The performance of three different shaped hulls was evaluated by experiments and computations to identify a hull form that provides low calm water resistance at cruise speed while remaining dynamically stable at high speed. The target cruise speed was at a length Froude number of 0.45, and the target high speed was at a length Froude number of 1.0.

The three hybrid hulls utilized a common round bilge after body shape derived from the NPL systematic series mated to different bow shapes:

_ Hull #1- Double Chine

_ Hull #2- Round Bottom with Spray Rail

_ Hull #3- Single Chine

The 1:20 model-scale experiments were performed at the SSPA Towing Tank to evaluate the calm water resistance and dynamic stability characteristics of the three hulls. Two displacements and up to three Longitudinal Center of Gravity positions were evaluated for each model. A computational study using STAR-CCM+, a Reynolds Averaged Navier-Stokes solver, was performed to investigate a limited number of the test conditions evaluated at SSPA. The computations included time-accurate runs designed to duplicate the dynamic stability testing methodology utilized in the experiments. Model #3- Single Chine was found to represent the lowest drag of the candidate hull forms at cruise speed while retaining dynamic stability at high speed. The calm water-resistance of this hybrid hull shape at cruise speed was found to be within 8.5% of a purely round bilge hull form as represented by the NPL systematic series.

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