The auxiliary propulsion of ship towed by kite appears as an efficient concept to reduce CO2 emmissions and fuel consumptions. Nevertheless, the influence of a kite may endanger a ship since a kite performs periodic dynamic flights. In order to anticipate and to evaluate the risks may due to a kite, simulations of a ship towed by kite are performed. Two approaches are developed: a frequency domain approach with a weak coupling between the kite and the ship, and a time domain approach with a strong coupling are developed. Both approaches are based on the Salvesen, Tuck and Faltinsen (STF) strip theory. Using the DTMB 5512 surface vessel combattant, it is shown that both approaches are consistent to the experimental fluid dynamic data and to the STF strip theory results. In calm water, the comparison between the time domain and the frequency domain approaches shows that with a kite excitation frequency near the natural roll frequency of the ship, a strong coupling in time domain is necessary regarding the roll motion. With a beam wave, the kite frequency excitation is highly modified. Consequently, a peak of excitation appears at the wave frequency which has an important influence on the roll amplitude. 

A substantial amount of research has been carried out in the past to enhance the testing techniques and to increase the accuracy associated with tank testing of sailing yachts. Majority of this work was associated with high budgeted campaigns; large models, long waiting times and high budgets became standard practice in the field. This led to lack of accessibility for low budgeted campaigns and for designers of ordinary sailing yachts to these tests. A research study has been initiated to investigate the scale effects associated with tank testing of sailing yachts. The intention has been to make best use of modern experimental and computational methods to understand the scale effects in conjunction with systematic tank tests. Both viscous and wave components were considered for investigation of scale effects in sailing yacht performance prediction. Four different scale models ranging from 1/4 to 1/10 of a TP52 yacht have been tested in the towing tank in upright and heeled condition while full, half and quarter scale analysis have been carried out with a RANS code. The wave pattern measurements were conducted for all upright and heeled cases with the use of three wave probes on each side. Variation of drag, side-force, running attitude and wave pattern have been investigated. This paper focuses on the experimental investigations both in the upright and heeled conditions.

Velocity Prediction Programs (VPPs) based on a steady-state equilibrium between aero- and hydrodynamic forces continue to be important tools when assessing the performance of yachts during the design process. Over the last decade a number of Dynamic Velocity Prediction Programs (DVPPs), which also allow study of the dynamic characteristics of the boat, have been developed. Most DVPPs are based on numerically solving the equations of motion of the yacht according to Newton’s second law with the aerodynamic forces being calculated from quasi-steady theory. This paper discusses whether this assumption of quasi-steady aerodynamics can be justified and also analyses the error introduced by such a quasi-steady analysis. Unsteady potential flow theory is used to predict the pressure distribution on an aerofoil-like, two-dimensional “slice“ of a mainsail carrying out harmonic oscillations both perpendicular to, and along the direction of the incident flow. Such types of motion occur when a yacht pitches or rolls in waves. Theoretical pressure distributions are compared to wind tunnel measurements on an oscillating, rigid mainsail model of 3.2 metre span and 0.447 metre chord length. Experiments were carried out at reduced frequencies ranging from k = 0 to k = 0.8, as the mainsail of an International America’s Cup Class yacht sailing upwind in waves typically encounters reduced frequencies in this range. It is found that predictions based on unsteady theory match the measured pressure distributions much better then quasi-steady predictions. This leads to the conclusion that, if the performance of the yacht is to be predicted on a time-scale shorter then the pitching period, this can be achieved best with an unsteady aerodynamic model. In the paper no attempt is made to investigate the influence of the flexibility of the sails, sail interaction, three-dimensional effects or phenomena related to dynamic stall.