As far as I understood (see this article) sails work in 2 ways:
- Running directly before the wind the sail essentially just pushes you forward. Your max speed here is essentially the wind speed.
- Running into/across (don't expect me to know the English nomenclature please :P) the wind the sails provide lift a little like an airplane wing does. Which, on modern ships, provides a lot more speed than running with the wind (can be up to several times faster or more).
It's also my understanding that the way square-rigged sails are set up they won't achieve the usual 'wing-shape' cross section that, say, a fore-and-aft rig will achieve.
Do a square-riggers sails also provide "airplane wing-style" propulsion, or do they only work in what the above article describes as the 'kite' type of providing push.
I'm asking because one of the linked questions at the beginning actually cites a Hornblower novel - in which I would expect the ship in question to be a square-rigger - wetting it's sails. And while the wetting of the sails also seems to have other effects (swelling of fibers making sails less permeable) it would seem that the 'aicraft-wing-style' (please let me know if there is a better term for this :P) propulsion would be a lot more important, seeing that it allows you to achieve higher speeds generally.