Judging sail camber on bought sails

Hi All

I have just received some new IOM sails from a old established sail maker… The sails look well made BUT, I for the life of me I cannot see any camber in the broad seams :mad:… It is as if the panels were joined on a flat table… How do I determine if I have dud sails or not??

Any advice before I demand my money back…


PS: I’l like to post some pics- any tips on how the photograph the sails so that one could “see” the cut of the sail?

North Sails has an image analysis program that does this. They start with a photo taken from the middle of the foot of the sail looking up.

Tape the head and tack of the sail to a flat surface. Tension the luff with just enough force to remove all but a hint of a wrinkle, (about 4 oz.). Then elevate the clew and adjust the position of the clew so that the sail sweeps down to the flat surface and becomes tangent to the surface just at the clew. The chord of the foot should be at an approximate 45 to 60 degree angle to the flat surface. Gravity will provide sufficient force to pull the shape into the sail as if it was filled with a 1 - 2 knot breeze. Draft stripes on the sail, perpendicular to the luff will assist in seeing the shape, though the broadseams will also show the shape too. Photograph from a long distance away so that the entire sail can be brought into focus.

A straight edge brought up to the luff will allow you to assess the luff round that was cut into the sail, though the sailmaker should be able to tell you both that number as well as the target % camber at the broadseams. If he can’t then he is making sail that may vary significantly from sail to sail.


Thanks Rod

I’m going to have a go at photographing the sails as you suggest… Thanks!

You’re welcome.

In my posting above the point of tangency should be the “luff”, not the clew.

Shows what happens when one tries to watch the Tour De France and type at the same time.

Sorry for any confusion I may have inadvertantly caused.


I’ve taken some pics, and removed the makers mark…don’t want to hurt his image. (He has suggested I send 1 set back- I bought 2 sets, 1 for a mate… and he will see what went wrong)
I’m not that keen as I don’t want to risk more money and I’ve lost confidence with this sailmaker- I’d prefer my money back…

Please all comments welcome…On the cut of the sails and what to do about it…

What is wrong with them? I see camber and also can see a slight amount of broad-seam when you lay them flat…notice the inability for the material to lay completely flat without any deformation.

These may be on the lean side but there is camber there.

Just my two cents, and I am a sail-maker as well.

Good first effort at configuring the sail for workbench analysis and photographing it for analysis. Both sails need to have the clews lifted a bit more, the reason is that the sail is becoming tangent to the flat surface several inches behind the luff. This causes the flat entry shape. By lifting the clew more, the material behind the luff will eventually lift off the table, and the curved leading shape of the sail will be revealed. Then one can draw a chord from luff to leech, measure the maximum depth to determine camber, measure from the luff along the chord to the point of maximum camber to tell where that is, and also measure the angle between the chord and the curve of the sail at the luff to figure the entry angle built into the sail.

Camber at each stripe should be calculated, and then the clew moved about a bit to put either more or less twist into the sail. Photos of the twisted configuration should be similarly analyzed. As the twist increases, the camber in the upper parts of the sail will decrease. A baseline of cambers should be taken with the sail configured for absoutely no twist at all, with the leech as flat as it can reasonabley made to stand.

Remember, the shape seen here is not the flying shape, that can be more closely simulated by holding the boat aloft and photographing the mounted, wind filled sail from the base of the mast. Here only the effect of the twist in the apparent wind will be missing from the photos.

To get the true flying shape, a small camera needs to be deck mounted, and the boat actually sailed.

Not many skippers or sailmakers make the above described measurements, and those who do, generally develop an appreciation for their sails, and what to do to make them perform better.

Rod Carr

Thanks for the comments Rod… I will have another go.

@RG-sailor this sail does lie perfectly flat … I can’t see any deformation at all. My mate has fitted his set to his Kite, and I will take mine along to our club on Sunday and get some input from our members…

I unfortuneately have only made single panel sails this far (for my Beili Hurricane 1000)

Life would probably be easier if you had a shaped sail to compare it to. My single panel sails develop a pretty good camber so I am thinking that the broad seams in a custom sail this size would have to be ever so slight and may not be very descernable without some form of pressure. On this assumption I am inclined to agree with Rod Carr that the only true test is how the sail flies when properly rigged. On the other hand …if you have doubts about the Sail-maker’s integrity for other reasons …!