Kevin, I not an expert just parroting what other more knowledgeable folks have said. Also, I don’t know the specs for your engine. I will use my Yanmar 4BY2-150 as an example.
Max WOT RPM is suppose to be 4,000. I get 3,960 RPM. I’ve seen 14-15 knots at WOT. Getting close to mfg recommended max RPM tells you your prop is properly pitched. I think my prop is right on.
It is not good for my engine to run more than 80% WOT RPM for more than a short period of time.
Max continuous recommended RPM for my engine is 3,200. Fuel consumption at that RPM sucks. I run it just to clear out the turbo every couple of engine hours or to dodge a BC Ferry. I get about 10-11 knots at that RPM but I am really loaded down for cruising most times.
My sweet spots are 2,800 RPM at about 8-9 knots and 3 GPH or 2,500 RPM at 2.4 GPH and a speed of about 7 knots.
Again I have a heavy boat with trim tabs, drop fins and a very clean bottom. Your numbers may vary.
It’s important to know your factory stated max WOT RPM and if 80% of that is your continuous RPM number.
