A semi-displacement hull optimisation study is carried out with the goal of reducing effective power. The subject of the study is a round-bilged semi-displacement vessel based on the AMECRC hull series. Three speeds are considered spanning Froude numbers from 0.5 to 1.0, thus taking into account different sailing regimes. The three speeds are weighted according to a approximate relative frequency of different sailing conditions, where the intermediate Froude number of 0.75 is considered to be the most important for this hull design. Semi-displacement hull optimisation is carried out for three hull parameters: 1. longitudinal center of buoyancy, 2. width of the transom stern, 3. depth of the transom stern. The parent AMECRC hull is characterized by a transom stern with width close to the maximum waterline width amidship. The transom width parameter was used to consider transom sterns that are narrower, going in the direction of the NPL hull series. Transom width was modified in both directions: towards shallower and deeper transoms. LCB was varied between -1 and 1 meter of displacement relative to the parent hull, or 2.5% of Lpp. 27 different hull variants are evaluated using calm water resistance simulations. Resistance results are used to obtain effective power, which was used to calculate weighted power based on relative frequencies of different speeds within the expected operational profile of the vessel.

semi-displacement parent hull

Semi-displacement hull optimisation study showed that for lower speeds, a forward LCB is beneficial, while for Fr =1, moving the LCB aft reduces resistance. Deeper transom benefits higher speeds, while shallower one reduces resistance at lower speeds. Hull performance was least sensitive to transom breadth, showing minor reductions at higher speeds with its reduction. Plots below show how different parameters affect resistance at different speeds.

semi-displacement-hull-resistance-vs-transom-depth-20-knots
semi-displacement-hull-resistance-vs-transom-depth-30-knots
semi-displacement-hull-resistance-vs-transom-depth-40-knots
resistance-vs-LCB-20-knots
resistance-vs-LCB-30-knots
resistance-vs-LCB-40-knots

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