Just bought an old Westerly 26'. The mainsail came with battens. They are about 3ft long and insert in the leach. I have read where some think that they are not necessary. What do folks think?
There are two possible questions here:
The first, is theoretical, "Should I have a battenless or battened main." Larry Pardey is an advocate for a battenless main because the battens in their pockets are a source of chafe and as he sees it you get such a small benefit from the increased sail area as to not be worth it.
The second question is directly related to your situation now, "Should I insert these battens in the sail I have." The answer to that question is undoubtedly YES. The sail you have has been cut for battens. In order to have a battenless main you need to specify at its time of construction that the leech be "hollow cut" or "sweedish cut". This means that instead of the leech making a straight line (or bulging out) it curves inward.
Since your sail has battens and pockets it is NOT hollow cut and unless you re-cut it it will not fly right without the battens. What will happen? The leech, unsupported by battens, will flitter. flap, flog and flap causing decreased performance as it disturbs the air at the end of the sail. More to the point the flogging in winds above 10kts will destroy the leech of the sail in a fairly short time, thus negating the idea of a low maintenance, battenless sail.
You can always, for educational purposes, hoist it (in moderate air) with and without the battens and see for yourself what it looks like and what happens. If you really want a battenless sail, talk to your sailmaker about re-cutting your sail.
Congrads on your new boat!