Ground speed/air speed
If you run your boat at idle,(or any other set RPM) through the channel, in both directions, with your GPS functioning properly,then add the two speeds together and divide by two, you will have your hull speed over ground without any current. Subtract your calculated hull ground speed at set RPM, from your speed running with the current, and you will have the speed of the current in the channel. I have done this a few times and the speed varies within the chanel. It is determined by not only the width of the channel, by by the depth of the water.
Last edited by Broken Glass; 09-16-2015 at 11:08 AM.
Reason: I left out half of the equation!
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