Design aspects of catamarans operating at high speed in shallow water

Abstract

The thesis describes the investigation into the design aspects of the high-speed displacement catamaran. This work is an extension of the existing database on the high-speed displacement hull form series namely the NPL series. The experimental test programme has been extended in the current research to investigate the influence of bulbous bows on the high-speed displacement catamaran performance in deep and shallow water conditions. Four bulbous bows have been developed by ranging bulbous bow's projecting length, between 1.25% to 6.25% of the length of waterline. These bulbous bows have been designed and faircd to the parent hull, NPL5b or known as a Model 5b of the NPL Series, whilst the after body and the fore body from amidships to 0.3Lpp are kept unchanged. However, the cross section parameter has been fixed at value 0.303 i.e. the ratio of the bulbous bow cross section area at forward perpendicular to the midship section area. Measurements of total resistance, wash, trim and sinkage have been made up to a Froude number of unity in deep and shallow water. In addition to the calm water tests, these models were also tested in regular waves covering a wavelength to ship length ratio AIT between 0.5 and 2.0 whilst the wave height was maintained at 0.030 m. Measurements of added resistance in waves, pitch, heave and wash cuts were made. Thin ship theory computer codes namely wavel3d.foT and wave3d3ss.foT have been used to validate the measured wash cuts. It was found that the experimental and numerical investigations provide a better understanding of the basic physics of wash, resistance and seakeeping of high speed displacement catamarans fitted with bulbous bows operating in deep and shallow water. The results of the systematic experimental investigation with respect to the influence of bulbous bows on wash, resistance and seakeeping provide invaluable information with a view to developing design guidance at the preliminary design phase and for validation purposes.