The 97th running of the Chicago Yacht Club Race to Mackinac set to start on Saturday, July 16, 2005 will be run under AMERICAP II for monohull boats. AMERICAP II has been used for the last two Mac Races and ghost scored for several prior races. The 2004 race, which began as a beat and ended as a drifter was a test for any rating system, including AMERICAP. US Sailing and your Mackinac Committee have spent considerable time and effort analyzing the 2004 race and listening to competitors. We are pleased to announce several improvements to the AMERICAP II velocity prediction program for 2005 and changes in the application of AMERICAP II to the Race.

Changes specific to the Race to Mackinac:

· The course configuration for 2005 will be selected on Friday afternoon prior to the race and announced at the skippers meeting to provide the greatest possible match of handicaps to anticipated weather. This decision will be based on the weather forecast data available at the time.

· A single number time-on-time rating for each course configuration will be provided and the handicap for the selected configuration will be used to score the Race. Elapsed time multiplied by the rating will provide corrected time. This can be done at any mark or point of the race as well as at the finish.

Changes to the AMERICAP II VPP for 2005:

· Revised aerodynamic model based on wind tunnel tests of upwind sails resulting in speed predictions that are more accurate and better assess the effect of stability on performance.

· Revised hydrodynamic model for stern overhangs based on tow tank testing of large scale models. Tests included immersion of transoms at various sailing speeds.

· Improved accuracy and speed prediction of canting keel designs.

· Improvements to the wave drag model.

· Correction of predictions of performance at very high speeds. Many modern designs are able to sail at speeds that exceed the theoretic maximums under the prior VPP.

· Improved consideration of friction drag of appendages providing for more sensitivity to the performance advantages of modern keel and rudder designs.

· IOR hydrodynamics to more accurately predict performance of older IOR designs.

· Improved treatment of heel drag.

These changes are a result of feedback from competitors in our continuing effort to improve Americap as a quantitative measurement based VPP rule. It is the belief of the Mackinac Committee that the strength of Americap lies in providing multiple handicaps for a range of course configurations that an all condition single number handicap cannot provide.

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