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.

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 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.

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.

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)

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)

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)

"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