Stuart M Roy
Naval Architect - Yacht Designer
YACHT & POWERCRAFT DESIGN SERVICES
There are procedures in common use to provide resistance predictions and hence powering estimates for most types of boat, including motor boats, fishing boats and tugs, as well as planing hulls before they get on the plane and when they are in the fully planing regime. But resistance prediction is not yet an exact science, leaving plenty of scope for towing tank testing of models and the progressive development of full-size prototypes. In addition each computational procedure is only applicable for a limited speed range and for boats falling inside an envelope of certain dimensional parameters and ratios.
The performance of sailing boats can also be predicted at the design stage by calculation procedures involving a combination of hydrodynamic and aerodynamic theories. The complete process of estimating the speed of a yacht on any point of sailing in a range of wind strengths involves the use of a sophisticated computer program known as a Velocity Prediction Program (VPP). The output from a VPP is often presented in the form of a polar plot (above) showing an envelope of optimum speeds for each wind strength and point of sailing. A designer would use a VPP program to evaluate possible options for a new sailing boat design, only proceeding to develop to a final design the one that achieved the best predicted performance.
Polar Performance Plot for a 10.1m cruiser-racer sailing in a range of wind speeds.
Predicted upright resistance for a 10.1m cruiser-racer.
Powering of Yachts & Boats 2