Join Date: Feb 2010
Location: Narragansett Bay
Thanked 593 Times in 569 Posts
Rep Power: 12
Re: Motoring RPM
Second the motion to buy an inexpensive laser tach. I got mine on Amazon for under $30. Tachs are often wrong. 50-100 rpm difference may be expected. More is a bad tach or wiring.
Hull speed has nothing to do with a proper engine/prop operations. Think about it this way. If you put a lawn mower engine in your boat, it could be operating perfectly well, but never reach hull speed. Put one from a battleship in there and it could be coughing and sputtering and get you to hull speed.
You should be able to make max RPM, under load, at wide open throttle. If not, the problem is most often the prop or drive train. The next, of course, is the motor.
If WOT is really only getting you to 60% of rated RPM, the engine is grossly lugging, even if you're getting the speed you like. Just like going up hill in too high a bicycle gear. You might be moving along, but you're killing your legs. It does not do instant damage, but it does take a toll over the long term.
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In the harsh marine environment, something is always in need of repair. Margaritas fix everything.