EDS Atlantic Challenge

7/29/01 Daily Routing Analysis of EDS Atlantic Challenge

Analysis Now Includes Gulf Stream Currents on Chesapeake Approach

	DAILY ANALYSIS FOR JULY 22, 2001 - Click Here
	DAILY ANALYSIS FOR JULY 23, 2001 - Click Here
	DAILY ANALYSIS FOR JULY 24, 2001 - Click Here
	DAILY ANALYSIS FOR JULY 25, 2001 - Click Here
	DAILY ANALYSIS FOR JULY 26, 2001 - Click Here
	DAILY ANALYSIS FOR JULY 28, 2001 - Click Here

We apply our "Force 4" routing software to evaluate possible routes for the competitors in the EDS Atlantic Challenge. The software utilizes boat polars and a 10-day MRF wind forecast to predict boat speeds at various times and locations, and then searches for the fastest possible route. This is always shown in red, and alternative routes in other colors (corresponding times and distances are color-coded). The alternative courses do not represent "second best" or "third best" solutions, but are constrained initially to various sectors relative to the rhumbline (e.g., to far right).

As the boats approach the Chesapeake, we now factor predictions of Gulf Stream currents into our routing solutions. We use interpretations of recent satellite data by oceanographer Jenifer Clark in our current-modelling program to produce a digital current model suitable for PC routing computations.

Below is the routing solution for Kingfisher, from its reported postion "34" at 0444 UTC on 7/28 to a point "8" approaching the entrance to Chesapeake Bay. Winds are shown at this starting time, and predicted currents are shown in blue. The favored route (in red) is mainly determined by the wind pattern, dipping south of the rhumbline to take advantage of the stronger winds. Note much longer times for northerly routes in the "Best Course Comparisons" box. However, there are some zigs and zags to optimize passage through the 2-knot eddy current (circular pattern) along the route. Compare to following graphic, which omitted current.

Actual track of Kingfisher to position K6 at 1643 UTC on 7/29, compared to predicted positions (black dots) on alternative courses at that time. It is slightly ahead of predicted position for the black (central) course, which it approximated, but behind predicted position for the optimal red course, which avoids the unfavorable current found in the Gulf Stream eddy (circular pattern around "K4").

Below the solution is recomputed with zero current, which eliminates the zigs and zags in the central portion shown in the above graphic. These current effects become much more critical with a headwind, and when winds are light.

Detail of above solution as tracks pass through Gulf Stream. The black dots on each colored route show predicted boat position 24 hours laterr, at 0444 UTC on 7/29.

Comparison: same situation but assuming constant headwind of 10 knots from 240 deg T. Here the routing solution is based solely on current, taking advantage of the southerly flow of the eastern edge of the 2-knot eddy, the westerly low at its lower edge and avoiding the strong easterly flow of the main Gulf Stream below the track.