sail shape

[henry Weber]

There have been several posts as to recogizing when a sail is blown out. My question to you guys is similar. On a typical classic design boat such as my H30 on a close reach with 12kts wind what should the camber and draft position be? Interested both for main and working jib. My guess would be camber 15%, and draft 45%. Now, as the sails age, say 5 yrs. and plenty of use, how much are these numbers likely to grow. Is it another 5% which is hard to see or is it 20% or more? A camber of 35% should be easy to spot.Thanks,Henry

 

[Bill Colombo]

Camber and Draft Position

Henry, Typically maximum draft position on a genoa should be at approx. 33% while mainsails are designed with the draft at about 45%. Camber varies with boat size whereas larger boats will have relatively flatter sails than smaller boats. Of course heavy air sails are also flatter than their light-air counterparts. On a 30 ft sloop a medium-to-full genoa will have a camber of about 1:8 or 12.5%. A mainsail is typically slightly flatter in the neighborhood of 11% on average. Sails do get deeper as they age and the draft moves aft in the sail. I think you would notice a 10% shift in max draft position. Take a photo and compare it to a new sail. One of the key areas for shape distortion is the leech or aft 20% of the sail. New sails have very clean "exits" allowing the air to flow freely off the sail. Old sails develop rounded exits which cause increased turbulence and drag in this area, robbing performance. Bill C.

 

[henry Weber]

camber and draft

Thanks very much, Bill, for your answer.