Storm Trysail-Transpac 65, 65ft Racing Yacht

Designer’s Notes

The goal of the Storm Trysail Club and Transpacific Yacht Club was to create a boat that could compete as a Box Rule and as an IRC or ORR performer. The benefit of a Box Rule – one that limits factors such as length, minimum displacement, draft, sail area etc. – is that it maximizes performance. The STP 65 rule promotes a high-performance boat for both inshore and offshore sailing, with tight enough parameters to minimize obsolescence. The “box” sets an LOA of 20 meters (65.6ft), displacement range of 13,000Kg to 13,400 Kg, beam range 4.5m to 4.8m, a lifting keel that allows a generous racing draft of 4.8m (15’ 9”); and a healthy sail plan. The lifting keel will reduce draft to 3.3 m (10’ 10”). Displacement/length and sail area/displacement ratios are between the TP 52’s and Volvo 70’s giving promise that the boat will deliver lively performance in long distance and buoy events. The STP 65 has a standard underwater package, meaning no canting keel, just a “lifting” keel and standard rudder configuration. The keel accommodates a draft of approximately 4.8 meters in its down position and 3.0 meters when fully retracted, facilitating entry into shallow harbors or marinas as part of the class rule, the lifting feature is not allowed while racing. The boat should begin planing slightly earlier than the TP52 yet have very similar upwind stability numbers. Our studies for ROSEBUD involved gathering weather data and race modeling for the owner’s proposed campaign and investigating rule variables to determine beam waterline, displacement, hull shape choices and appendage sizing that would best fit the schedule. A full program of worldwide events is anticipated which necessitated good all-around performance. We have the expectation that our new STP 65 design will have excellent performance under IRC. When analyzing the performance versus handicap under IRC of an STP 65 versus a fully optimized IRC boat of similar size, the key feature to consider is the lifting keel and the 4.8m draft. IRC does not directly measure righting moment so it is advantageous to achieve the highest righting moment (deepest Vertical Center of Gravity) for a given displacement. The weight of the lifting gear and associated extra structure of the keel fin and keel case raise the VCG causing a reduction in performance in all but the lightest winds. Other key features of our STP 65 design do not compromise the IRC competitiveness. The handicap effects of varying particulars of stern design such as length and slope of the aft overhang are very weak under IRC allowing us to draw the best shape for good all-around performance across the wind range. The rig is sized to give excellent light air performance but is not excessive with respect to IRC competitiveness. The STP 65 class spinnaker size is generous but can be pared down for IRC competitions if desired. Overall the STP 65 should be competitive under IRC but better in stronger winds when it is likely to break out downwind and outperform the handicap.