OK - this is something I spent a long time wondering about. I don't think your gonna like my answer much though.
Feel free to pick it apart, but I HAVE NEVER DONE THIS SO IT'S PURELY THEORY...
On the 23 IB the prop pocket starts going to lower and lower static pressure as the hull goes faster and it is pumping water up to fill the pocket; lots of water - you very quickly get to a point where massive increases in HP produce only minimal increases in speed. Kinda like having a giant water scoop on the bottom of the hull. I think the only way around that is to relieve the 'vacuum' in the fwd portion of the pocket - either by moving more water (takes HP) or introducing air so that you are not 'scooping' water. You would want it to be effectively more like a Jersey Speed Skiff. I suspect an air vent would allow the pocket to ventilate and would stop/minimize the scooping of water but then you have big time cavitation issues with the prop (and maybe erosion on the strut/rudder if fast enough) - I think you would then need a surfacing prop at a minimum. And a whole lot of experimenting. And long discussions with Ken at Prop Gods. Did I mention $$$$ for time? It would be a really cool research project though.
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