Structural Design of an High Speed Motor Yacht in GRP by Rules and direct FEM analysis

Abstract

The thesis is developed during an industrial internship in a specialized composite shipyard. The aim of the thesis was to develop a high speed motor yacht, able to reach a top speed of 55 knots, based on a proven design of a fast patrol vessel. The reference project is a 13.2 meter planning hull made of FRP (Fiber Reinforced Plastic) with propulsion consisting of two diesel engines (600HP) driving two waterjets and allows achieving a top speed of 45 knots. The high speed motor yacht is 13.5 meters in length with propulsion consisting of two diesel engines (820 HP) driving two surface-piercing propellers. The work included interior and exterior design of the vessel and structural calculations of the hull, while always having in mind its influence on the hydrodynamics effects encountered at such a high speed. The esthetical design and the general arrangement are defined in accordance with the top speed of the yacht that gives a baseline for its use, aiming at younger clients for weekend cruises, or to be used as a tender next to a larger yacht. Structural design of the hull was performed using RINA (Registro Italiano Navale) FPV (Fast Patrol Vessel) and HSC (High Speed Craft) Code. The hull is made from a vinyl ester composite. Single skin laminate with glass reinforcement is used in the bottom area to absorb the high loads. The sides of the hull are in sandwich construction with glass reinforced skins and balsa core to be lightweight and stiff. Stiffeners have a polyurethane core and are reinforced with hybrid glass-carbon and unitape carbon fiber. As composite materials are tailored and customized to the needs of a specific project they offer a great potential to optimize weight and cost. Optimization was performed in an iterative manner for each hull panel and stiffener laminate layout. Special consideration during the structural design of the hull was given to the transom. As opposed to the waterjet configuration the thrust loads from the surface-piercing propellers are absorbed by the transom. For that reason a FEM analysis of the transom was performed using ANSYS Structural software. The simulation was done in accordance with the complexity of the problem of modeling composite parts.