Diesel electric propulsion

[Sailor]

I have a question for the Knowledgable NAs around here. There are a ton of commercial vessels that use DGs. (Diesel Generators) and use the electricity produced to power electric drive motors. Our Navy has 2 classes of vessel that do this. MCDV (Maritime coastal defence vessels, and our diesel electric subs. My question is, why do yachts not use this method? The way I see it you could place the engine (Heavy and awkward) in a handy place and put a little electric motor right forward of the screw. this would eliminate heavy, costly shafts that are longer than they need to be, and would allow more flexibility of design in the planning stages. What's the deal with this. Or is it too expensive as of yet?

[Lew Barrett]

Well, I'm not an NA, or terribly in the know, but here is the link to the only major effort in the arena to which I am privy.
http://www.solarnavigator.net/fischer_panda_diesel_electric.htm

Seems very interesting to me; I even gave it a thought when I re-powered, but it seemed a bit radical. I thought it a better bet on a 37 foot Catalina, just as they did.

[Ian McColgin]

Power loss is the problem for small diesel-electrics. The loss of energy at each stage converting from thermal to mechanical to electrical to mechanical is more of a problem where you have little horsepower to spare than the losses of thermal to mechanical. In bigger than small yacht - well over 20 tons - applications, the inefficiencies of conversion may be outweighed by other considerations, especially propulsion gear location, performance range and design.

[garyspear]

The primary reason to use diesel generators to power the DC motors that drive the screw is to keep engine noise out of the water. the generators are mounted to the hull in a way to reduce noise as well. The Tagos Fleet at NAB in norfolk use this method. you can look on the usn's website and see if you can find a link. most boats don't use this beacause they are inherently noisy in the water. these ships deploy a sonar aray into the water and less noise is best.

My father was the senior port engineer on these boats before he died earlier this year and I was able to get a good look at this setup. on the scale that they need power and for the purpose the headace of this setup is worth it. i cant imagne that it could not be used on other boats though.

[RonW]

They do.....the queen mary 2 is the largest cruise ship in the world and it works just like that. Diesel generators producing electric, and the boat is being propelled by electric motors and is a all electric boat.
It has 4 electric pods at each corner of the boat, they look like giant trolling motors. Each pod has unbelievable horsepower.And the boat produces enough electric to run a small town, in fact I think it has a 10,000 people capacity, plus crew.

Ice breakers are set up this way too, being propelled by electric motors instead of diesel.Thats because a electric motor has about 6 times the torque of a equivalent diesel motor.

This is a neat system, it was first done in the very early 1900's by bananna boats delivering banannas. The system uses less fuel, trains are set up this way as well. But we have had too cheap oil, or did.

[Thorne]

Gotta be an economy-of-scale thing == good for large boats & budgets, but not for smaller of same.

The trolling motors keep getting larger every year, and although there are more powerful alternatives (golfcart motors, various commercial electric 'bottom ends') none are commonly available yet -- still more of an art than science.

Yahoo has an electric boat group with people who are DEEP into just this issue -

Subscribe: electricboats-subscribe@yahoogroups.com

[TimothyB]

Often, when folks talk about small diesel electric plants for boats or cars (being tested in scandahoovia) it is cited that the power losses mean you'll have to have a bigger plant for similar use. In a situation where all other things are equal, that would be true.

But as mentioned above, electric motors of size have great torque, and run extremely well when at low speed, unlike diesels themselves. So, if you slap on a larger, more pitched prop that is more efficient in the water than a smaller one you have more efficiency there. You have the gained efficiencies of using an electric motor at low speed/high torque. Depending on how this is setup, you can negate much of the theoretical loss from transmission and storage.

Also, it has been found that AC motors work much better for this sort of thing (in cars anyhoo) due to the very problem of transmission losses being solved by using AC instead of DC. It turns out that inverter losses can be fine tuned to be much smaller than the issues involved with using direct DC power and heavy cabling.

So, if you got yourself an AC generator, a hella AC motor sized for the job, a good Siemens inverter setup with regenerative circuits (they make these for electric cars) so you can generate power while freewheeling and a bank of NiCad batteries you would have a fantastic setup. It would cost twice or more what a regular diesel would (the inverter alone, for example, is $5k) but you would have 4 ways of getting power into your banks: Generator, Windturbine, freewheeling and solar panels.

