All i can say is my friend did some tests with diff rudder and strut setups in a water tes tank at uni and all the evidence he and his tutor who races full size offshore boats all showed a good % of increased performance.It might be hard to see but it is there,they also turn the struts round so the prop is further back from the strut blade which creates less drag.When water hits the strut blade it takes about 1" past the strut for it to join back together so if the prop is tight to the strut its in disturbed water whereas been 1" or so back its in clean undisturbed water again.It stands to reason if any blade is flat or blunt it will cause drag,the sharper or thinner it is the less drag.Also a flat rudder at the base is classed as a planing surface thus making your deep vee mono hull now a hydroplane
.Matt my rudder blade is like a knife,(sharp) its also rounded on the bottom edge and at the leading bottom corner (curved)this was done by my friend Ian Webster who i bought it off its also thinned considerably compaired to a stock rudder,i can only asume he did this for a good reason as he spends a lot of time arround guys who race competativeley.