Good points Paul,

Here some additional comments :

Scientifically speaking a boat is suspended at the water surface by nothing more then a pressure difference between the keel and the decks. It doesn't matter what causes this pressure difference to be present, by displacement (hydro-static pressure difference) or by planing (hydro-dynamic pressure difference). This first force is the result of the water pressure increasing when you dive deeper below the water surface and thus the ambient air pressure as present there. Planing is the result of a pressure build up under the keel line as a result of the onrushing water being slowed down or bend away from its initial direction. Example; as the hull moves through the water to particals are hitting the planing surface and are pushed out of the way to the side or downward. This creates a (dynamic) pressure zone under the keel line that is added the pressures created by displacement. This excess of pressure results in the hull being lifted higher out of the water till this system finds a new stable balance between the forces. But as this example makes clear, there is absolutely a significant amount of water displacement present, if only by the water that is being squirted out to the sides as (white foamed) water. So planing is not a concept that reduces wave-making drag, because it really isn't. We all know that wave system created by planing are very significant. The idea behind planing is to reduce the wetted surface area and its related wetted surface drag. In Gareth plots you can see this potential in the plots. his Michlet plots show that for higher speeds the amount of wetted surface area is much more important in determining hull drag then wave-making drag is.


Wouter