HULL FORM ANALYSIS AND STRUCTURAL OPTIMIZATION

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, highperformance 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. PREFACE The work conducted in this thesis has been very exciting and interesting because it involves designing an actual boat, which is in line with the future wishes of the authors. The methodology has involved developing new design tools and the research has been done in part, in cooperation with the Norwegian boat company Hydrolift who has provided us with boat parameters and good advice. A great deal of welcome help and advice has been given from:  Mr. Michael Morabito of the US Naval Academy  Christoffer Haarbye of Hydrolift Boats  Mr. Lorne Campbell of Lorne Campbell design  Fredrik Bolstad at Goldfish Boats  David Svahn, former student at KTH, with previous experience of modelling stepped hulls  Anders Rosen, Karl Garme and our supervisor Ivan Stenius, all from the Centre of Naval Architecture at the Royal Institute of Technology, in Stockholm, Sweden. Without their help and interest in the subject, this thesis would not have become what was initially intended. The research on the hydrodynamics of stepped high-speed craft is still a highly unexplored science, due to complicated fluid mechanical effects and lack of financial motivation. However, the topic has become more alive in the recent years, and this thesis is hoped to constitute as a contribution to the future research in the field of stepped powerboat running prediction. The authors have focused on different tasks within the project, responsible for items as follows: The hydrodynamic hull shape design and modeling has been mainly conducted by co-author Jørgen Strømquist, and the structural design and optimization model has been mainly conducted by co-author Jonas Danielsson. Jonas  Prestudy on market analysis, main particulars  Developing software for hull design  Fuel consumption  Developing and describing software for structural design  Structural design  Weight estimation Jørgen  Introduction  Prestudy on market analysis, main particulars  Prestudy on planing boats and stepped hulls  Empirical step analysis  Developing and describing software for hull design  Hull design and testing  Weight estimation