Tanker Spills: Prevention by Design (1991)

Before embarking on a technical analysis of alternative tank vessel designs, standard design and operational practices related to pollution prevention should be understood. This chapter will discuss the evolution of these practices, as well as the legal and regulatory framework governing the tank vessel industry. The discussion applies primarily to tankers, although some sections, as noted, apply to barges.

Crude oil and petroleum products have been carried in ships for more than 100 years. The practice of carrying the oil directly inside the single hull of a ship has been common since this type of ship was first built in 1886. The hull provided far better security for the cargo than barrels, or casks, which could split and spill oil, creating fire and explosion hazards.

Tanker designs established in the late 1880s remained virtually unchanged until shortly after World War II. Tankers commonly were of 10,000 to 15,000 DWT, with a single skin, the engine to the stern, and multiple compartmentation with either two or three tanks across. Cargoes were usually refined products, most often light or "white" oils, which were not considered polluting as they rapidly evaporated if spilled. The non-polluting cargo meant that tanks could be rinsed out with water (which then was dumped at sea), and the same tanks could be used for ballast (sea water).

Separate ballast tanks, other than the peak tanks (at the ends of the ship), were virtually unheard-of until after World War II.

After the war, the world economy expanded with a resulting huge increase in demand for energy in the form of oil. At the same time, a new shipping pattern evolved: Crude oil often was transported from distant sources, such as the Persian Gulf, to major marketing areas, notably North America, Northern Europe, and Japan, where the crude was refined and redistributed as product. These long voyages set the stage for a dramatic increase in ship size, which started about 1950. Between 1950 and 1975, the largest tanker in the world grew from about 25,000 DWT to over 500,000 DWT. (See Figure 2-1.) The numbers of tankers in the world fleet also multiplied many times over.

Meanwhile, significant technical developments were afoot, including the following:

• Welding replaced riveting, a major benefit to the tanker industry in assuring tightness of tanks. The practice initially led to some cracking, and ships breaking in half, but these problems were solved with better materials, welding, and design.

• The empirical, or rule-of-thumb, design approach was augmented and partially supplanted by theoretical techniques. This trend was facilitated by the introduction of computers in the 1950s and 1960s, and, in fact, was necessitated by the growth in ship size from vessels of around 500 feet to over 1,400 feet, with an increase in deadweight of over twenty-fold in less than 20 years.

• While the basic types of static and dynamic forces acting on ship structure had been known in general for years, it was not until the 1960s that naval architects were able to quantify the loads precisely and to carry out the stress analysis needed to design ships on a theoretically sophisticated basis. By the 1970s, reliable theoretical quantification of loads and structural response was common for tankers; however, practical service experience remains vital to verify structural integrity and detail design.

• As newer design techniques were introduced, "safety factors" (design allowances for unknown factors) were reduced, in the desire to keep costs down and to get maximum deadweight for minimum draft (the depth of water a vessel draws). The effect is shown in Table 2-1.¹ The significant reduction in ratio of lightweight (ship weight without cargo, crew, fuel, or stores) to deadweight directly reduces the cost of a ship per ton of cargo; this means a ship can carry more cargo for a given draft. It also implies more efficient structure, and, in general, less margin to tolerate construction or maintenance errors or unusual operational events.

• Structural weight reductions were accompanied by a reduction in the number (and resulting increase in size) of compartments; the intent was to lower construction cost and simplify operations. While this change has

been criticized on safety grounds, large tankers (with two or three longitudinal bulkheads, multiple transverse bulkheads, and a nearly continuous upper deck) seldom have stability problems experienced by other types of ships with much larger (relative to the size of the ship) open spaces. A valid concern with larger compartments is the increased amount of oil that could be spilled if the tank were breached.

As tanker design practices evolved, problems, of course, periodically surfaced. Among the more significant problems was buckling of internal structures, encountered in larger tankers in the late 1960s and early 1970s. The solution was use of more precise finite element and more sophisticated frame analysis techniques. The most dramatic problem from the industry standpoint was explosions, especially after three VLCCs exploded (two were total losses) in one week in 1969. The solution was inert gas systems, described in Chapter 3, which were mandated by international agreement for progressively smaller ships during the 1970s.

In sum, there are two key features of modern structural design of tankers. First, introduction of new stress analysis techniques (employing finite element analysis and three-dimensional frame analysis) have permitted reductions in the structural weight. This in turn has led to a substantial reduction in cost (steel, measured by weight, is a major component in ship cost), and a modest increase in cargo-carrying capability. Second, improved welding and steel-making techniques have led to increased use of high-strength steel in tanker hulls, with attendant economic benefits. Even with these more sophisticated methods, however, ship design still must be conservative because loads never can be precisely predicted for all environments.