Which is why more folks don't do it. It costs more to do it right :)

If you wanted to have a quick and dirty setup, DC and not terribly efficient you could probably scrape together the parts for it for VERY cheap. Second hand DC genset , DC motor from a forklift or golf cart, welding cable and a bunch of flooded cell batteries, plus a good regulator (the only thing you definitely don't want to skimp on) . This could be cheaper than buying a new diesel engine, but not cheaper than a used one probably. I'm guessing it would be about the same cost as that (given reconditioning and installtion), unless you had good scrounging luck.

And I second the recommendation to look at the electric boat group. :)

[garyspear]

Another consideration is that energy does not come free in a system. if you burn 3 gallons for a day with a diesel to go x miles. if you go x miles with the diesel/DCmotor setup you will use at least 3 gallons. (all other conditions being equal)

[JimConlin]

If being able to locate the engine somewhere else is the motive, it can also be accomplished with hydraulic pumps and motors. Also not without its drawbacks.

I think that the big motive for electric drive in icebreakers and buoy tenders is that they permit operating at very slow speed.

For large passenger vessels, the energy needs of the 'hotel' rival those of the propulsion system. Using the same engine for both is more flexible and redundant.

[John E Hardiman]

While most of the above posts have touched on minor reasons, the real reason that diesel -electric is not used extensively in yachts is......drumroll please.....

It is twice as heavy......

Most people want yachts that go relatively fast....and for a power boat...less weight is more speed. A small small diesel-electric set up only really works for very slow speed crusiers with large hotel loads where a 10% upsize in the generator is all the excess needed for propulsion, very similiar to cruise liners.

Edit..spelling

[RonW]

Right on Tim, right on.....

This is a very interesting propulsion system, and yes you can double or more your miles per gallon. The assumption or belief that it require so many miles per gallon and that is that, no matter how you configure it, is simply wrong, and have and is being proved and done.
But it is going to take some research into the subject to understand it.

First off you do not replace horses with horses, or a equivalent electric horse as with the diesel horsepower. In small boats, under a 100 ft. or so, you only use about 1/3 the horsepower in electric as you would in diesel. Solomon industries have proved this time and time again. And in some instances have used 1/4 and 1/6 the horsepower in electric as compared to diesel. That is the big exchange rate. It is due to the dramatic increase in torque per horse of a electric motor over a ice motor or internal combustion engine.

The original elco electric launches of the 1893 world trade fair in chicago, where mostly 36 footers for passengers and used a 5 horse electric motor, and can go as fast as 10 m.p.h. But these electric motors where trolley car motors and are about 3 feet in diameter with unreal torque power. You could not possibly run a trolley car on a 5 horse diesel motor, but yet it was done with a electric motor.

The other factor that is not being considered is the generator, it does not run all the time, but more like a 1/3 of the time with a d.c. setup, so the gen. produces enough electric to run the boat and recharge the batteries at the same time. Then it is turned off, till needed again, with no wasted electric, other then a exchange rate of about 12%.

Here is a elco system, it runs their electric boat for 75 hours off of 15 gallons of fuel. So how are you going to do this with a straight diesel engine. YOU AREN"T.............
http://www.electriclaunch.com/hybrid.htm

It is a ideal system for a 30, 40 of 50 footer trawler, sailboat, cabin cruiser.. On a smaller scale, the guys on the electric boat site are using small carry on honda generators, with a 5 gallong can to recharge their batteries with, by simply plugging their battery chargers into the little generator. Some of their systems that are set up for 24, 36, or 48 volts are simply using golf cart battery chargers.
Just that simple..

Solomon sets up all their systems into 120 or 144 volts, the higher voltage is more efficent and devolops higher torque. The a.c. motors are better then the d.c. motors but that means constant running of the gen, which may not be practical unless it is a larger boat and probably have more then one generator.

The world is changing, and technology is changing.
We had electric boats in the 1800's, and by the turn of the century(1900) there where twice as many electric cars as gas cars, but the rich that could afford a car, did not have electric at their country farms or summer homes so gas won .....

