Twist

[Malcolm Young]

Leech to top batten angle

Neil,You look at the angle of your boom compared to the angle of the top batten. You make them the same as a rough guide to initial twist set. You really don't sight up the leach as it falls off on a curve from the boom and then comes back in as you go up the sail. The tell tale at the top batten is a better indicator, however the top batten parallel to the boom is a good starting point.

 

[mortyd]

rick, be careful with terms. the induced drag caused by the 'lift' of your heeling hull moving through the water might be very significant, even compared to your 'drag coefficient.' three dimensional air- and hydrofoils are quite complex, but the more your keel heels the greater these forces get. with the boat straight vertical, they are zero.

 

[Jeff Bacon]

No one has mentioned the Reason for twist...

... twist is a necessary part of sail control due to the "Wind Velocity Gradient", which means that the wind blows harder higher up than it does at the waters surface. Since the wind is blowing harder higher up, that brings the apparant wind aft. We now have a situation where the apparant wind at the foot of the sail is different that at the head of the sail. The way to take advantage of this is through twist. Twisting the sail properly trims the top of the sail to the apparant wind evident at that height. Therefore, you can have a sail that is properly trimmed at every height even with different apparant wind angles. Twist dosen't "dump" air until the twist exceeds the proper trim for the apparant wind angle at the head of the sail.Sailing with not enough twist is the same as having the main sheeted in too tight on a reach.... it increases the heeling moment, and slows the boat down. Sailing with too much twist will reduce the effect of the wind on the sail at the head and straighten the boat up a bit.Jeff

 

[Phil]

Angles

Mortyd,Are you perhaps thinking of leeway angle, and not angle of heel?

 

[Jeff Bacon]

Rick, short answer.......no

When it's time to reef, it's time to reef.Only pointing out that too much twist will dump air, while an appropriate amount of twist would be considered proper trim, and would not be dumping air.Jeff

 

[mortyd]

rick, please email me at mortyd@nyc.rr.com

 

[mortyd]

rick, you didn't say anything wrong, just a little putting the cart up front, maybe; it's still a big boat pushing a lot of water, and there's nothing i ever saw in sail trim discussions that mentions water.