^^Metal slides.. Yuk, I still have bad memories of trying to haul down Blizzards main to put in a reef, with freezing hands half way between NZ and South America
. Those damned metal slides jamming and fighting every inch of the way even with the sail luffing. Though I have seen some HDPE coated ones that might just work for a while until the coating wears off. Do they allow the metal stem/plastic slide type, some of these look very strong.
A friend blames his knockdown/capsize (and dismasting) partly on a poorly set trysail that he couldn't get good luff tension on due to sticky slides. He ended up reaching rather than forereaching/dodging.
Size is tricky, too small, and it could be very hard to set, as by the time it's right for the boat it's blowing great guns
. To big and it's useless in a blow. To really get an idea you need to sail with a third reef in a decent blow and get a feel for the boat. Some boats will forereach quite well with just a headsail, making one almost redundant, in this case a small one would be fine, as it is a supplement rather than a necessity. Others really need a trysail of a decent size to hold the head
up, and are stiff enough to carry them in a good blow.
Like evans I think the offshore racing
guidelines are a good starting point, though they make no allowance for mast
height, ie a racing boat often has a huge mast
height for it's length and displacement
I'm pretty happy with a third or fourth reefed main for most stuff. This is as long as the main is strong, well made and looked after. A spare main below is a good backup. But trysails certainly can be useful, Ie for reducing wear on an expensive main, or to enable an old worn out main to have the last of it's life carefully extracted, by switching to the trysail when it starts to blow.
Still not sure the easiest way to deal with lazy jacks, boom bags and weird shaped masts (making separate tracks angle to one side) on a bigger boat, maybe just dropping the lazyjacks forward is the best bet.
On a lot of larger lightly crewed boats a trysail starts to get pretty unmanagable. I can't even remember if the 60 foot yacht I ran to Antarctica had a trysail? certainly there was never any question of using it unless the main was shredded.