No rpm gain

[Larry cessna]

Ok so i wanted to gain around 400 rpms as the boat should hit 3600 but i was only getting 3100 WOT. I took the prop to a prop guy and he reduced the pitch 2 inches. From a 19x17 to 19x15. I took the boat out for the first run and still 3180. The speed is good at 21knots. Any thoughts.

[loganmj]

I went thru this on my boat last season. My engines were hitting 2650 and should hit 3000+ rpm. I had 2" of pitch taken out and "half a cup" which I am not sure how that is quantified but it made the blades a little flatter and I hit 3000 now, but before I got props repitched I made sure engines were in good health (valves adjusted, new injectors, turbos rebuilt, full sea water side service), and bottom and running gear clean. FWIW, I didn't get any significant improvement in RPM after all the work was done to the engines..

Can you hit your target RPM in neutral?

What engine do you have?

Do you see any black smoke when running steady under way?

It could be something as simple as throttle cable adjustment, worn out turbo, dirty bottom, or possibly some other engine issue.

[loganmj]

Other thing to check if you haven't is to verify your Tachometer reading is correct. My tachs are off by ~100 rpm at cruise, and more at WOT.