Are Daggerboards and Trimtabs Necessary When Sailing Upwind With a Canting Keel?

The use of canting keels in conjunction with various appendage configurations has been used successfully on racing yachts ranging from the 6.5m Mini Transat yacht through to the Open 60 and Volvo 70 round the world racing yachts and even some of the maxi class racing yachts. Experimental tests were completed on two models of Mini-Transat yachts, one at 1/3rd scale and the second at 1/6th scale. Both models were tested at the towing tank facility at Southampton Solent University. The first of two towing tank models was fitted with an additional dynamometer able to measure keel forces in isolation from total hydrodynamic forces, the latter being recorded with the standard tank dynamometer. Hence the contribution of lift and drag generated by the canting keel alone, as compared to the total lift and drag generated by the complete hull and keel configuration, are studied using model scale experiments. This particular keel also was fitted with a trim tab which was set at 0, 5 and 10 degrees, enabling the further investigations to be made. The second model was used to investigate the overall sailing performance of a Mini Transat yacht, which sails with the keel canted to 25 degrees, firstly with and then without a dagger board. Extrapolated full size hydrodynamic results from the tests in conjunction with appropriate stability data and sail dimensions are then used in the Wolfson Unit’s WinVPP program to establish the sailing performance of the Mini Transat yacht for both conditions. The results of this investigation show that there is a fine balance in choosing the best appendage configuration which is dependant upon a combination of design cant angle together with wind speed and hence heel angle.