Great topic gentleman , looks like we are all thinking along the same lines.
A kiteboard has a static rocker curve which we see when the board sits on a table, in the water with the weight of the rider pushing down and the force of the water pushing up the kiteboard has a dynamic shape , the trick to good kiteboard design is that dynamic curve is an efficient quick shape offering great grip and minimal resistance.
D1 - a simple beam with forces along its entire length and the riders feet pushing down from the top.
D2 - a tapered beam with forces along its entire length and once again forces pushing down from the riders feet.
D3 - a tapered beam with the water pushing up from its first contact point and to the rear of the kiteboard, riders feet pushing down.
D4 - Simulated kiteboard moving to the left with water pushing up from contact point and constant to the rear of the board , riders weight pushing downwards through the footstrap positions.
The trick is to design the taper in the kiteboard to bend with a constant curve , this will give the board the most efficient pass through the water. A non constant bend will cause drag and can effect the very important water flow over the fins.