by GreenLake » Wed Jun 13, 2018 8:38 pm
Welcome to the forum. Good luck with getting your grandparents' DS going again. You'll have fun.
All models of the DaySailer are compatible in the sail they use - except insofar as some people have had accidents to their masts and "fixed" the mast by trimming off a bit. In that case the luff of the mainsail would be shorter. A full size main would be 20.5' by 10' (with the sail stretched to its fullest) but those sizes are the absolute maximum (or, put a different way, they correspond to the maximum length of the usable sail slot in boom and mast). So, despite coming out a bit smaller the way you measured it, it looks like you have a standard size sail.
You have various options in terms of sailmakers that will provide a new set of sails for you.
Basically, you have inexpensive sails made overseas, you have intermediately priced domestic sails and then fully high-end racing sails. And then, you may be able to buy used sails in various conditions and ranges of quality. (I'm personally happy to spend enough to get domestically made sails of (very) good quality, but not willing to spend a premium for real "racing sails"; if money is tight, your choice is used sails, if you can source them, or the inexpensive offshore sails).
You may read some of the older posts here to get an idea which sailmakers other users have had experience with. These sailmakers typically know the standard size for a DS sail.
Now, I mentioned "set of sails" because if your main is as old as you mention, your jib will definitely want to be replaced as well. Old sails, even if not visibly damaged, do not hold their shape any longer and are harder to trim (if they can be trimmed satisfactorily at all) and make sailing less enjoyable.
Sails are a "consumable" with a definite lifespan. Comparable to brake linings in a car. Or tires. Except that it's not as easy as tread depth to measure their end of life. A sail that flutters, even if trimmed has definitely reached the end, or, really, is way past it.
Sometimes, the "for sale" section of the forum will list used sails; or you could put a "want to buy" ad, if you are after a used sail.
Let us know if you have more questions.
~ green ~ lake ~ ~