Universal Diesel 5432 - Cruising RPMs?

The manual to the 5432 indicates max RPS of 2,800. We typically keep her at 2,100 RPM when cruising. I had a diesel mechanic say I needed to increase that for cruising, not just the occational carbon burn. Wondered what other E38s with same engine cruise at.

Hi,
Do you know why your mechanic said you should increase the RPMs--is it fuel efficiency, too much carbon build-up at lower RPMs or some other reason? I had one mechanic suggest that my 5416 Universal 16 hp engine should be run "hard and fast as if you just stole the boat" (which I didn't believe and didn't hire him again), another told me to operate it in a "sensible way and don't overdo it" (hard to know exactly what that means). The Universal engine manual states that the maximum RPMs for my engine is 2800, and it should normally be cruised at about 80% of that, so I cruise at about 2200. The engine sounds ok at that speed, and I don't seem to gain much additional boat speed if I increase the RPMs.
I'll be interested in what others think.
Frank

With a 3-blade fixed prop I also cruise at about 2100-2200, aiming at 6 knots or so. 2500 rpms yields 7 knots--but the stern squats. I can just about get to 2800 rpms, or close.

I cruised for more than 100 hours last summer in calm seas at 1700 rpm, or 5 knots (it's quieter in the cabin). Fuel burn was .49 gallons/hour (accurate: the 54 gallon tank took 51 gallons, and I knew the engine hours).

another data point

Frank has what I call a common sense take on the question. A mechanic that I have known for two decades always tells customers to first read their owner's manual for this information. i.e. there are no secrets to uncover.
My Universal manual recommended 2200 to 2600 rpm for steady running. We have the boat dialed in (prop size and pitch) for maximum cruising speed in smooth water for 2600 rpm. That's 7.0 kts with a clean bottom for us, and for the last several years that was achieved with a three blade "sailor profile" prop.

Different hulls will have different results.

When I push the throttle to the stop and it hovers around 2900 or a bit more, I get visible smoke in the exhaust and another two tenths of a knot. Strictly by the old manual information, we should be able to get to about 3000 rpm, but after all these years it seems like we are close enough to the goal.

Soon, we will start over in the fine tuning of the auxiliary propulsion system with a new Betamarine, but since the transmission ratio is almost the same it (hopefully) will not be too different in speed potential.
And there should be some blog entries once we are further along with the changes....

We usually set ours at 2000 to 2100 rpm and get 5.7 to 6 knots with a three blade feathering Max Prop. We sometimes use 2200, but it is louder and not much gain in speed.

With a three blade Max Prop pitched at 9.8" were we able to achieve a top RPM of about 2850. In delivery mode we typically used about 2400 RPM on our overnight passages, getting about 6.8 kts, though it was loud and fuel consumption was a bit high. More typically we went at ~2000 rpm to get 6 kts. Depending on how tightly you have that U clamp on the throttle it can be pretty hard to dial in exact differences between say 2200 and 2400.

Before you sweat the differences though, it would be good to ensure that you have the right prop by checking what your max rpm under load is. If anyone changed your prop it sure might be off, in which case these numbers won't mean a thing.