We have a Yanmar 4JH3-HTE, four-cylinder, turbocharged and intercooled, 2000cc, 100 hp engine.
Redline is 3800 (!) and continuous is 3600. 3000rpm is the fastest I will run it for any length of time; it does not sound or feel comfortable above that. The boat will reach hull speed
at about 2800 in reasonably calm water
so there's hardly any reason to do so anyway.
My usual cruising RPM is 2400rpm so long as I'm not fighting a tide or in a hurry; otherwise 2500 up to maybe 2700.
goes up apparently geometrically with RPM, so that's another incentive to keep the revs down. It must be said that we have a Bruton self-feathering prop which milks every last drop of power out of the engine at reduced rpms, making it more efficient. But the difference in fuel consumption is amazing; I guess 4 liters/hour at 2500 and 10 liters/hour at 3000; something like that.
I don't know if it's good for the engine to run it at 2400 but it sounds and feels right. The recommended speed of 2900 from here Yanmar Marine Engine Help
is just not right, at least not for our boat and prop.