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>Given a polar plot of the expected performance of a sailboat, given your
>present position, and given the place you want to get to, is there a simple,
>graphical plotting method one canue to determine the optimal course?

Without going into a great amount of detail to check this, I would think
the following would hold true:

Given a chart on which your desired course is plotted, superimpose the
polar plot over your current position on the chart and align it with the
current wind direction. Using a set of parallel rules (or equivalent
"rolling" ruler), align it to be perpendicular to the desired course such
that the ruler is between your boat and its destination. Bring the ruler
closer to your current position until it just touches the polar diagram.
Draw a line from your current position to the point of tangency. This line
represents the course that will give you the maximum rate of progress
towards your intended destination.

The second step will be to determine a limit for cross track error from the
desired course and to tack back and forth when this limit is achieved. This
effectively keeps the desired track centered on each leg of every tack.

This approach is strictly theoretical and will be compromised by practical
considerations.  Examples include, but are not limited to:

o  Sea state may limit pointing ability or be too hard on the crew for
   extended beats. Easing off a bit will make for a much more comfortable
   ride but at the expense of a sub-optimal course.

o  Prudent seamanship may suggest deviations from the optimal course to
   avoid charted hazards or to minimize the time one is in an area with
   heavy shipping traffic.

o  As the wind direction and sea state change, the "optimum" course will change
   along with it and needs to be recomputed.

o  Following the "optimal" course for each individual wind shift may result in
   a course that is less than optimal when considered over the entire voyage.
   (Consider the racing tactic of anchoring in light winds when caught in a
   foul tidal current.)

Hope this helps. Anybody have any other ideas?

							Tom

------------------------------------------------------------------------
Thomas Alley                                               alley@acm.org
KD2VH, Youngstown, New York                      Alberg 35, "Tomfoolery"



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Date: 15 Feb 97 08:32:13 EST
From: Bob.Trenkamp@gw.pps.com (Bob Trenkamp)
Subject: Re: Graphical solution
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--- Thomas Alley wrote:
Given a chart on which your desired course is plotted, superimpose the
polar plot over your current position on the chart and align it with the
current wind direction. Using a set of parallel rules (or equivalent
"rolling" ruler), align it to be perpendicular to the desired course such
that the ruler is between your boat and its destination. Bring the ruler
closer to your current position until it just touches the polar diagram.
Draw a line from your current position to the point of tangency. This line
represents the course that will give you the maximum rate of progress
towards your intended destination.
--- end of quoted material ---

Tom,

It's elegant - thanks. You're resolving any course into components parallel and
perpendicular to the desired track and selecting the course based upon maximum
component in the desired track direction. Neat. Thanks.

bob

   

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