Experimental Investigation on Resistance and Vertical Motions on a medum Speed Catamaran with Central Bulbs

It has been demonstrated [1, 2, 3] that a central bulb placed between the demihulls of a catamaran hull reduces its vertical motions and, partly, its resistance. Previous investigations made by the Author regarded a fast catamaran hull (FN : 0.4 – 0.8). with wedge hull lines and central bulbs placed in different longitudinal and vertical positions. In this paper a new catamaran hull, with faired lines, has been examined on a velocity interval defined by FN : 0.2 – 0.6. A 1:19 scale model was built and tested in resistance and seakeeping tests in regular waves at the towing of Trieste University. The original model without bulbs and in three different bulb configurations has been tested and examined. The results obtained outline the efficiency of these solutions, to improve the seakeeping criterion of catamaran hulls, without reducing their speed, although the bulb efficiency is more effective at higher speeds, close to FN = 0.6.