New Prop/Problems

[shallowangler]

I have a 16' flats boat with a 70hp Evinrude. I've gone through several props trying to get just the right combo.
-I had a 13 1/4 x 17. Got me out of the hole but top end was around 32mph and it suck the gas down.
-Next I tried a 13 1/4 x 19. Top end went up to 36 @ 5500 rpms. 36 is a nice cruising speed but I had way to many rpms to do it. Having to run wide open to get on a good plane.
-My 3rd try is a 12 3/4 x 21. Come out of the hole fine. Plane out good. My top end is 41mph at 5100 rpms.

I wish I could get the rpms up a little more but I can cruise at 36mph @4500 rpms which is good enough for me. It seems to get better gas mileage and motor hums good.

Now my problem. When I do wind it out to 5100 rpms and even a little less, get the motor trimed and moving pretty good the prop is sucking air in if I hit the slightest wake. This has not ever been a problem with the other two props other than taking a curve to sharp or something. I do have a hydrofoil on the cativation plate. W/ the other 2 props it is usually riding right at the top of the water. With this 12 3/4 it looks like it is 1 inch or so above the water at full speed.

Anybody have a fix for this? Should I try lowering the motor a little? Is that prop to small?
With motor trimmed all the way down the hydrofoil is about 1" or so above the bottom of the boat.

Thanks in advance for the help!
Rob