EFFECT OF HULL FORM VARIATION ON HYDRODYNAMIC PERFORMANCE OF A TRIMARAN SHIP FOR FAST TRANSPORTATION

The paper continues and completes the publication of a series of towing tank tests initiated several years ago in the frame of an interuniversity project partially supported by the Ministry of Education, University and Research among the Universities of Genova, Napoli and Trieste. Two equivalent hull designs have been designed to be suitable for a fast passenger and ro-ro ferry of medium dimension (about 800 passengers, 250 cars) on short routes typical of the Mediterranean and Northern Seas, with a design speed of about 38-40 knots. Comparison of the main resistance of these two different trimaran hulls (having different hull shapes but equivalent in terms of total displacement, main geometric parameters and significant form coefficients), tested in model scale with different side hulls positions will be addressed in the paper and results of a systematic series of towing tank tests taken on different configurations are presented. The first trimaran features a main typical fast round bilge hull having V-type bow sections with low flair and stern U-type sections closed towards the transom in both vertical and transversal directions. Side hulls were designed with hard chines forms with simple slightly convex bow sections, high deadrise angle of the main section and slightly warped aft straight sections. The main hull of the second model was chosen of Deep-V type with simple transverse section made of straight line having high deadrise angle at the main section, same length and displacement of the previous hull as well as same CP and LCB for an unbiased comparison of the residual resistance of the two alternative main hulls. The side hulls of the second model were designed assuming simple symmetric U-type section with a small transom. The towing test matrix of each of the two solutions includes a total of 24 configurations obtained by three longitudinal and four transversal outrigger position and two displacements and is reported in the paper under graphical representation of the residuary resistance coefficient and in tables with numerical values of the total resistance coefficient measured during the towing tank tests.