Happiness is...
 

On Thu, 22 Nov 2007 08:55:50 +0700, Bruce in Bangkok
wrote:

The Grand Banks hulls are semi-displacement hulls and probably produce
an optimum distance/fuel consumption at higher speeds so just puling
the throttles back will probably not accomplish a really major
increase in fuel economy.

Depends on what you call major.

By cutting back 15 % from maximum cruising speed to "normal", fuel
economy doubles as horsepower is cut in half.

Reducing speed another 20% below normal gives an additional 50%
improvement in NMPG.

GB42s can be made to plane if sufficient power is applied but that is
nearly impossible with our GB49, even with close to 600 hp available.

Happiness is...
 

"Wayne.B" wrote in message
...
On Wed, 21 Nov 2007 05:21:29 GMT, "Glenn \(s/v Seawing\)"
wrote:

This has got Dad and I talking about possibilities. He cruises on a GB42
&
I on my Gulfstar 41 Sloop. We've been trying to slow his boat down enough
so I can keep up on a regular basis. I was thinking of buying a small
fleet
of large dingies to tow behind him to slow him down, but that's an
expensive
option. Sounds like your idea may be well worth experimenting with. The


primary concern for me, would be damage to the transmission....those
puppies
are expensive.

Tell me about it. Four man days to get one out, two to rebuild it,
three to put it back in, and about two Boat Units worth of parts.

Maybe this'll help Dad cut down on his fuel bill. I
constantly tease him 'bout it...he normally burns 4.5gph while I about
2/3gph....when I'm motoring. I sure like his GB though...maybe when I get
tired of sailing (whenever that could be). :-)

What if he towed your Gulfstar? That would slow him down! :-)

Right, don't think this thought has not crossed my mind. It would sure
improve my fuel economy too...as well as the relaxation hours. :-)

Back to the transmissions; it seems that you've satisfied yourself that you
are not significantly risking damage to them...yes?

Thanks for being so helpful Wayne.

Glenn.
s/v Seawing.

Happiness is...
 

On Wed, 21 Nov 2007 21:27:16 -0500, Wayne.B
wrote:

On Thu, 22 Nov 2007 08:55:50 +0700, Bruce in Bangkok
wrote:

The Grand Banks hulls are semi-displacement hulls and probably produce
an optimum distance/fuel consumption at higher speeds so just puling
the throttles back will probably not accomplish a really major
increase in fuel economy.

Depends on what you call major.

By cutting back 15 % from maximum cruising speed to "normal", fuel
economy doubles as horsepower is cut in half.

Reducing speed another 20% below normal gives an additional 50%
improvement in NMPG.

GB42s can be made to plane if sufficient power is applied but that is
nearly impossible with our GB49, even with close to 600 hp available.


A Sea Horse built steel hull 49 ft. trawler yacht would probably have
a John Deere 100 HP engine installed and cruise at about 7 K using a
ridiculously low amount of fuel.


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

Happiness is...
 

On Thu, 22 Nov 2007 05:57:18 GMT, "Glenn \(s/v Seawing\)"
wrote:

Back to the transmissions; it seems that you've satisfied yourself that you
are not significantly risking damage to them...yes?

According to the manufacturer and all of the so called experts, we
should be OK. I like Jere Lull's sugggestion regarding feathering
props but I suspect there is a considerable expense to doing that,
plus some increased complexity risk.

Since the GB42 probably has smaller props, it might also be easier to
implement one of the jerry rigged solutions for preventing shaft
rotation.

Happiness is...
 

CalifBill wrote:
"Dan" wrote in message
...
HK wrote:


We've got some guests coming north from Florida this week for the
holiday. Two hours in the plane and they're here.
Like magic! Wow!

-dk

And 3 hours in airports!



That, too.

-dk

Happiness is...
 

