High Prop slippage help

[prokat22]

Boat is a 22' Prokat Catamaran, Yamaha F115's counter rotating, 2.15 gear ratio. I have calculated at 4500 RPM, I am getting 25 MPH, which equates to 27% slip. I have stainless props that are 17" pitch, I do not know the diameter, I would guess 13.25". At top end 5800 rpm I am getting 38 MPH, which shows @ 12% slip. I have always believed my engines are too high because I cannot trim out very far without the props airring out. Any help would be appreciated. Would 4 blades be the way to go for me? More interested in the 4000-4500 cruising range than top end.

 

[steelespike]

Re: High Prop slippage help

Its normal for slip to go up as prop speed goes down
Generally a 4 blade will improve low to mid range performance also
may improve handling at the dock. usually the best cruising speed is somewhere from just on plane to about 1000 rpm higher.
Not necessarily the slowest planning speed. Of course you would need a flow meter to tell the difference.