Asymmetrical planing catamarans are increasingly used in moderate to very high-speed applications due to some tempting qualities such as less wetted surface and better seakeeping behavior. The present numerical study attempts to provide new insight into hydrodynamics of such vessels by highlighting the distinguishing aspects and employing novel appropriate approaches to deal with them. A systematic investigation has been carried out on a prismatic geometry at various demihull separations (including zero separation, that is, symmetric monohull) and different trim angles in a wide range of speed coefficients, using a computational fluid dynamics solver. Obtained numerical results of steady-state resistance and lift forces are compared against different empirical methods. In order to offer an adequate explanation about the nature of forces and interference mechanisms, an analysis has been performed on viscous and pressure resistance components. Furthermore, the ability of the employed numerical method in estimation of wetted area pattern at the bottom of the planing hulls has been evaluated to provide explanation for some observed hydrodynamic behaviors of the asymmetric planing catamarans. It is seen that a significant reduction is reached in wetted surface area of catamaran configuration in comparison with corresponding monohull.

Properly adjusting the trim angle during the craft speed up will be extremely important in special cases as in sports competitions or military missions. In such applications, the goal of trim adjustment is to reach final speed in a minimum possible time which is an advantage to just passing the resistance hump. Present study tries to provide insight into how the angles of the drive system and trim tab of a planing craft should be changed during speed up so as to minimise the time to reach the final speed. This is a time-optimal control problem with the drive and trim tab angles as the control variables. Optimal control theory has been used previously for the motion control of marine vessels in the applications such as seakeeping, manoeuvring and navigation. This study introduces a new application of this theory for increasing the craft speed performance. Conventional empirical relations are used in the equations of motion for calculating hydrodynamic forces to develop the dynamic model. To calculate the forces due to the propulsion system, attempts are made to take into account the propeller, the drive system and the engine concurrently in a simplified manner. The solution algorithm is explained and the results for a planing vessel with two different longitudinal centers of gravity are presented. Optimal solution for control variables shows a simultaneity and similarity in trend with the hull instantaneous trim angle. However, the optimal signals are restricted by upper physical margins.

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