Model Studies for an Oceanographic Ship Derived From an Offshore Supply Vessel

Abstract

During the last few years, a number of operators of oceanographic research ships have considered the Gulf Coast offshore-oil-well supply vessel type for possible conversion to a research vessel. Such a ship of 155–165 ft length offers a number of attractive features; chiefly, reduced operating costs, and space for mounting portable or interchangeable equipment. The vessel's principal disadvantages reputedly are limited stability and a lack of seakindliness. An investigation of such vessels has recently been conducted by the Scripps Institution of Oceanography and the Department of Naval Architecture of the University of California. Model experiments were conducted to determine the resistance and powering characteristics, the motions in head seas, and rolling in beam seas. The transverse stability was computed for calm water and following seas. Four different hull forms were considered in these studiesa typical 155-ft-long single-chine supply boat;a round-bilge version of the same;a single-chine design developed to overcome several of the suspected deficiencies of Form 1 while still retaining the principal proportions; andan affine variation of Form 1 produced by multiplying transverse dimensions by 0.75 and increasing vertical dimensions by the same amount. It is concluded that the most serious deficiency of the vessel type is the tendency to slam in a head sea. This may limit the maximum speed in head seas. The small saving in resistance exhibited by both the narrower and round-bilge versions is insufficient to justify choosing either of these on this basis alone. In addition, both of these forms roll more severely than the two wide, single-chine forms. Finally, the increased freeboard of the third form results in an ample margin of stability. It is felt, therefore, that Form 3 provides a suitable basis for developing a research ship design.