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L. High-strength steel construction requires good surface preparation and good-quality coating, as scantlings are reduced.
M. Experienced high number of cracks in 165,000 DWT class due to use of high tensile steel.
3. What design changes would you suggest in future double-hull tankers?
B. Normally minimum class requirements for longitudinal bending moments insufficient. Deflections of secondary members important. Ballast tank amidships to reduce bending moment is a possibility. Details according to Tanker Structure Cooperative Forum (TSCF) recommendations.
C. Better accessibility to ballast tanks and light color paint in ballast spaces.
D. High-tensile steel should be restricted to internal structure. Reduction in steel thickness if coating thickness increased not to be allowed. Certification of outer shell structural welding inadequate and inconsistent. Surface preparation rules needed.
E. Standards for access, staging fittings, coatings should be mandatory rather than at option of owner.
F. Double hulls may be useful for smaller tankers (order of 45,000 DWT), less so for larger vessels. Perhaps a gradual double hull replaced by double bottom for larger vessels.
H. Requirement for inherent positive stability throughout ballast or cargo handling; light-colored coatings; high-volume, continuously monitoring hydrocarbon detection system; shipyard design and practices to be certified by class if high tensile steel used
I. Requirements for redundancy, alarm, and automatic changeover for steering gear in event of single failure. Increased powering requirement. Requirement for emergency propulsion.
J. Design specific to trade and size. What is applicable for an ultralarge crude carrier (ULCC) or VLCC is not applicable to smaller ships. In general, U and L tanks should be avoided for small size ships.
L. Longitudinal center bulkheads would improve stability.
M. Easy access for inspection should be included in structural design. Coating regulations, which inhibit development, should not be established.
1. Based on your experience, what are the advantages of double-hull tankers compared to single-hull tankers?
A. Always capable of ballasting to safe draft for immediate departure in case of emergency.