Have a search at www.boatdiesel.com, this has been covered many times.
There is also an article on this:
http://boatdiesel.com/Articles/Artic...ion.cfm&Y=2004

You will need to join the web site to read this one, ($25/yr, and
worth it every once and a while).

I to have a 6B in a trawler and have am OK with slow operation. My
normal cruise is 1400 rpm (6.7kn). Key here is to get the motor to
operating temperature (Idling, even at a fast idle will not do it, you
need to run the boat) and then make sure it stays at temp.

The 6B's at times have problems with their thermostats, so watch that
and if the temp falls off, then change it out 1st thing. I had to
change out mine at 400hrs, no problems after doing so.

When we run Christmas ships I spend a few hours at a time at 1100-1200
RPM, and the temp always stays up. So, again, the key here is get up
to temp (I usually run around 1700 or so to make sure I am up to temp)
and do not worry. Based on what I have seen from people who have been
around motors with high hours, I am expecting well over 10,000hrs on
my motor. Turbo included

-al-

On Sun, 05 Mar 2006 14:17:33 -0800, 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