View Full Version : Diesel/electric hybrid propulsion - experiences?

Andrew S/Y Rocquette
12-28-2005, 04:57 AM
Happy New Year all.

I've seen a couple of recent articles on the use of an electric motor linked into a charging generator/battery system recently.

General points seem to be:

1. electric motors have more even torque across their range.

2. diesel engines are relatively inefficient at the revs generally run.

3. therefore a 10hp electric engine will replace a 30hp diesel for the same output at the prop, and with significantly more torque at lower revs (v. useful for a long keeled old girl like ROCQUETTE, especially in reverse!).

4. The redundant diesel engine can therefore be replaced with a smaller generator, which is more fuel efficient in itself as smaller, and also which can be matched to the power output requirements for electricity generation - one example I saw replaced a 56 bhp engine with a 22 bhp generator.

5. systems can either be fairly simple and robust using the diesel purely to recharge the battery banks as and when required. One issue is space for the battery banks...alternatively it can be highly sophisticated and linked to smart charges and networked microcontrollers etc.

2 examples to quote: First is Classic Boat Magazine 206, August 2005 for 2 lake launches (simple installation), or alternatively as demonstrated in Water Craft 55, Jan/Feb 2006 (sophisticated installation).

What I'd like is anyone's experience of these systems and their pros and cons. Considering a retro-fit to ROCQUETTE in the next few years as her current engine is somewhat tired, also my father is commissioning a new-build narrow boat and I'd like to advise him on the possibilities for this for his canal boat - would be nice not to be sitting on a 48 bhp diesel as you're only chugging along scenic waterways at 4 knots...

Also, both the environmental friendliness and lower running costs seem worth while investing in - also although the electrics are going to cost more, it might be offset by the smaller generator unit as compared with a new larger diesel engine - so experience of installation and running costs also appreciated!



Andrew S/Y Rocquette
12-28-2005, 05:21 AM
See also this technical report (http://www.electric-boat-association.org.uk/technicalreport.htm) from the Electric Boat Association (http://www.electric-boat-association.org.uk) .

P.I. Stazzer-Newt
12-28-2005, 05:31 AM
The other Andrew was singing the praises of hybrid propulsion - but he was talking about Diesel/Hydraulic.

The major points were:
1. Installation flexibility - Put the engine where you want it.
2. Idiot resistant - Seems that many of the hire craft on the Norfolk Broads are now doing this.

Andrew S/Y Rocquette
12-28-2005, 05:40 AM

Yes - I'd initially looked into diesel hydraulic, but am rapidly being pursuaded maybe diesel electric is the way forwards...you can also build in redundant systems e.g. 2nd smaller back-up generator if desired, and can link also into mains when alongside, or wind and solar for trickle charging, and when sailing in a good breeze you can also unlock the shaft (if you have a fixed prop) and use the electric engine as a generator to charge the batteries as well...

I like the idea!

[ 12-28-2005, 05:42 AM: Message edited by: Andrew S/Y Rocquette ]

12-28-2005, 09:00 AM
Works for Norfolk Southern!
Diesel Electric has a strong history and is a well understood technology.

12-28-2005, 09:21 AM
Hello Andrew,
I see you have started working on your agenda for 2006 ! I do not have any experience with DC drives for marine applications but will comment nevertheless:

The DC motor exhibits a Torque vs. Speed characteristic that is dependent on the type of connection of the field circuit, viz., series, shunt, series + shunt (hybrid)or separately excited from an independent source.

It therefore has the makings of a very flexible prime-mover and as such, beats a diesel-engine hollow - or any other IC engine - on this count alone.

Current 4-valve-per-cylinder diesels have flatter Torque vs Speed curves but these inevitably exhibit steep slopes at start-up speeds.

That said and taking into acount the umpteen power-electronics/microprocessor-based packages available for DC motor control, the aforementioned characteristic may be brought to match - relatively easily - the characteristics of the load to be driven.

You would obviously need a DC supply to connect it to, originating from a DC generator - or an AC generator + rectifier - and/or a bank of batteries. The DC/AC generator could be tailored to operate on the most efficient operating point of (say) the diesel-engine driving it(normally at the speed at which the diesel-engine develops max.torque)

If there was nothing tangible associated with the diesel-electric set-up, British Rail and others would not have diesel-electric locomotives, nor would they be the solution for powering those gigantic lorries that one sees operating in quarries.

