanks and 10 wing tanks. Operational as well as casualty pollution hazards are comparable to those of a self-propelled tanker, with the added complication that no personnel are aboard when the vessel is underway. POLLUTION FROM NORMAL OPERATIONS Ballasting and Tank Cleaning Break Bulk Vessels The major source of pollution from break bulk general cargo vessels is in the intentional dis- charge of dirty ballast. As consumables, primarily fuel, are expended, displacement, draft and stability changes and may reach the condition that the addition of water ballast may be required. Some tankage may be available for clean ballast, but, in general, ballasting of fuel tanks will probably become necessary at some point beyond the expenditure of one half the consumables on board. Since the imposition of the MARPOL regulations, the use of clean segregated ballast tanks has been mandatory and the disposition of oily ballast at sea should no longer be a major problem. Tank Vessels, Crude and Refined Petroleum Products Until the MARPOL agreements came into effect, the greatest source of intentional discharge of contaminated ballast into the sea was from the operation of tank vessels transport- ing petroleum crudes and products. Tankers are normally one way product carriers and return voyages to the cargo source are in ballasted condition. MARPOL segregated bal- last requirements for tank vessels were summarized earlier in Section 2.4. The arrangement of the ballast tanks to meet operating requirements and to provide some collision and grounding protection is discussed later. Tank Vessels, Special Products Carriers The special prod- ucts carriers described in earlier discussions are predomi- nantly clean ballast vessels. Sea water will rarely be pumped into cargo tanks and sufficient tankage is normally provided, in the form of double bottoms and wing tanks, to serve as cargo tank protection as well as clean ballast tankage. Dry Bulk Carriers The typical dry bulk carrier operates in ballast over a significant portion of the operating life. Many trade conditions exist in which return cargoes are not available C013_003_r03.indd 673C013_003_r03.indd 673 11/18/2005 10:40:59 AM11/18/2005 10:40:59 AM © 2006 by Taylor & Francis Group, LLC 674 MARINE SPILLAGE—SOURCES AND HAZARDS and ballasting is required for adequate propeller immersion and seaworthiness. Bulk carriers are inherently stable and bal- lasting is not required for this purpose. As discussed earlier, sufficient cubic capacity is normally available in the wing and double bottom spaces to permit clean ballast operation. Combination Carriers The most common of the combina- tion carriers, the OBO, has the same general configuration as the dry bulk carrier and, accordingly, is generally capable of clean ballast operation. When in petroleum crude or product service, the OBO operates as a tank vessel and must comply with all relevant regulations. Hold cleaning between voyages with incompatible cargoes, however, is an additional source of pollution. In the example given in earlier discussions, the OBO discharges crude oil at Portland, Maine, proceeds in ballast from Maine to Hampton Roads and takes on coal at Hampton Roads for delivery to Japan. During the ballast voyage from Maine to Hampton Roads, the holds are cleaned by conventional means and the dirty oil washings discharged into slop tanks located in a pair of wings immediately aft of the cargo holds. A more complex situation arises for the bal- last voyage from Japan to the Persian Gulf, after discharging coal. Several days of manual labor are required to remove coal residue, followed by Butterworth cleaning to remove the fine coal powder remaining. The solids and wash water are discharged at sea in unrestricted zones, unless prohibited by environmental regulations. In general, combination carriers can be changed over from liquid to solid cargoes in a comparatively short time, say a period of 18 hours to two days. The reverse proce- dure may require more time consuming cleanup procedures. Operators, accordingly, will tend to prefer maintaining a given ship in a single cargo trade for seasonal periods, if per- mitted by the economics of the trade. Operational pollution problems are reduced in complexity when the occasions for cleaning between incompatible cargoes are minimized. Cargo Transfer, Loading and Unloading Liquid Cargoes Some pollution inevitably occurs as a result of fuel and cargo oil transfer between ship and terminal or between ship and lighter alongside. The majority of such incidents results, directly or indirectly, from human failure. Typical incidents include overflow through tank vents and hose failures. In most cases, proper monitoring or automatic control of cargo transfer and fueling operations will mini- mize the probability of oil spillage. Normal inspection routines should permit anticipating most equipment failures. The rapid development of the large crude oil tankers has been accompanied by the parallel development of offshore terminals to accommodate the deep draft vessels. The tankers moor to large “monobuoy” single point mooring buoys which are anchored permanently to the sea floor. Oil pipelines are led to the underside of