The International Measurement System (IMS) uses a computerized velocity prediction program (VPP) to calculate the performance of a meas­ured hull and rig in winds from six to twenty knots, at any sailing angle. A regatta is scored by comparing a yacht's performance with pre­dictions of the VPP. The winner is the yacht whose performance, relative to its VPP predic­tions, is the best, compared to all other yachts in its class or division.

This paper discusses different methods of malc­ing the comparison and accounting for various factors in the race such as wind shifts and cur­rent on the course. Decisions made by race man­agers and/or developers of scoring programs can significantly impact results. Illustrative examples show the effects that these decisions can have.

In 1994 the number of data points available for use in scoring yachts in custom courses doubled. Alternative ways of using these data are illus­trated by application to a sample regatta.

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