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Transpac adopts Rating System that incorporates weather

by Transpacific Yacht Club 28 Mar 17:58 PDT
2023 Transpac © Doug Gifford

At their March meeting, the Transpacific Yacht Club Board of Directors adopted a rating system based on weather predictions at the recommendation of the club's technical committee following their analysis of previous race data. The 2025 Transpacific Yacht Race will employ Time-on-Time Forecast Time Correction Factor (F-TCF) ratings calculated from the polar performance data from each boat's ORR certificate and weather predictions available on the morning of each start. Weather-adjusted ratings computed for each start day maximize the chances for each division to compete fairly against the entire fleet.

The first two days of Transpac are the most likely to have weather conditions that vary between the starts, which are staggered with three starts over five days, as boats work their way out of coastal waters and deal with potentially very different "Catalina Eddies". F-TCFs created on start mornings account for this variability in the early going. Farther offshore, boats are expected to encounter the trade wind reaching and running conditions Transpac is known for.

Stan Honey, who worked with the TPYC Technical Committee Chair and US Sailing's Head of Offshore Ratings Jim Teeters in the proposal for and development of the F-TCF scoring system, observed: "Overlays of HRRR forecasts with fleet tracking and satellite imagery for previous races has confirmed that the HRRR does a good job of forecasting the Catalina Eddy. Given the dramatic and varying effects that the Eddy has on the different Transpac starts, by using these forecasts the F-TCF system can reduce the likelihood that the starters in an unlucky day fall out of the running for fleet results the first day of the race."

US Sailing's Offshore Office will use Expedition routing software to predict each boat's elapsed time according to the rating rule's polar performance data, and the NOAA's HRRR and GFS weather forecasts available shortly before the start. They calculate F-TCF from these predicted elapsed times. The same system will be used in the 2024 Newport-Bermuda Race.

TPYC Commodore Bill Guilfoyle noted "The development of F-TCF represents one of the most significant improvements in ratings in recent memory. With three starts spread over five days, few races stand to benefit more from this innovation than Transpac." Incorporating start-day F-TCFs—rather than relying on a historical weather matrix— means that "Good sailors on well-prepared boats have less chance of being unfairly punished by the luck of the draw on weather," TPYC Vice Commodore Alan Andrews said.

The TPYC Technical Committee's analysis also included a review of the available handicap systems. Based on their recommendation, the TPYC Board of Directors voted to retain the ORR rating system as the best alternative for Transpac conditions.

For over a century, TPYC leadership has recognized the need for custom handicapping that accounts for the unique weather conditions of the Transpac course. These refinements are the latest in increasingly fine-tuned handicapping.

Facts

Ahead of the 2025 race, Transpac will announce calculation details including the model times of the HRRR and GFS models that will be used to calculate the TCFs for each race day, the boundaries used between the HRRR and GFS, and the weather-routing settings used in Expedition. Recognizing that our predictive tools are not perfect, Transpac uses best-in-class components and seeks continuing refinement. Combined HRRR and GFS weather models prove to be more accurate than historical weather averages. Expedition routing software is an industry standard.

Transpac acknowledges Jim Teeters and Chris Tutmark of the US Sailing Offshore Office for their assistance in both F-TCF and rating rule studies.

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