Effects of Double-Hull Requirements on Oil Spill Prevention Interim Report (1996) / Chapter Skim
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5 Data on the Design, Construction, Maintenance, and Operation of Double-Hull Vessels
5 Data on the Design, Construction, Maintenance, and Operation of Double-Hull Vessels
Pages 33-42
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From page 33... ...
The imposition of the double-hull design on the entire tanker fleet by OPA 90 (at least on most of the fleet trading with the United States) has focused attention in the maritime oil transportation and shipbuilding industries on how to build safe, economical double-hull vessels.
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From page 34... ...
PROBLEMS AND CONCERNS Perceived in 1990 The problems and concerns raised in 1990 regarding double hulls primarily dealt with effectiveness of the design in preventing pollution, the increased risk of fire and explosions, possible instability of damaged vessels, perceived salvage difficulties, increased hazards to personnel in double-hull spaces, concerns about ship structural integrity and the extensive use of high-tensile steels, and concerns about corrosion in double-hull spaces. Data pertinent to issues related to design, construction, inspection, and maintenance have been obtained from survey questionnaires sent to owners and operators of double-hull vessels, shipyards, classification societies, and naval architectural organizations.
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From page 35... ...
Verification of the procedures using large-scale model tests and actual collision data, is a necessary element of the approach because of the inherent difficulty in modeling highly contorted collapse modes and the relatively crude criteria still used to model plate- and weld-fractures during crushing. Eight of the papers presented at MARIENV '95 dealt with structural integrity in collisions.
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From page 36... ...
Navy conducted analytical studies and large-scale model tests for strandings (loadings normal to the bottom shell) and groundings (combined normal and in-plane loadings)
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From page 37... ...
DESIGN AND CONSTRUCTION Present Practices, Concerns, and Trends The present design will be summarized based on ship data received from shipowners and operators, shipyards, classification societies, and naval architects on double-hull tankers built since 1990. Design concerns about double-hull tankers were primarily based on the trend towards the greater use of higher-tensile steels and the importance of designing structural details properly to minimize the risk of fractures and the possible leakage of oil into the ballast spaces or into the sea.
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From page 38... ...
Many of the classification society rules now have fatigue criteria and fatigue assessment methods applicable to structural details to ensure fatigue strength. The International Association of Classification Societies has also been active in establishing unified requirements to improve the design and construction of double-hull tankers.
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From page 39... ...
Relying on the current experience with double-hull tankers, the committee will collect and evaluate data on current operational practices for double-hull tankers, current operational concerns, and future trends in operational practices, and possible effects of operational experience on future designs. Operational differences between double-hull and single-hull tankers will be assessed using data from a survey of owners and operators of double-hull tankers and on current research and literature.
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From page 40... ...
COMPARATIVE EVALUATION OF ALTERNATIVE SINGLE-HULL AND DOUBLE-HULL DESIGNS During the preliminary design process, tank arrangements and subdivisions are developed to suit owner requirements as well as classification society, flagstate, and other relevant regulations. Within the bounds of the regulations, the designer makes decisions on the location of the cargo block, the size and location of tanks, and the dimensions of the wing tanks and double bottoms.
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From page 41... ...
The areas covered by this questionnaire include ship characteristics data for double-hull tankers built or classed, percentage of high-strength steel used, and comparison of producibility of single-hull and double-hull designs of 90,000, 150,000, and 280,000 DWT sizes. Indicators of producibility may be based on differences in labor hours and cost for steel fabrication, machinery and outfitting, coatings, total construction time (from keel laying to delivery)
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From page 42... ...
The committee will rely on experience from double-hull chemical and product camers, as well as from the few double-hull crude carders built before 1990. After an exhaustive analysis of information from the surveys and expert testimony and a thorough search of the literature in the first phase of the study, remaining gaps in information will be filled by personal contact between committee members and individuals from various organizations and companies.
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