Diesel Electric - practical?

[NickCharman]

This winter, I have got to that time. To change the engine. I could do the normal thing and replace the 4-108 with a Beta 43 hp or similar replacement.

But I have read about installations where the engine is configured with a generator, running nearly silently in a really well sound-insulated box, on wobbly soft mounts, running at peak efficiency rpm, generating electricity (AC 110v presumably?) and the propulsion is electric motors on the shaft, and therefore also magically quiet. Side benefits of having loads of spare electical power for fridges, watermakers etc. Also theory says that if the engine is running at peak efficiency all the time, it can be smaller, lighter and be more fuel effficient than a normal engine/gearbox/shaft solution.

How practical is this really? No doubt possible, but is the expense so far outside the normal solution as to make it impractical? How does one scope up the pwer requirement?

Any one got experience of this? Or forget it, and trudge the well worn paths?

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[ccscott49]

Quite common on medium to big ships, also hydraulic power to shafts, which is better, more controllable, as the electric motors to be really controllable need to be DC. I've seen a cat with one engine (mounted midships, crossways), and two hydraulic drives to the props in each hull, very good it was aswell. Well worth investigating.

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[claudio]

DC Motors are bad news for maintenance. What's wrong with AC invertors, they've been around for the last 30 years or so and have been proved reliable and efficient. The current generation of ac motor control is far better than DC, in fact there is very little true DC equipment fitted to modern industrial machinery.

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[ccscott49]

What about diesel electric trains, cranes, oilrigs, pumps and numerous ships? A lot of these use silicon controlled rectifiers, with ac generation and dc motors. Some even use direct engine control, with DC generation, especially big drilling rigs and very big diesel electric digging cranes etc. AC motors prefer and are more efficient at constant RPM, not up and down, like cranes etc. DC motors are instantaneously available and produce max torque at minimum rpm or even stall.

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[AndrewJ]

I seem to remember that a VERY large cruise ship (one of the princess lines, believe built in Holland) which operates out of florida has just such an arrangement, generator to DC motors. The DC motors are mounted outside of the hull and can be rotated to thrust in any horizontal direction. The arrangement did away with the propellor shaft and stuffing box,
also the rudder. Course that might be outside the budget related to a smaller
vessel.

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[Alex_Blackwood]

Most modern Diesel Electric drives on medium/large ships are via some form of inverter to give a varying voltage and change of direction to the drive motor. these can be ac-dc for dc motors or ac-dc-ac for ac motors. the ac-dc-ac drives are either Pulse Wave Modulation (PWM) for induction motors, Synchroconvertor or Cycloconvertor for Synchronous motors.
These all have the common problems of heat dissapation and more importantly they all produce Harmonics in the vessels electrical system. Harmonics will cause all sorts of problems with other equipment especially if it has capacitors in the circuit. Fluorescent lights, computers, navigational equipment, TV's and friges. are all susceptable. This is overcome in ships by the fitting of tuned inductive/capacitive circuits, Harmonic Filters, these have to be designed for each particular installation. Needless to say none of the above is cheap!
If you install a straight ac-ac drive with a constant voltage to an induction motor you need to have a variable pitch prop. in order to alter speed and go ahead and astern.
All of the above systems would require a distribution system via a switchboard to cater for the propulsion system and the domestic system.
You still need batteries and charging system for when the engine is not running.
The simple answer to your question is: I suppose it is possible but I should think EXPENSIVE.

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[NickCharman]

An american solution?

Thanks for the contributions so far - I also put this on Cruising World BB in the USA - and have been pointed at a website of an operation who have developed a system for this type of thing - its at http://www.solomontechnologies.com/

Any views on this? Looks expensive - they have technology which was developed for the moon buggy and something they call Electric Wheel.

Quite interesting tho. Perhaps I'll have them spec it up.


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[qsiv]

Re: An american solution?

.. but at 144V DC, thats a LOT of batteries. Equally trying to source a 144V DC genny might be tricky. SOme of the boats had 2/3 tonne of batteries aboard...

What sort of displacement is your boat? What size is current engine?

