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What is the phenomena where the drag of an object in water will reduce when reaching a certain speed?

Saw video a few years ago, kid school project, a high speed boat holding a wing under water, drag pushing it back and then pop to front at speed

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When a motor is pushing a boat hull through the water, lots of fluid drag is generated, and the boat cannot travel very fast. But if the hull can be lifted up out of the water, the drag goes down very significantly and the boat speeds up.

You can do this lifting work with either a specially-shaped boat hull called a planing hull which lifts itself out of the water and skims along the surface when pushed forward, or with a hydrofoil which is a small wing immersed in the water which generates lift just like a airplane wing and holds the entire hull up and out of the water as it travels forward.

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  • $\begingroup$ The underwater wing that you are describing is actually called a hydrofoil. (See my avatar, for example.) A hydroplane is just a type of planing hull. $\endgroup$ – D. Halsey Dec 2 '20 at 19:19
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    $\begingroup$ @D.Halsey, you are right, will correct. -NN $\endgroup$ – niels nielsen Dec 2 '20 at 21:25
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This sounds like the solitary wave (or soliton) phenomena. Google John Scott Russell or the KdV equation for a historical discussion of the phenomenon

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