Last year I read where the french had reworked and was basically supercharging a little diesel engine, results where that it got better fuel economy, increased horsepower by almost 50% and almost tripled the torque curves. Bottom line is the little diesel was easily doing the work of a much bigger diesel that used over twice as much fuel. Now run the little engine on vegetable oil and tell the arabs to pack salt.

Hybrid systems in everything is coming..might be exciting except for the naysayers....

--I was writing as john posted, and yes their are problems with weight, speed and so forth, nothing is perfect..

[Mark Van]

Check out Somomon Technolagies.
www.solomontechnologies.com (http://www.solomontechnologies.com)

[garyspear]

lets not get offended. I did extensive work with the University of kentucky's electric car project. Most of it was with power consumption and this is what I base my opinoins on. I cling to carnot and the second law of thermodynamics. I'll look into what you're saying and see if i have oversimplified the problem. I think John's response is more to the point and is the biggest argument against.

[John E Hardiman]

First off you do not replace horses with horses, or a equivalent electric horse as with the diesel horsepower. In small boats, under a 100 ft. or so, you only use about 1/3 the horsepower in electric as you would in diesel. Solomon industries have proved this time and time again. And in some instances have used 1/4 and 1/6 the horsepower in electric as compared to diesel. That is the big exchange rate. It is due to the dramatic increase in torque per horse of a electric motor over a ice motor or internal combustion engine.


That paragraph has more smoke in it than a poorly tuned diesel that needs a valve job.

The amount of effective horsepower (ehp) required to propel a vessel is identical regardless of the prime mover. The same is true for shaft horsepower (shp) so long as the propellor is the same, and even if the propeller is re-optimized due to differing torque curves, the maximum difference would only be 5-10% in shp (lets say .65 for the diesel and .75 for electric).

Now for a 25 hp electric motor, the average efficency (i.e. ~1/2 load) is about 87% for a 240V DC, also about 88% for a 240V AC (wound or cage), and about 89% for Synchronous AC. Couple this to a basic generator or phase chopping motor controler efficency of ~85% and we get a power requirement in to the motor cables greater than the power requirement in the gearbox (using a very low estimate of 95% efficiency).

If we look at it in terms of horsepower required to be input (hpin) to get one ehp out at the prop, we get 1.62 hpin/ehp (1/(.65*.95)) for the diesel, 1.49 hpin/ehp (1/(.75*.89)) for direct electric of a battery, and 1.76 hpin/ehp (1/(.75*.89*.85)) for the diesel-electric. That is only a 8% advantage to the electric before you consider how the battries got charged or the weight to power requirements of a small vessel! And if you want to start arguing "thermal efficency" then lets start debateing where we draw that energy boundary. In that case, nuclear power has it hands down over all other choices in terms of documented efficency and safety.

I do this for a living, and I have been less than impressed with some claims that are out there. Lots of funny things going on with energy boundaries in the analysis. But don't take my word for it, go do a preliminary design yourself.

[Dan McCosh]

I think Solomon's claims are based on using two methods of determining horsepower--in effect using the rated brake horsepower of a diesel and comparing it to shaft horsepower of an electric. Even at that, they seem pretty optimistic.

[RonW]

Neat and interesting, I will add to the conversation (not being argumental at all) but as a point of disscussion.
There is a lot of hype and false claims in new energy, but some of it is interesting to say the least.

You mentioned if the propeller is reoptimized due to differering torque curves. A electric motor has basically a flat torque curve, unlike the ups and downs of a combustion engine due to r.p.m.'s

On solomon's old site which had a lot of good info (now they are sueing toyota saying they used their electric motor technology ) so their new site is vague.They said they quit using horsepower ratings, but went to foot pounds of torque value, as to what torque was required to turn what diameter prop to what r.p.m's level.
They did a lot of tank tests that where very interesting and informative. So they went to torque values instead of horsepower values as energy needed to do what.

