"Simple Simon" wrote in message
...
It does depend on the length difference as stated in the principles
of the venturi effect. The speed of the air is increased when it
is forced through a smaller area. The sail acts like one side of
a venturi in that the air has a smaller area to go through because
of the extra length. The air above that air on the surface of the
foil acts like a venturi also to a small degree. The net effect is
the air moves faster, the molecules become spaced farther apart
and the pressure is decreased. This decreased pressure is a greater
factor causing lift than the air pushing up on the windward side of
the sail.

You might know a lot but you need to learn more when it comes
to the practical application of single-surface foils used on sailboats.


If I didn't already know the answer, I'd be tempted to measure both sides
of my mainsail - to see if you were right.

Fortunately, I am not stupid enough to think that there is a significant
difference between the lengths of the windward and leeward surfaces. Where
do you get this rubbish from? Are you reading a "definitive" book on the
subject?



Regards


Donal
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