23 Ft Chris Craft Scorpion, It's a heavy boat. But I have a friend with the same boat. Was running a built 350 in it last year and it ran out at 67 mph. running a 19 pitch stainless, Cupped And vented. But of course it would tach out to almost 6000. All I was looking for was Approx 55 mph. Engine was not dynoed, but builder is claiming conservative HP at 375 and torque numbers higher. If I can get the boat to run at 5500 max it would give me 55 mph. with the current prop pitch and slippage. When I get the stainless back from being worked I 'm sure it will help, but if the engine won't tach out to where it should obviously the boat won't perform as I was hoping. I'm not a racer, but I've got a lot of money invested in a boat that goes 5 mph faster than it did before I invested it. I tried a new 21 pitch, lost rpm's and speed.