And I note that QM 2 has a set of 4 x 28 MW diesel-electric Rolls-Royce Mermaid units too. ;)

Uncle Duke
12-28-2005, 09:30 AM
You might check out the Solomon Technologies "Electric Wheel" system. It's been in use for a number of years and is pretty refined. Several nice papers here, and a good description of the system and it's advantages.
Electric Wheel (http://www.solomontechnologies.com/)

Andrew S/Y Rocquette
12-28-2005, 10:30 AM
Hi Cedric

Happy New Year to you in sunny Brazil! How's life?

Lucid and erudite comments (as ever!). Not sure if it is currently cost-effective to retrofit, but certainly interesting. Might have to await the next project (hopefully a new build...gotta dream!).

My father's having a 68 foot narrowboat built in the next couple of years: as it will be gadget-heavy anyway and will be all electric apart from the propulsion, why not go the extra step? Also the incremental cost of DC propulsion may actually mean it's practicable in that case...

Uncle Duke - thanks for the link. Will peruse.


[ 12-28-2005, 11:12 AM: Message edited by: Andrew S/Y Rocquette ]

Lew Barrett
12-28-2005, 10:40 AM
Fischer Panda has been working on hybrid drives for a number of years. Check this link:

Edited to add:
I think this installation is now about 2 years old; don't know what progress they've made since, but it's still featured on their site.



[ 12-28-2005, 10:58 AM: Message edited by: Lew Barrett ]

Graham Knight
12-28-2005, 12:09 PM
You'll lose your electric license discount!

Dan McCosh
12-28-2005, 12:13 PM
Diesel-electric for ship drives is also well understood. I think while the concept works, it is not so efficient as mentioned--where a 30 hp. motor can be replaced by 10 hp. There are intrinsic losses in the diesel-electric that would offset much of the prop efficiency gains. I would be suprised to see much more than 10-15% improvement. Integrating an onboard power supply into a diesel-electric drive system offers other benefits. All in all, it still is quite expensive.

12-28-2005, 12:31 PM
Hello Andrew,

Happy New Year to you too !

From recent personal experience, I would suggest spending a week on the island of Fernando de Noronha, 600km sharp-right into the Atlantic, off the north-eastern Brazilian coast, to evaluate our sunniness ;)

Your father´s upcoming 65 footer would seem nearly king size :rolleyes: . For one thing, the insulation on the DC Gen./Motor controls and of course the innards on the drives would need to be 100% pukkah .

Also makes you wonder if all drive equipment and components should need to comply with some degree of submersibility, as is required of Low, Medium and High Voltage electrical gear installed underground ? Definitely not trivial when dealing with rotating machinery, the intermediate coupling shafts, cooling louvers etc.etc.

That is a full plate for 2006, plus your on-going efforts managing Rocquette´s restoration from afar. ;)

12-28-2005, 12:47 PM
Dan McCosh wrote:

Diesel-electric for ship drives is also well understood. I think while the concept works, it is not so efficient as mentioned--where a 30 hp. motor can be replaced by 10 hp. There are intrinsic losses in the diesel-electric that would offset much of the prop efficiency gains. I would be suprised to see much more than 10-15% improvement.... You could be right :rolleyes: .

The big plus of diesel-electric drives seems to me to encompass the following:

1. Eliminate mammoth gear boxes between the prime-mover (diesel-engine) and the load, specially in locomotives and quarry lorries; a companion thread on the SS United States is illustrated with photos of the gigantic double-reduction gear box components as were used on steam-turbine-powered vessels.

2. Provide Torque on-tap - and thereby enhance manoeuvreability hundred-fold - over the whole Speed range of the vehicle/vessel.

Efficiency gains would only strenghten the case for its deployment.

