What to exspect after the change?

[mattsanders]

Boat: 15 foot Kingfisher trihull stick steer
Weight: 900 approx
Engine: 1977 Johnson 70hp
Prop: 13 3/4 x 17 ss prop
Speed: 32.9 MPH (GPS)
RMP: 5000 +/- 150rpm

Im Thinking of go to a 15 inch prop. What will the estimated result be in my speed and RPM?? Thanks

 

[steelespike]

Re: What to exspect after the change?

Your motor hp is rated at 5,000 I think you should shoot for about 5,500.
While I'm not sure how slick your trihull is; it seems to me you should be easilly over 35 mph.Maybe we can improve your setup. The antivent(cavitation) plate just above the prop should be about even with the bottom if the boat.I usually suggest you raise the motor to a point just before venting becomes a problem.The motor in excellent tune?Throttle opening all the way?Prop in excellent condition.
Bottom of the boat clean?With luck you could gain about 2 or 3 mph. And some rpm.
Then decide on a prop change.