still high rpms

[MaxOD]

I took a 21 pitch prop for a run this weekend and my rpm's are still too high for my liking. I have a 17.5 foot bowrider with the 3.0 volvo penta. It came with a 15X17 and I went to a 14.25X21. The strange thing is it seems to plane faster. When I hit it off the line the rpm goes to 4000 and holds till plane then ramps up to 5500 when I started to pull it back. At 5500 I was close to 40mph. I can cruise at 34mph at about 4200rpm, still a bit high for my liking. The boat also porpoises quite a bit even when trimmed low. I want to try a 23 pitch but the guy at the boat store thinks I am nuts, and he doesn't have one in stock. Do these #'s seem right for what I'm running and should I just live with the 21 pitch?

 

[steelespike]

Re: still high rpms

I wonder if the tach is accurate I think the boat would be at about 40+ mph
with the right prop.I think the 3.0 Volvo does run a little higher rpm than a mercruiser in a similar displacement.What is your max recommended rpm?
Usually you don't consider diameter when checking props. if its for the application diameter follows.The smaller diameter might be easier to spin but again usually not a consideration.You could certainly go with the 21 and just watch the rpm.