Dan McCosh
12-28-2005, 01:23 PM
Railroad train engines are diesel-electric to allow clutching the power to the drive wheels--something that wasn't a problem with steam which produced maximum torque at 0 rpm. Only recently have they included some batteries to recover power lost while slowing. Same for earthmoving equipment. Ships using diesel electric seem to need the systems for maneuvering as well--the local USCG commercial tug has such a powerplant. Diesel submarines are an interesting hybrid. I've never seen a power analysis looking at how they work.

12-28-2005, 04:10 PM
I will definetly comment on this one. And it is nothing but positive, these are fantastic systems.
And far superior to just a straight diesel engine.

If you go into the solomon website and look in the news section, you will find a link to 100 years of electric propulsion and some great articles and information. These systems where used a 100 years ago on freightliners, and then the railroads adopted it, submarines use this system and modern ice breakers use it due to its superiority over a straight diesel being hooked to the shaft.

Andrew your first post is pretty much dead on as to the basic facts, you also will get about 3 times the fuel economy.

In it's simplist form, it is a straight electric boat, but you can reduce your volume of batteries as you do not need as much amperage or fuel since you can recharge on board as needed.
Instead of plugging your battery charger into land electric of 120 or 240 volt and recharging your batteries, you simply plug the charger into the generator, no big complicated deal.

Zivan makes custom chargers that work off of incoming electric of 120 - 240 - and even 400 volts, then the outgoing current is customized to your battery voltage of 48-72-96-120 and even 144 volts.Also manzanita makes chargers that take 50 amps at 240 volts or 12,000 watts or 12 kws.That is enough to run a 16 horse electric and you can get bigger chargers going into the 400 volt system or use more then one charger at a time.
You will loose about 12% of electric in the exchange.

Curtis makes controllers that go up to a continuos cycle of 225 amps at 144 volts or 32kws enough to run a 43 horse electric motor.
And zilla makes controllers for twice the bucks that will run around a couple hundred horses.

As for generators you can go to the small and simple honda quiet chargers to a onboard low rpm diesel made for marine useage from fisher panda or westerburke. They are designed for this application, being quiet and even fitted into their own closed compartment with water cooling and water exhausting.Westeburke has a 7.6 gen, that weighs 395 lbs and use a 1/2 gal. of fuel a hour and will continuosly run a 8 horse electric.

You charger has to be set up to demand less then the gen will produce, so you set you charger up to draw about 6,800 watts and then you loose about 12% in the exchange rate and end up with roughly 6,000 watts of battery charging.

As for motor sizing, yes you only need 1/3 and even less in transferring from ice or internal combution engine to electric motor.This has already been proven hundred of times. Look at the solomon site, they have replaced diesel engines with their elect. motor up to 1/5 and 1/6th the size.And people reported it is more responsive and stronger then the diesel it replaced.On the solomon site one canal boat, a large one they replaced a 60 horse diesel with a 6 horse electric, I am sure the diesel was old and tired and probably only producing half that horse, but anyhow the captain at first try shoved the throttle full ahead and was promptly slammed down in his seat when the boat shot forward and with a puzzled look he said the diesel would never have done that even years ago. That was in england as i recall, the article should be in the news section or in comparing horse versus torque section.

The reason you can reduce horse power so much is due to the torque curve, and torque is a mesurement of a twsiting force, what better place to apply torque then to the shaft on a boat.
Roughly speaking your 30 horse diesel will produce approx. 30 ft. lbs of torque at about 2/3 throttle, then drop off dramatically. And very little torque from low rpm's or idling. That is why the prop can't be too large or high pitch as to not create too much resistance to the diesel at low rpm's or it will choke out and kill the diesel.
A electric motor has basically a flat torque curve and will produce the same torque at one rpm as they will at full blast.A elect. motor also produces approx. 6 times the torque as they do horse, so a 5 horse elect. will produce the same torque that a 30 horse diesel does at 2/3 throttle. That is the magic of it all.

And if you want to get more pollution free you can even run the diesel generator off of bio diesel or some of the refined vegetable oils.

The diesel for the generator will be approx. 1/3 the size of the diesel that you would use to propell the boat with, and the generator diesel does not have all the pressure applied to it by simply running the generator as the diesel for propelling the boat does.Lot less stress and strain.

Wonderfull systems, particularly for dissplacement hulls and at 3 times the fuel economy very economical. If you do your homework you could easily set up a system for about a 30 footer for around $15,000 to $20,000...

