Since the introduction of hydrofoils to the Moth sailing class in the early 2000’s foiling has become increasingly popular in sailing from windsurfers to large 75’ foiling monohulls. The last 3 America’s Cups have been competed on hydro foiling vessels. Design programs such as Velocity Prediction Programs (VPP) have become a key asset to America’s Cup teams to allow for the optimisation and testing of designs before manufacture. Presented is the development of a Six Degree-of-Freedom (6DoF) Quasi-Static Velocity Prediction Program (SVPP) and Dynamic Velocity Prediction Program (DVPP) for the 35th and 36th America's Cup foiling AC50 Catamaran and AC75 Monohull. The models have been validated against race data from the 35th and 36th America’s Cup showing good correlation for a wide wind range of 8 to 22 kn. The paper presents how the AC50 SVPP was used for analysis on the impact of Rudder Rake Differential (RRD) on overall performance, and predicting the optimal wind range for use of the light and heavy weather dagger boards on the AC50 Catamaran. The AC75 SVPP and DVPP were used to analyse the affect of hull shape and the main foils’ fixed angle-of-attack (AOA) on time-to-fight and peak velocity to determine optimal foil setup and pitch angle when foiling. The SVPP and DVPP use XFLR5 software suite to model the foils. Experimental data for a T-foil tested in the Australian Maritime College towing tank facility has been used to predict viscous and free surface effect adjustments to the predictions from XFLR5.

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