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These questions (one, two) about sail wetting/trimming raised another question for me. Disclaimer: I'm at best a novice sailor, and I've never sailed on a square rigger.

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.

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TLDR: Yes, square riggers can use the airfoil type propulsion, though not as effectively as a fore-and-aft rigged ship.

In slightly more detail, there are two reasons why this is the case.

Despite the name, a square-rigger can in fact turn its spars.

Spars are the things the sail hangs from, and they can be turned substantially from running straight across the vessel ('square' to the ship), enabling them to catch the wind from the side (a 'beam reach') or even slightly ahead (a 'close reach').

A square-rigged ship usually has some fore-and-aft rigged sails.

The mightiest windjammer usually has several headsails or jibs that will catch the wind at a greater angle than the square rigged sails, and smaller vessels often have sails rigged fore-and-aft between the masts, called staysails.

If it could not sail into the wind at all, a square rigger would be of only limited use. However square-riggers are very much more efficient sailing downwind. A rule of thumb is that a square rigger can sail about 6 points (70 degrees) from the wind. which means they have to sail nearly three miles in total distance to cover a single mile upwind. A fore-and-aft rigged boat can usually manage 45 degrees, meaning that it need sail only about 1.5 miles total distance to gain a mile upwind. That is why the great sailing ships always followed routes where the wind blew in the direction they wanted to go, even if it meant sailing further. I've heard it said that Australian ships would actually sail the wrong way round the world (or at least the wrong way round Antarctica) rather than try to sail upwind from one part of Australia to another.

The difficulty sailing to windward means that square riggers would do very complicated manouvers, essentially turning the 'wrong way' ( gybing, or 'wearing' as it was called) rather than trying to turn through the wind.

Here are some interesting video of square-riggers changing direction, including demonstrating some of the above facts.

https://www.youtube.com/watch?v=BxCKGS_bLKI

https://www.youtube.com/watch?v=v6DZIvMZWzQ

https://www.youtube.com/watch?v=B3jU9Xz_GHE

  • Good answer, thank you. Also appreciate explaining/translating sailing vocabular, the little I know of reading Hornblower novels as a kid is all in German. :) – fgysin Feb 26 '18 at 10:11
  • Hi DJClayworth! This is an awesome answer! For some reason, when I click on your first link, to the .pdf document file, I'm getting a 403 message that it's forbidden for me to access it. I don't know if it's a dead link or my browser, which is Firefox. I'd appreciate you checking it out, if you want, just in case there are other people trying to read it who can't. Thanks! – Sue Nov 1 '18 at 3:23
  • @Sue Fixed the link – DJClayworth Nov 1 '18 at 13:16
  • That looks great, and very interesting! Thanks! – Sue Nov 1 '18 at 23:56

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