Hydrodynamic Aspects of Transom Stern Optimisation

Orych, Michal, and Lars Larsson

5th High Performance Yacht Design Conference, Auckland, 10-12 March, 2015


In this work an explanation for an optimum transom size is proposed which takes into account the hull shape between the midship and the transom. A systematic stern modification is performed to study the influence of the shape of waterlines and buttocks on the resistance components. The aft body of a hull is designed in a way that gives a possibility to separate the effects of waterline and buttock curvature and to study their effect on the flow. The Froude numbers are chosen to provide information for wetted- as well as dry-transom conditions. To evaluate the performance of the hulls the SHIPFLOW steady state Reynolds Averaged Navier-Stokes (RANS) code with a Volume of Fluid (VOF) surface capturing method is used in combination with the k-ω SST turbulence model. The code was first thoroughly validated for a transom stern hull. The paper focuses on hydrodynamic and hydrostatic resistance components of the transom and of the rest of the hull. Physical explanations are given for the effects of the aft body hull lines. The transom size, waterline curvature and rocker effects are analysed. The results show that the optimum transom size depends on the balance between the hydrostatic and hydrodynamic force components and the explanation for this is also given.