Originally Posted by Blue Eagle
I read a piece about this a while ago that I think put the blame at the feet of coriolis forces and the different angles of attack that this creates with the wind hitting different heights on the sail.
Basically, assuming that you tune the sails to draw cleanly at the point of greatest belly in the sail - or between 1/3 and halfway up the sail, on one tack the slight difference in wind direction at the top of the sail will give you a beneficial increase in lift, whereas on the other tack it'll do the reverse - there's a diagram, but I don't remember just now where it is - does anyone else remember seeing or reading this?
I guess the effects are small, but with all else being equal, and particularly for a taller rig, perhaps it could create this 1/2 knot extra...?
What a load of CRAP.... the coriolis force has nothing to do with this. The coriolis force would vary, depending on the direction of the wind and what point of sail you were on, and should, if it exists at such a microscopic level, even out overall. If you think that coriolis force is going to be strong enough on such a small scale to effect boat speed by a significant percentage—hull speed on this boat is about 8 knots, so half a knot is about six percent—you're hallucinating.
The issue lies in a combination of the hull/keel shape, differences in the underwater profile of the boat on the two tacks, rig tuning, or in the instrument error or miscalibration.
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