The exact design of a particular tank vessel depends on many factors. There are 10 basic ship characteristics that must be considered:

• ship dimensions

• hull form

• machinery size, type, and location

• speed and endurance

• cargo capacity and deadweight

• accommodations arrangements

• cargo/ballast tanks arrangements

• subdivision and stability accommodations

• relative amounts of mild or high-tensile steel

• basic scantling and structural arrangement

Irrespective of any specific design chosen, however, the technical advances in the design process have fostered a number of difficulties. These concerns, involving corrosion resistance, design margins, and fatigue resistance, are detailed in Chapter 4. Suffice to say at this point, advancements in design techniques and analyses unquestionably have made modern tankers more vulnerable to failure under conditions of unusual stress, or less-than-diligent maintenance. This matter has been of considerable interest to the committee.

The committee also has noted that prevention of damage or rupture of structure due to collisions or groundings heretofore has not been a design consideration for merchant ships, except in rare cases (e.g., barriers to nuclear reactors and, to a lesser degree, chemical carriers and liquified natural gas carriers). In attempting to reduce pollution risk, incorporation of these additional criteria into tanker design practices warrants serious attention.

Finally, it should be noted that design practices, while technically oriented, have a direct bearing on cost, and this is a factor in design decisions. The process is essentially circular, for the following reasons.

Because the structural rules, which are developed by classification societies, determine the weight and thus a major component of the cost of the ship, "class" decisions to a large degree control cost. The differences among classification societies—non-profit groups in competition—are factors that attract clients (shipowners who pay fees to "class" their ships). At the same time, classification societies are managed fundamentally through boards of directors composed mainly of shipowners but with some representation from shipbuilders, insurers, and government. This situation offers the potential for conflict of interest, in that it makes this aspect of the industry essentially self-regulating.

The owners' interest in maintaining reliable ship structure has kept class rules, in the majority view, to a high technical standard. Nonetheless, it must be acknowledged that competition among classification societies and among shipyards has produced strong pressure to produce a minimum cost ship that will perform to an adequate structural standard.

Ocean-going barges have been used in the shipping industry for many years. In the United States especially, barges have become extremely important in coastal transportation, particularly since World War II. There are two

principal reasons. First, under U.S. manning regulations, a non-propelled cargo section pushed or pulled by a tugboat requires a much smaller crew than a tanker, thus offering a major economic savings. Second, structural and safety requirements have been less stringent for barges. Until recently, unmanned barges could be built to lesser scantling (dimensions of structural members) requirements than ships with cargo sections of the same size. In addition, the absence of a crew meant that unmanned barges could escape many of the safety requirements (related to fire fighting, life-saving, anchoring, etc.) imposed on tankers. Similarly, barges had more liberal (lower) freeboard assignments² than ships and usually could be operated without ballast, thus providing substantial economic advantages.

In recent years, many of the differences in technical standards between tankers and barges have been eliminated, and the U.S. Coast Guard has applied structural provisions of international tanker conventions to larger barges. However, the manning requirements remain quite different, and this—besides encouraging the continued use of barges—influences vessel design, including the choice of appropriate alternative for pollution control.

The basic design process for offshore barges carrying petroleum products is similar to that for tankers. Structurally, barges are somewhat different in that they tend to have heavier side structure (to accommodate loads from contact with piers, locks, and tugboats), and they have greater breadth than tankers of the same length.

Tankers generally operate between single or multiple loading and discharge ports. When tankers were smaller in the 1950s and early 1960s, they often loaded and discharged alongside a pier, usually in a harbor. As ships got larger, requiring deeper ports, new port complexes were constructed, principally in the Middle East, Europe, and Japan. While many of these facilities were essentially conventional, with a sheltered port and a permanent fixed pier, the tanker industry also developed offshore multi-buoy moorings (MBMs) and, eventually, single-point moorings (SPMs).

Tankers are loaded near the midship point by shore pumps, or gravity if storage tanks are elevated, through hoses or "hard-arms" (hard pipe structures with swivel connections) connected to the ship's piping system. Tankers commonly have pipes on deck and running down to the ship bottom. When a tanker is discharging, the ship's power drives cargo pumps, usually located in a pump room between the engine room at the stern and the cargo tanks. The cargo is pumped up to the deck, and then ashore through the hoses or hard-arms. The process is essentially identical for the handling of crude oil, fuel oil, or refined products. Most tankers have two, three, or more separate piping and pumping systems, so as not to intermingle cargoes of different grades or characteristics. These systems are powerful enough to transfer

cargo in an emergency, provided they remain intact; however, setting up the system to drain cargo from a damaged tank quickly is difficult, because the installed transfer piping suction is on the tank bottom and the oil remaining normally will float above the suction. A more detailed discussion of cargo systems can be found in Chapter 4.