"Wayne.B" wrote in message
...
On Thu, 22 Nov 2007 05:57:18 GMT, "Glenn \(s/v Seawing\)"
wrote:

Back to the transmissions; it seems that you've satisfied
yourself that you
are not significantly risking damage to them...yes?

According to the manufacturer and all of the so called
experts, we
should be OK. I like Jere Lull's sugggestion regarding
feathering
props but I suspect there is a considerable expense to
doing that,
plus some increased complexity risk.

Since the GB42 probably has smaller props, it might also
be easier to
implement one of the jerry rigged solutions for preventing
shaft

rotation.

Do you have room to install a collar, with a small disc for
a cable actuated caliper of some sort. Like a bicycle
brake, only larger.


SBV

Happiness is...
 

"Bruce in Bangkok" wrote in message
...

If you really want to get the best fuel/hour figure do
what the
trawler yachts do and stick in a couple of 50 HP engines,
run them at
about 35 HP which will be at a high enough power setting
to keep the
engines from carboning up and be pretty economical.


That wouldn't produce a big enough wake to satisfy Wayne.

SBV

Happiness is...
 

On Thu, 22 Nov 2007 21:34:48 -0500, "Scotty" wrote:

Do you have room to install a collar, with a small disc for
a cable actuated caliper of some sort. Like a bicycle
brake, only larger.

The collar would probably be easy although there is nothing available
off the shelf that I'm aware of. The difficult part would be creating
a secure attachment point for the caliper. Given the forces involved,
the caliper itself would need to be hydraulically actuated like a disc
brake.

Happiness is...
 

"Wayne.B" wrote in message
...
On Thu, 22 Nov 2007 21:34:48 -0500, "Scotty"
wrote:

Do you have room to install a collar, with a small disc
for
a cable actuated caliper of some sort. Like a bicycle
brake, only larger.

The collar would probably be easy although there is
nothing available
off the shelf that I'm aware of. The difficult part would
be creating
a secure attachment point for the caliper. Given the
forces involved,
the caliper itself would need to be hydraulically actuated
like a disc
brake.

Something like a handbrake on a forktruck would work.

Happiness is...
 

On 2007-11-22 22:32:03 -0500, Wayne.B said:

On Thu, 22 Nov 2007 21:34:48 -0500, "Scotty" wrote:

Do you have room to install a collar, with a small disc for a cable
actuated caliper of some sort. Like a bicycle brake, only larger.

The collar would probably be easy although there is nothing available
off the shelf that I'm aware of. The difficult part would be creating
a secure attachment point for the caliper. Given the forces involved,
the caliper itself would need to be hydraulically actuated like a disc
brake.

Motorcycle disk brake might be most adaptable.

I'd feel safer if the brake disengaged if the engine powered up or
something's going to break some time.

Quick thought: airplane "parking" brakes and mid-80s Subaru clutches
hold pressure until the brake (or clutch) is depressed. Perhaps the
transmission's hydraulic pressure could be tied in.

Feathering prop is probably simpler, easier and cheaper in the long
run, and it's proven technology.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

Happiness is...
 

Jere Lull wrote:
On 2007-11-22 22:32:03 -0500, Wayne.B
said:

On Thu, 22 Nov 2007 21:34:48 -0500, "Scotty" wrote:

Do you have room to install a collar, with a small disc for a cable
actuated caliper of some sort. Like a bicycle brake, only larger.

The collar would probably be easy although there is nothing available
off the shelf that I'm aware of. The difficult part would be creating
a secure attachment point for the caliper. Given the forces involved,
the caliper itself would need to be hydraulically actuated like a disc
brake.

Motorcycle disk brake might be most adaptable.

I'd feel safer if the brake disengaged if the engine powered up or
something's going to break some time.

Quick thought: airplane "parking" brakes and mid-80s Subaru clutches
hold pressure until the brake (or clutch) is depressed. Perhaps the
transmission's hydraulic pressure could be tied in.

Feathering prop is probably simpler, easier and cheaper in the long run,
and it's proven technology.



