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post #31 of Old 04-08-2012
Stu Jackson
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Re: Garmin GPS 72H and VMG?

Originally Posted by danielt63 View Post
I'll jump in with a recommendation here... For an upwind/downwind course, you only need one waypoint.

The upwind and downwind marks make a line. Project that line as far upwind as you can and put your waypoint there. Going to the upwind mark then means maximizing VMG and downwind means minimizing VMG, no matter what direction the wind is actually coming from.
I suggest you reread this topic. I earlier mentioned that there are TWO different VMGs that can be used, going upwind.

1 --- The 1,000 mile away waypoint which should be based on wind direction (assuming it is constant, which we all know it is not). The CONCEPT here is to get the best UPWIND VMG based on the wind direction, since the start line is not always exactly perpendicular to the true wind direction, and the first waypoint is not always exactly dead upwind. It alerts you to the favored tack. The 1,000 mile away waypoint should be on the same bearing as the true wind direction.

2 --- The waypoint to the first upwind mark, to be used to judge the layline (currents notwithstanding).

They are two SEPARATE and distinct uses of the VMG function from a GPS unit.

Stu Jackson, Catalina 34, 1986, M25 engine, Rocna 10 (22#), Maple Bay, BC, Canada
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