VPRS is a new rating system for ballasted monohull yachts, developed for the Poole Yacht Racing Association (PYRA).
VPRS stands for Velocity Prediction Rating System. It is a mathematical model that uses a range of well-established analytical and empirical techniques to estimate the resistance of the hull and the power available from the sails, based upon a set of hull and sail measurements. These are used to calculate the speed potential of a boat in a variety of conditions.
The average predicted speed is then used to derive a rating, given in the form of a Time Correction Coefficient (TCC).
Although the model has in part been designed to ensure that ratings are in line with observed performance, no subjective adjustments are made to the calculated rating. The model may be updated or improved from time to time in the light of experience, but any such changes will be applied to all boats. The average difference between VPRS and IRC ratings across the PYRA fleet is currently less than 1%.
The design of the model will not be made public so as to discourage owners or designers from attempting to exploit the constraints of the model in order to gain unfair advantage.
The necessary measurements are normally supplied by boat owners. A guide to these is provided on the measurements page. We reserve the right to compare these with our database of yachts already rated and, where significant differences exist, to substitute standard hull measurements - unless an owner can produce suitable evidence to support their own measurements. We can provide assistance with measuring if required.
VPRS will be evaluated during the 2010 season. It will not be used to calculate official results or award prizes this year, but the trial results will be published for comparison on the results page here - and on the PYRA web site.
It would be greatly appreciated if all PYRA members could check their boat details and advise any errors or updates.
Feedback and new applications for rating are welcome via the contact page.
