Waterjet testing techniques for powering performance estimation using a single catamaran demihull

A new series of highly efficient medium-speed wave-piercing catamarans is under development \nto reduce the environmental impact of fast sea transportation. They will operate at \nspeeds where mutual interference between waves and increased resistance produces the characteristic \nhump in the ship's resistance curve. The challenge is the assessment of the effects \nof the change in operating conditions on the waterjet propulsion system. Waterjets are used \nfor high-speed multihulls due to their high efficiency when operating at speeds beyond hump \nspeed. However, they are generally not used for medium-speed applications due to the assumed \ndecrease in efficiency at lower speed. \nA series of self-propulsion tests of a high-speed wave-piercing catamaran at medium-speeds \nwas carried out to study the influence of the hydrodynamics at medium-speeds on the waterjet \npropulsors. The model tests were carried out using load varied (i.e. British method) \nself-propulsion testing in calm water. Due to size requirements of the model, a single demihull \nwas utilised in close proximity to the side wall of the towing tank which acts as the plane \nof symmetry, reflecting waves generated by the demihull and therefore providing the correct \nblockage effects and wave interference for the non-existing second demihull. \nThe results were validated using full-scale sea trials data for the vessel under consideration \nand for waterjet unit performance comparisons, a set of benchmark data was supplied \nby the waterjet unit manufacturer. The model tests showed that the propulsion unit at \nmodel scale is capable of reflecting the characteristics of the full scale waterjet. Furthermore, \na new, thrust based extrapolation method was introduced and utilised with the results of \nthe experimental testing carried out for the waterjet propulsion study. The results of this \nextrapolation were in correlation with the available full scale powering sea trials data.