How about if we look at a real world example that is operating.
Elco electric launch, one example, their 24 foot launch has a waterline length of 21ft and 6 inches, gross weight of 3500 lbs, not counting passengers of 8 to 10, so add another 1600 lbs making a total of 5100lbs. It has a top speed of 5.8 knots and uses a 3 horse electric motor to do this with.
In my humble math equasions- the square root of the waterline length is 4.6 and multiply that by 1.3 hull speed it comes to 6 knots and they say it does 5.8 knots. Accordingly to dissplacement speed charts at a multiplication of 1.3 times the waterline length, it should require (approx)one horse for every 500 lbs of gross weight. That would be a 10 horse diesel, so how are they getting by with only a 3 horse electric. I say or believe that the torque values are playing a very important role in the twisting of the shaft that is turning the prop.
Could you make that boat run to these specs with a 3 horse diesel?
http://www.electriclaunch.com/24ft%20launch.htm

So much of our math is based around horsepower equivalents, but when we go to other sources of energy, higher torque values and lower horsepower values, might work as well or better.
As in a comparison of the electric motor, which has basically a flat torque curve, from a few r.p.m's to thousands of r.p.m's where a combustion engine does not operate this way.

[Stari27]

Try looking at GFAST or http://www.feys.org/. They too a 52 ft cruiser with twin diesel v-8 and coverted to a single straight 6 and alternator. Cut the fuel in half. The genset is the "get home motor. Facinating until they gave me a price for my 1957 34 ft Richardson cabincruiser---try $48,000. I can buy allot of gas for that. I am still facinated with the theory and practice. But how do I conver the joy stic to work with the two chromed transmission levers on the Fortuna.

[Stari27]

Try looking at FAST or http://www.feys.org/. They too a 52 ft cruiser with twin diesel v-8 and coverted to a single straight 6 and alternator. Cut the fuel in half. The genset is the "get home motor. Facinating until they gave me a price for my 1957 34 ft Richardson cabincruiser---try $48,000. I can buy allot of gas for that. I am still facinated with the theory and practice. But how do I conver the joy stic to work with the two chromed transmission levers on the Fortuna.

[John E Hardiman]

You mentioned if the propeller is reoptimized due to differering torque curves. A electric motor has basically a flat torque curve, unlike the ups and downs of a combustion engine due to r.p.m.'s

Totally incorrect.
DC motor troque is inversely proportional to speed. http://lancet.mit.edu/motors/motors3.html
AC motors have a very peaky torque curve based upon phase lag (power factor). www.reliance.com/pdf_elements/b7113.pdf
Synchronous motors can be made to be flat, but that drops efficency by dropping the power factor.

They said they quit using horsepower ratings, but went to foot pounds of torque value, as to what torque was required to turn what diameter prop to what r.p.m's level.
They did a lot of tank tests that where very interesting and informative. So they went to torque values instead of horsepower values as energy needed to do what.

Torque @ rpm is hp....and hp is the units of power (i.e. energy over time)...energy is meaningless to propulsion unless you give it a rate. This is why true energy efficency is measure in things like sfc @ a given heating value.

How about if we look at a real world example that is operating.
Elco electric launch, one example, their 24 foot launch has a waterline length of 21ft and 6 inches, gross weight of 3500 lbs, not counting passengers of 8 to 10, so add another 1600 lbs making a total of 5100lbs. It has a top speed of 5.8 knots and uses a 3 horse electric motor to do this with.
In my humble math equasions- the square root of the waterline length is 4.6 and multiply that by 1.3 hull speed it comes to 6 knots and they say it does 5.8 knots. Accordingly to dissplacement speed charts at a multiplication of 1.3 times the waterline length, it should require (approx)one horse for every 500 lbs of gross weight. That would be a 10 horse diesel, so how are they getting by with only a 3 horse electric. I say or believe that the torque values are playing a very important role in the twisting of the shaft that is turning the prop.


Where are you getting a 10 horse diesel from? I make that hull (if well designed) as having a beam of 4.6 ft a draft of 1.5 ft and a wetted surface of ~80 sqft. Friction drag is 24 lbs and and Cr is ~ 1.4 Cf at this Froude # giving a total resistance of 57.6 lbs. ehp is then ~580 ft/ls-sec which would require, from our prevoius discussion ~ 1.78 bhp to drive it.

