Transpac 2003

Recap of Transpac Race 2003

Everyone knows that to navigate the Transpac successfully, you have to duck under the light winds of the Pacific high and sail to the south of the great circle route - the question is when. Routing software computes all possible routes for your boat's performance characteristics (polars) for the predicted wind and suggests an optimal route from start to finish. In a race like the Transpac, however, the wind forecast is unlikely to hold up over the time necessary to reach the finish, and for best results the routing solution should be computed with updated wind forecasts day to day.

Routing solution for Cal 40 fleet, starting July 1. The "Force 4" router finds the "red" route optimal, with comparison routes shown in other colors. The corresponding times for each route (in hh:mm) is shown in the 'Best Course Comparisons' box, color-coded to match the route. The graphic shows an intermediate point at 1500 UTC on July 3. The black dot on each route shows predicted boat position at that time (wind vectors are also shown from the 10-day forecast). The right-hand column of the box shows distance to the destination (here Oahu) in nm from the black dot.

The actual reported positions of Ralphie (upper boxes) and Illusion (lower boxes) at 1500 each day are shown by boxes labelled with the date of the report. Upper Box 3 shows reported position of Ralphie at 1500 on 7/3, slightly behind the predicted position (black dot to left on red route). Ralphie closely followed the pre-race routing provided by Local Knowledge for the 1st week. Lower box 3 shows Illusion at same date and time.

Routing solution for Cal 40 fleet at 1500 on July 4. Predicted positions (black dots) on optimal and comparison routes are compared to reported positions for Ralphie (upper box 4) and Illusion (lower box 4). Ralphie is sailing slower than the predicted route based on its polars, whereas Illusion is sailing faster than predicted (despite a slower rating). Winds have strengthened, with reaching conditions for the Cal40 fleet.

Routing solution for Cal 40 fleet at 1500 on July 5. Predicted positions (black dots) on optimal and comparison routes are compared to reported positions for Ralphie (upper box 5) and Illusion (lower box 5). To this point Ralphie is following the optimal red route, but not sailing quite as fast as predicted. Illusion is sailing the somewhat slower blue route (about 1 hour slower if followed all the way to Oahu), but faster than predicted.

Routing solution for Cal 40 fleet at 1500 on July 6. Predicted positions (black dots) on optimal and comparison routes are compared to reported positions for Ralphie (upper box 6) and Illusion (lower box 6). Illusion has moved north to consolidate its lead, bringing it close to the red route, but behind the predicted time to follow the route from the start. Ralphie continues to sail the route, but not as fast as its polars. The winds are shifting to the northeast, a transition from reaching to jibing conditions.

Routing solution for Cal 40 fleet at 1500 on July 8. Predicted positions (black dots) on optimal and comparison routes are compared to reported positions for Ralphie (upper box 8) and Illusion (lower box 8). The red, black and blue routes have converged, corresponding to the 3 black dots now on the red route. The difference between following the red and blue route is just 8 nm, and 25 nm for the red vs. the black route.

Routing solution for Ralphie from its reported position at 1500 on July 8, showing actual (box 10) and predicted positions on optimal and comparison routes at 1500 on 7/10. This solution uses an updated wind prediction not available to Ralphie, which nevertheless closely approximated the route to the finish (boxes 9-14). In lighter jibing conditions Ralphie is sailing somewhat ahead of its polars. At this point the fleet has passed below the Pacific high, reflected in the region of very light wind to the north of the July 10 position.

Complete original routing solution for Ralphie, and winds predicted for 1500 on July 8.

A big call for Pegasus, starting with Pyewacket on July 6. The "Force 4" routing solution shows a clear preference for the more southerly route taken by Pegasus (lower boxes)

Routing solution from reported solution of Pegasus (and approximate position of Pyewacket) at 1500 on July 7 to its position at 1500 on July 10. The solution predicts an advantage of a couple hours for the route taken by Pegasus, with generally stronger winds. By July 10 Pyewacket was following in Pegasus' wake and that lead persisted the rest of the way.

Congratulations to our "Local Knowledge" clients: Reinrag^2, using our Force 4 router, 1st in Div 3; Tabasco, 2nd in Div 4; and Ralphie, 4th in the 10-boat Cal 40 fleet.