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[sailorman]

there was a german manufacturer who made an electric drive & featured in yachting monthly some years ago (5 > 10 yrs).
u require a greater battery capacity that may well equal a normal engine weight, but u can then run a smaller / lighter diesel genny @ constant revs.

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[julianl]

Here are a couple of links for manufacturers:

http://sql.fischerpanda.de/product_eng_1_57.html

From looking at the FEYS website you might think that it is a dead company because they don't seem to have updated the news section for over a year which is curious since there was a big article published in a US magazine (Passagemaker) in June this year about an installation in a 40 foot boat. I get the impression that the FEYS system doesn't really scale down too well for the sort of power you're talking about but looks very interesting as an alternative to 200HP or greater conventional diesel replacement.

The second link is possibly more interesting to you. I think someone further down this thread already alluded to "a german manufacturer"; well, I suspect they were thinking of the Fischer Panda WhisperProp system.

Finally, here is a link to a rather detailed article on re-powering a big boat (50m) but it is still interesting some of the detailed discussions of the various issues:

<A target="_blank" HREF=http://www.vripack.com/articles/propulsion.htm>http://www.vripack.com/articles/propulsion.htm</A>

Hope that helps. Do post any other info you come across in your research.

- Julian

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[Jcorstorphine]

A friend used to own a very old yacht which did not have room for a diesel engine down in the bowels of the boat but there was room for a DC motor. The engine as you mention was fitted out of the way. The problem in those days was that it being DC used tramcar type speed control with all sorts of resistors and bare copper contacts. Every few weeks all of the contcats had to be cleaned.

Going back to present day, a 30 kw 415 Volt generators will cost you about £5 to £7K ish (depending on where you buy it and how new it is) a 30 kw motor will cost about £1k and a frequency invertor for speed and reverse will cost about £3k so you are looking at a spend of £10K.

If you talk to Lancing Marine they do a 30 kw unit based on a Ford unit, talk to BERL for a 30 kw 415 motor (make sure they know it will be used with an invertor as it may need a constant speed fan) and talk to ABB for a frequency invertor.

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[Jcorstorphine]

A friend used to own a very old yacht which did not have room for a diesel engine down in the bowels of the boat but there was room for a DC motor. The engine as you mention was fitted out of the way. The problem in those days was that it being DC used tramcar type speed control with all sorts of resistors and bare copper contacts. Every few weeks all of the contcats had to be cleaned.

Going back to present day, a 30 kw 415 Volt generators will cost you about £5 to £7K ish (depending on where you buy it and how new it is) a 30 kw motor will cost about £1k and a frequency invertor for speed and reverse will cost about £3k so you are looking at a spend of £10K.

2nd hand diesel gen set from www.dieselgenerators.com will cost about £3.7K

If you talk to Lancing Marine they do a 30 kw unit based on a Ford unit, talk to BERL for a 30 kw 415 motor (make sure they know it will be used with an invertor as it may need a constant speed fan) and talk to ABB for a frequency invertor.

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[qsiv]

You may also find here

I'm contemplating this for the next boat - I need something very light, and already have 24V aboard for the keel canting hydraulics, so it is quite practical. The boat, although 40', displaces less than 4 tonnes and is very easily driven...

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[reeac]

You mention "peak efficiency rpm". The fuel consumption per bhp at various speeds is available for most marine engines and is usually minimum at mid-revs.- say 2000-2500 rpm depending on the engine and this usually gives an acceptable boat speed so it seems to me that you can attain this peak efficiency without having any unusual arrangements. Having an "electrical link" will, in any case introduce an additional set of power losses and reduce overall efficiency. I always understood that the point about diesel-electric drive was to give a means of starting and accelerating a heavy load from rest - not a frequent requirement in the world of smallish boats.

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[Birdseye]

Whats the point?
1/ you wont be able to use a smaller diesel unless you have serious battery capacity to effectively lop off the peak demand. Dont forget the power losses in the wiring and motors - likely to be at least as much as a gearbox
2/ With same size engine, it must cost more. Probably will with a smaller engine and large battery bank.
3/ Be very surprised if it didnt weigh a lot more.
4/ More to go wrong.
5/ If you start to use the lots of electricity available, it doesnt come for free.