Tankers operate on many different trade routes and serve thousands of delivery points. Most tankers load cargo in one area, take it to another area for discharge, and then return empty to a loading area. Thus, tankers typically are loaded roughly half the time, and otherwise are ''in ballast." To deal with buildup of sludge, and to clean tanks between switches of grades in product trades, cargo tanks are cleaned periodically. For many years this was done with either cold or hot water. And, until the late 1960s, sea water often was placed in some empty cargo tanks for the ballast voyage. These practices, of course, led to some mixing of oil and water, and discharge of rinsing or ballast water inevitably caused some pollution of the seas. Concern about this "operational pollution" led to a series of new practices mandated by international conventions in the 1970s; these are among the provisions described later in this chapter.³

Another measure adopted widely by the tanker industry in the post-war years was lightering (or lightening), the process of transferring cargo from one floating vessel directly to another. Lightering is used principally to remove cargo from larger vessels to make them lighter (and to reduce their draft), to allow them either to enter a harbor or to approach a pier to discharge remaining cargo. Sometimes the entire cargo is removed offshore ("lightering to extinction"). Lightering is relevant to the present study because its use may be encouraged by the Oil Pollution Act of 1990, which prohibits some tank vessels from approaching U.S. shores.

Nearly all types of dry and liquid cargo, in bulk or in containers, can be transferred by lightering. Crude oil often is moved in this manner, at least in the following areas:

• the English Channel;

• Argentina;

• the Mediterranean, Middle East, and Far East;

• the lower Delaware Bay (where barges are commonly used to take some cargo out of larger arriving tankers, to allow them to proceed to refinery terminals farther up the Delaware River);

• the U.S. Gulf of Mexico; and

• San Francisco Bay.

Lightering became common in the U.S. Gulf of Mexico in the early to mid-1970s, when crude oil imports increased rapidly along with the size of

ships. With no resolution of the debate on the wisdom of deepwater ports, lightering was the industry solution for accommodating the largest tankers, which could not be berthed in shallow U.S. harbors even in lightened condition. Lighters in the 50,000 to 80,000 DWT size range were employed; at times, probably six to eight of these vessels were engaged full-time in the Gulf of Mexico and the Caribbean. Then, as oil imports declined and the first—and still only—U.S. deepwater port (LOOP, 18 miles off the coast of Louisiana) came on stream in early 1982, use of lightering dwindled.

Now, with crude oil imports increasing again, imports of refined products rising, and the LOOP operating at full capacity, tanker activity in the Gulf—including lightering—will intensify once more.

Another offshore facility, TexPort, is under consideration by an oil company consortium; it would be located 27 miles off Freeport, Texas, where there are no depth constraints to even the largest tankers. At its greatest proposed capacity, TexPort could handle nearly a third of the present U.S. oil import volume (about 100 million tons per year). The consortium estimates that this facility will be operable five years after local, state, and federal regulatory hurdles are overcome.

Reliability and Safety of Lightering. The industry took several steps in the early 1970s to assure the reliability and safety of lightering. Special techniques involving large fenders, special mooring arrangements, and ship handling techniques were explored at both model and full-scale levels, to develop the best methods for mooring and maneuvering two ships together. Lightering with both ships underway was found to be, in many instances, the preferred method, as the best course could be determined with regard to wind and waves, thus simplifying ship handling. Also, with both ships underway the mooring of the smaller vessel alongside the VLCC could be accomplished with full control over the lighter. The procedures for maneuvering vessels, mooring, and handling cargo were codified in a detailed Ship To Ship Transfer Guide (International Chamber of Shipping, 1978).

The committee is unaware of specific records kept on the safety of lightering, but, based on inquires to concerned industry organizations, there is no evidence of any major accident or pollution incident stemming from lightering of tankers.⁴

Tank vessel design is an important factor in the economics of tanker transportation, and this should be taken into account when considering future design changes. The basic principles involved are described here; a fuller explanation, including the economic impact of specific design alternatives, can be found in Chapter 6.

There are three basic categories of costs that comprise the total cost of carrying oil by tanker. These are:

• Capital cost, the predominant component of overall cost for tankers of nearly all sizes. It may be expressed either as the vessel price or as a down payment plus loan payments, just as with a house. Tankers are expected to last 15 to 30 years, so operators must think in terms of depreciation or capital recovery.

• Operating costs, covering the crew, maintenance and repair, stores, supplies, insurance, overhead, and administration. This is the second largest component of overall cost and is heavily influenced by vessel cost (which affects insurance rates), the complexity of the vessel (which affects maintenance and repair), and the size and nationality of the crew.

• Voyage costs, including fuel, port charges, piloting, and berthing tugs.

There are economies of scale in the tanker industry, as shown in Figure 2-2. In other words, a large tanker nearly always can carry oil at a substantially cheaper rate than a smaller tanker, assuming there is adequate cargo to fill the ship and that the ports can accommodate large vessels.

There are three main reasons for the economy of scale: (1) The amount of steel needed to contain a given quantity of cargo does not increase in proportion to the deadweight of the ship; (2) The horsepower needed to propel the ship at service speed does not increase nearly in proportion to the increase in ship size (offering economies in both vessel price and subsequent voyage cost for bunkers); and (3) The size of tanker crews seldom is related to vessel size. Thus, a crew of 20 to 25 will suffice for both a small tanker (20,000 to 30,000 DWT) and a ship 5 to 10 times larger.

