Design and hydrodynamic performance of trimaran displacement ships

To meet the demands for increasing the speed and improving the seakeeping behaviour of \ncommercial and naval ships, this thesis investigates a new type of ship configuration - \nThe Trimaran Displacement Ship, it features a slender centre hull and two small side \nhulls. The design methodology and hydrodynamic performance of this new ship concept \nhas been investigated through design studies, model experiments and theoretical analysis. \nPotential advantages of the trimaran ship are, lower wavemaking resistance at high speed, \nlarger deck area, and improved seakeeping behaviour compared with existing ship types. \nFirstly, existing marine vessel types, both monohulls and multihulls, are reviewed with \nregard to their advantages and limitations. The new trimaran concept and its background \nis then described from its initiation by a desire of inheriting advantages and avoiding \nlimitations of these existing ship types. Namely, achieving the low resistance of slender \nmonohulls and large deck area of multihulls, whilst eliminating the speed limit of \nconventional monohulls and the stiff roll motion of catamarans. The review of the \ntrimaran ships design studies shows the potential applications of this new concept in \ncommercial and naval roles. \nThe feasibility of the new concept and the methodology required for its design are \ninvestigated through the concept design studies of. a trimaran fast ferry (Figure 1) and the \nhull form design for a trimaran model ship (Figure 2) for seakeeping experiments. This \nprovides an initial view on the design procedure and basic design considerations for the \ntrimaran ship. The parametric study in the trimaran ferry design gives the basic \nparameters for trimaran hull forms. \nHydrodynamic performance of the trimaran ship has been investigated through model \nexperiments and theoretical analysis on seakeeping, resistance, and manoeuvrability. \nGood agreements between theoretical predictions and model experiments have been \nachieved. This shows the merit of the computer programs developed during the \ninvestigation so they can be used in future trimaran ship designs for hydrodynamic \nperformance assessments. A three dimensional theory is used in the trimaran motion \nanalysis. Roll damping characteristics of the trimaran ship has been examined by \nincluding viscous effects in roll damping which can be derived either by simulating \ndamping data from free decay experiments or by direct computation, that has been shown \nto improve the roll motion predictions. Systematic investigation into the wavemaking \nresistance of the trimaran ship reveals the relationship between the side hull configuration and the resistance performance. Wave cancellation effects can be achieved when the side \nhulls are appropriately located to further reduce the wavemaking resistance of the \ntrimaran ship. A manoeuvrability study concentrated on the effect of the side hulls on the \nturning ability of the trimaran ship as well as the effect of side hull propulsion. \nFollowing the hydrodynamic analysis of the trimaran ship, the design procedure and \ngeneral considerations in trimaran ship design distinctive from other ship types are \nproposed and discussed with particular reference to stability and hydrodynamic \nperformance. Trimaran hull form options are also discussed alongside some other design \nconsiderations. \nThe thesis concludes that the new trimaran displacement ship shows superior \ncharacteristics in some hydrodynamic aspects over existing marine vessels, particularly in \nresistance and seakeeping, and therefore there is no reason why this novel concept can \nnot be translated into real ships.