Jurgen Seebacher of Naples, FL asks:

How was vessel speed and current speed determined during your voyage? Did you rely solely on GPS, or did you use a separate speed sensor. If you used an impeller type sensor, did you have any problems with fouling of the impeller?

Jim Leishman responds:

The NORDHAVN 40 was equipped with GPS and a Raymarine speed indicator - using a paddle wheel impeller. The impeller gave us speed through the water and was also used in conjunction with our electronic compass to give us true wind speed and direction. About half-way around the world the "through water" speed began to read erratically as did the true wind speed. We think the transduce went bad as we were able to check the impeller and it was never fowled.

As far as figuring current speed and direction we relied upon our GPS. It does not take long to become familiar with the speed of the boat through calm water at given RPMs and when we saw our GPS speed increase of decrease from what was normal at that given RPM and noting the offset between the magnetic compass heading and the course over the ground - it was fairly easy to calculate the current.

I personally think the true wind speed and direction should be calculated using the GPS information. There is possible error from either magnetic heading and paddlewheel speed - or GPS speed and course over ground so each has it's drawbacks. I would feel little necessity for through water speed.....

Thanks for your interest,

Jim Leishman

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