RATING RULES: Evolving the VPP

Published on March 8th, 2013

WHAT’S NEW FOR THE ORR RULE IN 2013
The Offshore Racing Rule (ORR) was first used in the 2006 race season, and is now the prominent rule for distance racing throughout North America. Events such as the Newport Beach to Cabo San Lucas Race, Chicago Yacht Club Race to Mackinac, and the Marion to Bermuda Race all use ORR.

ORR is based on a non-public Velocity Prediction Program (VPP), with the performance factors having recently gone through some small modifications. Here’s what’s new for the ORR Rule in 2013:

– Hull Drag: the model for wave drag (residuary resistance) has been adjusted slightly to include the results of new tank test data

– Sail Aerodynamics: the algorithm for de-powering offwind sails (man and spinnaker) has been adjusted to reflect wind-tunnel test data

– Sailing Dynamics: adjustments to how dynamics such as tacking and accelerating effect the ratings (boat speed predictions)

– Rudders: the effect of rudder span in generating lift has been reviewed, particularly with respect to deep rudders

– Code Stability: the calculation of best downwind VMG has been made more robust, in particular for very light boats with very large sails

ORR website

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