Tamaroak wrote:
Let's say you just took delivery of a used 27000# trawler powered by a
single Cummins turbo-diesel 220, model 6BT5.9M. You want to get maximum
miles per gallon out of it and know the slower you go, the better, but
these motors don't like to go slow for a number of reasons. Of course,
you also want it to last forever because it might cost $10,000 to
rebuild it, not including pulling it out and putting it back in..

What would you consider a minimum cruising speed, with an occasional
shot at 2000 rpm just to clean things out?

Capt. Jeff



Be guided by Cummins & just ask them. The usual thing is over 1/2 -2/3
for continuous running. Long term light load continuous speed is not
good & after a while you'll stop giving it the regular bursts.

The negative effects can be overstated, there is a ferry around here
that even made it into the Cummins news magazine for it's number of
hours without overhaul, I've forgotten the exact number just now, but it
was well over 20000hrs with not much more than standard servicing & it
was in the situation you describe, lightly loaded, 0600-2300 X 365 days.
It was (is) run at reasonable high revs. They slip the ferry every 2-3
yrs & the intention was to re-engine every 3 years last I heard they had
left it there.

Again always ask Cummins & this para. is well against what Cummins will
say but.................. if you have a situation when you are
essentially overpowered, you can overprop if the usage is well managed
(i.e. the engine must never be run at a throttle setting where any extra
will not result in the engine easily increasing revs) This will give you
same boat speeds at lower engine revs & make the engine produce more
torque, it means you must operate it as a lower powered motor(i.e. you
don't have the option to give it full throttle even if the storm front
is coming). Again not ever recommended & especially not by Cummins. The
marine versions of some engines have a different governor on them so
excess torque can't be made below a related safe revs, but this is not
to be relied upon.

Funny story?? The liar Krause was carrying off the Cummins powered
lobster boat lie for months as it was being imaginary built, doing all
his online searching as he does, trying to make the lie plausible. As
always with liars he was exposed by the easy detail he had no clue about.

The imaginary boat was launched (I suspect a charter person he pays to
take him fishing it seems twice a year?? was having a boat built) & of
course I asked how the Cummins bloke enjoyed the ride?? Needless to say
he had no clue about what I was asking, even took it that I'd said there
was something wrong with the Cummins!!!:-)

Too funny; for big new Cummins engines like that it's a condition of the
warranty that one of their reps visits the boat & goes for a run, "just
to ensure everything is operating correctly" but in reality they do it
to make sure the boat is NOT overpropped, if it is they say so & tell
you the warranty will start when the correct prop is fitted. The
internet has given the lying idiots a new tool but being tools
themselves they still don't know anything.

K