Of course, tanker economics depends on more than cost structure, because tankers in international trade are essentially regarded as commodities. This is because tankers of similar size and characteristics are essentially interchangeable. Thus, market factors driven by supply and demand will play a dominant role in the actual shipping rates ultimately earned by tanker owners.

In summary, when considering possible design changes, the impact on capital costs, operating expenses, and the marketplace should be borne in mind.

As economic concerns drove the tanker world to increasingly larger ships, the size increase resulted in two important safety improvements. First, the number of ships needed to carry the world's ever-growing demand for petroleum was far less than it would have been with smaller ships. The increase in traffic and congestion would have been enormous if maximum ship size had remained at the World War II level (16,500 DWT); about three times the

FIGURE 2-2 Tanker transportation economics. Source: Temple, Barker & Sloane, Inc.

roughly 6,000 ocean tankers (over 5,000 DWT) now sailing the world seas would be needed.

Second, larger ships generally discharge cargo at remote locations. This has kept them at distance from some, though not all, of the world's busiest harbors. However, the United States was very slow to adopt deepwater ports, offshore SBMs, and other new facilities to accommodate the largest tankers. Thus, it remains common in the United States to see tanker drafts limited to roughly 40 feet, which restricts tanker size to a maximum of roughly 60,000 to 80,000 DWT. By contrast, most of the rest of the world deals with much larger ships at more remote locations.

These changes may have helped control the incidence and impact of pollution, albeit indirectly. The industry also took other steps in its continuing concern for the consequences of groundings and collisions. Structural solutions (i.e., "crash-proofing") were studied, although they never achieved prominence or widespread adoption. Instead, the industry concentrated on:

• radar and electronic navigation, which became important for ships of all types but particularly tankers;

• harbor and coastal traffic control systems, which became prominent in much of Europe and were adopted to a lesser degree in the United States;

• ship handling and bridge team simulator training, which were promoted by some tanker operators and were adopted in a number of prominent fleets, though by no means universally;

• research on ship maneuverability, to the point that prediction of ship maneuvers became commonplace in tanker design and operation; and

• an international agreement covering crew training and licensing, ratified by many nations though not yet by the United States.

The effectiveness of these measures, either individually or collectively, is difficult to assess. Data on serious tanker casualties do seem to show that tanker accidents have decreased over the last 10 years, based on the ratio of accidents to the number of tankships in service worldwide. However, a comparison of accidents to a general measure of exposure—ton-miles per year of oil and products shipped—while demonstrating a decrease in casualties since the mid-1980s, does not show such a clear safety improvement. (The data were presented in Figure 1-9.)

This section discusses the evolution of international conventions and laws related to tank vessel design and pollution prevention, as well as the current status of enforcement activities related to tankers operating in U.S. waters.

Tankers must satisfy a substantial number of design requirements when initially constructed, for purposes of safety and pollution prevention. These requirements fall into three broad categories: international legal requirements, domestic legal requirements, and classification society requirements.

The International Maritime Organization (IMO) is the United Nations agency responsible for maritime safety and environmental protection of the oceans. All of the world's major shipping nations are members of IMO. Each member nation is encouraged to accept the international agreements adopted by IMO. These include 22 full conventions or treaties and 17 codes (as of December 31, 1989) as well as numerous resolutions containing recommendations and guidelines.

Regulation of ship design for safety and pollution prevention is achieved primarily through three international conventions:

• The International Convention on Load Lines (1966), or ICLL;

• The International Convention for the Safety of Life at Sea (1974) and its 1978 Protocol (SOLAS); and

• The International Convention for the Prevention of Pollution from Ships (1973) and its 1978 Protocol (MARPOL).

The ICLL establishes the deepest draft to which a ship can be safely loaded. These "loadlines" are commonly seen as the "Plimsoll Mark" line

on a ship's side. Historically, the objective of the loadline was to assure that ships were not so overloaded as to run undue risk of sinking, or to create unsafe working conditions.

The overall objective of SOLAS is to assure safety of the crew, ports, passengers, ships, and cargo, and, indirectly, the environment. Among the more important provisions are: (1) subdivision and stability requirements, to prevent ships from capsizing, and to ensure survival under specified collision and grounding damage circumstances; (2) general construction principles, to ensure the ship is strong enough for its intended trade; (3) safety equipment requirements, to assure the carriage of sufficient life-boats and other safety equipment; (4) fire protection requirements, to ensure that ships could withstand certain fire damage and fight fires effectively; and (5) radio telegraphy requirements, specifying the communications and navigation equipment ships must carry.

Both ICLL and SOLAS have the indirect effect of preventing oil spills and consequent marine pollution. The MARPOL convention seeks to prevent pollution directly, both from normal operational discharges and accidents. MARPOL specifies design, equipment, and procedural requirements to prevent pollution of the seas from oil, chemicals carried in bulk, harmful substances carried in packages, sewage, and garbage. Each of these five potential sources of pollution is addressed in regulations set out in an annex to MARPOL.

