I just sold a suit of new sails to a customer. I just spent the whole morning measuring his sails yesterday. If you supply the proper measurements to any sailmaker, they can use that to make a sail that will fit. You want used, which is fine, so you should make some measurements yourself. You can go out and find the P, E, J, I measurements, which are the basic figures for sailmakers, but boat manufactures sometimes have different rigs, or boat owners bastardized their boats so these measurements might not be accurate. To be more totally accurate, it is best to measure the distance of your forestay, mast, boom, etc. so you know for sure. You can measure old sails, buy you should stretch them out first (tightly). You need to know the type of sail slugs or bolt rope or luff tape, etc. that go into mast/boom slots (or are they external?), the luff tape slot if you have roller furling, etc. When you buy a used sail, you buy a used sail. They might be newer than what you have, but they are still used. If you can find one that was for the same boat, that would be best, because one would think that the tack set backs and rises are similar, etc. track positions are the same, etc. so that it will give you a better fit. You might think your boat is 36 years old, but it still is a boat that works and if you build a sail to exact measurement specifications of your boat, then you will get the best product and your boat will sail better despite its age. But, I understand new is expensive and used is not so. So, measure up your boat so you know what YOU have and not some measurements that may have changed with different models, etc. to get the best fit.
