Bruce in Alaska wrote:

Bernie, ever wonder how all those diesel engines, at Truck Stops,
Idle all night long in cold weather, and still are able to pull BIG
Loads, the next morning, day in and day out, and still have 40K hours
between InFrame Rebuilds?

You can't compare truck engines and boat engines. As is often pointed out,
there are no downhills at sea. Truck and automotive duty is relatively
light compared to a marine engine which is essentially always going up hill.
The truck engine will frequently reach full power for short periods and get
nice and toasty. Then it coasts without cooling off a lot. This is very
different than marine duty cycle.

An occasional all night idle is a very small part of a trucks total
operating time. If a diesel is sized such that the boat can almost never
use the full power, it will never get up to the proper operating range. If
the prop is too small, as is often the case with yachts, even a headwind
that nearly stops the boat may not get the engine into the proper range.
You are never going to noticably compromise your properly sized diesel by
running it lightly when necessary. If it is too big for the boat or you
always baby it, you may have early problems.

We go through this a lot in sizing generator engines. It's nice to have one
that will handle the peak loads but, if there is a big spread between that
peak and normal operation, generator time to overhaul may suffer.

You are right though that newer governors are improving the situation. The
new electronically controlled engines can run at light loads for much longer
periods; maybe forever. There are still alot of diesel engines out there
(like mine) with governors that a pre WWII mechanic would have felt right at
home with.

--
Roger Long