Tanker Spills Prevention by Design (1991) / Chapter Skim
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2 Tank Vessel Design, Operation, and Regulation
2 Tank Vessel Design, Operation, and Regulation
Pages 29-54
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From page 29... ...
The discussion applies primarily to tankers, although some sections, as noted, apply to barges. TANK VESSEL DESIGN AND OPERATION Tanker Design Crude oil and petroleum products have been carried in ships for more than 100 years.
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From page 30... ...
· 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.
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From page 31... ...
TANK VESSEL DESIGN, OPERATION, AND REGULATION 31 , ~ ID Do Go Cry I_ V o CD ._ sit Cal En of \ V .— , ~ ._ I_ ~ ID 3 ~ ° ,= En A: 5 .
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From page 32... ...
First, introduction of new stress analysis techniques (employing finite element analysis and three-dimensional frame analysis) have permitted reductions in the structural weight.
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From page 33... ...
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 (ship owners who pay fees to "class" their ships)
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From page 34... ...
However, the manning requirements remain quite different, and thisbesides encouraging the continued use of barges influences vessel design, including the choice of appropriate alternatives for pollution control. The basic design process for offshore barges carrying petroleum products is similar to that for tankers.
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From page 35... ...
Sometimes the entire cargo is removed offshore ("lightening to extinctions. 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.
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From page 36... ...
The committee is unaware of specific records kept on the safety of lightering, but, based on inquiries to concerned industry organizations, there is no evidence of any major accident or pollution incident stemming from lightering of tankers.4 Economic Considerations 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.
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From page 37... ...
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.
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From page 38... ...
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.
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From page 39... ...
(The data were presented in Figure 1-9.) LEGAL REQUIREMENTS FOR VESSEL DESIGN AND POLLUTION PREVENTION 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.
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From page 40... ...
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.
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From page 41... ...
Sources: Exxon Marine and Clarkson Research Studies Ltd. arrangement.
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From page 42... ...
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.
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From page 43... ...
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)
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From page 44... ...
Domestic Legal Requirements 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.
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From page 45... ...
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.
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From page 46... ...
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.
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From page 47... ...
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.
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From page 48... ...
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.
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From page 50... ...
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From page 51... ...
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From page 52... ...
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)
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From page 53... ...
Flag states may issue load-line certificates; however, these also conform to applicable international convention requirements. Ships sustaining damage to an extent that cancels valid class status still may obtain insurance coverage for salvage purposes at exorbitant rates.
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From page 54... ...
1914, October 21, 1986, 46 USCG 5101 et seq., and regulations promulgated thereunder, 46 CFR Parts 1 et seq., 172. SOLAS legislation and regulations for tank vessels are implemented under 46 USC 3301 et seq.
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