On Mon, 26 Dec 2005 14:00:59 +1100, "K. Smith" wrote:

there's a further assumption
that the quantum AND direction of off track forces will remain constant
throughout the leg; both rarely happen.

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Not true. If you monitor COG vs bearing to mark and keep them equal,
the "off track forces" can vary all they want, same thing if you are
monitoring (and minimizing) XTE.

The old fashioned way was to estimate current set over the entire leg,
plot a graphical solution, and steer a constant offset. At the end of
the leg you got to find out the accuracy of your estimate and
calculations. With GPS you get constant feedback.