We are talking about a sail which is a single-surface foil here.
Proof that the Venturi effect is what provides the lion's share
of the lift in the system is the fact that the sail is shaped
by the pressures on either side. Because the sail's convex side is
always facing the area of lowest pressure proves the venturi effect
is in action. (This is not true only on a dead run where the shape is
caused by wind action on the windward side of the sail)


Professor em. of Physics Weltner shows here how misunderstood
Bernoulli equation can be:

http://www.rz.uni-frankfurt.de/~weltner/Mis6/mis6.html

The good professor is confusing a descriptive term (longer path)
for a causative agent (lower pressure). The longer path is not the
cause of the lower pressure. The lower pressure is caused by the
speeding up of the air molecules because of the SHAPE of the path.
Use the wrong shape and you will not get lowered pressure.

When it comes to producing low pressure there is no wrong shape.
Pressure differentials are a characteristic of lift and dynamic drag.
What shape object wrong or otherwise does not generate an area of low
pressure when moving thru the air? Low pressure is simply caused by a
solid object (regardless of its shape) in a relative airflow. Low
pressure alone does little to cause lift. Low pressure from a relative
airflow does little to pull or suck the solid object or allow the
higher pressure to push the object in the direction of the low
pressure.
The shape of the object allows this low pressure to generate a
substantial amount of lift. This is very easy to prove.

The
shape is the key to lowering the pressure efficiently and without
excess drag - not the longer path.

Because the shape confers a longer path does not mean it is the longer
path that is the cause. The shape of the foil is important not the longer
path. The so-called longer path descriptor is ONLY a descriptor.
This seems to go over the heads of so many professorial types who
are all too involved with nomenclature.


Aerodynamist Martin Ingelman-Sundberg ownsite with articles :

http://www.marv.nu/undersajtm.html

And, this chap is talking only of airplanes and probably has never
sailed in his life and is also unfamiliar with single-sided foils that
are shaped by the wind.

Thanks for the links but I still know I'm right when it comes to
sailboats.

Capt. Neal
http://www.homestead.com/captneal/index.html

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