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# Why are Trimarans So Fast?

## There are a few things that are important for boat speed. You need to convert the force of the wind into movement. So you need large sails. You need stability sideways, this is covered by a heavy keel on a keelboat, and with a wide sailboat if it’s a trimaran (or catamaran). You need a streamlined hull to reduce the friction that is generated through the water. You should also have lightest possible boat, extra weight only slows you down.

A keelboat needs a huge weight at the bottom to get a good stability. This extra weight makes the hull wide to get good buoyancy. The wider hull increases the friction thought the water. You could in general say that to calculate the max speed of a keelboat you take the root of the waterline in feet and than multiply it with 1.34 and you will get the maximum boat speed in knots. (speed = 1.34*root(lengt_in_feet)).

A 40 feet boat will get a hull speed of 8.47 knots. You need an extremely high thrust to exceed the hull speed.

There is three ways to exceed the hull speed. Either you have an enormous thrust, but that’s not a viable option. Or you build a craft that is planning. If a boat is planning the hull resistance will decrease drastically, and you can reach great boat speeds. The third option is to build a hull that is at least 10 times longer than it’s wide. Then the hull speed formula is not viable any longer and you could increase you boat speed above the hull speed formula.

This is what trimaran and catamaran is using. They have very long/narrow hulls and thus gets very low resistance through the water, even if they have multiple hulls.

So the reasons a trimaran sail so fast is due, great stability without all the extra weight of a keel. And the hulls could be very narrow since they have multiple hulls and no excess weight.

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