Live steeeem here, dead steeeem there.

Happiness is...
 

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)

Happiness is...
 

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

Happiness is...
 

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

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.

I don't know if I'd call it a study, but based on my own statistics
there is a definite save, even with the drag of a freewheeling prop.
My situation may be different than some however since the engines are
oversized for 95% of my typical usage. As a result, running both
engines slowly is not only bad for them, but they would be operating
just above idle speed which is not an efficient operating point.

By running on a single engine, it is operating closer to it's design
point which is not only more efficient but minimizes potential
maintenance issues like carbonized valves, rings and exhaust manifold.

My statistics for RPM vs fuel burn vs horsepower vs speed agree fairly
closely with Beebe's numbers. Of course there is a fudge factor in
his equation which is different for every hull shape. It turns out
that the Grand Banks hull form is at the low end of the efficiency
scale.

Happiness is...
 

On Nov 24, 5:23 pm, Bruce in Bangkok wrote:
... 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 ...

I suspect it depends on the engines and the props. I spent some time
with a gent in Niuatoputapu who had been a commercial fisherman and is
a shipyard owner and was totally convinced that running one engine
used less fuel. But, when he installed fuel flow meters he found that
it was slightly less efficient to run a single than a double at
cruising speed and he got noticeably better mileage using both engines
at a slightly slower speed on his 50 foot trawler yacht... In his
case I suppose the drag of the prop was more costly than running the
engines with a light load. YMMV, as they say, but if I had engines
that were big enough to fit with flow meters I'd certainly install
them and test the possibilities.

-- Tom.

Happiness is...
 

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.

Happiness is...
 

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)

Happiness is...
 

On Sat, 24 Nov 2007 23:37:52 -0500, Wayne.B
wrote:

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

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.

I don't know if I'd call it a study, but based on my own statistics
there is a definite save, even with the drag of a freewheeling prop.
My situation may be different than some however since the engines are
oversized for 95% of my typical usage. As a result, running both
engines slowly is not only bad for them, but they would be operating
just above idle speed which is not an efficient operating point.

By running on a single engine, it is operating closer to it's design
point which is not only more efficient but minimizes potential
maintenance issues like carbonized valves, rings and exhaust manifold.

My statistics for RPM vs fuel burn vs horsepower vs speed agree fairly
closely with Beebe's numbers. Of course there is a fudge factor in
his equation which is different for every hull shape. It turns out
that the Grand Banks hull form is at the low end of the efficiency
scale.


I think that your case is where the "don't run the engines at low
load" came from. If you have a couple of them great big motors in case
you want to go fact and you end up running them at 1.000 RPM for days
at a time I suspect that they will carbon up pretty good as I'm not
sure how well the pumps are calibrated for speeds just above idle.

During the first oil crunch I was working at a power plant in N.
Thailand and the word came down from the Air Force to run the
generators at 90-95% of rated power as they said that was the most
efficient power setting.


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

Happiness is...
 

On Sat, 24 Nov 2007 20:38:22 -0800 (PST), "
wrote:

On Nov 24, 5:23 pm, Bruce in Bangkok wrote:
... 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 ...

I suspect it depends on the engines and the props. I spent some time
with a gent in Niuatoputapu who had been a commercial fisherman and is
a shipyard owner and was totally convinced that running one engine
used less fuel. But, when he installed fuel flow meters he found that
it was slightly less efficient to run a single than a double at
cruising speed and he got noticeably better mileage using both engines
at a slightly slower speed on his 50 foot trawler yacht... In his
case I suppose the drag of the prop was more costly than running the
engines with a light load. YMMV, as they say, but if I had engines
that were big enough to fit with flow meters I'd certainly install
them and test the possibilities.

-- Tom.


I'm glad to see your message as it was always my feeling that shutting
down an engine was the way to go but I never had flow meters and
really had no way of checking my "feeling".


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

Happiness is...
 

