Two engines, single prop?
 

Hi all. I am looking for a long-range trawler and notice that many
converted fishing boats and other interesting (for me) ships have just one
engine. Many of the two-engine ships are semi-displacement ships. I
don't like those much. I just want two engines for when I'm in the middle of
the ocean. So there my question. Given that there is plenty of space in the
engine room, are there systems that would allow me to to fit a second engine
and switch between the two engines WITH EASE?

What I would actually like best (and what would be cheapest I suppose) is to
have to half power engines driving the single prop at the same time but I
suppose any system that would allow me to do that would be quite expensive.
I know it can be done though, since e.g. on the Denmark to Iceland ferry I
was told they use 4 engines to drive 2 props and selectively add or take off
engines based on power requirements (or engine failures I suppose)

So.... anyone?

Thanks

Y wrote:
Hi all. I am looking for a long-range trawler and notice that many
converted fishing boats and other interesting (for me) ships have
just one
engine.

The problem would be to balance the two engines. Which is why you
typically see either 1 shaft per engine or one generator per engine and
a electric motor driving the screw.

In the navy on a destroyer we could run on any combination of 4 boilers and
2 shafts. Guess all you need is steam power!!
G
"Y" wrote in message
...
Hi all. I am looking for a long-range trawler and notice that many
converted fishing boats and other interesting (for me) ships have just one
engine. Many of the two-engine ships are semi-displacement ships. I
don't like those much. I just want two engines for when I'm in the middle
of
the ocean. So there my question. Given that there is plenty of space in
the
engine room, are there systems that would allow me to to fit a second
engine
and switch between the two engines WITH EASE?

What I would actually like best (and what would be cheapest I suppose) is
to
have to half power engines driving the single prop at the same time but I
suppose any system that would allow me to do that would be quite
expensive.
I know it can be done though, since e.g. on the Denmark to Iceland ferry I
was told they use 4 engines to drive 2 props and selectively add or take
off
engines based on power requirements (or engine failures I suppose)

So.... anyone?

Thanks

In article ,
Y wrote:

Hi all. I am looking for a long-range trawler and notice that many
converted fishing boats and other interesting (for me) ships have just one
engine. Many of the two-engine ships are semi-displacement ships. I
don't like those much. I just want two engines for when I'm in the middle of
the ocean. So there my question. Given that there is plenty of space in the
engine room, are there systems that would allow me to to fit a second engine
and switch between the two engines WITH EASE?

What I would actually like best (and what would be cheapest I suppose) is to
have to half power engines driving the single prop at the same time but I
suppose any system that would allow me to do that would be quite expensive.
I know it can be done though, since e.g. on the Denmark to Iceland ferry I
was told they use 4 engines to drive 2 props and selectively add or take off
engines based on power requirements (or engine failures I suppose)

So.... anyone?

Thanks

A fellow I met with a large (90-foot) "expedition yacht" told
me his arrangement was a single propeller shaft driven from the
main diesel engine, but also incorporating a hydraulic drive unit.
In the event of main engine failure, the two generators could be used
to turn the main shaft via this hydraulic coupling.

Many military vessels use diesel-electric drive, where the actual
shaft is turned by a very large electric motor. This allows
many coupling arrangements by electrical switching of the current
to the main motor, but this is generally too expensive for most
private yachts.

On Wednesday 19 January 2005 07:14, James Hebert wrote:

A fellow I met with a large (90-foot) "expedition yacht" told
me his arrangement was a single propeller shaft driven from the
main diesel engine, but also incorporating a hydraulic drive unit.
In the event of main engine failure, the two generators could be used
to turn the main shaft via this hydraulic coupling.

Many military vessels use diesel-electric drive, where the actual
shaft is turned by a very large electric motor. This allows
many coupling arrangements by electrical switching of the current
to the main motor, but this is generally too expensive for most
private yachts.

I figure he must be driving the generator on the main shaft as a motor
then? Interesting emergency solution indeed. But I wonder, what would
the power output of that 'engine' be and will be able to move you very far.

I'd love to get some real cost figures for a real electrical propulsion
system as that seems to do precisely what I am looking for.
Buy four or six cheap and small diesel engines to drive one electric
engine. First I thought that driving the engine indirectly in this way
would create some humongous losses BUT after some research I just did I
found that the losses due to the conversion from diesel power to electric
are no more than some 10% and even better that you more than make that up
by always running your (way cheaper) engines at much better load (60%)
by selectively switching off the ones you don't need. Of course that
load is much better for the engines too. So actually it turns out to
be cheaper to operate and gives truly amazing redundancy.
Installing some kind of battery (electric car? fuel cell?) might also
allow you to move without starting the engines at all and thus (if
for short spells with a battery) in total silence...
I am really excited about these possibilities! Problem is, nobody seems
to sell or install these things? And I *really* don't think this is a
DIY project... Perhaps the technology is still too new or not (yet?)
popular enough.

