LouC wrote:
I would not worry about trying to achieve the minimum RPM to keep it on plane, actually your main concern, and this is very important, is that the engine reaches its specified maximum rpms at wide open throttle. If it does not then the engine will be laboring much of the time even though you do not realize it. That will increase combustion chamber temperatures and can result in burned exhaust valves and the need for early engine repairs. So to repeat, as far as prop choice, the first thing you decide is do you want aluminum or SS, then, make sure your rpms are what the engine manufacturer says they should be.
Years ago when I got my present boat it had the wrong prop on it, and it would only turn up 4200 RPMs at wide open throttle. The spec from OMC was 4600-4800. I went from a 14.4x19 to a 15x17 and it was right on the money at 4700. It doesn't sound like a lot but it is and for long engine life you need to get that right.
Keep in mind that you have a small engine pushing a close to 3000 lb boat against a wall of water and if it under-revs its going to strain.
What were your wide open RPMs with the prop you had?
Thanks LouC
It makes perfect sense to want the engine turning the right rpms to achieve the right power.
The 14.5" 19p 3 blade prop is the right spec for my boat so I'll stay with the same but get a SS prop.
With my current aluminum prop the boat was turning about the right rpms, although I didn't push it over 4000.
When I had 4000 I still had a bit left on the throttle.