Annex I of MARPOL addressed the prevention of pollution from oil, and it and certain SOLAS provisions include these major requirements:

• Segregated Ballast Tanks (SBT). Oil carriers over 20,000 DWT built after dates specified in MARPOL '78, and tankers over 70,000 DWT built after dates specified in MARPOL '73 (see Figure 2-3), are required to carry ballast in SBT. Only in severe weather can additional ballast be carried in cargo tanks. In such cases, this water must be processed and discharged in accordance with specific regulations.

• Protective location of SBT. The required SBT must be arranged to cover a specified percentage of the side and bottom shell of the cargo section.⁵ Thus, the protectively located segregated ballast tanks (PL/SBT) are intended to provide a measure of protection against oil outflow in a grounding or collision. To be credited, each wing tank or double-bottom tank must meet certain minimum width or depth requirements, respectively (generally 2 meters).

• Draft and trim requirements. To assure safe operation of the vessel in ballast condition, the SBT must be of sufficient capacity to permit full submergence of the propeller. They are to provide a molded draft (d) amidships of not less than d = 2.0 + 0.02 L, and a trim (horizontal tilt) by stern not greater than 0.015L, where L is the ship length in meters.

• Tank size limitations.⁶ To minimize pollution in case of side or bottom damage, the maximum length of cargo tanks is limited to values between 10 meters and 0.2 L, depending on tank location and longitudinal bulkhead

FIGURE 2-3 Time frame for implementation of MARPOL and SOLAS.

Sources: Exxon Marine and Clarkson Research Studies Ltd.

arrangement. The maximum volume of each cargo tank may vary up to 22,500 m3 for side tanks and up to 50,000 m3 for center tanks, depending on tank arrangement and location.

• Hypothetical outflow of oil.⁷ Formulas establish the maximum allowable hypothetical outflow of oil in case a cargo tank is breached at any location on the ship. For the purposes of these calculations, the regulations

specify certain assumed longitudinal, transverse, and vertical damage. The key damage assumptions, where B is the ship's beam or breadth, are:

Side transverse extent: B/5 or 11.5 meters, whichever is less

Bottom vertical extent: B/15 or 6 meters, whichever is less

• Subdivision and stability. For a specified assumed shell damage, the regulations require that tank subdivision and ship features be such that, under certain specific damage conditions: The final water line is below any opening leading to progressive down-flooding, and the heeling angle (tilt to one side) does not exceed 25 degrees (or 30 degrees if the deck edge is not submerged).

• Crude Oil Washing (COW). New crude oil tankers must be fitted with an effective tank cleaning procedure that uses cargo oil as the washing medium. COW is a superior system of cleaning cargo tanks using the dissolving action of crude oil to reduce clingage and sludge. Furthermore, elimination or reduction of water washing has helped reduce operational oil pollution of the seas.

• Inert Gas System (IGS). This system supplies the cargo tanks with an atmosphere lacking in oxygen so that combustion cannot take place. Treated flue gas from main or auxiliary boilers, inert gas generators, or other sources may be used for that purpose. This important safety system is described in more detail in Chapter 3.

• Slop tanks. Tankers must be fitted with slop tanks of specified capacity to retain on board all slop, cargo drainage, sludge, washings, and other oil residues. Their discharge then is monitored in accordance with the regulations.

The IMO Conferences of 1973 and 1978 together produced fundamental changes in the way tankers are designed and operated. The significance of these changes in relation to the present study will be summarized here. Most important is the fact that the "MARPOL vessel" represents the current standard, against which any further design changes should be measured. MARPOL also set a precedent by establishing major retrofitting requirements for tankers, applying new equipment requirements (IGS and either SBT or COW) to existing tankers for the first time. The following other points may be less obvious.

Historically, control of pollution from operations had been accomplished through the "load on top," or LOT, system.⁸ This method was highly dependent on the vigilance of the crew and was difficult to monitor; MARPOL introduced structural means of achieving the same goal, clearly an advantage. However, these provisions involved inherent difficulties. The introduction of segregated ballast basically changed tankers from deadweight-

limited carriers to cubic-limited carriers, and this in turn tended to increase the amount of oil outflow in groundings.⁹ This drawback was noted by the drafters of MARPOL; the result was increased pollution risk in some accidents for newly built SBT crude carriers, and even most "black fuel" carriers.

The time frame for implementation of MARPOL and SOLAS requirements, including SBT/PL, is shown in Figure 2-3. Even now, the world fleet remains a mix of carriers, many of which are exempt from these SBT and SBT/PL regulations due to age or year of construction. About 35 percent of the world tanker fleet over 10,000 DWT has SBT, and about half of these ships have SBT protectively located (Clarkson Research Studies, Ltd., 1990), thus meeting full MARPOL requirements.