Since you are in the UK. you need to get in touch with the uk electric boat society, they are all up and down the thames.They can show you what they are using and getting on your side of the pond.

Gary E
12-28-2005, 05:41 PM
Originally posted by RonW:
Westeburke has a 7.6 gen, that weighs 395 lbs and use a 1/2 gal. of fuel a hour and will continuosly run a 8 horse electric.

If you do your homework you could easily set up a system for about a 30 footer for around $15,000 to $20,000...Ron,
Even if all the other data is in the ballpark and is assumed correct... the typical marine diesel at full load will use 1 gal/hr per 20HP..and a lot less when at moderate load...that makes that generator that uses 16gph not so good in my book...

THen you say the price of a typical instalation for what I am going to assume a single engine boat is $15 to $20K... wow, lota buks.. for how much HP? to drive a 30 ft boat at what speed?

If this was so usefull how come a major mfg has not latched on to this?

As far as subs go... subs have been electric since they found out they cant run diesel underwater... Dont ask or even think about costs for a sub... since when did the govmnt? The nukes are able to stay down as long as the food lasts... smile.gif

[ 12-28-2005, 05:44 PM: Message edited by: Gary E ]

12-28-2005, 07:55 PM

I have no idea where you are coming up with a 16 gph figure, that is way off base.
Here is the westerburke site.
The 7.6 kw diesel marine generator has a 11 horse diesel, and westerburke has in plain print fuel consumption of .53 gal per hour. So maybe some one should inform them they are way off.

And you could put together a system for under $10,000 it just all depends on the quality of the system and the components that one would choose.

And why hasn't anyone else picked up on these systems, Well sorry to inform you but they have.
Have you ever heard of elco electric launches, they have hybrid systems, or how about duffy electric boats, thay have them too, and had a big 30 footer that was very nice with a 96 volt system. And if you took the time to look at the solomon web site listed above, they install hybrid systems as well, and in some rather large ocean going sailboats.

I am with andrew, a subject like this is brought up, and you have far too many negative posts condemming the system by those that have no idea in the world how it even begins to work.

Uncle Duke
12-28-2005, 10:11 PM
Gary asks:
If this was so usefull how come a major mfg has not latched on to this? Uhmmm...Solomon's Electric Wheel is offered as an option by Lagoon, Conser, Gold Coast, Nimble, Hinckley, and others.

Builders (http://www.solomontechnologies.com/Solomon%20new/Builders.html)

Thought you'd want to know....

Andrew S/Y Rocquette
12-29-2005, 05:23 AM
Thanks all for their comments - especicially Cedric (was than an invite to Brazil...? smile.gif ) and Ron.

Not sure it will be cost effective with ROCQUETTE at the moment, but hopefully prices will come down in the next year or three so I'll nurse her diesel a bit longer...

Cheers all

Edited to add: This month's UK Yachting Monthly magazine I picked up this morning has, by coincedence, an article by Nigel Calder on...diesel electric propulsion systems! Great minds think alike, or fools seldom differ? Hmm...

[ 12-29-2005, 05:28 AM: Message edited by: Andrew S/Y Rocquette ]

12-29-2005, 05:23 AM
On the Solomon under "INSTALLATIONS OF INTEREST" they give some good comparisons.
Anyone have a quote for a complete system?

12-29-2005, 08:15 AM
Ok, why do you got to them for an electric motor and batteries? And probably pay a premium price.
Why not buy a large DC motor, controller, batteries, and generator and put this together yourself?

Lots of information and suppliers are out there on electric motor propulsion.

12-29-2005, 08:23 AM
quick look on ebay shows this.

http://cgi.ebay.com/ebaymotors/Briggs-Stratton-Etek-DC-Electric-Motor-New_W0QQcmdZViewItemQQcategoryZ46093QQitemZ4599488 921QQrdZ1

An example here

Andrew S/Y Rocquette
12-29-2005, 08:23 AM
Exactly what I'm thinking - so has anyone actually done this on a yacht rather than outboard, and who can comment?

