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Suggested Citation:"Appendix F." National Research Council. 1998. Double-Hull Tanker Legislation: An Assessment of the Oil Pollution Act of 1990. Washington, DC: The National Academies Press. doi: 10.17226/5798.
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APPENDIX F Methodology for Determining the International Tanker Supply

The international tanker fleet is comprised of a wide mix of vessels varying in size, type, and age. Vessel sizes range from less than 10,000 deadweight tons (DWT) up to 550,000 DWT. Vessel types are differentiated by hull type (e.g., single, double) and ballast tank configuration (e.g., segregated, protectively located). Tankers are designed for specific commercial purposes, such as crude oil trades only, product trades, and the shipment of other commodities including combinations of oil and ore; oil, bulk cargoes, and ore; chemicals; asphalt; acid; edible oils and juices; and liquefied gases. Because of this diversity of vessel types and purposes, it is important to list the assumptions used to arrive at the international tanker supply (i.e., number of tankers and total tonnage).

After discussions with invited experts (including Dr. Stopford of Clarkson Research Studies Ltd., Mr. Shawyer of E.A. Gibson Shipbrokers Ltd., Mr. Lunde of International Association of Independent Tanker Owners (INTERTANKO), and Mr. Kulukundis of INTERTANKO and London and Overseas Freighters), the committee determined that the following assumptions formed a reasonable basis for its analysis of the international fleet:

  • Clarkson's existing and newbuilding tanker databases are accurate after adjustments based on input from Lloyd's, the American Bureau of Shipping, and Det Norske Veritas. (These adjustments were provided to Clarkson for incorporation into subsequent versions of its databases.)
  • Only tankers of more than 10,000 DWT are included.
  • The International Convention for the Prevention of Pollution from Ships, adopted in 1973 and amended in 1978, Regulations I/13F and I/13G (MARPOL 13F and 13G) are adopted by all countries except the United
Suggested Citation:"Appendix F." National Research Council. 1998. Double-Hull Tanker Legislation: An Assessment of the Oil Pollution Act of 1990. Washington, DC: The National Academies Press. doi: 10.17226/5798.
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  • States. Therefore, mandatory vessel retirements are determined by MARPOL and not by the Oil Pollution Act of 1990 (P.L. 101-380) (OPA 90), which bans non-double-hull tankers from U.S. waters no later than 2015 but does not preclude them from trading with other nations.
  • Because the committee is examining the impact of mandated retirements only, economic or other types of retirements not driven by MARPOL 13G are excluded.
  • MARPOL retires tankers based on delivery date. The Clarkson database used by the committee gives the year, but not the month, of delivery. Therefore, in the year of mandatory retirement, half of the vessel's deadweight is deleted from the supply. The full deadweight is deleted from all subsequent years.
  • Tankers without double hulls that comply with MARPOL are retired at 30 years of age. (Double-hull tankers are unaffected by MARPOL retirement provisions.) MARPOL tankers are identified as those built from 1983 onward, plus those identified in Clarkson's database as having double sides or double bottoms, or having been built after 1979 and having segregated ballast tanks.
  • All pre-MARPOL tankers will use hydrostatically balanced loading (HBL) in order to trade to 30 years of age. HBL results in an 8 percent loss in cargo carrying capacity for all pre-MARPOL tankers from age 25 through 30.
  • Because of the OPA 90 lightering exemption, no tankers of more than 120,000 DWT are excluded from trade to the United States until 2015.
  • Because of the current tight market for chemical tankers, these vessels are excluded from the supply of product tankers.
  • Oil-bulk-ore carriers are identified separately.
  • All government-owned military supply tankers, specialty tankers, and gas tankers are excluded from the supply.
  • The deadweight of newbuildings is added to the supply based on the month and year of delivery. The full deadweight is included in all subsequent years. When delivery month is not specified, delivery is assumed to be at the beginning of the fourth quarter (i.e., 25 percent of the vessel's capacity is added to the supply in the year of delivery).

The committee's supply analysis is based on tanker fleet statistics (including orders) as of October 1, 1995.

Suggested Citation:"Appendix F." National Research Council. 1998. Double-Hull Tanker Legislation: An Assessment of the Oil Pollution Act of 1990. Washington, DC: The National Academies Press. doi: 10.17226/5798.
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Page176
Suggested Citation:"Appendix F." National Research Council. 1998. Double-Hull Tanker Legislation: An Assessment of the Oil Pollution Act of 1990. Washington, DC: The National Academies Press. doi: 10.17226/5798.
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Page177
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The passage of the Oil Pollution Act of 1990 (OPA 90) by Congress and subsequent modifications of international maritime regulations resulted in a far-reaching change in the design of tank vessels. Double-hull rather than single-hull tankers are now the industry standard, and nearly all ships in the world maritime oil transportation fleet are expected to have double hulls by about 2020.

This book assesses the impact of the double hull and related provisions of OPA 90 on ship safety, protection of the marine environment, and the economic viability and operational makeup of the maritime oil transportation industry. The influence of international conventions on tank vessel design and operation is addressed. Owners and operators of domestic and international tank vessel fleets, shipyard operators, marine architects, classification societies, environmentalists, and state and federal regulators will find this book useful.

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