SeaSail – A Numerical Method for the Determination of Added Resistance of Sailing Yachts in Seaways

Yacht Research Unit Kiel, in cooperation with Technical University Hamburg and the university ENSIETA in Brest/France, have developed a method for the numerical prediction of added resistance in waves, dedicated to sailing yacht investigations. The method features full six degrees of freedom capability and inclusion of any arbitrary (measured or empirical) sea state spectra. It allows to take into account any number of foils of the appendage set of the yacht, taking into account their added masses, radiation forces acting on the fin due to ship motion and excitation forces acting on the fin due to waves. In addition the method is capable to calculate the thrust, generated by the oscillation of the fins flow angle of incidence.
The method is based on linear strip theory with some nonlinear extensions. It is capable to consider the exact (even asymmetric / heeled) hull shape using a panel method for the analysis of the flow forces on the sectional strip. It takes into account ballast bulbs, lifting surfaces like keel fins, rudders and wings. It solves the equation of motion of the ship in 6 DOF and takes into account, that pitch and heave motion takes place in the centre plane of the heeled yacht.

<b>SeaSail is fully validated</b>
SeaSail has been validated against tank test results for an ACC Yacht. To this purpose an ACC yacht was towed in a wave tank in head seas. It has to be kept in mind, that in the tank tests surge is suppressed for measurement purposes, affecting the results, while SeaSail uses full 6 DOF. The diagram below gives the added resistance in waves RAW in a natural wave spectrum. A tabular description of the wave spectrum of the last AC venue, Valencia, is taken into account. Good agreement can be observed.

Added resistance in waves for a natural spectrum in different wind ranges

<b>Wave generated wing thrust</b>
A typical example of the special ability is a study of the thrust generated by wings of an AC yacht moving in a natural sea spectrum. In the example below various longitudinal wing position have been investigated.
Diagram below gives the wing thrust operators over harmonic wave length for the different longitudinal wing positions, showing a quite significant impact on magnitude as well as peak placement by the longitudinal position.


Wing thrust operators for different longitudinal wing positions over wavelength
SeaSail is ready to be used for any project, where added resistance of the yacht is subject to optimization.