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Old sails made new?
I think that this whole "Old sails made new things" is a bit of a scam. If all that you care about is that the sail look white, feel a little stiff and be triangular then this might be a good idea, but otherwise it’s a bad joke. As a sail ages the fibers elongate, permanently stretching longer than their original length. More elongation takes place in the high stress areas of a sail, (typically the leech of the sail) than takes place in lower stressed areas of the sail. As it does, the camber of the sail moves aft resulting in a sail with poorer performance (especially to windward) and a sail that is more inclined to produce larger heeling angles. As the fibers elongate they become more stretchy so not only does the sail cloth assume a permanently poorer shape, but the sail shape dynamically changes more dramatically towards an adverse shape as the windspeed increases resulting in a sail that powers up in a gust with its camber moving aft which is exactly the opposite of what is desirable.
A very good sailmaker can sail on a boat, take pictures and then recut the sail, which is a process in which a number of the seams are opened up in the leech of the sail and then carefully re-broad seamed and then stitched back together again. Done well, this restores the static shape but does nothing for the greater tendency of an older sail to stretch under sail.
Depending on the specific cloth, new sailcloth has a filler between the fibers. This filler is pressed into the cloth under great heat and pressure and fills the spaces between the fibers. These fillers provide the structural function of transferring loads from one fiber to another and resisting stretch on the bias. The heat provides and initial set to the sailcloth fibers reducing the tendency for a new sail to stretch. The fillers are also what make modern Dacron sail cloths feel stiff and crinkly when new. Over time these break down. Flogging sails and crumpling the sail really accelerate that deterioration process which is why you see racers rolling their sails or carefully flaking them.
These sail rejuvenation places essentially claim to replace those fillers. The problem is that the old fillers are still mostly in place but are just not fully bonded any longer and so partially prevent any new filler from entering the sail in the manner that is necessary for the filler to act structurally. To be effective, the new filler needs to be implanted in the sail under high heat and pressure. The problem here is that heat applied to older fibers shortens their life by making them more brittle, prone to fatigue and also reduced the stiffness of the fiber, which further increases the amount of elongation for a given load. With the stitching and hardware on the sail, the rejuvenation companies also cannot achieve the level of pressure necessary to properly bond these fillers.
So what comes out of these rejuvenation shops may look and feel like a new sail, but it really isn''t improved in terms of flying shape or sailing capabilities.
Respectfully,
Jeff
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