"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

Happiness is...
 

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

Happiness is...
 

"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

Happiness is...
 

On Sun, 25 Nov 2007 07:20:49 -0500, "Roger Long"
wrote:

It simply has to take more horsepower so push a twin screw boat with a
single engine than with both. One prop is dragging and whether it is fixed
or freewheeling, it is going to increase the overall resistance. The thrust

Snipped

money?

A mechanic I talked to recently told me that he sees a significant
difference in interior condition and time between overhauls on sailboats
that live on moorings or have engine driven refrigeration compressors
because owners of those boats tend to idle for long periods to charge and
cool.

You are confirming my own experiences regarding running on one engine
to save fuel is something I have never been able to achieve. Assuming
normally sized engines.

And, I'm sure that essentially running a diesel engine at idle
continuously is probably bad for it but I have never been able to
detect the, so called, glazing of the cylinder walls that is a
supposed result. Every diesel engine I have taken apart had cylinder
walls that looked exactly the same as any other engine, a slick
polished surface.

But anyway, Thank you for the comprehensive comments.

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

Happiness is...
 

On Sun, 25 Nov 2007 07:20:49 -0500, "Roger Long"
wrote:

Engines that are idled a lot simply get overhauled a bit sooner. If you
don't have good reasons to idle, why throw away your engine time which =
money?

That's the way I understand it also. Instead of getting maybe 5,000
hours between overhauls, you end up with 3 or 4,000 instead. With a
turbo it can be a lot worse than that.

I have some hard numbers for single vs low speed twins on my own boat,
based on a relatively small number of data points. Running both
engines slowly to achieve about 1.0 x SQRT(LWL), the best fuel economy
I've been able to achieve is 1.4 NMPG.

Running single engine with the other one freewheeling I have been able
to get 1.7 NMPG.

The boat has sight guages on the tanks so that I can measure fuel burn
to within 5 gallons accuracy. The boat is a heavily loaded,
semi-displacement GB49 with total weight in the of range 60 to 70,000
lbs. The engines are 2 stroke DD 6-71s, naturally aspirated, rated at
280 hp each. They will hit their rated max of 2400 RPM at WOT.
Props are 4 bladed 30 x 25, reduction gears are 2.5 to 1.

With both engines the boat will reach 1.0SQRT(LWL) at 1200 RPM,
burning about 5 gph total (about 85 actual hp). Single engine at 1500
RPM, same speed, burns about 4 GPH (68 actual hp) .

Since it seems reasonable to assume that the overhead of running a
large engine slowly is greater than a small engine, it is entirely
possible that a different outcome would be obtained with smaller
engines running closer to their rated power output.

Happiness is...
 

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)

Happiness is...
 

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

Happiness is...
 

Roger Long wrote:
The bigger the diesel, the more of a factor this is
which is why railroad engines are seldom shut down for maintenance.

Roger, I am under the impression that railroad diesels are run at pretty
high "idle". In fact when waiting for the various commuter trains to get
out of the way around here I get the impression of a pretty fast running
engine when they are stopped. They do not sound anywhere near idle. Is
this the case just when they are dropping off and picking up and/or is
there another time when they actually idle slower?
Red

Happiness is...
 

Bruce in Bangkok wrote:
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.

Why didn't Yanmar put a thermostat in this engine? Is there any
disadvantage to having the thermostat?

Stephen

Happiness is...
 

On Sun, 25 Nov 2007 17:49:19 -0800, Stephen Trapani
wrote:

Bruce in Bangkok wrote:
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.

Why didn't Yanmar put a thermostat in this engine? Is there any
disadvantage to having the thermostat?

Stephen

Well, I think that they did. At least the 2GM20 I owned had a
thermostat and the parts book shows two, a normal temperature one for
freshwater cooling and a low temperature one for salt water cooling.


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

Happiness is...
 