the monobuoy along the sea floor, from the shore tanks. Flexible hoses are led from the buoy to the midship pumping station on the tanker, usually by a tending launch. Means for mooring the tanker and connecting up to the oil hoses are under constant development and are reaching a high level of reliability. It is not expected that operations of the offshore terminals, under proper control, will represent a major source of pollution. The lightering of petroleum crude from deep draft tank- ers offshore to draft-limited ports is a major activity at U.S. coastal ports. The majority of the existing shuttle tankers are relatively small 40,000 DWT to 50,000 DWT vessels. Shuttle tankers operate between transit vessels and terminals over one-way distances generally less than 100 miles. In some cases the service is limited to a lightening operation to reduce the transit tanker draft to the allowable terminal draft. It is anticipated that pending U.S. legislation will address the lightering issue by allowing existing single skin transit tankers to be served by double hull shuttle tankers discharg- ing to U.S. coastal terminals. It is understood that the mini- mum allowable standoff distance between transit tanker and coastal terminal will be 60 miles. Shuttle tankers operate on short voyages, with frequent encounters with large transit tankers and terminals, through heavily travelled shipping channels. It is anticipated that requirements for environmental protection for this class of tankers will be demanding, considering the nature of the ser- vice and proximity to environmentally sensitive coastal areas. Dry Bulk Cargoes Earlier discussions of combination oper- ations included mention of solids pollution from hold wash- ings when converting from dry bulk to liquid bulk operations. Of far greater importance is the harbor pollution occurring at dockside from the simple transfer, by grabs or similar mechanical devices, of dry bulk products between ship and shore storage facility. Over a long period of time, dry bulks spilled between ship and pier accumulate and become a local, but significant cause of harbor pollution. While many of the commodities are inert, others, including coal and some ores have an adverse effect on the ecology. The cargoes involved are of low value and command low freight rates, hence there is little incentive to control spillage of small, but accumula- tive, quantities into harbor waters. POLLUTION FROM CASUALTIES The magnitude of a particular oil spill, or other pollution casualty, is a function of ship type, ship size and nature of the incident. Tank vessel collisions or groundings involve the greatest magnitude of pollution resulting from individ- ual casualties and, accordingly, will be considered in some depth in these discussions. Other vessel types are considered briefly. Break Bulk Vessels Pollution resulting from rupture of fuel tanks, as a result of collision or grounding, is the only significant casualty of this class of shipping likely to result in pollution. Less important is the potential rupture of deep tanks carrying various special cargo oils, primarily edible oils. Figure 1, showing a typical section through a cargo hold, indicates that double bottom C013_003_r03.indd 674C013_003_r03.indd 674 11/18/2005 10:40:59 AM11/18/2005 10:40:59 AM © 2006 by Taylor & Francis Group, LLC MARINE SPILLAGE—SOURCES AND HAZARDS 675 tanks are normally assigned to fuel oil or ballast service. The largest general cargo vessel operating under the U.S. flag has a maximum fuel oil capacity, including all double bottoms, deep tanks and settling tanks, of about 3700 tons. About 83 per cent of this tankage, or about 3000 tons, is in the double bottoms. In general, the operator will tend to carry a mini- mum weight of fuel oil in order to maximize cargo dead- weight, hence somewhat less than the 3700 tons of fuel oil is likely to be aboard. The largest double bottom fuel tank in this particular vessel holds about 280 tons. A one-compartment damage collision, assuming damage from the side to the centerline, could expose 465 tons of fuel oil to the sea. Two-compartment damage, again from the side of the centerline, could expose about 900 tons of fuel capacity to the sea. A grounding inci- dent, in which the bottom shell is opened to the sea for a con- siderable portion of the ship’s length, could expose as much as 2/3 the double bottom fuel capacity, or about 2000 tons, to the sea. These values represent the maximum quantities likely to be exposed following a casualty. A considerable portion of the fuel would be released to the sea in any of these incidents. Magnitudes of such spills are significant but small relative to the catastrophic effects of a comparable tank vessel incident. Unitized Cargo Container, roll-on/roll-off and unitized cargo combination vessels in liner service are larger and higher powered than the break-bulk vessels, hence carry greater quantities of fuel oil. Arrangements of fuel, ballast and cargo oil tanks are varied and fuel oil may be located in bottom, wing or deep tanks. In general, the mode of release of fuel oil to the sea would be as discussed for break bulk vessels, with the quantities somewhat greater. A