Corrected Time Sailing in Transpac
by Transpacific Yacht Club 6 Jul 2023 00:07 BST
2023 Transpac © YB system
Most trophies awarded in Transpac are based on not on an entry's elapsed time but their score in corrected time, both within their division and overall in the fleet. How is this determined?
Since the entries in this race are of varied sizes and styles of design, a system is needed to equalize their performance under handicap. Transpac uses a system called the Offshore Racing Rule (ORR), which relies on detailed measurements of the boat, its keel and rudder(s), the spar, the sails and even the crew weight to predict the speed potential of the boat at all wind angles and wind speeds. The calculated speed potential becomes the basis for rating of the boat.
This is determined using aero- and hydrodynamic models within a VPP (Velocity Prediction Program) developed by ORR for wind speeds between 6 - 24 knots and all wind angles for which the boat's performance can be predicted.
Race managers at Transpacific Yacht Club have developed a matrix of values for this range of wind speed and angle that represents a historic average of conditions in a typical Transpac race. Each entry's Transpac rating is thus calculated using this model and expressed in terms of a Time-on-Time (ToT) coefficient. The boat's rating in ToT multiplied by its elapsed time is the corrected time for that boat.
In the PASHA HAWAII YB tracker system ORR scoring is determined by making some assumptions about the boat's recent speed and the distance left to the finish (DTF). The DTF is divided by the average speed of the boat in the last 24 hours, giving an estimate of when the boat will finish and its elapsed time. This in turn is multiplied by the boat's Transpac ToT rating, yielding a projected Corrected Time. The fleet's corrected time estimates are then ranked in the Leaderboard.
Of course, conditions can change, affecting the speed of the boats, as well as tactical moves that can either speed up or slow down a boat's progress towards Diamond Head. And the actual weather conditions may also vary from the scoring model matrix, which can also have an effect on rated performance.
Nonetheless, this is the most fair and objective approach with current technology in rating and scoring for a race of this length.
Current division leaders in corrected time are as follows (in order of start date), with overall ORR position in (***):
- Boatswains Locker Division 7: Mike Sudo's Beneteau First 47.7 MACONDO (6th)
- smithREgroup Division 8: Dean Treadway's Farr 36 SWEET OKOLE (12th)
- Ocean Navigator Division 4: Bill Mckinley's Ker 46+ DENALI3 (3rd)
- Cabrillo Boat Shop Division 5: Dave Moore's SC 52 WESTERLY 52 (1st)
- PASHA HAWAII Division 6: Cecil and Alyson Rossi's Farr 57 HO'OKOLOHE (18th)
- EPIC Insurance Division 9: Justin Shaffer's MOD70 ORION (1st of 2)
- Cal Maritime Division 1: Sebastian Moshayedi's Bakewell-White 100 RIO100 (34th)
- SD Boatworks Division 2: Ivan Batanov/Lawrence Andrews' R/P 51 ZERO GRAVITY (43rd)
- Whittier Trust Division 3: David Clark's SC 70 GRAND ILLUSION (28th)
As of the 1100 PDT tracker report, Justin Shaffer's MOD70 ORION will be the first Transpac entry to cross the finish line at Diamond Head. At a DTF of 461 miles and an average speed of 27.1 knots, this means her remaining time on the course is about 17 hours, with a projected finish early tomorrow morning. If she maintains these average speeds in the mid-20s on her final approach - which is quite possible in the windy channels between islands - her finish could even be much earlier in the pre-dawn hours.
The tracker data reverts to being Live without the 4 hour delays once boats are within 200 miles of the finish - this will likely be tonight for ORION.
All entries in Transpac can be tracked on the YB system, sponsored by Pasha Hawaii. The positions, speeds and headings of each entry can be found on this system on either the browser of app versions. There is a built-in 4 hour delay for each entry, except when within 200 miles of the finish when the tracker goes live. Use this link to follow the fleet: cf.yb.tl/transpac2023#
For the July 5th Race Analysis video with Transpacific YC's Dobbs Davis, tune in to the TPYC YouTube channel:
Here the fleet's positions are shown on the tracker and explanations of their tracks towards their final approach towards the finish.
For more information on the 2023 Transpac, visit transpacyc.com.