Resistance extrapolation for ships with a wetted transom stern

This paper studies the viscous resistance of a ship with a wetted transom stern, and its scale effect. For predicting the resistance of a ship with immersed transom stern from model-test data, in MARIN’s procedure the form factor is computed from double-body flow not for the transom-stern hull form, but for a hull smoothly extended at the stern. The drag contribution of a wetted transom and its recirculating flow is thus kept outside the viscous-resistance scaling, which implies there is no scale effect on the transom drag. Computations for 10 different ships actually show that the transom drag is similar for model and ship, but is often somewhat larger at full scale. Dependent on the magnitude of the transom drag, this causes a 0-3 per cent underestimation of the full-scale resistance in double-body flow by MARIN’s procedure. In comparison, straightforward model-to-ship extrapolation with a form factor for the transom-stern hull would cause up to 10% underestimation of the full-scale resistance. We also compare with a recent proposal from Korkmaz et al (Ocean Engineering 266, 2022) in which form factors for the ship and model with immersed transom are determined separately.