Re: What constitutes a "planing hull"?

[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.