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Old 08-02-2012
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Re: Navigation Problem

HS is right. If you have a paddlewheel speedometer already, then maybe you can go out some time when you're not racing and sail different courses in various tidal conditions, and put the data together yourself.

Note, however, that

velocity of vessel over ground =
velocity of vessel over water +
velocity of water over ground.

Each of these three quantities has a magnitude and a direction. Your GPS will tell you the magnitude and direction of the first quantity. Your paddlewheel will tell you the magnitude, but not the direction, of the second quantity; that direction is determined not just by your heading but also by your leeway.

Here's an idea: is the water shallow enough for anchoring? Find a windless day and anchor out. Then your paddlewheel will tell you the drift, and your boat's average heading as it swings to the current will tell you the set (or rather, its reciprocal).

Alternatively if it's too deep to anchor you can try motoring into the current so that your GPS tells you you aren't going anywhere.

Sounds like a fun experiment!
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