In new vessels, the attempt to satisfy MARPOL requirements in the most economical way has led to two changes in ship proportions. First, to make up for cubic lost to SBT, tankers became deeper in relation to their length; the length to depth ratio (L over D) is now lower, and the ratio of draft to depth (H/D) has decreased, because freeboard is increased. Second, in the interests of economy and with improving hull form design, ships generally were made broader and shorter, as breadth is a cheaper dimension to increase than length. Thus the ratio of length to beam (L/D) generally has decreased.

In comparing pre-MARPOL to SBT ship designs, four general observations can be made (U.S. Coast Guard, 1973) that are relevant to the present study: (1) Depth must be increased in SBT ships to obtain sufficient volume for ballast; (2) for a given cargo volume, the ballast volume increases a great deal in SBT ships—in the range of 234 to 334 percent, which is indicative of the additional area that must be protected from corrosion; (3) expected oil outflow in groundings increases by up to 90 percent in many SBT designs; and (4) the greater depth (for a given draft and deadweight) in SBT designs means that deck and bottom plate thickness can be reduced significantly.

Implementation of IMO conventions is not straightforward, because the procedures—and their effectiveness—can vary. Requirements are imposed on a vessel through its flag state. (The flag usually is carried at the stern with the city of registry and ship's name.) Each tankship therefore is governed in design, arrangements, and construction by the international agreements ratified by its flag state.

Nations that have formally ratified or approved IMO conventions usually implement the requirements through legislation. When a vessel is judged to have been designed and built to international standards, the flag state issues a certificate for each convention to which the vessel complies. Each certificate is valid for five years, provided an annual inspection—afloat—demonstrates that the ship has been maintained in accordance with convention

requirements. After five years, the ship undergoes a major inspection and, as deemed necessary, renovation, prior to renewal of the certificate.

In traditional maritime nations, the inspection of vessels for compliance with both international and domestic requirements usually is carried out by government agencies, such as the Department of Transport in the United Kingdom, the Coast Guard in the United States, and the Coast Guard in Canada. Increasingly, with open registry or "flag of convenience"¹⁰ ships, however, enforcement and inspection is conducted on a contract basis, in which the flag state contracts for all these services to be handled by a classification society.

In addition to complying with international convention requirements, ships must adhere to any additional requirements imposed by the flag state. Compliance becomes further complicated when nations, as port states, impose unilateral requirements.

There are very few unilateral port state requirements related to basic ship design and construction that represent a variance or extension of the international standards. Unilateral regulations imposed by port states usually deal with matters such as employment of pilots, hours in which ships can operate particular channels, use of tugs, and other issues peculiar to a certain locale. The United States, however, has imposed several requirements that vary significantly from international standards, as described in the following pages.

Each flag state may require its own vessels to meet any set of regulations deemed appropriate. The regulations may apply as vessels travel anywhere in the world. However, each port state may require foreign-flag vessels entering its territorial waters to meet its own set of regulations. Foreign-flag ships have the option of either abiding by port state requirements or not traveling in those waters.

Flag state requirements are subject to continual monitoring. Basically, this is handled by yearly inspections, which are fairly routine, and with more thorough inspections occurring at five-year intervals. No extension can be granted for five-year surveys.

IMO conventions do not specify penalties for noncompliance, other than removal of the current certificate. They direct that penalties (by indictment, warning, fine, or imprisonment of the person(s) responsible for the violation) be imposed by the flag state.

Classification societies establish standards, guidelines, and rules for the design, construction, and survey of ships. There are eleven leading classifica-

tion societies, as represented by the membership of the International Association of Classification Societies (IACS).¹¹ A ship that has been constructed in accordance with the rules of a society is issued a classification certificate. To maintain their classification, vessels must be presented for survey at regular intervals.

Class requirements essentially are concerned with the structural integrity of the ship and its propulsion and steering systems; they do not address safety equipment or crew qualifications. Class requirements embrace: (1) materials for hull and key machinery components; (2) structural design requirements including scantlings (dimensions of structural elements) and details of all structure and key machinery components (i.e., main engine, shafting, propeller, etc.); and (3) supervision, inspection and certification of manufacture of steel, welding, machinery components, hull structure, etc.

These requirements must be met for the ship to comply fully with international convention requirements and to obtain more favorable insurance rates.¹² The requirements are not statutory in nature; however, under the SOLAS Convention, each ocean-going ship¹³ must have a Safety Construction Certificate attesting to the adequacy of the construction. Being "in class" does not, in itself, satisfy SOLAS requirements, but, when authorized, a classification society may issue a SOLAS certification on behalf of a flag state.

Once a ship has been delivered, it can maintain its "in class" status only by meeting continuing survey requirements of the classification society. Essentially, the ship has to satisfy the society of its suitability to continue trading by passing both hull and machinery surveys at various intervals. Surveys can be of either a continuous or periodic nature, or a combination thereof.

Historically, periodic surveys were set up based on a system of annual and special surveys. Annual surveys do not include in-depth inspection of the ship's machinery and structure, unless there is cause for concern. Special surveys of hull and machinery are spaced at four-year intervals, although the society often grants a "year of grace" unless there is a compelling reason to deny it. Therefore, special surveys tend to fall at age 5, 10, 15, etc. The basic purpose of the special survey system is to assure the vessel's ability to trade successfully until the next scheduled special survey.