Edited to add: also see here (http://boatdesign.net/Directory/Propulsion/Electric/) for a boatdesign.net link to various maufacturers...hi ho! It's a quiet day in the City today...


[ 12-29-2005, 09:04 AM: Message edited by: Andrew S/Y Rocquette ]

Dan McCosh
12-29-2005, 12:05 PM
The claims about efficiency for hybrids appear to be based on some rather strange assumptions. In the tech paper for the electric boat, it says a 6 kw genset will power an 8 kw electric motor. This is obvious nonsense.
The torque vs horspower comparison also is meaningless, as horspower is the multiplication of torque and rpm.
A better way to look at this is that the 6 kw is about 8 hp. If the generator diesel is a 20 hp. unit, you have already lost 2/3 of the theoretical hp. making the electricity. A reduction gear would hardly be that inefficient--a 30 hp diesel provides about 100 ft/lb of torque at the shaft with a 2:1 reduction gear.
Anyway, it ought to be obvious that if you could actually triple the efficiency of a powerplant that is 32 percent efficient it would be 100 percent.
The actual advantages are mainly the flexible installation, and the ease of supplying aux power to the vessel. It would be worthwhile for that alone, but at three times the cost of an equivalent diesel, it isn't all that attractive.

12-29-2005, 01:08 PM
It is probably a little too late to get into this thread and I am not so sure I should, but here goes:

1. Some of the numbers you guys are using are not right. Yes, I know you found them on someone’s web page who should know, but... In Naval Architecture, the definition of horsepower is:
hp = 2*Pi*torque*RPM/550
torque is in lb ft
1 hp = 746 Watts
1 hp = 2,545 BTUs/hour

BHP = brake horsepower = HP at coupling
SHP = shaft horsepower = BHP with accessories and gear
EHP = effective horsepower = resistance of the vessel, measured at towline

Note that it doesn’t matter if the horsepower comes from gasoline, Diesel, electric or steam. 1-horsepower is one horsepower.

Marine gear and accessories usually lead to some efficiency loss. I usually allow 3% for gear alone. Accessories like hydraulic plants and alternators must be individually figured. I also usually allow 2% efficiency loss for bearing loss. Oh, and don't forget propeller efficiency (a new subject).

The 3% loss in a typical Diesel installation is presumably not a loss for electrical propulsion. However, Diesel-electric propulsion has significant heat loss when converting Diesel torque to electrical power. So, claims of significant superior efficiency of optimized Diesel-electric versus optimized Diesel alone are highly suspect.

2. The standard rule of thumb in Yacht Design and Naval Architecture for a Diesel engine running at an efficient speed places fuel usage at 16 hp per gallon per hour. The Yacht Designer or Naval Architects job is to specify the engine that will most nearly run at the most fuel-efficient speed most of the time. If this is not done, the guy didn't do a good job or the service of the vessel has variable power needs that do not allow the most efficient engine.

3. When would electric propulsion be best?

Electric propulsion is great (efficient) when you often need torque at low speed but still need to go fast sometimes. This is why ferries use them (along with reduced engine room manning requirements).

It is good when you need to be quiet.

It is good if you can charge batteries from a grid, though the cost of the batteries in both economic and environmental harm can be high.

Conclusion: Electric propulsion is efficient for some services (variable speeds) but not all. Diesel propulsion is more efficient than diesel-electric when operating at optimized speeds. At variable speeds, Diesel-electric can be efficient compared to Diesel alone if most of the time is spent at low speeds but the advantage is not as large as reported in this thread.

How do you plan to use your boat? Most of us maneuver away from the dock, move up to cruising speed and stay there for most of the time. This service would favor Diesel alone if significant time at cruising speed is desired. It would also favor electric propulsion (power from grid, without Diesel generator) if most trips were short enough to run entirely on batteries.

If you need long duration and are constantly maneuvering at low speed and occasionally need high speed, the Diesel-electric propulsion may be competitive.

David Mancebo

Mark Van
12-29-2005, 01:14 PM
I don't think that it is 3 times the cost of the equivelent diesel, especially if you would have a generator anyway. You can easily spend over $20,000 on a diesel inboard and genset. The Solomon drive, with batteries and generator, is around $30,000 for the equivelent of a 40 hp diesel inboard.