Could you make that boat run to these specs with a 3 horse diesel?
http://www.electriclaunch.com/24ft%20launch.htm

Yes, as I just proved.

So much of our math is based around horsepower equivalents, but when we go to other sources of energy, higher torque values and lower horsepower values, might work as well or better.

That is a prop efficency problem, not a prime mover one.

As in a comparison of the electric motor, which has basically a flat torque curve, from a few r.p.m's to thousands of r.p.m's where a combustion engine does not operate this way.

Again, the part about a flat torque cure is incorrect. Generated torque increases as efficency decreases in electric motors.

I think you need to sit down and learn about marine propulsion from a good un-biased text rather than an ad brochure.

[RonW]

originally posted by John Hardiman
Where are you getting a 10 horse diesel from? I make that hull (if well designed) as having a beam of 4.6 ft a draft of 1.5 ft and a wetted surface of ~80 sqft. Friction drag is 24 lbs and and Cr is ~ 1.4 Cf at this Froude # giving a total resistance of 57.6 lbs. ehp is then ~580 ft/ls-sec which would require, from our prevoius discussion ~ 1.78 bhp to drive it.


Unfortunately elco does not have a properly designed launch, their 24 footer has a beam of 7ft. & 2 inches. Sporting a 15 inch diameter by 12 inch pitch prop, being turned by a 3 horse electric.

Solomon's ad on their 6 horse. Scroll down and it shows a flat torque curve. They also claim it turns a 15 inch diameter prop up to 1200 r.p.m.'s which is the maximum r.p.m.'s for that motor. According to a prop chart from weston farmer, to turn a prop of that diameter to those r.p.m's he says it takes a 15 horse diesel.
http://www.solomontechnologies.com/pdf/motorspecsheets/ST37_specs2.pdf

I researched the hell out of electric propulsion for 2 years, it is interesting and we will be seeing more of it. Unfortunately for a straight battery system it takes 1800 lbs of lead batteries to do the work of, or have the energy that 60 lbs of gasoline does or approx. 10 gallons. The hybrid systems are real neat, but good marine generators like westerburke or panda from germany start at about 10k for a small one. By the way, there is a german electric boat site that sells a 21 footer that does 18 plus m.p.h. and they ski behind it, of course big wide ski's.
I wonder what the opinions and conversation on hybrid systems in boats will be 10 years from now....

[John E Hardiman]

Unfortunately .....(snip)
I wonder what the opinions and conversation on hybrid systems in boats will be 10 years from now....


I just mistyped and lost a 1 long hour posting...:o ...I'll try to redo it all in the morning.

Some points I can recall before I loose them.

Using your data on the elco, required diesel is still only 2.3 hp. The prop on the elco has 40% slip and needs 840 rpm and 31 ft-lbs torque to deliver 5 hp. The prop is most likely not optimized for the speed given. Most likely reason is the BAR is reduced to allow greater power applied at high slip during maneuvering.

Propeller diameter is only slightly linked to prime mover hp. I have built a 30" wheel that drove a 3700 lb hull to 4.7 knots in 300 feet from a standing start with 0.75 hp. I can drive an aircraft carrier at 5 knots with just 500 hp, I just can't accelerate it very fast. The high hp given as rules of thumb based upon vessel weight are for maneuvering, they are not generally for speed requiremnents.

There are some big holes in the Solomon ad. 6 hp out @ 1100 rpm means torque is only 28 ft-lbs, not the 35 shown in thier graph and not the 37 claimed. Additionally, the rated amps of 32 and voltage of 144 VDC gives an electrical hp of 6.1 for a 97+% efficient DC motor? I think not given 3 phase windings and the cooling fins on it. Finaly, the "prop power" curve shown is meaningless or worse. As only a diameter is given and no speed of advance,pitch,blade #, BAR, etc...it offers no meaningful information.

I believe electric propulsion has it's place. So do GT's, DCD's, and others. However , I'll wait until fuel cells are perfected and save a lot of weight and space.