On Sun, 25 Nov 2007 21:37:55 -0500, "Roger Long"
wrote:

My 2QM20 has a thermostat. It is also a very cool running engine. I have
heard several places that they are among the coolest running diesels in
common use and mine seems quite happy running that way. I have also heard,
but not substantiated, that this engine runs just as well, or better, with
the thermostat removed. I don't recommend it or plan to do it though.

The 2QM20 has a precombustion chamber which I don't think is common in small
diesels. This might account for different operating characteristics. It
might also account for their reputation for lasting a long time with poor to
non-existent maintenance. With a precombustion chamber, a clogged injector
maybe isn't consentrating the combustion into hot spots on the piston head.
I'm speculating a bit and would like to know more however.

Yanmar's factory parts books lists two thermostats and two overheat
sensors for the small engines. One for salt water cooling and a higher
temp one for freshwater.

Also all the small Yanmar engines and I assume the larger engines use
pre-combustion chambers as do Caterpillars and many other engines. The
idea of the pre-combustion chamber is that the fire starts there and a
gout of burning fuel is injected into the combustion chamber rather
then simply spraying a jet of fuel into the combustion chamber. I
believe it is intended to provide better flame propagation and
improved combustion.

I would hesitate to recommend that anyone remove the thermostat unless
the engines is equipped with a temp. gauge as in some cases removing
the thermostat actually increases cylinder head temperatures.

It seems contrary to logic but on some engines - there was a Ford V-8
I remember - that actually run hotter without the thermostat as the
thermostat in addition to controlling temperature acted as a orifice
and restricted the speed of coolant flow through the block and head.


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

Happiness is...
 

On Sun, 25 Nov 2007 20:10:04 -0500, Wayne.B
wrote:

On Sun, 25 Nov 2007 07:20:49 -0500, "Roger Long"
wrote:

Engines that are idled a lot simply get overhauled a bit sooner. If you
don't have good reasons to idle, why throw away your engine time which =
money?

That's the way I understand it also. Instead of getting maybe 5,000
hours between overhauls, you end up with 3 or 4,000 instead. With a
turbo it can be a lot worse than that.

I have some hard numbers for single vs low speed twins on my own boat,
based on a relatively small number of data points. Running both
engines slowly to achieve about 1.0 x SQRT(LWL), the best fuel economy
I've been able to achieve is 1.4 NMPG.

Running single engine with the other one freewheeling I have been able
to get 1.7 NMPG.

The boat has sight guages on the tanks so that I can measure fuel burn
to within 5 gallons accuracy. The boat is a heavily loaded,
semi-displacement GB49 with total weight in the of range 60 to 70,000
lbs. The engines are 2 stroke DD 6-71s, naturally aspirated, rated at
280 hp each. They will hit their rated max of 2400 RPM at WOT.
Props are 4 bladed 30 x 25, reduction gears are 2.5 to 1.

With both engines the boat will reach 1.0SQRT(LWL) at 1200 RPM,
burning about 5 gph total (about 85 actual hp). Single engine at 1500
RPM, same speed, burns about 4 GPH (68 actual hp) .

Since it seems reasonable to assume that the overhead of running a
large engine slowly is greater than a small engine, it is entirely
possible that a different outcome would be obtained with smaller
engines running closer to their rated power output.


Interesting. Have you tried other fractions of "hull speed" to see if
the same ratio of one engine fuel consumption to twin engine
consumption remains the same?

As an aside all 6-71's weren't rated at the same power and one of the
differences was the injector s. They came with different colored tags
as I remember. If you are interested in improving fuel economy (and
losing horse power) talk to an experienced Detroit diesel mechanic
about changing injectors. It might give you a bit better economy, if
you are interested.


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

Happiness is...
 

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)

Happiness is...
 

On Sun, 25 Nov 2007 20:19:46 -0500, Red wrote:

Roger Long wrote:
The bigger the diesel, the more of a factor this is
which is why railroad engines are seldom shut down for maintenance.

