Thanks for this very interesting topic, I had no idea how much time and how many words could be devoted to VMG...just ask google! I look forward to digging in to learn more but Tim, you have the key issues teed up for us. Yep, speed over ground will be faster on a tack off the wind, and it also results in better VMG as opposed to sailing as close to the wind as our boats will go. How much off the wind makes optimal VMG? Stay tuned, or chime in, because I have not found the answer yet! There are so many factors, even with a single sail. Introduce a headsail or mizzen and, well, oh my. But Tim's assumption that we (with amas) are really trimarans is correct, and the importance of that is related to the amount of heeling we do/don't do. And then there is the issue of rudder angle, which provides both lift (who knew) and drag (I DID know that). The trimaran aspect (minimal heeling) and the rudder issue are both factors that go into the weather vs. lee helm, which also varies depending on wind strength and tack angle...and so on! And these both factor into VMG...somehow. Oh, and btw, the hydraulic drag (caused by hull moving through water) that needs to be overcome is LINEAR with respect to speed, which is completely different that the drag in air, which increases exponentially with speed. This is important because you get to "keep" all of the increase in speed you get by sailing a bit off the wind. If that was not the case one would experience diminishing benefit from falling off the wind to increase ground speed, as some of that speed would be spent overcoming the non-linear drag you would experience sailing through a sea of air.
Well, I'm no physicist but I am intrigued by the sailing geeks I have begun to read on the sailing blogs. If anyone is interested in a deeper dive from one of the better sources I found you can look at this string:
http://www.cruisersforum.com/forums/f48 ... 02231.htmlBest,
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