Strength and hydrodynamic performance of a multihull vessel

Abstract

The use of catamarans as an alternative to more conventional monohull high speed vessels for transport, naval and offshore applications is on the increase. This uprising trend is a direct consequence of the global demand for commercially and militarily efficient vessels that offer high speed, potential for improved Sea-keeping at speed, relatively low hydrodynamic resistance in waves and a more useable deck area. The configuration and hull geometry of catamarans are very critical to achieve improved sea-keeping and other hydrodynamic performances. The Round Bilge hull form is one of the most prominent hull geometries in use for the design of displacement-type multi-hull vessels. An alternative hullform series to the Round Bilge, catamarans, named the Deep-V Catamaran series (DVC), has been developed recently at Newcastle University. Early studies on the DVC concept based on this series indicate that the hull form may have better resistance performance than the Round Bilge. However, other important characteristics of this concept such as the motions and wave-induced load response characteristics are still unknown. There is also a lack of understanding of the general hydrodynamic characteristics of the DVC concept in comparison to the Round Bilge hull form. This study contributes to the understanding of the motions and wave induced load response characteristics of the DVC concept. It is also intended to advance the structural design methodology of the DVC concept and its subsequent application as better alternative to the Round Bilge hull form. The study involved the experimental and numerical investigations of the motions and wave-induced load response characteristics of the DVC concept by using a prototype model of “The Princess Royal” which is the current research vessel of Newcastle University. The experimental studies involved the motions and wave-induced response measurements in regular waves at both zero and forward speed conditions. The results obtained were validated using alternative potential flow-based numerical codes in frequency domain. The benchmark study indicates that the numerical codes are capable of producing acceptable results. A comparative study using a representative model of the Round Bilge hull form with the DVC model was conducted in order to establish a direct basis for the comparison of the motion and hydrodynamic load performances. The results obtained from this comparison reveal that the DVC may have better sea-keeping characteristics and is less sensitive to wave loads than the Round Bilge hull concept in critical heading conditions. A further comparison of the experimentally validated numerical predicted loads with those obtained using the International Association of Classification Societies (IACS) approach was completed. The study confirms that the IACS approach over predicts the loads by up to 40% in Beam Seas and Quartering Seas when other components of IACS rules are not considered. A simplified structural analysis of the DVC model using the Finite Element Method was also completed to demonstrate the effects of the predicted loads on the strength of the hull structure with emphasis on the cross-deck structure, which is the most sensitive structural element of the vessel. Overall, the study highlights the promising characteristics of the DVC concept in comparison to the Round Bilge hull form and provides data required for the preliminary design of catamarans using this concept.