Roger, I am under the impression that railroad diesels are run at pretty
high "idle". In fact when waiting for the various commuter trains to get
out of the way around here I get the impression of a pretty fast running
engine when they are stopped. They do not sound anywhere near idle. Is
this the case just when they are dropping off and picking up and/or is
there another time when they actually idle slower?
Red


I think that railway engines are basically generator prime movers and
run at a constant RPM all the time. At least that is the way a power
plant engine runs. It always runs at approximately rated RPM
and the governor makes small adjustments up or down to maintain the
proper frequency.


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

Happiness is...
 

On Mon, 26 Nov 2007 23:03:52 +0700, Bruce in Bangkok
wrote:

Interesting. Have you tried other fractions of "hull speed" to see if
the same ratio of one engine fuel consumption to twin engine
consumption remains the same?

I have tried 1.0SQRT(LWL) and 1.1 - as Beebe and others predict, 1.0
is more efficient. 1.0 is about as slow as I'm willing to go, and
then only over longer distances where I'm already committed to running
day and night.

As an aside all 6-71's weren't rated at the same power and one of the
differences was the injector s. They came with different colored tags
as I remember. If you are interested in improving fuel economy (and
losing horse power) talk to an experienced Detroit diesel mechanic
about changing injectors. It might give you a bit better economy, if
you are interested.

Yes, I've considered replacing the injectors and may do it at some
point.

Injector N55, Fuel Output Min.24 - Max.30
''''''' N60 "''''''''''''' 30 - '' 36
'''''''' N65 ''''''''''''''' 40 - '' 46
'''''''' N70 ''''''''''''''' 38 - '' 44
'''''''' N80 ''''''''''''''' 44 - " 50

I believe that I have the N80s at this point, so in theory I could go
all the way down to N55s. That would clearly reduce power and torque
but it's not obvious what the impact on economy would be. It could
also have an adverse impact on the present reduction gear ratio and
prop pitch.

Happiness is...
 

On Mon, 26 Nov 2007 19:36:09 -0500, Wayne.B
wrote:

On Mon, 26 Nov 2007 23:03:52 +0700, Bruce in Bangkok
wrote:

Interesting. Have you tried other fractions of "hull speed" to see if
the same ratio of one engine fuel consumption to twin engine
consumption remains the same?

I have tried 1.0SQRT(LWL) and 1.1 - as Beebe and others predict, 1.0
is more efficient. 1.0 is about as slow as I'm willing to go, and
then only over longer distances where I'm already committed to running
day and night.

As an aside all 6-71's weren't rated at the same power and one of the
differences was the injector s. They came with different colored tags
as I remember. If you are interested in improving fuel economy (and
losing horse power) talk to an experienced Detroit diesel mechanic
about changing injectors. It might give you a bit better economy, if
you are interested.

Yes, I've considered replacing the injectors and may do it at some
point.

Injector N55, Fuel Output Min.24 - Max.30
''''''' N60 "''''''''''''' 30 - '' 36
'''''''' N65 ''''''''''''''' 40 - '' 46
'''''''' N70 ''''''''''''''' 38 - '' 44
'''''''' N80 ''''''''''''''' 44 - " 50

I believe that I have the N80s at this point, so in theory I could go
all the way down to N55s. That would clearly reduce power and torque
but it's not obvious what the impact on economy would be. It could
also have an adverse impact on the present reduction gear ratio and
prop pitch.


True, but this raises the question of whether you are actually
developing " X" amount of horsepower at "Y" RPM. I assumed from a
previous post that you were calculating H.P. from fuel consumption
figures which is really just a ballpark calculation.

Given that the 71 series are no longer made what are rebuilt injector
prices like? Or have they gone out of sight because a lot of people
would rather have the old all mechanical engines then the new
electronic models?


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

Happiness is...
 

