To meet the demands for increasing the speed and improving the seakeeping behaviour ofudcommercial and naval ships, this thesis investigates a new type of ship configuration -udThe Trimaran Displacement Ship, it features a slender centre hull and two small sideudhulls. The design methodology and hydrodynamic performance of this new ship conceptudhas been investigated through design studies, model experiments and theoretical analysis.udPotential advantages of the trimaran ship are, lower wavemaking resistance at high speed,udlarger deck area, and improved seakeeping behaviour compared with existing ship types.udFirstly, existing marine vessel types, both monohulls and multihulls, are reviewed withudregard to their advantages and limitations. The new trimaran concept and its backgroundudis then described from its initiation by a desire of inheriting advantages and avoidingudlimitations of these existing ship types. Namely, achieving the low resistance of slenderudmonohulls and large deck area of multihulls, whilst eliminating the speed limit ofudconventional monohulls and the stiff roll motion of catamarans. The review of theudtrimaran ships design studies shows the potential applications of this new concept inudcommercial and naval roles.udThe feasibility of the new concept and the methodology required for its design areudinvestigated through the concept design studies of. a trimaran fast ferry (Figure 1) and theudhull form design for a trimaran model ship (Figure 2) for seakeeping experiments. Thisudprovides an initial view on the design procedure and basic design considerations for theudtrimaran ship. The parametric study in the trimaran ferry design gives the basicudparameters for trimaran hull forms.udHydrodynamic performance of the trimaran ship has been investigated through modeludexperiments and theoretical analysis on seakeeping, resistance, and manoeuvrability.udGood agreements between theoretical predictions and model experiments have beenudachieved. This shows the merit of the computer programs developed during theudinvestigation so they can be used in future trimaran ship designs for hydrodynamicudperformance assessments. A three dimensional theory is used in the trimaran motionudanalysis. Roll damping characteristics of the trimaran ship has been examined byudincluding viscous effects in roll damping which can be derived either by simulatinguddamping data from free decay experiments or by direct computation, that has been shownudto improve the roll motion predictions. Systematic investigation into the wavemakingudresistance of the trimaran ship reveals the relationship between the side hull configuration and the resistance performance. Wave cancellation effects can be achieved when the sideudhulls are appropriately located to further reduce the wavemaking resistance of theudtrimaran ship. A manoeuvrability study concentrated on the effect of the side hulls on theudturning ability of the trimaran ship as well as the effect of side hull propulsion.udFollowing the hydrodynamic analysis of the trimaran ship, the design procedure andudgeneral considerations in trimaran ship design distinctive from other ship types areudproposed and discussed with particular reference to stability and hydrodynamicudperformance. Trimaran hull form options are also discussed alongside some other designudconsiderations.udThe thesis concludes that the new trimaran displacement ship shows superiorudcharacteristics in some hydrodynamic aspects over existing marine vessels, particularly inudresistance and seakeeping, and therefore there is no reason why this novel concept canudnot be translated into real ships.
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