Is this practical?

I have a 35 ft boat with a very old 671 diesel with a 1.5 to 1 reduction gear.
I am installing a 6 HP Petter diesel aux which will probably give me about 3 KW
of electric power when coupled to a generator. I have a really nice 5 HP 24 VDC
PM continuous duty motor and a DC motor controller that can handle 375 AMPS.
When my main engine gearbox is in neutral, it is fairly easy to turn the shaft,
not a lot of friction. If I put the boat in gear and crank my starter motor
with the fuel shut off to the main engine, I move some water with the prop, not
a lot, but it is turning slow and doesnt seem to bog down the starter much
motre than if the gearbox were in neutral.

I'd like to just put a flat (no protruding center coupling) chain sprocket
between my propshaft coupling faces and have the coupling bolts go through
holes in the sprocket to affix the sprocket firmly between the flanges when
they are recoupled. That should only move my prop back an distance equivalent
to the thickness of the sprocket. I propose to have the DC motor set up to
drive the propshaft through roller chain which would only be connected in case
of a main engine failure. I'll figure out the right ratios between the motor
sprocket and propshaft sprocket to avoid overloading the DC motor. If my main
engine is diabled, do you think this set up would get me home using the Petter
driven gen as a power source? I'll probably use a 110 AC gen and convert it to
24 DC with a power supply. Even one or two knots might help in a jam.

Your thoughts? Any good web info on this type of setup?

I've thought about an electric drive while I was working on
Lionheart's shaft alternator problems. Lionheart is an Amel Sharki 41
ketch.

The shaft alternator is driven by one of those flat serpentine belts
used on newer cars that has a lot of little V's on the inside of it
from a large pulley permanently clamped to the shaft, which turns
under sail to provide power. The alternator sits on top of the shaft
behind the transmission on a little stand to hold the belt tight.

I don't see why that couldn't work backwards letting a motor drive
that pulley in your application. If you are going to have AC power
available, why not ditch the DC power nonsense and go with a variable
AC motor speed control and a suitable AC drive motor straight off the
alternator, making it all more efficient. There are some whopping
variable-speed AC motors available from electrical supply places.
746W/horsepower, you'd have about 6 hp off a 5KW genset at full
throttle. It'd be a long road home.....

A very old 6-71 has just been broken in if someone changed its oil
when they were supposed to. Is it hard to start in its condition?



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

I don't claim to know all the math for coverting the AC to DC, etc. But I
have seen a similar set up using hydrualics.

This was on an old 45ft work tug converted for coastal cruising and family
dive boat..

They had a single 671 with a sprocket between the shaft coupling halves,
like you discribe.. The generater was a Westerbeke (unknown size) but but
had a medium size hydraulic pump driven off a PTO. This was normally used
for deck winches, windlass, etc. However, all they had to do was slip the
chain onto the sprocket and they had emergency 'get home power'..

I'm not sure of what type of reverse gear this engine had and it there ever
was any problem turning it in nuetral.

The owner claimed he did 300 miles in Baja on that arrangement when the 671
broke down.

Just something I remember seeing, FWIW.

Steve
s/v Good Intentions

You say you have about 3 kW available. By the time you go through the
controller, motor, perhaps a gearbox, and chain drive how much power are you
going to be able to deliver to the prop?
And this assumes that you have the prop, it does not have a rope wrapped
around it, the stern gland hasn't seized, the shaft hasn't broken ... etc
etc. If what you are after is an alternative drive, I'd make it totally
independent of the existing system. What about borrowing the largest
trolling type motor you can possible power, and seeing how that goes.

David

"BOEING377" wrote in message
...
Is this practical?

I have a 35 ft boat with a very old 671 diesel with a 1.5 to 1 reduction
gear.
I am installing a 6 HP Petter diesel aux which will probably give me about
3 KW
of electric power when coupled to a generator. I have a really nice 5 HP
24 VDC
PM continuous duty motor and a DC motor controller that can handle 375
AMPS.
When my main engine gearbox is in neutral, it is fairly easy to turn the
shaft,
not a lot of friction. If I put the boat in gear and crank my starter
motor
with the fuel shut off to the main engine, I move some water with the
prop, not
a lot, but it is turning slow and doesnt seem to bog down the starter much
motre than if the gearbox were in neutral.

