What constitutes a "planing hull"?

[paulfromyork]

It is my understanding, wrong though it may be, that a boat is planing when it rides on top of the water rather than through it, much like a water ski at speed. And I’ve been reading up on speeders and hydroplanes, but I’m still confused. What makes a hull a planing hull as compared to anything else? Even a flat rock will plane on the water if you throw it correctly. ??

[westwind]

A canoe shaped hull is a displacement hull. No large flat area at the transom so it won’t plane in any reasonable way.

[garry-in-michigan]

All boats are displacement boats at rest. What makes a boat plane is speed and the shape of the hull. basically a planing hull has a square stern. A displacement boat narrows at the stern so less energy is needed to move the boat at slow speed. The length of the hull is a major factor in higher speed efficiency. So a planing hulll travels on top of the water, while a displacement hull travels through the water. So what about our latest fast attack boats which have two torpedo like power pods under water while the main platform rides above the waves ? How would you classify hydrofoils ?

[rudderless]

Think olive pit…use your lips to eject an olive pit without blowing..your lips will spread apart as you push the pit forward with your tongue and then your lips will push the pit out past half way. A displacement hull will spread the water apart and then the water will come to home, pushing the boat forward.

A planing hull is designed to travel faster than the water will come home. That hull works best as far out of the water as possible. So more planing area all the way to the back is best.

I did try a Hurricane 10 on the families 18′ canoe once. Thought if I went fast enough it would plane out. With my 200lb friend in the front all it did is lift him high out of the water and I was damm near under water. The water fulcrum was too far forward.

There is a hull..like a stepped hull that can do both?? Not sure but I think so..

Sorry for the pit anology …some might read something else into it…

[Pete]

Any water hull either machine or natural powered that receives some hydrodynamic(HD) and maybe some aerodynamic (AD) lift that reduces it’s displacement from it’s at rest buoyancy displacement of water the weight of which equals the hulls gross weight. The degree of planning is related to the amount of hydrodynamic and aero lift. A true displacement hull is one that pushes thru it’s weight in water for each water line length traveled. A true planning hull is lifted on to the water surface due to the HD and AD lift but there is still some portion of the rear planning area that is displacement, the volume of which is dependent on hull design and gross weight.

There are some high performance sail boats that are planning hulls at speed. America cup sailboats are semi displacement planning hulls and the world speed record for the Vistas hydrofoil sailboat at 75.2 mph is a wind powered design.

https://en.wikipedia.org/wiki/Speed_sailing_record

Displacement hulls can have a blunt rear transom although not the best design for such a hull due to water separation at rear with extra drag at speed.

A hydro foil hull is lifted clear of the water so it might be classified a non planning non displacement hull except for the hydrofoils that are displacement hull pieces that provide water that lift by hydrodynamic forces. So maybe it is a semi displacement non planning hull.

[paulfromyork]

WOW! This is complicated, but I think I get it. I know about displacement. Archamedies, I think it was? He figured it out taking a bath. I think he was trying to measure volume so he could accurately figure density. (Is it really gold or not?) And that come home thing is why it looks for all the world like water is coming over the stern when you’re on plane, and suddenly chop the throttle. Thank’s guys! "Ask A Member" has never disappointed me.

[Author]

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