[Pericles]

Those of you of an inquisitive nature might be prompted to hop over to the US Powerboat Show at Annapolis and visit Glacier Bay Inc. http://www.usboat.com/boat_show.cgi?exhibitor_id=539&boat_show_type=usps

There you would be introduced to the OSSA Powerlite concepts for diesel electric propulsion. http://www.ossapowerlite.com/faq.htm

I sent enquiries to both Fast Electric Yacht Systems and OSSA, but only Bruce Nelson from OSSA had the courtesy to reply. We shall be continuing our discussions upon his return from Annapolis.

Diesel electric propulsion has significant advantages, not the least being the high torque ability of electric motors to drive more efficient propellers at lower revs. Read their site, it is all explained very well.

Pericles

[mcdenny]

Would this all make more sense if we thought of the genset as the "engine" and the electric motor as the "transmission"? I believe that is the reason locomotives use the genset - traction motor setup. Since the motor can produce full torque at 0+ RPM you, in effect, have an almost infinitely high gear ratio transmission.

As John says, there is no free lunch in thermodynamics. Putting more gadgets between the energy input (burning fuel) and the output (prop thrusting water backwards) can't increase the efficiency, can only reduce it. If the opposite were true you'd have the makings of a perpetual motion machine.

Practically though, a hybrid might might do better ON AVERAGE because the ICE can run at its most efficient load & speed to get the most out of its fuel and store that in a battery to be used as needed by the motor, which can have better efficiency over a broader range of power output than an ICE.

Thats the main way a hybrid car saves gas - its doesn't run the ICE all the time, never mind regenerative braking. Drive a Prius at a steady 35 mph and the engine will shut off until the battery runs down, then run for a little while to drive the car and charge the battery, then shut off again.

This notion has limited application to boats, however, as cars need lots of power to have acceptable acceleration, far more than they need to maintain speed while sailors generally aren't so concerned about acceleration. A hybrid would pay if the boat spent a good bit of time running very slowly but also needed to cruise at a much faster speed Thousands of these hybrids already exist- think trolling motor on a bass boat.


The confusion over stating that a 6hp motor drives a heavy displacement boat as well as a 15 hp ICE comes from the rating system. Generally the motor rating is for continuous duty while the ICE rating is at wide open throttle, hardly what a prudent sailor would consider "continuous" duty. A thirtyish footer going 7 mph with 15 hp is only going to need about half that to go 6 mph so just slowing a bit drastically reduces the power needed. Did the 15 hp ICE just become a 7.5 hp ICE?

[garyspear]

Thank you john. I love the real world examples and obvious experience. This discussion has really given me some good jump off points for consideration.

EE or ME?

[TimothyB]

Excellent posts John. Reminded me of my first Physics classes. :)

Well, you're correct. But the thing is, what we're looking for is efficiency as related to how much fuel gets burnt to get X Nautical miles, not so much the idea of actually comparing horses.

In practice, electric motors are a heck of a lot easier to tune (their power curve) than an ICE. So, it becomes easier to get a better prop on there given a particular hull configuration and hydrodynamic conditions assumed during the average case. We can match the power curve to the usage curve expected more easily. Is this an engineering problem with a purely ICE boat? Yep. But most folks use off the shelf stuff for their ICE plant, and so they are definitely not working at optimal ranges. Electrical motors are easier to find in varying power curves.

As an aside, this is why Hydraulic transmissions are so great. You can run the diesel at its optimum RPM all the time and use the hydraulic system to feed that power to the prop any way you like. So you could get this efficiency that way as well. You can't recharge the hydraulic pressure from a wind turbine tho. :)

There is the fact that while sailing (assuming a sailboat) you can get free energy to help propel your boat when you need it via freewheeling, a wind turbine, solar, whatever. Its not a lot of energy, but even 10% is 10% less.

If we were to look at the electric system/motor as a transmission (as mentioned above) I think it becomes more clear how to approach the problem. Add to that the relative freedom of placement for the ICE powerplant and it gets even better. And you have the great fortune of being able to swap out your ICE for absolutely ANYTHING that can generate electricity... fuel cells, a gas/alcohol/veggie oil/hamster powered genset, an alien solar panel you found in Brazil... whatever :) It means that your prime mover is a DC motor with a VERY big MBTF and will fail an order of magnitude less than the ICE plant, which you can replace with anything you happen to have on hand and with no expensive twiddling and alignment.