considerable portion of the wing and bottom tankage of unitized cargo vessels is piped only for ballast, thus lessening the probability that only fuel tanks would be breached in the event of a colli- sion or grounding. Tank Vessels Fuel tanks are of relatively minor importance in the case of tank vessels involved in casualties. Fuel is generally con- fined to two or three deep tanks and settling tanks and rep- resents a small portion of total tankage exposed to the sea following a casualty. The evolution of tanker design since the early 1950’s, with respect to pollution from collision and grounding, was considered briefly in earlier discussions. Collision and Grounding Protection The cargo section of a modern tank vessel is arranged with the minimum number of tank divisions to meet loading, trim and safety requirements. Crude oil tankers may have as few as five tanks along the cargo length, divided into port, center and starboard tanks by a pair of longitudinal oiltight bulkheads, resulting in a 3 ϫ 5 matrix of cargo tanks. A sixth pair of wing tanks, des- ignated “slop tanks”, may be located immediately forward of the machinery spaces, to accommodate cargo oil or cargo tank washings. A typical cargo tank arrangement is shown in the outline arrangement, Figure 4, illustrating the tank arrangement of the EXXON VALDEZ, Table 1. This design meets the MARPOL requirements for segregated ballast and limitations on cargo tank volume prevailing at the time of the construction contract in 1984. Wing tanks numbers 2 and 4 are designated as segregated ballast tanks within the cargo spaces. A great variety of segregated ballast tank arrangements have been adopted to meet the mandated protection of 30% to 40% of the shell in way of the cargo tanks. The most common arrangement consists of two pairs of wing tanks, as in the EXXON VALDEZ, Figure 4. A less common alterna- tive is to provide a continuous double bottom in way of the cargo tanks to carry most of the ballast, while providing sig- nificant grounding protection. This arrangement, typical of tankers carrying refined products or chemicals, is illustrated in Figure 5. By the time of this writing in the spring of 1990, a series of major casualties had occurred during the 1989Ϫ1990 period. These events were followed by a period of intense investigation and legislative activity directed to development of improved means of minimizing the consequences of col- lisions and groundings. The widely publicized grounding of the EXXON VALDEZ in Prince William Sound, with an esti- mated outflow of 11 million gallons of crude oil, resulted in extensive environmental damage and massive cleanup efforts by EXXON and state and federal agencies. Figure 6 shows, diagrammatically, the extent of damage, involving eight of the 11 cargo tanks. It is estimated that 60% or more of the cargo outflow would have been retained had the EXXON VALDEZ been designed and built with a continuous double bottom. It is ironic to note that the EXXON VALDEZ design was based in part on the earlier design of the 188,700 DWT B. T. SAN DIEGO class of tankers which were built with double bottoms. The recently enacted Oil Pollution Act of 1990, dis- cussed further in Section 5, establishes requirements for double hulls for tank vessels operating in U.S. waters. Requirements include specific minimum values for depth and breadth of double bottoms and wing tanks, respectively. In anticipation of these requirements, designers and build- ers have developed designs of “environmental” tankers and a significant number of building contracts have been let for construction of these vessels. A variety of cargo tank configurations have been devel- oped for double hull tank vessel designs. The most widely proposed is a variation of the conventional arrangement, Figure 4, wherein the longitudinal bulkheads are located well outboard to form relatively narrow segregated ballast wing tanks, in association with a continuous double bottom. Two innovative concepts recently developed are the Japanese EPOCH design, Figure 7, and the Danish product tanker design, Figure 8. The latter evolved from a successful series of bulk carrier designs. It should be noted that double hull design to meet antici- pated regulatory safety requirements does not require new C013_003_r03.indd 675C013_003_r03.indd 675 11/18/2005 10:40:59 AM11/18/2005 10:40:59 AM © 2006 by Taylor & Francis Group, LLC 676 MARINE SPILLAGE—SOURCES AND HAZARDS FIGURE 4 General arrangement, 215000 DWT tanker EXXON VALDEZ. Source: National Steel and Shipbuilding Company, San Diego, California, Reprinted with permission of Exxon Corporation, Houston, Texas. C013_003_r03.indd 676C013_003_r03.indd 676 11/18/2005 10:40:59 AM11/18/2005 10:40:59 AM © 2006 by Taylor & Francis Group, LLC MARINE SPILLAGE—SOURCES AND HAZARDS 677 MACHINERY SPACE AFT PEAK (SWB) 87 6 5 4 3 2 1 DT FORK PEAK A P CARGO TA NK CARGO TA NK CARGO TA NK BALLAST BALLAST B 4 MIDSHIP SECTION F. O . CARGO TANK NO. 8 P CARGO TANK NO.7 P CARGO TANK NO.6 P CARGO TANK CARGO TANK CARGO TANK CARGO T ANK CARGO TANK CARGO T ANK CARGO TANK CARGO TANK CARGO TANK NO.5 P S.W. BALLAST NO.4 P S.W. BALLAST NO.4 S CARGO TANK NO.3 P CARGO TANK NO.2 P CARGO TANK NO.1 P MACHINERY SPACE F.O. NO. 8 C NO. 7 C NO. 6 C NO. 5 C NO. 4 C NO. 3 C NO. 2 C NO. 1 C CARGO TANK NO.1 S CARGO TANK NO.2 S CARGO TANK NO.3 S CARGO TANK NO.5 S CARGO TANK NO.6 S CARGO TANK NO.7 S CARGO TANK NO.8 S F. O DT (SWB) WL F P LBP B 15 B D BALLAST FIGURE 5 Outline arrangement of typical product carrier. Source: U.S. Department of Commerce, Maritime Administration. C013_003_r03.indd 677C013_003_r03.indd 677 11/18/2005 10:41:01 AM11/18/2005 10:41:01 AM © 2006 by Taylor & Francis Group, LLC [...]