A Reynolds-Averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for Wind- Assisted commercial ships. The modelling challenge presented by large separated flow structures in the wake of the sailing ship points to a conscientious validation study. A validation data set, consisting of hydrodynamic forces acting on the ship sailing with a leeway angle, was collected at the Delft University of Technology towing tank facility, for bare-hull and appended cases. Four hull geometries were selected to represent of the Delft Wind-Assist Systematic Series. Appended cases were designed to represent a broad range of appendage topologies: Rudder, Bilge-keels, Skeg, and Barkeel. The direct validation exercise for the bare-hull case was successful, with the validation level for the sideforce equal to 9.5% (fine mesh: 9M cells). An extended validation statement is made for simulations for the entire series. This exercise was successful for leeway angles equal to = [3 , 6 ]. The validation level (base mesh, 3M cells) for each force component is: ′=12%, ′=17%, ′=10%. The validation for appended geometries was not regarded as successful, with the exception of the Rudder case. The numerical uncertainty is the dominant contribution for the validation level, motivating a proportionate refinement of the grid. Here, it is sufficient to achieve parity with other contributions to the uncertainty within the larger context of the project.

Since the first introduction of an expression for the assessment of the side force production of a sailing yacht as function of leeway and heel, based on the results of the Delft Systematic Yacht Hull Series, in 1981, considerable changes in appendage layouts and planforms have taken place. The side force production as function of the leeway and heel played only a very limited role in the present VPP calculations and remained therefore for many years somewhat undervalued. The last years more attention has been paid to the subject in particular caused by the necessity to asses the yaw balance of (large) sailing yachts and the introduction of maneuvering models for yachts under sail. This report shows the developments and presents a new assessment model which yields far better results for a large variety of appendages. The results of this study are presented in the present paper.

In order to be able to calculate the forces on the keel and rudder of a sailing yacht more is to be known about their interaction. Both for determining the yaw balance of a sailing yacht as for the maneuvering it is of importance to have a good assessment on these forces because they determine the yaw moment to a large extent. Therefore a research project was set up in the Delft Shiphydromechanics Department to investigate the influence of the keel on the rudder. Aim was to improve on the side force prediction of keel and rudder and to assess the wake of the keel and the downwash on the rudder in various conditions. Based on the measured results the the previous developped formulation within the DSYHS for the keel residuary resistance is validated and a new formulation for the downwash behind the keel is presented. In addition the expression within the DSYHS for the sideforce on the yacht is improved for higher aspect ratios.