Genoa-How much draft

[Aac]

Hi all

I've neen searching the forums and net for information on how much design draft is typically built into genoas. Draft is something that is mentioned 1000s of times; without numbers however the term is useless. How much is a lot of draft and how much draft should a flat pointing sail have.

The only numbers I can acutually find is at Neil Pryde sails http://www.neilprydesails.com/pdfs/N...oam%20Luff.pdf which shows a picture like:



Here we see a draft of 16% for the unfurled genoa.

So my question is: for moderate conditions, say 10 to 15 knots wind and a 140% geona, how much design draft should there be.

Also, why is it so difficult to get information on such an important topic; do sail makers consider sailors too stupid to understand numbers; maybe I shouldnt speculate.

[puddinlegs]

The short answer to your question is that "it depends". Not what you want to hear possibly, but there are way too many variables in hull and rig design to have a one draft fits all answer. Sailmakers will also design for specific locations and intended use (a 140 laminate for crewed racing, or a dacron 140 on a furler for short handed cruising? Are your shroud bases on the rail, or more inboard?). Sailmakers are not around to pull your chain or fool you. If you've talked to one that can't give you a reasonable answer FOR YOUR BOAT, then find another.

[turbulicity]

If you are really curious about the built-in camber, call your sailmaker. But, bear in mind that nobody can claim and ideal number for this. It all depends very strongly on wind speed, pressure, temperature, point of sailing, heel etc... Even when all the conditions are known, it is a long shot to predict the flow. Take it from an aerodynamicist, your best bet is to play around and get a "feel" for how to use your genoa most efficiently. Pay attention to telltales.

[Liquorice]

This will start you off:
Amazon.com: Sailmaker's Apprentice (0639785801771): Emiliano Marino: Books