CONCEPTUAL DESIGN OF A HIGH-SPEED SUPERYACHT TENDER : HULL FORM ANALYSIS AND STRUCTURAL OPTIMIZATION

Abstract: The focus of this thesis is to create a new conceptual design for a Superyacht Tender. This type of boat is usually primarily focused on aesthetical and practical aspects. However there are costumers requesting performance, which will be the main focus here. A supplementary task is to find ways to apply an engineering approach in the design of a recreational craft, in order to help small craft manufacturers optimize their products’ performance. The resulting design is intended to fill up the void of large, high- performance superyacht tenders, with its lightweight hull and powerful engines. In order to succeed in this, an analytical model for performance prediction will be created and structural optimization based on available methods will be performed. The motivation for this is that the industry today is dominated by a trial-and-error approach based on experience and testing, and most manufacturers of recreational powerboats apply little or no analytical methods in their designs. Predicting resistance on twin stepped hulls is a great challenge and it has not been possible to find any established methods suitable. For this reason, a model for estimating power requirement and running trim of such hulls has been developed. The model is based on Savitsky (Savitsky 1964) theory and a single step performance method developed by David Svahn (Svahn, 2009). The new developed model in this project has been benchmarked to an existing powerboat, with good results. The boat used as benchmarking is the Hydrolift C-31, where all the parameters needed was received from Hydrolift. The new method has been used to design and position steps for the superyacht tender. The required power has been used to select engines and drives, and the installation of these has been looked into closer. In order to minimize weight and lower resistance, structural optimization has been performed. A method for optimization of sandwich and single-skin panels with stiffeners has been extended to take face, core and stiffener strength as well as stiffener and plate stiffness into account. Also, various structural layouts have been designed and compared to find the most efficient setup. The results from the optimization model showed that the best choice was a carbon fiber sandwich as material in the panels when considering weight. The carbon fiber construction saved approximately 25% weight compared to fiberglass in the hull, and by introducing a sandwich, additional weight could be saved and the complexity of the structure could be reduced. High-speed small craft are subject to ISO rules, which only apply up to speeds of 50 knots. The ISO rules are sometimes viewed to lack in margins which is why DNV’s HSLC rules has been used in this project. The results from the structural part showed lower weight than expected, about 3900 kg dry weight. With 8 passengers including luggage and semi-filled tanks, the resistance model showed that the new design should be able to travel at 65 knots with 1250 horsepower installed.