ok, there was a thread stating that the VMG from most GPS units was only calculated using the vector to waypoint vs. initial vector (when you hit the Goto waypoint button) and NOT using it vs. the current actual vector of travel. The prior would be a poor way of calculating a real VMG (velocity made good) to a mark in a sailing race. I posed this question to Garmin support on the web and I got the following response. Any debate? Makes me feel all warm and fuzzy!
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<br>Thank you for contacting GARMIN.
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<br>It is real time data. The VMG us updated continuously with all other data and not just on an initial vector. Good question, I had to check to be sure.
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<br>Have a nice day!
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<br>Larry Keegan
<br>Product Support Specialist
<br>GARMIN International
<br>1200 E. 151st Street
<br>Olathe, KS 66062 US
<br><br><br>[color:blue][b]Jake
<br>[color:blue][b]Nacra 5.2 (2112)

The continuous update matches what I have observed in practice, and I cannot imagine any other way of doing it.<br>Alan Thompson<br>I20 - San Diego<br><br>

True, What good would just using the initial vector be? One would have to keep pushing the button to know if one was doing better or worse. The way it constantly changes indicates that it is recalculating the that component of your velocity vector, but I'm no expert, that's just what I understand it to be doing.
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<br>In the absence of true wind direction info (which is only really valid when the windward mark is really directly upwind), the marks' locations have to be entered and then the VMG function is a boon. Works great downwind!
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<br>Where do you guys mount your GPS? It would be great if Garmin made a GPS that had big numbers one could read from 6' away, say when trapped out fully and the device is on the boom.
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<br>;-)<br><br>

I agree - I was quite surprised when I saw the thread that VMG by most GPS units was calculated by using the initial vector vs. current vector.
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<br>I have an Etrex legend and have used the accessory "handlebar mount" mounted to my tiller (have to be carefull not to slap it when switching sides with the tiller extension). It does loose a substantial amount of waterproofing to the battery compartment this way and I have yet to find a better way to waterproof it with the handlebar mount (it replaces the stock battery cover that has the rubber seal - no seal with the new back). I'm open to any ideas.<br><br>[color:blue][b]Jake
<br>[color:blue][b]Nacra 5.2 (2112)

This device is designed specifically for sailing and addresses most of the shortcomings of Garmin units: www.velocitekspeed.com.

Interesting device. Can someone explain to me how this works? How can it tell what your VMG is if it doesn't know where the destination is?

From the velocitek website:

The S5 takes GPS speed readings every second to get your actual speed. The device then uses trigonometry to extract the component of your actual speed that is aligned with the upwind-downwind line defined by two reference locations you stored in the device's memory (the direction of this line corresponds to the line that the imaginary powerboat traveled along in our example). This process is repeated every second and the results are displayed on the oversized LCD screen.

Please have a look at this discussion:

http://www.catsailor.com/forums/sho...amp;Main=67990&Search=true#Post68271