Yes Jax,

The sail works because it is curved. It provides the force to move the
boat on a Reach and on a Close Haul.

Since you don't know why and are denying the statements you've made in
replies.Both about the curve and force vectors, it is time for
enlightenment.

I'll try. I was just made aware of the Newtonian Theory this past
season. This discussion group made me aware of it and I have brought
into it. So, I'm not pretending to be an expert BUT I damn well know why
the curve on the Lee side is necessary, I've done some studying;

Newton said for every ACTION there is created an EQUAL and OPPOSITE
REACTION.
So that Action on the lee side of the Sail causes the air to go in
a leeward motion. This is caused by the CURVE in the sail ( On a wing it
would be the curved section of the airfoil)
This Leeward action of the air away from the Lee side of the sail
creates a need for air on the Lee side of the sail. This need is
supplied by the relative stationary air, behind the deflected air
caused by the curve on the leading edge of the curved sail. This air
rushes against the Lee side of the after section of the curve sail and
slides off the leech of the sail. This Force of Air is the ACTION,
Newton Law needed to create the REACTION from the air on windward side
of the sail.
There is another action that takes place with the air sliding off
the Leech. It is called the COANDER EFFECT. This is caused by the
surface tension on the boundary layers causing the air sliding backward
to turn and aid the reaction force

Now, the curve of the Sail is necessary to keep the air in contact with
the sail (Boundary flow) until we want it to separate with the minimum
turbulence to allow the forward air to slide down and over the after
part of the sail

My apologise to all you informed sailors for my crude attempt to explain
Newton's Law (F=ma). To all but Jax who had his chance

I"ll need a:"DRINK TO THAT" for venturing where Angels fear to thread

Ole Thom