Originally Posted by DanS
Originally Posted by MrEZgoin
I kept myself occupied trying to work out a formula in my head for VMG as a function of tack angle. 120 makes it easy and I believe leads to VMG = V/2. If I was able to tack through 90 degrees AWA as performance boats surely can, that would improve to V/sq(2). I'm sure there's a general formula involving a trig function, but I couldn't quite figure it out without pencil and paper

Hah, thanks for the challenge.grin I was able to visualize it by making angles with my hands -- would have looked pretty funny to anyone nearby. I believe the formula you're looking for is:

VMG = V cos(TackAngle / 2)

The results agree with your two examples.

Dan cheers


Very nice! That sure looks correct.

All this made me curious to look for the polars for the boat and I found a 2014 R&C version "subject to sea trials".
It has max speed at around 80 degrees TW with the genoa, further ahead than I would have guessed.

M4000 "Lio Kai"