Tri-hulled catamarans with side hulls configuration decreasing dives or lifts at speed which also decreases drag coefficient

摘要

A boat may have one, two or more hulls having rearward facing steps (26) on the side thereof to cause a rearward void and thus reduce drag on the sides when travelling at speed. Advantageously a boat may have two side hulls (16, 17) and a rearwardly placed, unstepped, intermediate hull (18). All hulls are joined by a crossdeck (not shown). Forwardly the side hulls (16, 17) define a forward flow passage (43) above the waterline and below the crossdeck and rearwardly similar flow passages (44) are defined between respective side hulls and the intermediate hull. The sum of the cross-sectional areas of the rearward flow passages are equal to, or greater than, the cross-sectional area of the forward flow passage whether the boat is static or in a planning condition. The rearward expansion of the flow area is achieved by the steps (26) and may be augmented by similar stepping of the undersurface of the crossdeck.