I'd like to just put a flat (no protruding center coupling) chain sprocket
between my propshaft coupling faces and have the coupling bolts go through
holes in the sprocket to affix the sprocket firmly between the flanges
when
they are recoupled. That should only move my prop back an distance
equivalent
to the thickness of the sprocket. I propose to have the DC motor set up to
drive the propshaft through roller chain which would only be connected in
case
of a main engine failure. I'll figure out the right ratios between the
motor
sprocket and propshaft sprocket to avoid overloading the DC motor. If my
main
engine is diabled, do you think this set up would get me home using the
Petter
driven gen as a power source? I'll probably use a 110 AC gen and convert
it to
24 DC with a power supply. Even one or two knots might help in a jam.

Your thoughts? Any good web info on this type of setup?

"BOEING377" wrote in message
...
Is this practical?

I have a 35 ft boat with a very old 671 diesel with a 1.5 to 1 reduction
gear.
I am installing a 6 HP Petter diesel aux which will probably give me about
3 KW
of electric power when coupled to a generator. I have a really nice 5 HP
24 VDC
PM continuous duty motor and a DC motor controller that can handle 375
AMPS.
When my main engine gearbox is in neutral, it is fairly easy to turn the
shaft,
not a lot of friction. If I put the boat in gear and crank my starter
motor
with the fuel shut off to the main engine, I move some water with the
prop, not
a lot, but it is turning slow and doesnt seem to bog down the starter much
motre than if the gearbox were in neutral.

I'd like to just put a flat (no protruding center coupling) chain sprocket
between my propshaft coupling faces and have the coupling bolts go through
holes in the sprocket to affix the sprocket firmly between the flanges
when
they are recoupled. That should only move my prop back an distance
equivalent
to the thickness of the sprocket. I propose to have the DC motor set up to
drive the propshaft through roller chain which would only be connected in
case
of a main engine failure. I'll figure out the right ratios between the
motor
sprocket and propshaft sprocket to avoid overloading the DC motor. If my
main
engine is diabled, do you think this set up would get me home using the
Petter
driven gen as a power source? I'll probably use a 110 AC gen and convert
it to
24 DC with a power supply. Even one or two knots might help in a jam.

Your thoughts? Any good web info on this type of setup?


Probably more practical than a setup that I used on a 50' workboat that had
a 671 in it. I used a Briggs & Stratton 2.5 HP gas engine as an auxiliary
generator to top off the 24 VDC batteries when the main engine wasn't being
used for a few days (bilge pumps were pretty active on that boat!). I
mounted this auxiliary high above the propshaft, on a couple of heavy 2x12
planks. I also rigged an auxiliary bilge pump at one side of the B&S engine,
with the 24VDC generator on the other side. I could run either by slipping
the V-belt over the appropriate pulleys.

I then noticed that the auxiliary engine shaft was roughly parallel to the
prop shaft, so rigged a split pulley around the prop shaft and got another
real long V-belt so that I could drive the prop shaft from the B&S engine.
This wasn't too good, since the pulley ratio was about 3:1. The B&S engine
needed to turn maybe 3000 RPM to yield full HP, but the low pulley ratio
bogged down the engine quite a bit. The B&S engine might have died a quick
death if I asked it to work full-load for a day or two. But still, I could
motor around at a couple of knots in protected waters.

I never had to use this emergency system, as my 671 was very reliable. Just
as well, because, in retrospect, it was a pretty dumb contraption. Your
concept is OK, and it will likely work. How long, in an emergency, is
another question. Cooling, of all segments, is critical. Bearing alignments,
lubrication and vibration control too. I think I'd overhaul the 671 first.

Ed

We're sort of doing this on Fintry.

We have a Perkins 6-354 that was driving a 30 kw 220VDC genset that we're
going to use for hydraulics, primarily for a sixty horse bow thruster, but
also for docking capstans, crane, windlass, etc. The main reason for not
driving the hydraulics off the Cat 3406 main is that while docking, you
probably want the main to be idling most of the time, just when you want to
be taking sixty horse for the thruster.

In the conversation with John Champion at American Bow Thruster, he asked
about get-home.

We've ended up specifying an extra hydraulic motor driving a roller chain
sprocket on the propeller shaft. We've calculated the sprocket sizes so
that the shaft will turn the right rpm with the available horsepower (sixty
less losses). We'll put the chain over the two sprockets only when needed.
For short term use, lubrication is not a real issue -- hitting it with an
oil can every few hours will get us home from anywhere. This may get messy,
but it's an emergency.

So, while your idea should work, and my instinct tells me that 6hp may be
enough, I'm not sure I would go electric. For one thing, a 6hp diesel will
not drive a 5hp electric motor. For another, you'll turn on the motor with
the shaft stopped, so you'll need enough torque to start it turning. That
will require careful design.

