Surfboard flex and pressure distribution in planing hulls

Pressure distribution under the hull is a very important topic when discussing surfboard flex.

The simple entry level scenario for planing hulls is shown below. It's  implications include those related to  full hull flex vs tail tip only flex.

In the water pressure distribution is obviously different from the typical land test scenario whereby the board is supported at two points, with all the upwards 'beneath the hull' pressures located around those points, with none in between.

The diagram below applies to a steady state planing situation, pumping the surfboard and turning it will alter the pressure distribution and position of the stagnation line.

Those who advocate tail tip flex (as opposed to flexing the entire hull ) should not that there is very little pressure at the tail of the board ( at least for a typical surfboard, I'l explain exceptions to this rule later ) thus there is little force available for tail deflection.

If on the other hand the entire board flexes then much more of the water pressure can be used to flex the board, thus increasing efficiency dramatically.

Rider stance and board length complicate the issue somewhat, particularly with shortboards, but the basic analysis is correct, and is a good place to start.  


http://www.bluejacketboats.com/planing_boat_theory1.htm