A sailboat can sail faster than the wind

In order for a sailboat to move, it has to feel wind on its sails coming from at least 45 degrees off the bow (a little less on some boats) to provide power. When the boat moves, the boat's speed makes it feel like the wind is coming from more in front of the boat than it really is (like sticking your hand out a car window - there seems to be lots of wind from the front because your hand is moving through the air). Using vector addition, the boat speed is subtracted from the true wind to generate the apparent wind which the boat feels. In this example, with a true wind of only 17 knots off the stern quarter, a boat moving through the water at 23 knots actually feels an apparent wind of 12 knots at a 45 degree angle off the bow, enough to move a fast hull (a cat or trimaran, a planing dinghy, sailboard or kiteboard) at that speed.

diagram of wind triangle

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