Very old technology... WWII T-2 Tankers, for example, used electric
propulsion. For a yacht, IMO, it's fairly impractical. Cost, weight,
space, environment, and long term owner maintenance are issues which would
require resolution. Most systems on boats are very reliable and well
proven. A properly set up and maintained single diesel will last forever
and give few problems. Redundant fuel systems (including tankage) increase
reliability significantly. A larger displacement slower turning diesel will
give more satisfaction in a displacement hull. For the nervous a get home
hydraulic drive powered by the generator set should suffice as back up.
Again, redundant fuel systems for each engine including the gen set greatly
increase reliability.

Butch
"Y" wrote in message
...
On Wednesday 19 January 2005 07:14, James Hebert wrote:

A fellow I met with a large (90-foot) "expedition yacht" told
me his arrangement was a single propeller shaft driven from the
main diesel engine, but also incorporating a hydraulic drive unit.
In the event of main engine failure, the two generators could be used
to turn the main shaft via this hydraulic coupling.

Many military vessels use diesel-electric drive, where the actual
shaft is turned by a very large electric motor. This allows
many coupling arrangements by electrical switching of the current
to the main motor, but this is generally too expensive for most
private yachts.

I figure he must be driving the generator on the main shaft as a motor
then? Interesting emergency solution indeed. But I wonder, what would
the power output of that 'engine' be and will be able to move you very
far.

I'd love to get some real cost figures for a real electrical propulsion
system as that seems to do precisely what I am looking for.
Buy four or six cheap and small diesel engines to drive one electric
engine. First I thought that driving the engine indirectly in this way
would create some humongous losses BUT after some research I just did I
found that the losses due to the conversion from diesel power to electric
are no more than some 10% and even better that you more than make that up
by always running your (way cheaper) engines at much better load (60%)
by selectively switching off the ones you don't need. Of course that
load is much better for the engines too. So actually it turns out to
be cheaper to operate and gives truly amazing redundancy.
Installing some kind of battery (electric car? fuel cell?) might also
allow you to move without starting the engines at all and thus (if
for short spells with a battery) in total silence...
I am really excited about these possibilities! Problem is, nobody seems
to sell or install these things? And I *really* don't think this is a
DIY project... Perhaps the technology is still too new or not (yet?)
popular enough.

A few years ago, I was able to go all thru the old Huron LIghtship in
Port Huron, MI. I was surprised to see that it had 2 old 671 GM
Graymarine diesel engines driving one prop thru a common gear box. The
ship still had to be towed from its dock on the St. Clair River to its
location about 5 miles north in Lake Huron because of the current at the
mouth of the river.

Seen at the Seattle Boat Show:

A new 39-foot power catamaran with optional diesel/electric drive
system.

Hi, I do remember seeing a marine transmission that tied two engines
into one output shaft. It was in a trade paper, I'll have to see if I
still have it at home. It was a commercial unit that only allowed one
engine to be in gear at a time. I'll look for it tonight.

On Wednesday 19 January 2005 15:26, Butch Davis wrote:

Very old technology... WWII T-2 Tankers, for example, used electric
propulsion. For a yacht, IMO, it's fairly impractical. Cost, weight,
space, environment, and long term owner maintenance are issues which would
require resolution. Most systems on boats are very reliable and well
proven. A properly set up and maintained single diesel will last forever
and give few problems. Redundant fuel systems (including tankage)
increase
reliability significantly. A larger displacement slower turning diesel
will
give more satisfaction in a displacement hull. For the nervous a get home
hydraulic drive powered by the generator set should suffice as back up.
Again, redundant fuel systems for each engine including the gen set
greatly
increase reliability.

Butch


I actually read it was first used on ships in combination with steam
engines, so yes, that ain't too new BUT technology has advanced quite a bit
in the mean time. It might just be time to look at the technology again now
with new materials, power semiconductors and better electric
motors available. I think it looks pretty exciting. Of course you'd
want to get a picture of the cost. As far as availability, I found this:

http://www.abb.com/global/abbzh/abbzh251.nsf/wfrmMainFrame!ReadForm&db=/global/seitp/seitp161.nsf&v=17E96&e=us&ep=&c=F061D79CE14FC002C1 256BFA0051BB3A

If the link is broken, just search for 'azipod' on the abb home page.
I think ABB at least is thinking there is future in it.