Special surveys become increasingly rigorous, at least in theory, as a ship gets older. The first special hull surveys will include, for example, a general examination of the most critical parts of the ship structure. By the second special survey, a more thorough examination is conducted, including measurement of the thickness of certain key structural members. The third

special survey includes a comprehensive examination of the ship's structure and measurement of thickness of structure.

Continuous surveys, in lieu of special surveys, are applied particularly to machinery, and sometimes to the hull. Under this system, various parts of the ship are inspected by classification surveyors during port calls, while the vessel remains in service.

One approach to conducting structural surveys on large tankers is described in Appendix C. The inspection of the vast structural areas of a modern VLCC (see Table 4-2) requires more time than is usually available while a tanker is in port, making operator inspection while the ship is underway and in ballast an attractive and economically efficient option.

When significant damage has occurred, or is suspected, which might affect the vessel's seaworthiness, the ship's owner is required to call in classification surveyors to inspect the damaged area. The surveyor then has three options: To allow the ship to continue trading "in class," to specify temporary repairs, or to require permanent repairs before the vessel can again be regarded "in class."

The U.S. implementing legislation for Annex I of MARPOL applies not only to seagoing ships of U.S. registry, but also to foreign-flag seagoing ships while in U.S. waters. The law authorizes the inspection of such ships, while in a port or terminal under U.S. jurisdiction, for compliance with the requirements of MARPOL. If a violation is found, the ship may be detained until authorities determine that it can proceed without undue threat of harm to the environment.

In some respects, U.S. law exceeds the requirements of MARPOL. For example, in U.S. waters, crude tankers between 20,000 and 40,000 DWT were required to have SBT or COW by 1986, or upon reaching 15 years of age, whichever occurred later. Product tankers in the same range were required to retrofit to SBT or operate dedicated clean ballast tanks by 1986, or upon reaching 15 years of age. Neither of these measures were required under MARPOL. Only one example of a flag-state requirement going beyond international requirements related to tanker design (other than for ice-navigation capability) has been identified outside of the United States: Finland's imposition of a large surcharge in imports of crude oil carried in single-hull ships.

The Oil Pollution Act of 1990, enacted on August 18, requires that all ships trading to U.S. waters meet standards that exceed the construction and design requirements of MARPOL in compliance with a phase-in schedule. Specifically, all new tank vessels (contracted after June 30, 1990 or delivered after January 1, 1994) operating in U.S. waters or the Exclusive Economic Zone¹⁵ must be fitted with double hulls. Existing single hull tank

vessels are permitted to operate until the time limits set forth in the Act; the timetable ends January 1, 2010. Existing tank vessels with a double bottom or double sides meet a separate schedule that ends in 2015.

A number of exceptions are provided to the requirements for double hulls. Tankers used exclusively for responding to oil spills, and tank vessels under 5,000 gross registered tons (about 10,000 DWT) fitted with a double containment system, are exempt. Also exempt until January 1, 2015, are tank vessels unloading or discharging at a deepwater port, off-loading in a lightering operation more than 60 miles from U.S. coasts, and under 5,000 GRT.

In the United States, the Coast Guard is responsible for regulations and enforcement related to tank vessel design, construction, and safety. Specifically, the Coast Guard is responsible for safety of life and property at sea and protection of the marine environment under provisions of Title 46 of the U.S. Code, Part B—Inspection and Regulation of Vessels, and 33 U.S. Code, Chapter 33—Prevention of Pollution from Ships, respectively, and other laws. Regulations prescribed by the Coast Guard incorporate American Bureau of Shipping (ABS) rules. In carrying out inspections and vessel design plan reviews, the Coast Guard may rely on ABS reports, documents, and certificates (46 USC 3316).

Vessel design plans are subject to Coast Guard approval, and inspection and review of plans and construction is a Coast Guard responsibility. The Coast Guard has delegated selected parts of its responsibility in this regard to the ABS, except for major safety aspects such as stability and fire fighting. The Coast Guard accepts ABS plan review and inspection as part of the certification process for new vessels, or vessels undergoing a major modification without review or attendance by Coast Guard personnel. The Coast Guard maintains an oversight program, overseeing approximately 20 percent of all ABS plan approval and inspection activities (U.S. Coast Guard, 1989b).

The Coast Guard is also responsible for ensuring that vessels are maintained to the appropriate standards. For this purpose, the Coast Guard requires inspection of U.S.-flag tank vessels every two years. Tankers, however, are often on a five-year operating and drydock cycle, conforming to most classification society survey intervals. In practice, this can mean that

in a five-year period, the Coast Guard may have to conduct more than two biennial inspections on the vessel.