If the main is soft mounted, you need to think about the fact that the shaft
will be moving around -- either mount the get home motor on the main engine
or look at how much relative motion the chain drive will accept.

One thing to do carefully. Ask your propeller manufacturer or naval
architect what shaft speed will absorb the horsepower you have available at
the shaft. This has to be done in steps, because then you have figure out
how fast the boat will move at that shaft speed and adjust the number for
the slip at that speed. This is one place where having hydraulic or
variable speed electric drive would help, as you can accelerate the shaft
slowly up to speed as the boat gets moving, taking only as much HP at each
speed as you have.
--


Jim Woodward
www.mvFintry.com


..
"BOEING377" wrote in message
...
Is this practical?

I have a 35 ft boat with a very old 671 diesel with a 1.5 to 1 reduction
gear.
I am installing a 6 HP Petter diesel aux which will probably give me about
3 KW
of electric power when coupled to a generator. I have a really nice 5 HP
24 VDC
PM continuous duty motor and a DC motor controller that can handle 375
AMPS.
When my main engine gearbox is in neutral, it is fairly easy to turn the
shaft,
not a lot of friction. If I put the boat in gear and crank my starter
motor
with the fuel shut off to the main engine, I move some water with the
prop, not
a lot, but it is turning slow and doesnt seem to bog down the starter much
motre than if the gearbox were in neutral.

I'd like to just put a flat (no protruding center coupling) chain sprocket
between my propshaft coupling faces and have the coupling bolts go through
holes in the sprocket to affix the sprocket firmly between the flanges
when
they are recoupled. That should only move my prop back an distance
equivalent
to the thickness of the sprocket. I propose to have the DC motor set up to
drive the propshaft through roller chain which would only be connected in
case
of a main engine failure. I'll figure out the right ratios between the
motor
sprocket and propshaft sprocket to avoid overloading the DC motor. If my
main
engine is diabled, do you think this set up would get me home using the
Petter
driven gen as a power source? I'll probably use a 110 AC gen and convert
it to
24 DC with a power supply. Even one or two knots might help in a jam.

Your thoughts? Any good web info on this type of setup?

One thought.... After 20 years of diesel boating I have had to limp home
3 times...(I have almost always had twins) Two times from prop issues
and once due to a broken shaft... If you are looking at a "get-home"
solution I would lean towards something that is 100% redundant. Even
with Spare shaft and a low pitch wheel, you still have single point of
failure with the strut, etc. If you do decide to go forward with
this I would suggest getting a very low pitch wheel and dumping the
gearbox.



Jim Woodward wrote:
We're sort of doing this on Fintry.

We have a Perkins 6-354 that was driving a 30 kw 220VDC genset that we're
going to use for hydraulics, primarily for a sixty horse bow thruster, but
also for docking capstans, crane, windlass, etc. The main reason for not
driving the hydraulics off the Cat 3406 main is that while docking, you
probably want the main to be idling most of the time, just when you want to
be taking sixty horse for the thruster.

In the conversation with John Champion at American Bow Thruster, he asked
about get-home.

We've ended up specifying an extra hydraulic motor driving a roller chain
sprocket on the propeller shaft. We've calculated the sprocket sizes so
that the shaft will turn the right rpm with the available horsepower (sixty
less losses). We'll put the chain over the two sprockets only when needed.
For short term use, lubrication is not a real issue -- hitting it with an
oil can every few hours will get us home from anywhere. This may get messy,
but it's an emergency.

So, while your idea should work, and my instinct tells me that 6hp may be
enough, I'm not sure I would go electric. For one thing, a 6hp diesel will
not drive a 5hp electric motor. For another, you'll turn on the motor with
the shaft stopped, so you'll need enough torque to start it turning. That
will require careful design.

If the main is soft mounted, you need to think about the fact that the shaft
will be moving around -- either mount the get home motor on the main engine
or look at how much relative motion the chain drive will accept.

One thing to do carefully. Ask your propeller manufacturer or naval
architect what shaft speed will absorb the horsepower you have available at
the shaft. This has to be done in steps, because then you have figure out
how fast the boat will move at that shaft speed and adjust the number for
the slip at that speed. This is one place where having hydraulic or
variable speed electric drive would help, as you can accelerate the shaft
slowly up to speed as the boat gets moving, taking only as much HP at each
speed as you have.

Yes, there's a single point of failure -- actually points -- everything
from the stuffing box aft. Everything on a boat is a compromise of some
sort, and that includes the get home.

