Design of a Common Modular - SWAS(S)H for Offshore and Harbour Support Vessels

Abstract

Safety and Environmental sustainability as the key aspects, the thesis predominantly focuses on European shipbuilding business of Windfarm, Harbour and Offshore Support Vessels. The thesis proposes use of SWATH concept to design a Trimaran like Small Water-plane Area Single (Stabilized) Hull popularly termed as SWAS(S)H. As described in literature, the excellent sea-keeping characteristics of this design make it an ideal choice for vessel types selected, but the design present itself with many drawbacks. The objective of this thesis is to eliminate or minimise the effects of these shortcomings. The first task of this thesis was to design a hull that is not only practical and efficient technically but also economically. To ensure economic and practical feasibility, thesis developed the concept of common modular hull, improving productivity with reduction in production time and cost. Based on market research, it was decided to build modular hulls of lengths 18m, 21m and 24m. The idea being that the forward and aft modules of combined length 15m, are common to all hulls, while parallel middle body like modules of lengths 3m can be added to extend the length of the vessels from 18m to 24m. This resulted in total of five (5) vessel types of three (3) different hull lengths. A common scantling structure for all the hulls was designed using DNV-GL HSC for the longest vessel length of 24m. The same scantlings are used for all the three hull lengths to ensure modular continuity. The below mentioned optimisation methodology was used with major focus on increasing the operational speed from 14-17 knots to 20 knots while reducing the fuel consumption & emissions, to an extent which is comparable to currently operational catamarans. The 18m hull was selected for towing tank test to facilitate largest model size with good scaling factor to ensure better results. The resistance of 18m mathematical model hull was successfully validated by towing tank test and with validated mathematical model, the thesis proved a reduction in resistance and power consumption in range of 21% to 25% for the three hull lengths. In conclusion, this thesis provides a design that has power consumption in range of less than 10% variance from the currently operational catamarans, while having superior stability and sea-keeping characteristics.