Experimental investigation into wave-induced design loads on a large moored catamaran

Abstract

A new concept uses a large catamaran, Gas Cat, as a floating natural gas processing, storage and offloading facility. The concept design of the vessel is based on two retrofitted very large crude carriers allowing for the processing and storage of 1 million bbls of condensate and approximately 240,000 m3 of liquid natural gas. Key to the development of this concept is the accurate estimation of the wave-induced cross-demi-hull loads experienced by the catamaran in a variety of operational scenarios. Model experiments were conducted in the model test basin of the Australian Maritime College using a 1:78 scale model of two full-form hulls, converted into a catamaran configuration, to measure the wave-induced forces and moments. Tests were conducted in head, beam and oblique seas for two hull spacings and a range of wave heights. The experimental results show that for the range of wave conditions tested, good linearity of the forces and moments can be expected with respect to wave height. This allows the results to be used to determine expected loads for a range of wave conditions. Changes in demi-hull separation were found to have little influence on the measured cross-demi-hull loads. Forces and moments were the least for the head sea condition; therefore, in order to minimise the wave-induced loads on the vessel, it is recommended that it be allowed to weathervane with the prevailing swell direction. The forces and moments which may be expected in Timor Sea 10,000-year return storm conditions have been estimated based on the model results. These provide valuable data for the preliminary design of an appropriate structural configuration for the vessel.