The good news -- single screw boats are much less likely to have propeller
and shaft problems than twins, and most of those are from hitting something.
While it is certainly possible to imagine something that would take out
Fintry's propeller, it is unlikely. The shaft is 5.75" diameter, which is
way oversize for 400hp at 400 shaft rpm. The propeller is right behind
considerable deadwood. The propeller itself is massively built. (see
http://www.mvfintry.com/pix/sternqtr800.png)

So while it isn't perfect, it's a relatively short money answer to a main
engine failure in mid ocean....

As far as doing without the gearbox (if I understand you correctly), by
using a low pitch wheel, the numbers don't work. The boat's designed for a
59" wheel and you simply can't turn a propeller anywhere near that size
without substantial reduction, in this case 4.5 to 1.

--
Jim Woodward
www.mvFintry.com


..
"Ed" wrote in message ...
One thought.... After 20 years of diesel boating I have had to limp home
3 times...(I have almost always had twins) Two times from prop issues
and once due to a broken shaft... If you are looking at a "get-home"
solution I would lean towards something that is 100% redundant. Even
with Spare shaft and a low pitch wheel, you still have single point of
failure with the strut, etc. If you do decide to go forward with
this I would suggest getting a very low pitch wheel and dumping the
gearbox.



Jim Woodward wrote:
We're sort of doing this on Fintry.

We have a Perkins 6-354 that was driving a 30 kw 220VDC genset that
we're
going to use for hydraulics, primarily for a sixty horse bow thruster,
but
also for docking capstans, crane, windlass, etc. The main reason for not
driving the hydraulics off the Cat 3406 main is that while docking, you
probably want the main to be idling most of the time, just when you want
to
be taking sixty horse for the thruster.

In the conversation with John Champion at American Bow Thruster, he
asked
about get-home.

We've ended up specifying an extra hydraulic motor driving a roller
chain
sprocket on the propeller shaft. We've calculated the sprocket sizes so
that the shaft will turn the right rpm with the available horsepower
(sixty
less losses). We'll put the chain over the two sprockets only when
needed.
For short term use, lubrication is not a real issue -- hitting it with
an
oil can every few hours will get us home from anywhere. This may get
messy,
but it's an emergency.

So, while your idea should work, and my instinct tells me that 6hp may
be
enough, I'm not sure I would go electric. For one thing, a 6hp diesel
will
not drive a 5hp electric motor. For another, you'll turn on the motor
with
the shaft stopped, so you'll need enough torque to start it turning.
That
will require careful design.

If the main is soft mounted, you need to think about the fact that the
shaft
will be moving around -- either mount the get home motor on the main
engine
or look at how much relative motion the chain drive will accept.

One thing to do carefully. Ask your propeller manufacturer or naval
architect what shaft speed will absorb the horsepower you have available
at
the shaft. This has to be done in steps, because then you have figure
out
how fast the boat will move at that shaft speed and adjust the number
for
the slip at that speed. This is one place where having hydraulic or
variable speed electric drive would help, as you can accelerate the
shaft
slowly up to speed as the boat gets moving, taking only as much HP at
each
speed as you have.

If you are going to have AC power
available, why not ditch the DC power nonsense and go with a variable
AC motor speed control and a suitable AC drive motor straight off the
alternator, making it all more efficient. There are some whopping
variable-speed AC motors available from electrical supply places.
746W/horsepower, you'd have about 6 hp off a 5KW genset at full
throttle. It'd be a long road home.....

A very old 6-71 has just been broken in if someone changed its oil
when they were supposed to. Is it hard to start in its condition?

Yes, hard to start unless preheated or shot with ether. Runs OK once started.
OLD... ex navy 1944. Estimate over 20,000 hrs w/o OH. Will have to consider AC
drive motor idea. Doesnt speed control involve a $$$ variable freq inverter?
Or are you talking about brush type motors?

They had a single 671 with a sprocket between the shaft coupling halves,
like you discribe.. The generater was a Westerbeke (unknown size) but but
had a medium size hydraulic pump driven off a PTO. This was normally used
for deck winches, windlass, etc. However, all they had to do was slip the
chain onto the sprocket and they had emergency 'get home power'..

Hmm, sounds good, maybe I could use hydr.instead of elec. The Petter 6 HP aux
diesel has a main shaft that runs at 3600 RPM and another shaft that runs at
1800. I could drive the AC gen off the main shaft and a hydr pump off the 1800
RPM shaft. When I needed to use the hydr for get home motive power I could just
run the AC gen with no load. I dont think an unloaded gen takes much parasitic
power from the engine. I guess I could use an orbit type hydr motor with roller
chain to drive the propshaft sprocket, those orbit motors have tremendous low
speed torque. Thanks to everyone for all the great suggestions.