Experimental study on catamaran hydrodynamics

Abstract

In the last decade, the main concerns of the maritime industry are the reduction of fuel and carbon emissions. IMO (International Maritime Organization) has introduced relevant conventions and improvements in fuel economy standards for ships. Thus, different research projects have been developed to improve the energy efficiency of ships, reducing fuel consumption and carbon dioxide emissions. The flow around the catamarans is a complex hydrodynamic phenomenon due to the interference effects that occur on the free surface between the bodies of the catamaran. The flow around the ship hull has a wide variety of physical fenomena, many of which are relevant for the study of resistance. The two important aspects of the interference effects associated with the catamarans with direct influence on the hydrodynamic performances are: the viscous interference due to the asymmetric flow around the bodies with direct effect on the development of the boundary layer and the wave interference generated at the free surface from the interactions between the wave systems generated by each hull. First set of towing tank tests have been performed to evaluate the ship resistance of the catamaran hull, interference between wave system of the hulls and to analyse the hydrodynamic parameters of the flow. To evaluate the effect of the central bulb positioned between the hull bodies on the ship resistance, six different sets of experiments were carried out for seven speeds corresponding to Froude numbers between 0.20 and 0.80. Six different configurations of the bulb considering three different depth and two position along the hull (bow and stern) have been considered. The calculations revealed that residual resistance can be reduced by using a central bulb between the catamaran hulls by up to 10%. This happens when the bulb is positioned at the bow and the stern and for Froude numbers 0.4-0.6.