live aboard boat

What engines, specifically?

Our Cummins (450C) ratings are quite clear in all their documentation:

High Output
This power rating is intended for use in variable load applications where full
power is limited to one hour out of every eight hours of operation. This rating is
for pleasure/non-revenue generating applications that operate less than 300
hours per year.​

Nothing there about a 10-30% load factor. Clear restriction on using full power (WOT).

-Chris

https://cumminsengines.com/ratings-and-definitions

"High Output (HO)
This power rating is intended for infrequent use in variable load applications with a load factor of 10-30 percent. Full power is limited to one out of every eight hours of operation. Reduced power operation must be at or below 80 percent load.

Typical High Output applications are sportfishers, motoryachts, and cruisers."


I can read that as rated to operate at or below 80% load, but only infrequently as low as 10-30% load, and only at full power 1 out of every 8 hours.

-Chris

So the 10-30% load factor is a lower limit, the engine isn't to be operated that low for long periods?

The Cummins lingo on that web page is very hard to figure out what they're trying to say exactly.

I've spent decades in parallel engineering/management career, and flying jets. In both, load factor and duty cycles are dealt with constantly, are very specific, and exceeding them can be costly. So I tend to take them very literally. The mushy wording in the Cummins definition is painful. I emailed Cummins for clarification, and they gave me a local sales office to contact. This is unquestionably an engineering issue, not a sales issue, so that is more frustrating. I'll have to pursue this further when I get time.

Don't know, but it looked like one way to interpret it.

Especially in light of commonly-cited strictures against running diesels under-loaded or at lower-then-recommended operating temps for long periods of time.

-Chris

I've long heard it was bad to idle diesels, but over-the-road truckers idle their trucks all night quite often. As far as temperature, I assume the thermostat would mostly cut off coolant when the engine drops to the set temp, and with no air cooling in a boat, it should stabilize at that temp...? But combustion chamber temps and exhaust temps would be much cooler than when under load.

Yes, but boat engines are water cooled. On most of the diesels the coolant temps come down when you idle (or never come up all of the way). The electronic diesels have gotten better at maintaining engine temp while idling, but on most of them they're still about 10% less than at cruise......whereas a lot of Detroits would be 30% less.......

I've been looking at a 2013 Caterpillar Marine Engine Selection Guide that associates the term "load factor" with the type of vessel and not the speed of the engine. Examples of phrases in the guide are "Fast commercial and passenger vessels and cruising yachts with moderate load factors" and "Fast patrol craft and fast yachts with low load factors."

Those are the ratings.......E rating is fast patrol craft and fast yachts with low load factors (this would be the highest HP version of that engine.

I wouldn't touch a stern drive on a boat that sits in saltwater year round. The saltwater eats the stern drives alive.

Yeah, but I've also begun to hear more recently they're not told not to do that. For whatever reasons...

And as J says, water cooling is different. Ours won't even come up to temps when idling (or at least it would take a loooooong time); they need a load to get warm enough so the thermostat will kick in.

-Chris

I found a blast from the past here on YF that might help in understanding what "load factor" actually is: www.yachtforums.com/threads/calculating-engine-load-factor.8661/