Neither Honda nor Toyota have made a real success of their hybrid cars. If they cant, with all their resources, why are you going to do so on your boat?

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[Paulka]

The power out of a generator is an illusion, and here is why :

The efficiency of any generator or electric motor is 80 - 85% at best.
To propel your yacht, you'll need : one diesel engine, one generator, one motor driver, and one motor,
Thus, the global efficiency of ~ 70% (.8 x .85) for a generator - electric motor.
The efficiency of the driver will be around 85 - 90%.
Thus, 60% (.8 x .85 x .9) for an ensemble generator - driver - electric motor.
What does this means?
It means that a little over half the energy out of the diesel will reach the propeller!
Connecting the propeller directly to the diesel, via a gearbox, will get at least 95% of the energy to the propeller.
This means as well that you'll have to burn nearly twice as much fuel to provide the propeller with the same energy.

Further, the weight and volume of the generator, driver, motor, will be enormously higher than the weight and volume of any gearbox, the maintenance of the driver, made of sophisticated electronics, not really loving sea water, all add to the price (not only financial) you will pay just to have a "high tech" propulsion system.
Not to speak about the bigger diesel needed to provide the propeller with the same energy!

I would bet for about twice the weight, and three times the price to get the same energy to the prop.

Of course, such systems are in use on many commercial boats, but are certainly unpractical for yachts under say .... 40 - 50 meters (130' - 150')

Sorry for the desillusion.

Paul

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[kingfisher]

Vetus

Vetus is currently developping the diesel-elctro drive
http://www.vetus.nl/producten/mainns.asp?productid=115&lang=2


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[oldharry]

I would have thought the best small boat solution is to use hydraulic drives. The engine can then be placed anywhere in the hull, it is fully and instantly controllable, and you havent got all those electrics to go wrong in the marine environment.

I recently did some work on a fine ex RNLI hull from the early 60s, which had twin Gardeners running hydraulic drives. This allowed a watertight engine room (copper lined!) in the event of capsize and meant that any failure in the sterngear was fully isolated both from the machinery space, and from the rest of the hull, being in a seperate watertight compartment. The hydraulic motors themselves could of course run totally immersed if need be, allowing the lifeboat to continue even with a major sterngear problem.

An electric drive train would have been totally useless in this application, and for the same reasons I would have thought it impractical for a small boat other than inland.

There is 'The Electric Boat Company' somewhere in the Midlands, who specialise in battery powered Canal boats, who could no doubt assist with motors and control gear. But I do not know their address.

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[pvb]

You know, it might just be practical...

...though, even if it is practical, it might still not be good value (although what is "good value" when we're talking about boats?). But electric propulsion is certainly intriguing, and the pleasure in manoeuvering silently into a marina berth must be immense! From your profile, we can see that the fact that you're a fan of unstayed rigs means that you're already prepared to embrace different ideas, so you're probably a good candidate to try electric power on behalf of the forum!

You've already looked at the which contains a lot of detailed justification and some very interesting fuel efficiency calculations. Solomon seem to be the leaders in electric boat propulsion, at least in the relevant 30-50ft seagoing category. Take a look also at this old <A target="_blank" HREF=http://www.sailnet.com/collections/articles/index.cfm?articleid=matthe0954>SailNet article which also focuses on a Solomon motor.

It's apparent that it can't work as simply as the "generator + motor" idea which you first floated. You need a big battery bank as well - around half a ton of batteries in fact - but it may be possible to accommodate these in a way which won't upset your boat's stability.

It might be worth your while having a look at a Solomon-powered boat; it could convince you to give it a try. Please keep us advised.



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[oldharry]

Re: the myth of silence....

Ummm - the only way of running an electric boat silently is by using batteries. A generator is always - but always - going to make noise! If anyone could come up with a way of silencing the exhaust and vibes from a halfway decently powerful diesel - a fortune awaits that man!

Even an electrically powered boat makes a little noise - i have an electric outboard which is brilliantly quiet compared to the Yam 2 i use the rest of the time.

The pain is lugging enough batteries around to give a decent cruising range! Having a genny puttering away in the dinghy to power the outboard really totally defeats the object!

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