On Tue, 27 Nov 2007 09:45:46 +0700, Bruce in Bangkok
wrote:

True, but this raises the question of whether you are actually
developing " X" amount of horsepower at "Y" RPM. I assumed from a
previous post that you were calculating H.P. from fuel consumption
figures which is really just a ballpark calculation.


Without some way of measuring torque, that is the best you can do. 17
hp per gph is a pretty good approximation.

Given that the 71 series are no longer made what are rebuilt injector
prices like? Or have they gone out of sight because a lot of people
would rather have the old all mechanical engines then the new
electronic models?

Newly manufactured parts are available from various sources including
DD dealers. I've heard reports of some difficulty getting new
cylinder kits but the DD service center that I used in North Carolina
had no problem.

Happiness is...
 

On Mon, 26 Nov 2007 23:52:29 -0500, Wayne.B
wrote:

On Tue, 27 Nov 2007 09:45:46 +0700, Bruce in Bangkok
wrote:

True, but this raises the question of whether you are actually
developing " X" amount of horsepower at "Y" RPM. I assumed from a
previous post that you were calculating H.P. from fuel consumption
figures which is really just a ballpark calculation.


Without some way of measuring torque, that is the best you can do. 17
hp per gph is a pretty good approximation.

No. I wasn't casting aspirations about calculating H.P. from fuel
consumption, other then meaning that it is an approximation. I was
more talking about your comment referring to propellers and gearboxes.

Given that the 71 series are no longer made what are rebuilt injector
prices like? Or have they gone out of sight because a lot of people
would rather have the old all mechanical engines then the new
electronic models?

Newly manufactured parts are available from various sources including
DD dealers. I've heard reports of some difficulty getting new
cylinder kits but the DD service center that I used in North Carolina
had no problem.

Given the umpteen million of those things that must have been
manufactured I assume that parts will be available for some time to
come. I worked on a pair of original Detroit Diesels installed in a
landing craft. They started on the first turn of the starter and ran
about 10 PSI of oil pressure most of the time. It didn;t seem to
bother them at all. Finally the owner did an overhaul on them and got
the oil pressure up to a more healthy figure but they didn't seem to
actually run any better.

As another aside I worked on some Russian truck cranes that had a
exact copy of the 6-71 engine in it. It had the old single spring
governor that used to run away and they parked them outside our
office. At idle the engines wold sit there surging and we used to make
bets on which one would run away and crater. None of them ever did
though. They were such an exact copy that GMC injectors were an exact
drop in fit.


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

Happiness is...
 

In article ,
Bruce in Bangkok wrote:

Given that the 71 series are no longer made what are rebuilt injector
prices like? Or have they gone out of sight because a lot of people
would rather have the old all mechanical engines then the new
electronic models?

71 Series Injectors are still being built in the After-Market Parts
Business, by a whole passel of OEM's. The same is true for MOST of
the Overhaul Parts for ALL of the DD 53, 71, and 92 Series engines.
About the only thing you can't get NEW, is the Block itself.

Bruce in alaska
--
add path before @

Happiness is...
 

"Bruce in Bangkok" wrote in message
...


I think that railway engines are basically generator prime
movers and
run at a constant RPM all the time. At least that is the
way a power
plant engine runs. It always runs at approximately rated
RPM
and the governor makes small adjustments up or down to
maintain the
proper frequency.


A train engine will increase RPM as the electric load goes
up.

Happiness is...
 

On Tue, 27 Nov 2007 14:54:25 -0500, "Scotty" wrote:


"Bruce in Bangkok" wrote in message
.. .


I think that railway engines are basically generator prime
movers and
run at a constant RPM all the time. At least that is the
way a power
plant engine runs. It always runs at approximately rated
RPM
and the governor makes small adjustments up or down to
maintain the
proper frequency.


A train engine will increase RPM as the electric load goes
up.


I guess I assumed that because they drove a "generator" that they were
generating A.C. .
Bruce-in-Bangkok
(Note:remove underscores
from address for reply)