Structure design of a sailing yacht hull by rules and direct method

Abstract

The thesis was done at Perini-Navi shipyard, Viareggio and at University of Genoa, Italy. Thesis is divided in two parts. Fist part is scantling of the main frame for a sailing boat and in second part it has been performed the finite element analysis (FEM) of the structure. Scantling (main dimensions), for the yacht of 58 m in length has been done according to the American Bureau of Shipping (ABS) rules, Guide for Building and Classing Offshore Racing Yachts (ORY). The purpose of the scantling is to become familiar with the structure design of the sailing yacht and also to understand how to apply the rules. Material that shipyard is using for the construction of the sailing yachts is aluminium. Because of aluminium nature and big use in shipbuilding industry, one chapter is dedicated for this material with all properties, alloys, advantages and disadvantages. The scope of the work was to perform the FEM analysis for the specific parts of ship hull. As shipyard already had FEM analysis of the entire hull, in agreement with shipyard and university, in this thesis were investigated main mast base foundation and connection of the keel with the structure of the yacht. During the building of the hull, main mast for sails was changed and main mast base foundation that was already built does not satisfy for new loads coming from the main mast. Because of that, it is necessary to verify this structure on new loads. Also, purpose of this first model was to become familiar with the software features. So it was analysed difference between shell and solid elements, influence of mesh on the results, linear and nonlinear analysis. Nonlinear analysis has been done because the structure was exceeding yielding stress of 215 MPa for aluminium. After, when all analysis has been performed, it was necessary to propose the solution to shipyard; how to solve the problem on existing structure and how to adapt the new structure for this kind of loads. Second model is connection of the keel with the structure of the yacht. Keel is 8 m long and total mass of the keel; aluminium structure with the lead inside is 65 tons, and according to the rules, keel must withstand its own mass acting in centre of gravity. To satisfy the rules criteria and to prove direct method that have been used for the calculation of the keel deflection and stresses, FEM analysis of the keel – structure connection has been done. The analysis expected to show that deflection of the keel is 41 mm and the analysis showed that deflection is 74 mm at centre of gravity and more than 200 mm at the end of the keel. After, it was necessary to verify the stresses and deflection on the hull structure where the keel is connected. Connection between structure and keel is with the pin. The models were made separately, because of the complexity to simulate pin connection and the forces measured by probes on the keel are transmitted to the structure. But analysis showed that deflection is quite small at hull structure and that structure is very well design.