Model tests were conducted at the Davidson Laboratory to investigate the effect of following seas on the added resistance of the PACT (Partnership for America's Cup Technology) base America's Cup hull. A 1 :8 scale model of an International America's Cup Class yacht was provided by Team Dennis Conner and was refinished with funding from US Sailing to its original lines as the PACT base hull. Using this hull (canoe body with no appendages), model tests were conducted in the following seas condition. Upright, resistance tests were carried out at constant speed in both smooth water and regular waves of varying length and slope. The model was free to heave and pitch while restraining all other degrees of freedom.

The data analysis revealed that at wavelengths approximately greater than two model lengths, the added resistance of the model is negative. A negative added resistance implies that the average drag force of the model in a particular following sea is less than the still-water drag of the model at the same speed. At wavelengths below this point, the added resistance of the model is greater than the still-water resistance. Furthermore, the form of the data suggests that at waves longer than were tested in this experiment (wavelengths greater than five model lengths), the added resistance of the model converges to the still­water resistance. The experiment also verifies that the added resistance is proportional to the square of the wave height.

The pitch and heave characteristics of the model as expressed in the form of response amplitude operators are independent of wave slope. This is to say that for a particular motion, the response amplitude operators for each wave slope overlap one another.

The results of these model tests were to be used as a database for the IMS Pitching Moment Project established in an attempt to quantify the sensitivity of radius of gyration on yacht performance. Also, these results were to be used to validate CFD estimates of added resistance.

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