1. Running: This method catches wind from behind the boat. In the old days this is the only way square rigged ships could sail. Reaching America from England, for example, required a smart navigator to follow the trade winds to get a "push" from east winds.
2. Tacking: Modern sailboat & yacht designs leverage Bernoulli's principle. Using this method, sailboats for thr first time could adjust their course and sail upwind, but not directly upwind. As air rushes over the forward curved edge of a sail, which is a longer distance than the shorter path on the aft side, lift is generated. The lift translates into a suction that pulls the boat! How cool is that? The same principle applies to aircraft airfoils/wings. Air rushing over the top curved section of the wing generates reduced pressure/suction and causes lift.
Below is a chart that shows the various angles a modern sailboat can sail. Note the 45 degree cone in the front. This is referred to as the "no sail zone". If you sail in this direction you are "in irons" or shackled in a sense, from achieving lift. To propel forward you need to "tack" or steer at the edges of this cone to achieve Bernoulli's lift. The benefit of which sucks you forward. It's a COOL feeling to tack upwind. Racing boats have a large inventory of sails (20+ sails) to maximize this ability to tack upwind.
3. Engine power: No brainer here. Obviously a sailboat can move forward if it has an engine. When entering/exiting a crowded harbor, for example, it is quite risky to sail. To ensure precise control of the boat, all sails remain lowered while in or near a crowded harbor and the boat direction controlled by engine thrust & steering alone.
Signing out,
Joe
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