12-29-2005, 01:42 PM
Check out this website:http://www.feys.org/System/our_system.htm
I called them for replacing two 110hp 6cyl in my 34' Richardson. Estimated cost was $48,000, including $16,800 for a 4 cyl Yanmar, but not including any instalation. Great idea but too expensive.
:( :( PetrB

12-29-2005, 01:51 PM
On diesel electric hybrid cars, someday many of them will be in the wrecking yards.
Perhaps then I can go and get an afordable electric hybrid to put in a boat.

[ 12-29-2005, 01:52 PM: Message edited by: sdowney717 ]

Dan McCosh
12-29-2005, 01:51 PM
Bainbridgeisland is saying what I was attempting. Re the cost: last time I priced a 29 hp. Yanmar it was about $7,500, compared to the $20,000 quoted for the electric hybrid. The diesel includes a 100 amp alterator, adequate for most onboard electrics. A high-kw genset would be a different animal, of course, but as a powerplant alone, the hybrid cost is quite high.

Probably the most suitable installation for many sailboats would be an electric drive driven mainly by batteries, with a smallish genset recharging it. This wouldn't provide sustained power, but would get you into and out of most harbors. Recharging could also be supported by the usual windmills, solar panels, etc. A purpose-built sailboat would use the battery pack for ballast--it's mainly lead anyway.

12-29-2005, 02:36 PM
The second paragraph of Don McCosh´s post above, seems to sum it up, at least as dictated by the present scenario of outlays.

Assuming 90% efficiency for each of genset and motor, and say 30 % for a small diesel at its most efficient operating point , will provide for an overall efficiency around the mid-20´s %

12-29-2005, 03:11 PM
I still like this idea. All you need is to make enough heat to create steam powered jet.


12-29-2005, 04:59 PM
A couple of years ago I bought a new 1.9 VW diesel, the same that VW uses for their marine package, for under 2,000US$. I was new and was delivered to my doorstep for that price. I added a 180 amp alternator, starter, heat exchanger, gear box for under 1,000US$. The motor reportedly produces 54 HP. For a complete new setup I invested less than 3,000US$. It seems like the store bought system for the electric boat is a little on the high side?
There was a question ask about suitable electric motors at a lower price. I once bought a big ass electric motor .... generator to build an electric car. It was a starter motor for an airplane. For the size of it the motor must have been 83 cylinders? I didn't build the car and my brother built a giant welder from the generator. Surplus plane starter might be a source for motors?

12-30-2005, 07:42 AM

Thanks for the compliment and welcome to our sunny land !

In "People and Places" I have posted some pics on Fernando de Noronha.

12-30-2005, 07:48 AM
fuel cells may eventually show up on your boat in 20 to 30 years.
If you go to electric motors for propulsion the ultimate power source will be a fuel cell.
This article has quite a lot of information on what is happening right now and it looks pretty good.

Ian McColgin
12-30-2005, 08:21 AM
I was glad to see bainbridgeisland's remarks as sometimes enthusiasm overwhelms the practical.

For displacement hulls less than 30 tons, it's hard to beat the reliable simplicity of a solid diesel attached to a Hundestead or Sabb type controllable pitch propeller. You'll need a reduction gear but could dispense with the clutch and no need of a reverse. One might also consider the pricy but hydro-engineering trescool autoprop.

I could see some hulls where the advantages of more flexible location for main engine and drive unit would be so great, especially if one went in for a great deal more electric demand than I personally find fits life afloat, that diesel-electric or diesel-hydraulic make some sense, but at the cost of some important efficiency, especially all that waste heat.

Of course, if one operates entirely at high latitudes and sails in the winter, perhaps the rather vast waste heat of diesel coupled with hydraulic fluid cooling or alternator cooling could be solved by heating the boat and (as we did on the tugs) key parts of the deck.



Ed Burnett
12-30-2005, 09:35 AM
It is interesting to see this conversation going so far without someone mentioning propellers.

The fact of the matter is, a fixed pitch prop can absorb only a limited amount of power at low revs (determined by its pitch and diameter etc.), and this is way below the maximum power that a typical marine diesel is capable of delivering at those revs.

