Beating Upwind
Making your way upwind by sailing alternately one way across the wind and then the other is called beating upwind, and the process of changing from one direction to the other is called tacking. Generally the legs between tacks would be much longer in relation to the size of the vessel than in this diagram! To put that another way, the pictures of the boats in all these diagrams are very much out of proportion to the dotted lines showing the track of the boat. Exactly how long each leg is normally depends on how much sea room you’ve got.
(If you can’t understand how it’s possible to sail upwind at all, even at an angle to the wind, see Sailing Upwind.)
The most obvious way to tack is to turn upwind, as in the diagram above, but as you get closer to sailing upwind, the forward force on the boat diminishes (there is an optimum angle for best upwind progress, which is a little further off the wind than the closest possible angle to the wind) and eventually the wind starts to push against your movement. If you lose forward motion altogether, the rudder doesn’t work any longer and you can’t steer your boat at all. One way to avoid this problem is to tack downwind. It might look inefficient, but because you keep moving all the time it can be the best way to progress. Whether it is or not depends on your boat and the conditions – and possibly the skill of the crew.
Don’t make the mistake of calling the whole process tacking downwind – that’s just the process of turning round to go onto the other leg. You’re still beating upwind.
A proa beats upwind differently. A typical sailing boat is symmetrical side to side, and changes tack by presenting the other side to the wind. A proa is symmetrical end to end, keeps the same side to the wind all the time, but changes which end goes forwards.
Proas have twin hulls, a sort of catamaran, but because they’re symmetrical end to end not side to side the twin hulls don’t have to match, and one of them is the main hull and the other one is just an outrigger. They’re the Polynesians’ traditional sailing vessel. And very good they are too.
(If you want to know more about proas, there’s lots to be found on the internet, of course – look ’em up on DuckDuckGo. I like this one: Why a Proa?)