Yes, calling cummins is by far the best thing because your questions
answer can only be found knowing all the specs of *your* boat and the
conditions you are moving through.

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

Tamaroak wrote in news:Fd2dnbJAg-bp2pbZRVn-
:

these motors don't like to go slow for a number of reasons

Huh?? Where'd you hear this nonsense? A diesel doesn't like to go slow?

What reasons do you know about to go with this??

A friend, who should never have been allowed to drive a 56' Hatteras away
from the dock, ran its twin 8V92TA, twin turbocharged train engines at idle
for many years before I came along. I must admit there was a "little
carbon" in the waterboxes that came out when I "opened 'er up" offshore of
Charleston. It looked something like a ship blowing the boilers..(c;

These idled-for-years old Detroit Diesels had ONE little weak injector
spring in one engine when the diesel shop pulled them all apart for
inspection for the massive survey the buyer paid for when he sold it. ONE
spring! To start them, you simply flipped the switch to ON and barely
touched the start button and they jumped to life, even stone cold.

I don't believe Dan hurt them treating these beasts like the boat was a
trawler all those years he owned it.

Sure made a big cloud of carbon (cough)(cough)(choke)(gasp) 5 miles
offshore...(c; I told him I was trying to hide the brown trail he was
leaving when the mascerator pump was emptying those massive dirty tanks...
(c;

Tamaroak wrote

these motors don't like to go slow for a number of reasons

Larry wrote:

Huh?? Where'd you hear this nonsense? A diesel doesn't like to go slow?

What reasons do you know about to go with this??


Suggest you check out "wet stacking".

Usually requires and idle RPM around 1,400 RPM to prevent.

Lew

On Sun, 05 Mar 2006 22:59:31 -0500, Larry wrote:

What about my diesel cars that hardly ever leave the city? I've never seen
this phenomenon while sitting in the traffic for hours on end, idling along
to the next traffic light.....??

Maybe it isn't as serious as it's imagined.....??

The problem as I understand it, is particularly acute for turbo
engines. If the turbo does not get spun up to speed and temperature
on a fairly regular basis, it will carbon up and require big $$$s to
fix. When I was shopping for a new diesel genset 2 years ago I
avoided all turbo engine options for exactly that reason.

In a diesel car, particularly an underpowered car like a Mercedes 220,
you will almost surely do enough hard accelerating to avoid wet
stacking.

Larry wrote:
Larry wrote in
:


I could see it would carbon up if you just ran the engines in an
unloaded condition in neutral for long periods of time....


Thinking about this, I cannot help but think about those engines in the big
trucks that are left idling for 8 hours, virtually unloaded, while the
driver is sleeping in his sleeper at the truck stop. I suppose he burns
off all the deposits when he drives off down the interstate in the morning.

You need to develop enough reject heat to keep the cylinder walls hot
enough to prevent wet stacking.

The spec I always seen is to idle somewhere between 1,300-1,500 RPM,
depending on engine.

Lew

On Mon, 06 Mar 2006 15:46:46 GMT, Don W
wrote:

In
the vending business our diesels would probably accrue 2000+ hours
per year.

How was their reliability longevity?

In article t,
Lew Hodgett wrote:

Larry wrote:
Larry wrote in
:


I could see it would carbon up if you just ran the engines in an
unloaded condition in neutral for long periods of time....


Thinking about this, I cannot help but think about those engines in the big
trucks that are left idling for 8 hours, virtually unloaded, while the
driver is sleeping in his sleeper at the truck stop. I suppose he burns
off all the deposits when he drives off down the interstate in the morning.

You need to develop enough reject heat to keep the cylinder walls hot
enough to prevent wet stacking.

The spec I always seen is to idle somewhere between 1,300-1,500 RPM,
depending on engine.

Lew

the above, is really not the problem. The real problem is running a
diesel engine below operating temps, for extended periods (months)
of time, with no at operating temps operation. If the engine is
operated below operating temp, carbon will tend to build up on
combustion path surfaces, and it will not be removed, or burnt off,
by normal temp operation. This is aggrivated in exhaust driven turo
systems, because the Exhaust Side turbo also isn't running at designed
temp and will accumulate excess carbon buildup.

This whole "WetStacking" business is more a minor problem of operational
terminology, that an actual mechanical problem that needs alternate
operational techniques to solve.

If the engine is running at designed temps, with the thermostat in the
open condition, usually will allleviate and excessive carbon buildup.
Any operation with loads of 25% or more of rated HP, for more than 10%
of total operational hours, will be more than enough to deal with an
preceived problems of this nature for Normally asperated diesel engines.
For a exhaust powered turbo diesel, if your exhaust side turbo is
running at operational temp, your fine, no matter what the cooling
system is doing, and that will usually be at somewhere around 10
to 15% of rated HP, loading.

All this is variable, depending on the engineering of the engine design,
and most OEM's will have a Spec published for minimum ehgine operational
temps and loadings for extended operational times.

Me

Hi Wayne,

Wayne.B wrote:
On Mon, 06 Mar 2006 15:46:46 GMT, Don W
wrote:


In
the vending business our diesels would probably accrue 2000+ hours
per year.


How was their reliability longevity?

We had really good reliability with the Cummins. The problems
we had were mostly related to fuel / fuel filters, etc. The engines
themselves were fine.

As far as longevity, I can only comment out to ~4000 hours, because
I sold the business after two years. During that two-year period
we did not have to rebuild an engine or turbo, and at the end the
vehicles were all in good running condition.

OTOH, we only got about 8MPG on the vans, and when I sold the business
diesel had become more expensive than gasoline! :-( It is very strange
to me to see diesel selling at a premium, because it has been much
cheaper over most of the last 40 years, and is a lower grade product
IIRC.

Don W.

Don W wrote:

Is "wet stacking" a problem that is unique to boats?


Not really.

Wet stacking happens when the engine system does not come up to
operating temperatures for extended periods.

If the engine is allowed to idle around 1,500 RPM, sufficient reject
heat is generated to eliminate the problem.

Lew