Dennis said exactly what I was thinking. I can't think of any time when VMG shouldn't be the metric. Most boats have polars that are flat or concave between 170 and 190. As I understand it this is likely because the boat has more wetted surface area when it is flat in the water. Regardless of spin or wing you should get crew weight to the leward side and cheat to the wind as much as the boat will allow to maximize VMG. A preventer helps for safety and a whisker pole helps keep the headsail open. With both you can probably come up as much as 10 or even 20 degrees - again, as needed to maximize VMG. All things being equal, jibe when your angle to the mark is slightly more than double the amount which you're off 180°. This will also be about the same time that your VMG as a percentage of wind speed will start to drop. My apparent wind meter has demarcations between 160 and 200. I try to stay out of that region...it sucks.
Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD Apr 5, 2024 17:31:27 Dennis C. via CnC-List <cnc-list@cnc-list.com>: > Personally, I think sailing to polars can be challenging. I prefer to use > VMG. VMG rules for windward/leeward race courses! Bear with me on this. > > First, a couple of definitions used by Touche's Nexus instrument system. > > Velocity - speed and course > VMG - velocity made good wind based. The velocity directly upwind or > downwind. > WCV - waypoint closure velocity. The velocity made closing on the set > waypoint > > Okay, if your instrument calculates VMG (wind based), simply steer the boat > to maximize VMG. Done! > > If your instruments do not calculate VMG (wind based), here's how to get your > GPS to closely approximate it. First, many GPS systems show VMG which is > actually WCV when a waypoint is set. If you set the upwind (or downwind) > mark as the waypoint, WCV will incur more error as you approach the layline. > Visualize it. As you approach the layline, your WCV will decrease to zero as > you near 90 degrees to your course to the mark. (If you overstand, WCV will > turn negative as you've sailed past your mark.) > > So, set a waypoint 10 miles directly upwind or downwind of the race mark. > Now your GPS WCV will closely approximate VMG (wind based). Steer to > maximize WCV and your course(s) to the mark will be optimized. > > -- > Dennis C. > Touche' 35-1 #83 > Mandeville, LA >
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