The end plate effect is very real. I learned that long ago when windsurfing, if you can setup your sail so you can rake the sail back and the foot touches the board, you add power.. You can feel the acceleration immediately. Especially in winds below 15 knots. As the wind builds above that, everyone starts to achieve hull speed and the nuances of sail theory and fine trim are less critical. This leads me to believe that sails made for light winds should be fuller and deck sweepers and sails made for higher wind areas, should be flatter and high cut. My 2 cents.
Chuck Resolute 1990 C&C 34R Atlantic City, NJ ----- Original Message ----- From: "CNC boat owners, cnc-list" <[email protected]> To: "CNC boat owners, cnc-list" <[email protected]> Sent: Thursday, May 8, 2014 5:08:47 PM Subject: Re: Stus-List Technical sail discussion Joel and Dennis, If you really want to understand the how of why of sail aerodynamics, I would suggest reading the book "the art and science of sails" by Tom Whidden. He thoroughly debunks the Bernouli theory as applied to sails. His theory is quite complex but well explained in the book and has nothing to do with pressure diferential of the Bernouli theory, but end plate effect is very important. James S/V Delaney 1976 C&C 38 Oriental, NC ----- Original Message ----- From: Joel Aronson via CnC-List To: Dennis C. ; [email protected] Sent: Wednesday, May 07, 2014 8:59 AM Subject: Re: Stus-List Technical sail discussion Dennis, My limited understanding of aerodynamics is that if the foot is not on the dock then the higher pressure is allowed to "leak" under the foot to the low pressure side, diminishing lift. That's why they now have tips on airplane wings. If the cabin causes upward deflection, that may be more than offset by maintaining the pressure differential. But either way, you are +6 sec./mile! Joel 35/3 Annapolis On Wed, May 7, 2014 at 8:51 AM, Dennis C. via CnC-List < [email protected] > wrote: <blockquote> I recently re-filed my PHRF certificate to get +6 seconds for a roller furler. Subsequently, I just had the luff my Mylar/Kevlar 155 cut down to fit on the furler. My sailmaker cut a bunch off the foot. I was chatting about loosing the sail area with one of the really good sailors in the club. He said it may actually be a good thing that the foot is higher off the deck. He said with the older narrow IOR designs, deck sweeper genoas may cause the slot to be less efficient. Might increase the bubble in the main. In my simplistic mind I kinda see where he's coming from. The slot gets restricted at the deck by the cabin. The lower part of the air flow would get pushed upward into the bottom of the main. A higher foot allows some flow to escape and keep the air flow lines smooth in the lower slot. Does this make sense? Dennis C. Touché 35-1 #83 MandevilleLA Sent from my iPhone _______________________________________________ This List is provided by the C&C Photo Album http://www.cncphotoalbum.com [email protected] -- Joel 301 541 8551 _______________________________________________ This List is provided by the C&C Photo Album http://www.cncphotoalbum.com [email protected] </blockquote> _______________________________________________ This List is provided by the C&C Photo Album http://www.cncphotoalbum.com [email protected]
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