Originally Posted by xavierlh1
Seems counter-intuitive. Doesn't bending the mast allow the main to be fuller, and more powerful?
One of the ways sailmakers achieve sail shape is with luff curve. Put the fingers of your left hand together and have them straight. The tips of your fingers is the curve of the luff of your mainsail. Take the index finger of your right hand, hold it straight. Now put the luff of the mainsail, tips of your left fingers on the mast (right hand index finger) such that you're touching the inside of the finger (mast finger can curl toward the luff fingers). Keep the mast straight, let the middle fingers of your luff hand bend such that all the tips of your fingers are touching the straight mast. Your fingers on your left hand are now bent demonstrating the draft developed by putting a curved surface on a straight stick. Now bend your mast, as your right index finger bends, the luff (the tips of the left fingers) follow and straighten out. The sail is now flat or close to flat. A flatter sail develops less lift
and the wind
can come from a direction closer to parallel to the sail without causing it to luff. The sailmaker
has to know something about the bend characteristics of the mast in order to put the curve in the right place on the luff.
On the other hand if you bend the middle of the mast aft you will get a fuller sail (Or break your index finger).