I don't necessarily disagree with the idea of having to run the diesel at 3600, but how necessary is it Really? If you are getting to hull speed at significantly less than 3600, the extra rpm and fuel is wasted anyway. If it is so necessary, why is there a detent in the throttle that kicks is back to about 2500 as soon as one lets go of the throttle lever?
Is the diesel really going to recognize a 400 rpm difference and is it worth a two inch pitch change to regain that difference ?
One cannot run at 3600 in no wake zones either....
You don't run a gas engine in a car all day long at max rpm, why would you do that with a puny little two cylinder diesel in a boat that goes nowhere fast anyway.
3600 would usually be the max rated RPM that you should be able to attain in flat water with a clean bottom and prop. You would then want to run the engine somewhere between 70% and 80% of wide open throttle. Yanmar even recommends as much as 10-20 minutes per hour at WOT after prolonged low load operation to keep the engine clean and running strong. These engines prefer to be loaded in this type of application and to have the prop well sized..
Because it is like driving your car up a steep hill in fifth gear all day long instead of finding the right gear for the grade. The max RPM suggestion, made by most all small marine diesel engine companies, is done with good reasoning.
If your prop is over pitched you are essentially over-loading your engine at all engine speeds throughout the RPM range. By doing this you cause your engine to lug and work harder at lower torque and HP than it was specified & designed for. When you add a high output alternator or decent alternator load this gets even worse.
Over propping leads to such things as more frequent exhaust elbow plugging's, soot and carbon and sometimes the cooling systems can have a tough time keeping up because the RW pump GPH is RPM based. Higher RPM equals more water flow. When you give your engien the same "load", at a considerably lower RPM, the RW cooling system may not be able to keep up.
Many manufacturers, including Westerbeke and Universal, will specifically void the warranty if your not within the specified RPM range when at WOT. Most want to see it within +/- 100 RPM
On our boat, with a 44HP Westerbeke, we were over pitched when Norm at West By North sent us an improperly pitched Campbell Sailor. It was off less than 300 RPM yet in the month we used it, while waiting for the correct prop, the soot on the transom was horrible, the worst we've ever experienced, and it is usually very, very light, if any. It did not matter how slow I went, even at below hull speed, the engine was working harder than it should have at that RPM/HP/torque curve, especially when you added in the alternator loads. With the new prop all the sooting is gone...