Large medium-speed catamarans are currently under development as a new class of vessel forudeconomically efficient and more environmentally sustainable fast sea transportation. Theiruddesign is based on current high-speed catamarans, to adopt advantages such as large deckudareas and low wave-making resistance, but they will operate at lower speeds and carry audhigher deadweight to obtain higher transport efficiency. They operate at speeds around theudmain drag hump, where the wave-making drag coefficient is at its maximum. Hence this speedudrange is usually avoided by boat designers no precise guidelines for hull form design of largeudmedium-speed catamarans are present to operate efficiently in this generally unfavourableudspeed spectrum.udLiterature has been surveyed to derive hull form parameters that provide low drag for monohullsudand catamaran vessels. Based on these findings a hull form family was developed withuddemihull slenderness ratios ranging from 9 to 15 and the hydrodynamic performance wasudevaluated at Froude numbers from 0.25 up to 0.49 to derive design parameters with theudlowest drag and highest transport efficiency. These parameters corresponds to vessel sizesudfrom 110 m to 190 m and speeds of 16 to 41 knots. A novel CFD-based approach has beenuddeveloped to provide more accuracy to the final drag prediction at full scale. It was verifiedudusing results of model scale experiments of a 98 m and a 130 m catamaran and validatedudwith results obtained from sea trial measurements, in deep as well as in shallow water. Furthermore,udits capability to replicate the flow past a typical deep partially ventilated transom has been investigated using model scale experiments. The key advantage of this method is that the same computational mesh can be used for model-scale verification and full-scale predictions.udThe computational full-scale simulation approach was found to be capable of predicting theuddrag force within 5% of results derived from full-scale measurements and extrapolated modeludtest data. In addition it has been shown to correctly predict steady and unsteady shallowudwater effects. Also the ventilation process of the transom stern has been experimentallyudvalidated and the ow feature in the stagnant zone past the partially ventilated transom wasudidentified as a non-shedding squashed horseshoe vortex. The lowest drag can be achieved for catamarans with demihull slenderness ratios of 11 to 13 and hulls of 150 m in length provided highest transport efficiency for speeds of 20 to 35 knots at a light displacement, and 170 m and 190 m for a medium and a heavy displacement respectively.udFinally, when comparing the results to contemporary large and fast catamarans carryingudequivalent deadweight and travelling at the same speed, fuel savings up to 40% can beudachieved if a hull of 150 m instead of 110 m length is used. This demonstrates that large mediumudcatamarans have the potential to be a fuel-efficient alternative for a successful futureudof fast sea transportation.
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