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UBC Theses and Dissertations

Using parabolic waterlines to reduce the resistance of a trimaran Vyselaar, Daniel P.


Traditional ship design practices suggest that the optimum hull shape minimizes the beam of a vessel. However, recent studies on coaster tankers and typical west coast fishing vessels show that the addition of parabolic bulbs to a vessel's parallel mid body can significantly reduce the wave making resistance. These parabolic bulbs are added at the waterline and create their own wave pattern. The waves created by these bulbs can interact with the shoulder wave system of the base hull in a beneficial manner for certain speed ranges. Previous parabolization studies have been primarily experimental in nature, and have focused on vessels with small length to beam ratios, typical of workboats. This thesis uses both numeric tools and experimental approaches to alter the waterlines of a slender, high speed trimaran. A Michell's integral based solver and a Rankine source panel method were used to predict the wave making characteristics of the trimaran. A parametric study, varying the size and location of bulbs, was performed first on only the centre hull to identify beneficial arrangements. The study has then been extended to the trimaran to evaluate the additional wave interactions from the outriggers. Calculations done by both numeric methods predicted reductions in wave resistance due to the increase of the trimaran's beam at the waterline. Experimental work confirmed the differing wave interactions seen as a result of hull form parabolization, and a new trimaran form was designed that reduced the total resistance of the vessel by up to 6%.

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