... Taggart, “Ship Design and Construction”, The Society of Naval Architects and Marine Engineers, 1980 2 Dillon, Hoffman and Roseman, “Forty Years of Ship Designs Under the Merchant Marine Act, 1936Ϫ1976”, Transactions, The Society of Naval Architects and Marine Engineers, 1976 3 National Academy of Sciences, National Research Council, “Evaluation of the Hazard of Bulk Water Transportation of Chemicals—A Tentative... SPILLAGE—SOURCES AND HAZARDS c) Enhanced navigation systems—Long term objectives include the integration of satellite and terrestrial navigational aids, electronic updating of charts, and automatic position plotting Safety objectives include installation of grounding and collision avoidance systems and “dead man” alarms Problem areas to be addressed include international standardization of data format and transfer,... Guard, CG-388 Chang, et al., “A Rational Method for the Prediction of Structural Response Due to the Collision of Ships”, Transactions, The Society of Naval Architects and Marine Engineers, 1980 Reckling, “Overall Structural Response of a Ship Struck in a Collision”, Transactions, Society of Naval Architects and Marine Engineers Spring Meeting/STAR Symposium, 1980 Poudret, et al., “Grounding of a Membrane... National Research Council, 25 March, 1990 Laredo, Beghin and Garguet, “Design of the First Generation of 550,000 DWT Tankers”, Transactions, The Society of Naval Architects and Marine Engineers, 1977 Long, Stevens and Tompkins, “Modern High Speed Tankers”, Transactions, The Society of Naval Architects and Marine Engineers, 1960 Oil Pollution Act of 1990, Conference Report to accompany H.R 1465 Tanker... AM 680 MARINE SPILLAGE—SOURCES AND HAZARDS FIGURE 8 Burmeister & Wain double hull product tanker design Source: Burmeister & Wain Skibsvaerft A/S technology As noted earlier, LNG, LPG and a variety of special products carriers have all been built with double hulls, as mandated by regulatory requirements Special Hazards in Tanker Operations In addition to collision and grounding, the following hazards. .. AM 682 MARINE SPILLAGE—SOURCES AND HAZARDS perhaps just as effectively, from the pressures of the insurance industry Some suggested directions for study in improvement of design and operation are included in the following discussion Operational Measures Dirty Ballast This source of pollution should be largely eliminated with the imposition of MARPOL regulations requiring segregated ballast and the... Arrangement and Structure The recently enacted Oil Pollution Act of 1990, Reference (12), mandates that all tank vessels of 5000 gross tons or larger, operating in waters subject to jurisdiction of the United States, must be of double hull construction by the year 2015 The law includes explicit phase-out time tables for retiring existing tank vessels, depending upon year of delivery and type of cargo... Tanker—Correlation Between Damage Predictions and Observations”, Transactions, Society of Naval Architects and Marine Engineers Symposium on Extreme Loads Response, October 1981 Poudret, “Collisions and Groundings—Practical Analysis Methods”, Arctic Section, Society of Naval Architects and Marine Engineers., March 1982 Wierzbicki, Shin and Rady, “Damage Estimates in High Energy Grounding of Ships”, presentation to Committee... command and control systems and condition monitoring of main and auxillary machinery systems and components b) Maintenance reduction—To maintain a safe operating condition, inspection and maintenance procedures must be maintained at acceptable levels, while recognizing the constraints of reduced crew size © 2006 by Taylor & Francis Group, LLC C013_003_r03.indd 682 11/18/2005 10:41:04 AM MARINE SPILLAGE—SOURCES. .. 10:41:02 AM MARINE SPILLAGE—SOURCES AND HAZARDS hazards and pollution problems The responsible regulatory agencies were active in studying and regulating various special hazardous cargoes long before oil pollution was recognized as a major hazard Accordingly, safety codes and regulations have been formulated and effectively enforced for a long period of time Regulations of the U.S Coast Guard, for example, . Group, LLC 670 MARINE SPILLAGE—SOURCES AND HAZARDS result such vessels are able to operate with clean ballast only and no ballasting of fuel tankage is normally required. Roll-on/roll-off or trailer. for depth and breadth of double bottoms and wing tanks, respectively. In anticipation of these requirements, designers and build- ers have developed designs of environmental tankers and a significant. Francis Group, LLC MARINE SPILLAGE—SOURCES AND HAZARDS 681 hazards and pollution problems. The responsible regula- tory agencies were active in studying and regulating vari- ous special hazardous