It's nice to see that you're looking to learn more about sails, & what makes them viable vs. non. As well as some of the why behind these things.
The answers to the questions which you're asking, however, aren't easy ones to answer via text. Your best bet is to find a kind, well experienced member
(of said unfairly maligned group, racers) and have them look at perspective sails with you. That, someone who's done a LOT of sailing, and or is/has been a sailmaker
The obvious defects don't need mentioning. But as to judging condition & how much life a sail has left in it requires experience gained by time trimming & looking at many different sails, for a good number of hours (likely numbering in the hundreds, or thousands).
As to performance, some of it can be easily assessed shoreside, by an experienced eye. But other aspects can be a good bit tougher to determine without taking the sail out on the water
Albeit, to some degree, things like draft
position & whether or not a sail's blown out can be judged by hoisting a sail & sheeting it in while tied to the dock
. But even this isn't fool proof, as with sails designed for moderate to heavy air, some kinds of defects in them, or how truly stretched out they are wont show up until they're hoisted & tested when the breeze is up. Which, generally speaking, you can't do while in your slip, or tied to an end tie.
Also, judging much of what you're asking is infinitely more complex now than it was 10 or 20 years ago, because there are a HUGE number of types of laminates & sail cloths out there now compared to then (plus more new ones every week). And you might wind
up running across some of them which are perfectly viable (sails), but that are made of a kind of sail cloth/laminate was only made for say 3 years, 15 years ago.
If you can, it'd be best to work with places which sell 2nd hand sails which allow you to return them after you do a detailed inspection
of the sail if you don't like them. And also if/when you find a sail/sails which are good candidates to your eye, then have your sailmaker
do a detailed inspection
of them for you. Preferably with you there at the time, so that he/she can point out the good & bad points of each sail.
Also, any sailmaker worth the title will also be able to tell you if sail X, while being "too big" for your boat, would make a great candidate for you if it's cut down in size. That, and some can even tell you if sail Y, while being a bit baggy/blown out, might make a good candidate for a nip & tuck (facelift). As despite it's being baggy, if a few of the seams are opened up, & resewn differently (like taking in trousers at the waist), the sail would serve you well, & be worth the cost of it's purchase
, in addition to it's modification.
Also, don't dismiss the performance aspect so casually. As say, take a pre-loved main for example. It's cloth, stitching, & hardware
may be in good shape, however, it may be one of those which is blown out & the draft
has migrated a bit further aft than your rig's controls can correct for. And if this is the case, flying such a sail can cause:
- excessive heeling, like by an additional 5-10 degrees, unnecessarily
- said heeling & other lost
performance factors could easily cost you a knot
or more of speed.
- excessive weather helm
, including enough to cause your rudder
to cavitate, lose it's bite on the water
& have you involuntarily rounding up or even inadvertently tacking.
- needing to reef early to avoid the any or all of the above, & this subsequent loss in power can make you much more prone to pitching/hobby horsing. Or even cause issues beating off of a lee shore.
And there's more, but I gather you get what I'm saying. I'm not trying to be rude, it's just that there are a LOT of sailors out there who have ZERO idea with regards to what I stated above. And purposefully desire to stay in the dark about such things.
If you have specific questions, feel free to run them by me, & I'll do my best to answer them. And good luck on finding what your looking for too.