On Sat, 24 Nov 2007 08:03:34 -0500, "Roger Long"
wrote:

Another nice thing about a shaft brake. You can hook it into the
transmission shift mechanism so it engages whenever you shift to neutral.
This lets you shift from forward to reverse faster and with less wear and
tear on the clutches.

Shaft brakes are also nice to have if you need to be towed. I've heard of
lots of cases of people down in the engine room trying to wrap chains and
ropes around their spinning shafts to save the transmissions while being
towed home.


This "running one engine to save fuel" story has been popular for
ages, but I have always wondered about it. If it takes X horsepower to
drive a hull through the water at Y speed then is there any real gain
in running on one engine since, assuming no loss in speed the single
engine must produce the same horse power as the two had previously
done. And the drag on the non powered propeller needs to be included
in the equation.

At least in my own case, twin 60 HP diesels with Hurst transmissions,
I find that shutting down one engine and locking the propeller on the
shutdown engine results in either losing speed or using a lot more
throttle.

I can't give any definitive figures but running both engines at a
reasonable speed seemed to give the best ratio of distance/fuel.

Have there been any studies made of shutting down one engine? I know
that Beebe published some RPM/Miles/fuel consumption charts but those
were for a single screw drive.

If there is any published data available it would certainly
interesting to know.


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

On Sun, 25 Nov 2007 10:23:55 +0700, Bruce in Bangkok
wrote:


This "running one engine to save fuel" story has been popular for
ages, but I have always wondered about it.
...
Bruce-in-Bangkok

The run one, stop one approach is likely to succeed with
spark ignition engines. At low throttle they incur pumping losses
to keep that vacuum going in the inlet manifold.

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

Brian Whatcott Altus OK

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.

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.

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.

I 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
(Note:remove underscores
from address for reply)

"Bruce in Bangkok" wrote in message
...


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".


My guess is that idling during smoke or lunch breaks does not constitute
running at low power for a long time. My understanding is that a diesel
engine is happiest running at a constant RPM under a load that represents
about 80 percent of the engines power rating ... either in HP or watts.

Another issue that enters the picture is if a turbocharger is used or not.

The operator's manual for the Volvo diesels in our larger boat recommends
running at 200 RPM below WOT for maximum engine efficiency.

Our other boat, (single engined 36' GB) has two engine speeds .... 1700 rpm
or Off.

Eisboch

Bruce in Bangkok 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.

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.

I 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.

The issue with my motor, the Yanmar 2QM15, is that it runs cold at low
RPM. I can verify this. It's amazing how long it stays cold with no
load. This would be bad for it, right?

Stephen

"Stephen Trapani" wrote in
message ...

The issue with my motor, the Yanmar 2QM15, is that it runs
cold at low
RPM. I can verify this. It's amazing how long it stays
cold with no
load. This would be bad for it, right?


Yes. That is the main reason to not let a diesel sit at idle
too long. Low temp AND lower oil pressure at idle. For
years truck diesels have had a 'high idle' setting ( either
by air or electric solenoid, manual cable, or lately via
computer) so they can run them at night while parked.


SBV

On Sun, 25 Nov 2007 08:11:30 -0800, Stephen Trapani
wrote:

Bruce in Bangkok 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:

snipped

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.

I 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.

The issue with my motor, the Yanmar 2QM15, is that it runs cold at low
RPM. I can verify this. It's amazing how long it stays cold with no
load. This would be bad for it, right?

Stephen

If your engine runs cold put a thermostat in it. Your Yanmar should
warm up like any engine and stay the same temperature from then on.
Running an engine at a lower then designed temperature is not the way
to go.

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

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

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)