On Wed, 28 Nov 2007 04:04:59 GMT, "Glenn \(s/v Seawing\)"
wrote:


"Bruce in Bangkok" wrote in message
.. .
On Sun, 25 Nov 2007 20:10:41 -0500, Red wrote:

On Sat, 24 Nov 2007 23:49:00 -0500, Wayne.B
wrote:


On Sat, 24 Nov 2007 22:12:41 -0600, Brian Whatcott
wrote:


Diesels don't have this problem, and so are less wasteful at low
revs.


That's true but they have maintenance issues if run at low speed/low
load for extended periods of time.

Bruce said:
Yes there "seems" to be that but mention of "it is bad to run the
engine at low poser" seems confined to the boating world. I've worked
many construction jobs where diesel engines were started in the
morning and shut down at the end of the day. During smoke breaks or
lunch they just sat there and idled. Cranes are a perfect example,
that spend most of their life at very low power settings.

Generator sets - I've never seen a gen set operating manual that said
"run this engine at high power settings".

Not that I'm advocating idling your diesel for days and days but I do
wonder about the people who worry about letting the engine idle. I've
seen people that would hardly let the poor old thing cool down before
stop-cocking it, "because it is bad to let the engine run at low
load".

The Perkins I have in the sail boat has a continuous rating of 3,000
RPM and for years I ran it at 1500 - 1800. When I overhauled it I
could see no evidence of abnormal wear or carbon or any other evidence
that slow running harmed anything.

have the feeling that someone once said "it's not a good idea to
idle a diesel for a long time" and as the message passed from dockie
to dockie it became an urban legend and now everyone is worried about
idling the engine.

But what do I know?

Bruce-in-Bangkok

Bruce, I suspect that all this came about as there are different types
of diesels out there, and *some of them* surely cannot be safely idled
for long periods. I knew a few tow truck operators that drove ford
diesels that told me that if the engines were not equipped with
high-idle switches the engines consistently did not last that long (tow
trucks spend a lot of time at idle). On the other hand, guys that drove
some other brands of tow trucks said they didn't need the fast idle, the
engines lasted just fine. My Dodge/Cummins pickup truck owner's manual
says to avoid idle any longer than 3-5 minutes - kind of a bitch since I
spend half the day in traffic.
In boats we have some (mostly older now) slow-turning diesels that
can be run all year at low speeds without any harm. But I suspect that
most of the newer, lighter, fast turning diesels of recent vintage are
better off above idle.
One more thing... *most* people I've observed around here driving
their boats into the dockage area are idling anyway. By the time they
are docked the engine is already sufficiently cooled and needs no more
idling at the dock, yet they usually spend another five or ten minutes
wasting fuel.
Red


I suspect that you are correct. I recently set the governor on a
Gardner 6 cylinder that turned a roaring 1,000 at full throttle and
drove a 50 foot teak junk at 7 - 8 knots.

My personal thoughts about diesels is that if you idle them for days
and days it is not good. However some idling followed by running them
at rated speed is not harmful.

I may be wrong but I've been treating them that way for a lot of years
and they haven't complained yet =:-)
Bruce-in-Bangkok
(Note:remove underscores
from address for reply)

Okay, so it's been educational reading this thread.

It'll be another couple months to go, but I imagine Dad and I will do some
experimenting with fuel consumption in the GB42, with both engines throttled
back & one enging at a time shut down (probably alternating every couple
hours). Any ideas of where to look for appropriate fuel flow meters for
these?

I have another question, that's been brought up by reading this thread. My
own boat (GS41) has a Perkins 4-108. I have always been redicent to operate
it more than say 1350. What would the safe operating RPM be for this
engine? Reasonable cruising RPM?

Thanks!

Glenn.
s/v Seawing.


According to the Perkins manual the 4-107, the predecessor to the
4-108 had a maximum continuous rating of 37.5 HP @ 3000 RPM. As the
major difference between the 4-107 and the 4-108 was the change from
wet to dry liners on the 4-108 your RPM would be the same.

However, as my 4-107 is a bit long in the tooth I normally run at
2,000 - 2200 RPM

Please note: that the maximum rating is horse power at a specified RPM
If you were producing more horse power then the RPM should be
reduced.

Another note: Fuel consumption at rated H.P. is listed as 0.43
Lbs./BHP/Hour.

A Westerbeck added page shows the following:

High Speed Intermittent Rating - 47 HP @ 4000 RPM
Maximum Continuous Rating - the same as Perkins
Fuel consumption:

1500 RPM 0.5 GPH
1750 0.57
2000 0.66
2250 0.75
2500 0.82
2750 1.0
3000 1.3

Over the years I have arrived at 3/4 gal per hour (or about 3 Lt./Hr)
as an average fuel consumption at 2000 - 2200 RPM


Bruce-in-Bangkok
(Note:remove underscores
from address for reply)