How can boats sail faster than the wind

KQED is a proud member of. Always free. Sign In. KQED Inform. Save Article Save Article. Mike Osborne. Sep 11, World Europe Powerboat. World North America Powerboat. World Oceania FishingBoating. World Australia FishingBoating.

World New Zealand FishingBoating. How to sail faster than the wind. Vestas Sailrocket 2 in Walvis Bay, Namibia. Read more. Topics Sailing Weatherwatch Meteorology Wind power features. A little digression: the sideways components of wind and water on the boat make the boat heel tilt away from the wind, as is shown in the diagram below. These two horizontal components have equal size but opposite direction: as forces they cancel, but they make a torque tending to rotate the boat clockwise.

This is cancelled by another pair of forces. The buoyancy and the weight are also equal and opposite, and they make a torque in the opposite direction. As the boat heels to starboard, the lead on the bottom of the keel, which has a substantial fraction of the weight, moves to port and exerts an anticlockwise torque. These two torques cancel.

So now back to our question:. Lots of boats can — especially the eighteen footer skiffs on Sydney Harbour. Ask a sailor how, and he'll say "These boats are so fast that they make their own wind", which is actually true. Ask a physicist, and she'll say that it's just a question of vectors and relative velocities. Downwind diagram at left is easy. If the wind is 10 kt, and the boat makes 6 kt in the same direction, then the crew feels a wind of 4 kt coming over the stern of the boat.

The true wind v w equals the speed of the boat v b plus the relative wind v r. So you can't go faster than the wind. When the wind is at an angle, we have to add the arrows representing these velocities vector addition. The faster that the boat goes, the greater the relative wind, the more force there is on the sails, so the greater the force dragging the boat forwards.

So the boat accelerates until the drag from the water balances the forward component of the force from the sails. Why are eighteen footers always sailing upwind? In a fast boat, there's no point going straight downwind: you can never go faster than the wind. So you travel at an angle.

But if your boat is fast enough, then the relative wind always seems to be coming mainly from ahead of you, as these arrows show.

So the eighteen footers never set ordinary spinnakers: they have asymmetrical sails that they can set even when they are travelling at small angles to the apparent wind.