The graph below shows the power and torque curves of a small diesel and compatible prop. The black lines show the power that the diesel can develop, and the power that the prop can absorb at the same revs. The blue lines represent the torque that the engine is capabale of and the torque that the prop requires to turn at that speed. The assumption is that the prop is matched to the engine at or near maximum revs and power which is the way one would try to arrange things.


A normal diesel has ample torque at low revs relative to what it takes to turn a fixed pitch prop. Arguing that an electric motor of some sort is better in this application because of its ability to develop greater torque at low or zero revs is simply not relevant.

Land vehicles can benefit from the torque characteristics of electric motors at low revs, fixed pitch props can't.

Now for the qualifications. These comments apply to fixed pitch props on displacement vessels. Planing boats are a different kettle of fish, as are variable pitch props.

On another note, consider the following:

A modern diesel engine burns something in the region of 280 g/kW h. For example, 30hp (+/- 23kW) for one hour needs 23 x 280 = 6.44kg of fuel, which is 7.4 lt or 1.6ish gallons.

At the other end of the system is the propeller, which is perhaps 55% efficient, ie. 55% of what you put into turning it gets converted into useful thrust.

All that is being disussed here is the means of turning the rotation of a diesel engine's crank shaft into rotation of a propeller shaft. A normal gearbox will do this for the loss of around 5% of the power. That 5% is what is up for discussion here in terms of improving efficiency. Anyone suggesting that they can put all sorts of other stuff in place of the gearbox and improve the efficiency of the whole system by over 300% has some work ahead of them when it comes to convincing me.

Cruise ships especially have something to gain from diesel electric for various reasons, one of which is that they need lots of electricity for other things on board anyway. Ie. pushing the ship along is only part of the total power requirement of the ship. Vessels for inland waterways may also come into this bracket but auxilliary sailing yachts are very different.

12-30-2005, 10:12 AM
It is kind of a shame that most persons will agree with you. It is a nice dream when we think that an electric motor or some other device will rid us of the sound of a diesel drive motor. Then again, why do many sailboats use a diesel that sounds like something that should be used for an industrial cloths washing machine, chug chug and more chug? Then again how do us folks in the Americas relate to a kettle of fish?

Dan McCosh
12-30-2005, 10:33 AM
Diesels got popular mainly for two reasons: the engine itself has a very high thermal efficiency, arguably the most efficient way to turn fuel into power known, at least in small sizes. Secondly, the fuel itself has a high energy content per liter. The combination creates a power system with very high energy density--which means that the range per fuel volume/overall mass is very good. None of the alternatives mentioned can match it. If you are going to power a boat with fuel, it really has no peer.

Ed Burnett
12-30-2005, 10:35 AM
Gerald, I agree it would be wonderful if there were an equally practicable alternative to diesel.

Sails seem to work pretty well!

12-30-2005, 11:39 AM
A few hard core articles on what has already been done with hybrids might be interesting.

From a maasive icebreaker, check out the size of the ship, speed and range as well as electrical system.

On the other end of the scale at 20 to 30 ft. launches at dissplacement speeds.

And a couple articles on hybrid systems as to reliability and range, disscussing the toyota prius a popular hybrid car.

Gary E
12-30-2005, 12:12 PM
Not counting the ones that are over 100 yrs old...

Here is the list of current boats....

~ Present ~

The Bixby Family
Bolton Landing, NY 1893, 36' Launch "St. Louis"
William D. Forster
Mystic, CT 1995, 24' Classic Launch "Edison"
William Marshall Chester, CT 2000, 19' Classic Launch "Anna W."
Mr. Stephen P. Upham III Saratoga Springs, NY 1996, 14' Serenity "Sis"
Tom & Bonnie Cox Peoria Heights, IL 2003, 24' Classic Launch "Electra"

Ifin its Sooooooo good, why so few?

And the list of those for sale....

