Pacific Cup 2002

PACIFIC CUP 2002 ROUTING - DAILY ANALYSIS 7/19/02

with Local Knowledge Marine Software - www.goflow.com

Local Knowledge has a unique approach to tactical (weather and current) routing. For an overview of our routing software CLICK HERE. To see what makes our approach more effective, CLICK HERE.

FRIDAY JULY 19\8: "Force 4" routing solution for Class G from reported position "3" of Pegasus77 at 0800 on 7/15/02, using 10-day MRF forecast on that date and approximate polars for Pegasus. The optimal (quickest) route is in red, with other routes computed for comparison. Times (in hh:mm) for each are shown in the "Best Course Comparisons" box, color-coded to the route.

Subsequent reported positions of Pegasus are shown as "4," "5," "6" and "7" (at 0800 on 7/19); with predicted winds at 0800 on 7/19. Up until point "5" she closely followed our optimal (red) "Force 4" routing solution and posted better distance-made-good for several days than the faster boats by keeping to the south of the fleet. During the last two days, however, she went well north of the optimal route and has lost ground.

Force 4" routing solution for JBird III (leading Class G on corrected) from her reported position at 0800 on 7/15, using 10-day MRF forecast on that date. Subsequent reported positions are shown as "4," "5," "6" and "7" (at 0800 on 7/19). She appears to have followed the "black" route, some 50 minutes slower but still close to optimal. The black dots on each colored route show predicted boat position at 0800 (1500 UTC) on 7/19. Distances from the dots to the destination waypoint is shown in the right-hand column (in nm). Compared to prediction, JBird is just slightly behind. The ability of the router to predict position is a crucial test its ability to test all routes and determine the quickest solution, and of the accuracy of the wind-prediction model.

Force 4" routing solution for Octavia (leading Class E) from her reported position "4" at 0800 on 7/15. Subsequent positions are shown at "5," "6," "7" and "OC" (her position at 0800 on 7/19). Positions of the rest of fleet are also shown at that time. This fleet was able to sail the rhumbline, optimizing speed and sailing minimum distance. Octavia did this best and is in the best position at this latest report according to the routing solution.

EXAMPLE OF ROUTING IN PACIFIC CUP

If the 2002 Pacific Cup started at 1300 PDT, on June 26, the initial wind distribution would look like this. There is very little difference in distance sailed along the Great Circle route (blue line) and rhumbline (red line), only 8 nm, but both appear to pass very close to the light wind center of a high pressure system, and it looks like the preferred route would be to go around this well to the south, despite the extra miles. To find the best route for a race of this distance, however, you have to look days ahead and optimize for the race as a whole. This is hard to do in your head, which is where routing software comes in. Below we discuss a routing solution by Local Knowledge's "Force 4" tactical program (the same router is used Offchart Racer). This is the way that the top professional navigators do it - and you can do it just as well with this software.

Wind distribution 3 days later, on June 29. The light wind region has moved north and a bit west, above the rhumbline, so you don't need to go very far south to avoid it. The routing software takes into account wind variations point to point and time to time, and also maximizes route for the wind angles and your boat's sailing characteristics (polars).

"Force 4" routing solution for start at 1300 PDT on 6/26, for a fast boat (Andrews 70; compare to solution below for J120). The quickest route is always shown in red, with alternative routes shown for comparison. The times in the "Best Course Comparisons" box are color-coded to the route (in hh:mm), and indicate very little difference between the red, green, blue and black routes. Of these, the blue and black are small variations of the red, but the green is quite different. Analysis (below) shows that it trades off more distance for extra wind in the early days to almost equal the shorter red course. Force 4 is unique among routing programs in that it shows you these quantitative alternatives, so you can judge how flexible you can be in actual routing without giving up too much time.

Predicted positions and winds at 0100 on 6/28 PDT (0800 UTC) are shown by black dots on each colored route. The right-hand column of the "Best Course Comparisons" box gives distance in to the destination from that dot. While the "boat" on the green route has gone considerably further due to the stronger winds in the south, it is almost 70 nm behind in terms of distance to the destination. This will narrow over the next few days.

Predicted positions and winds at 0800 on 6/29 PDT (1500 UTC). The "boats" on all but the yellow and magenta routes have gotten under the high, and are pulling ahead. The "boat" on the green route continues to have better wind and has pulled within 50 nm of the red.

Predicted positions and winds at 0100 on 7/2 PDT (0800 UTC). The "boats" are now all sailing in equivalent winds, but the southerly boats have the better angle and the most northern (yellow and magenta) are well behind. The green "boat" is now in the lead, in terms of distance to the destination, but is not in quite as good position as the red.

Predicted positions and winds at 0000 on 7/3 PDT (0700 UTC). The green and red routes are about to converge, with the green "boat" several miles behind. The magenta route has also converged with the red, but that "boat" trails by almost 85 nm . Note that where a route is upwind or downwind, the router shows the average course direction, which must be achieved by tacking or jibing back and forth. This applies to the "red" boat in this portion, until it can turn left further ahead and reach the rest of the way to the finish.

Predicted positions and winds at 0200 on 7/4 PDT (0900 UTC). Despite the very different routes sailed by the red and green "boats" they will end up less than 10 nm and less than a half hour apart. This is so close that which way you go may depend on other factors, such as the route taken by your main competitors. The red route is also more sensitive to the predicted position and motion of the high, and this may be a reason to take the green.

The routing solution of course depends on the boat. Below is the solution with the same assumptions about wind and starting time, but using J120 polars instead of Andrews 70.

For information about our 2006 Pacific Cup Wind & Routing Software Package: Click HERE.