The Coast Guard is also required to determine whether foreign-flag tank vessels can operate safely in U.S. waters. Regulations require that each foreign-flag tankship be inspected or examined at least once a year, with detailed inspections for vessels over 10 years of age. In practice, Coast Guard inspections of foreign-flag tank vessels do not routinely include internal inspection of the cargo or ballast tanks. The Coast Guard relies on the flag state or classification societies to conduct internal tank inspections.

A 1989 study conducted by Coast Guard staff found that hull structural examinations of foreign-flag vessels "are at best minimal" (U.S. Coast Guard, 1990b). The study team also found that, in general, neither U.S.-flag nor foreign-flag vessels are prepared for Coast Guard inspections. Moreover, a shortage of trained or experienced inspectors results in short-cutting, deferred discretionary inspections, and, overall, barely adequate performance. A technical problem with important consequences is the difficulty of conducting internal inspections of large tank vessels while they are in service (because of difficult access to high or remote areas). The majority of defects in tank or hull structure, especially in vessels over 80,000 DWT, are found by the owner or classification society (considerably more man-hours are expended in inspections by these parties than by the Coast Guard).

The Coast Guard's field inspectors generally felt that the Coast Guard needs to do an independent, thorough internal investigation of large tank vessels at pre-set intervals. "The burden of safety assurance," the report states, "is falling more and more on the Coast Guard." According to the Coast Guard, economic pressures of the last decade, which have forced cost-cutting in the maritime industry, have resulted in major reductions in industry engineering staffs. As a result, many organizations have become reactive, rather than proactive, in handling inspection and maintenance.

Coast Guard inspection efforts are not sufficient to ensure structural safety of oil tankers. The Coast Guard deployed about 250 hands-on inspectors on more than 36,000 vessel inspections requiring 380,000 staff hours. In FY 1988 and FY 1989 combined, the Coast Guard performed more than 3,300 inspections of tankers, totaling more than 25,000 staff hours in hull inspections alone (see Table 2-2).

The Coast Guard spends between 11 and 36 person-hours for each inspection of hull structure related to a hull examination, inspection for certification, or reinspection. This effort is only a small fraction of the time needed to conduct a thorough examination of a tank vessel (see Chapter 4).

The preceding discussion makes a number of important points that are relevant to the present study.

First, the prevention of oil outflow from groundings and collisions has not been a primary consideration in tank vessel design practices to date. Furthermore, advances in design have made modern tankers more vulnerable to failure under conditions of unusual structural stress, fatigue, or less-than-diligent maintenance. These facts are worth considering in taking steps to reduce pollution resulting from accidents.

In addition, the assessment and selection of alternative vessel designs should consider the impact on tanker economics, including capital costs, operating costs, and the marketplace. Enforcement and inspection capabilities are additional considerations. As noted, Coast Guard inspections already are considered barely adequate. Additional requirements for particular structural configurations, especially those increasing the need for proper maintenance and inspections, will add to the existing workload. A more detailed discussion of inspection concerns can be found in Chapter 4.

Finally, the committee was particularly impressed by two related facts concerning ship structural design and survey standards. First, responsibility for establishing and verifying adequacy of construction standards seems to be divided among multiple parties, including a ship's flag state administration, its classification society, and, to a degree, the International Association of Classification Societies (IACS). Second, the sophisticated computer design techniques pursued by the most advanced classification societies, while producing very efficient structures in terms of weight and cost, also have eroded traditional margins.

Uniform criteria for more robust structure could be established through joint review of structural design standards by IACS, the IMO, and the Coast Guard. Further, in light of the tangle of responsibilities regarding construction standards, and the fact that many classification societies do not belong to IACS (and perhaps do not possess the requisite technical capability to implement the more sophisticated design techniques), the Coast Guard and IMO, together with IACS, could undertake a comprehensive study aimed at aligning standards. The objective would be to develop linkage between statutory construction standards, as specified in SOLAS, and the actual standards adopted by classification societies. Such a study should recognize the capabilities of various societies and how each functions in relation to IACS, IMO, and to its government.

Clarkson Research Studies Ltd. 1990. FAX to D. Perkins, National Research Council, Washington, D.C., August 31, 1990.

Cutter Information Corp. 1990. Oil Spill Intelligence Report. Newsletter published by Cutter, Arlington, Massachusetts, June 14, 1990.

International Chamber of Shipping. 1978. Ship to Ship Transfer Guide. London: Witherby.

U.S. Coast Guard. 1973. Note by the United States—Report on Study I Segregated Ballast Tanker. Report prepared for IMCO International Conference on Marine Pollution, London, October 8-November 2, 1973.

U.S. Coast Guard. 1989a. Navigation and Inspection Circular 10-82. Published by the Coast Guard, Washington, D.C., September 18, 1989.

U.S. Coast Guard. 1989b. Marine Safety Center internal memorandum, May 25, 1989.

U.S. Coast Guard. 1990. Report of the Tanker Safety Study Group, Chairman H. H. Bell (rear admiral, USCG, retired). Washington, D.C.: U.S. Department of Transportation.