Year Length Model Color Asking Location
1989 30' Elco Classic, w/o trailer, w/canopy White $ 100,000 WI
1997 24' Elco Classic, w/trailer, w/canopy White $ 77,000 Elco
2001 19' Elco Picnic, w/trailer, w/canopy Blue $ 30,000 NH
1997 19' Elco Picnic, w/trailer, w/o canopy White $ 28,000 Elco
2000 19' Elco Utility, w/trailer, w/o canopy Blue $ 25,000 Elco
1899 33' "Original" Elco Classic, w/o trailer, w/o canopy White $ 77,000 Elco
1998 14' Elco Serenity, w/trailer Green CALL Elco
1962 18' Hudson River Packet, w/3 HP Elco Drive, w/trailer, w/o canopy Blue $ 25,000 Martha's
1935 16' ElectriCraft, w/1 HP Elco Drive, w/o trailer, w/o canopy
pic 1, pic 2, pic 3 Wood $ 33,000 Elco
2005 15' 6" Canadian Electric Boat, w/trailer, w/canopy - typical
pic 1, pic 2 Blue

Ok, so there are a few more not regestered in the first list....

Now, look at the price?... datz economy???

[ 12-30-2005, 12:21 PM: Message edited by: Gary E ]

12-30-2005, 02:49 PM
Ed Burnett wrote:

Cruise ships especially have something to gain from diesel electric for various reasons, one of which is that they need lots of electricity for other things on board anyway. Ie. pushing the ship along is only part of the total power requirement of the ship.... I am really intrigued with your posting. :rolleyes:

Obviously there are other electrical power requirements on a cruise ship. specially in the luxury-liner class.

Could these have swayed the decision of fitting 4 X 28 MW Rolls Royce Mermaids on the recently launched British luxury liner QM 2 ?

12-30-2005, 10:47 PM
I've no experience, thought about it a lot. I used to use an electric trolling motor on my 20' keel sloop. It was good enough. I worry about generators on board affecting my fastenings, and my compass. Just a thought. Let us know if you try.

Clan Gordon
12-31-2005, 01:08 PM
Some interesting points have been made re the use of electric power in small boats on this posting, but I will confine my comments to larger vessels.

As Dan and Ed and others have said......

There is no question that if one is designing a power plant for a ship that operates mostly constant speed, then electric drive rates far poorer than direct drive for;
- weight
- cost
- fuel efficiency

That is simply because ALL the systems require a prime mover (diesel, gas turbine or whatever) and because of the greater conversion losses that prime mover needs to be bigger than the direct drive drive equivalent. That also means it consumes more power meaning more fuel. Then there are the extra components needed;

1) prime mover
?) gearbox
?) shaft
6) propeller

1) prime mover
2) electrical generator
3) switchboard and transformers
4) electric motor and its speed control gear
5) prop shaft
6) propeller

All these extra bits cost space, weight and money.

It is for these reasons that large commercial ships DO NOT use electric drive unless;
a) there are some benefits to be obtained from locating the prime mover remote from the propulsor
b) the vessel's hotel/service electrical load is large and to build a separate electrical plant just to supply this might be inefficient

Even if there is a wide speed/propulsion load range - the usual solution to match the propeller to the diesel is the controllable pitch propeller - not electric drive.

Examples of a) include;
- locating the gas turbine generators for the QM2 up near the funnels where the large intake/exhaust ducts are not a big problem
- locating the electric propulsion motor in a pod in the sea thus freeing up internal space for cabins etc in a cruise ship
- locating the diesel generators on a semi-sub drill rig on the upper deck and the DP thrusters 30m below in the pontoons

Examples of b) include;
- cruise ships where the hotel/air conditioning load can be 11MW or more
- drilling vessels which have a large electric load when working, and much reduced when in transit

Most cruise ships are rather low powered and the hotel load is a large fraction of the propulsion load. Having ONE electric power station on board makes sense in this situation. But some recent cruise ships stuck with direct mechanical drive.

There are very strong arguments that the QM2 should NOT have had electric propulsion because her propulsion load is so high (unlike most cruise ships). Lets say she needs 88MW at the propellers. With a conventional direct drive system she could have installed say 89.MW of prime mover to do this. With electric transmission losses it would need to be about 100MW.

However, the points made above about location of gas turbines and putting electric motors out of the ship and in the sea were obviously factors in the decision, as is the ability to easily rotate one of the multiple engines in and out of duty (for servicing).