Personally, even if the total consumption rate was the same or higher for a system like this, which it isn't when you toss in things like cogeneration and recharging from free sources (which are easier to engineer into a vessel when you have freedom of placement), I would still use it for the freedom and flexibility it offered.

[John E Hardiman]

Thank you john. I love the real world examples and obvious experience. This discussion has really given me some good jump off points for consideration.

EE or ME?

Naval Architect & Marine Engineer; and P E in NA&ME....so it's all mine...keel to truck, cutwater to dunce cap...:D

[John E Hardiman]

Well, you're correct. But the thing is, what we're looking for is efficiency as related to how much fuel gets burnt to get X Nautical miles, not so much the idea of actually comparing horses.


That's correct, and that's why large, moderate speed, high power transports (think displacement cruiser, bus, truck, train, containership, and jumbo jet) are more economical...on the overall analysis they use less fuel to deliver a ton of goods/people. It is no use having a sfc one half that of a larger system if it take you 3 time longer to get there or you have 1/3 the capacity. Small is not beautiful in the transport world. The best thing is to run a steam, GT, or ICE prime mover-genset at 100 power all the time, and this is what cruise liners and power companies do; adding and removing gensets as power demands require. The prime mover always run at 100% power. If you wanted to be really efficient and light weight in sfc, you could build several pulsejet-turbo-alternator gensets for your electric and cut them in/out as needed.

One of the hard points to get across is the overall "green-ness" of things. Take the solar-cells and rare earth permanent magnet DC motors that you cite (BTW, 25-50 hp AC multi phase locked squirrel cage motors are far superior to DC motors in MTBF in my experience) . Present construction methods and materials (they are called "rare earths" for a reason) show that the savings generated by these items will never repay the energy debit (im mining and processing) paid to produce them. That's why everone serious about "saving the environment" uses lower efficency but less manufacturing energy debt motors.

Many of the points you make are good, but thay are not all interchangeable. There is no one "best" answer for all requirements, only "better" for the specific design requirements.

[sdowney717]

Altair Nanotechnologies has a new fast recharge lithium battery they are putting in cars and trucks
http://finance.yahoo.com/q/h?s=ALTI

read the news on the company. Perhaps someday we will see an all electric boat running off fast charge lithium batteries.
They recharge in just a few minutes.

[Zane Lewis]

If you are talking about displacement speed aplications for an auxilary in a yacht and looking at electric then you must also consider Hydraulic. And I know which is likely to last longer in a marine environment.
For yachts with varying load from very light motor sailing to punching into a big head sea the ability electric or hydraulic or a variable pitch prop give are huge. All allowing you to run a larger prop than a conventinal drive would allow.
With a conventinal drive you have to be able to make full revs at full load at low hull speeds which means most of the time the engine is underloaded when runing at reduced revs or motorsailing.

Electric or Hydraulic could be expected to be only 85% efficent compaied to a direct gearbox at 96%. However this can be more than made upfor by the ability to get more drive from your prop and being able to optimise your engine speed to match the required horse power you need at any given time.

Both options would be more expensive than direct drive. In NZ $ for a 10-30hp diesel allow $1000 for a closed loop transmittion pump, $700 for a motor, add an oil tank, a filter $40 some Hoses $500 and an exturnal thrust bearing for your prop shaft say $2500-$3000 all up.
Cheer's

Zane

[Zane Lewis]

Sorry forgot to note above that you will find as others I think have mentioned that D/E drives are only found in Crusie liners due to the high electrical requirements of maintiaining pasengers. Most comercial ships are large scale piston engined, Google "Wartsila". And navel and high performance shipping may use turbine engines in addition to diesel engines.

[TimothyB]

One of the hard points to get across is the overall "green-ness" of things. ... savings generated by these items will never repay the energy debit (im mining and processing) paid to produce them. That's why everone serious about "saving the environment" uses lower efficency but less manufacturing energy debt motors.

Many of the points you make are good, but thay are not all interchangeable. There is no one "best" answer for all requirements, only "better" for the specific design requirements.

Absolutely, and I was not talking about total energy debit, but energy debit per dollar more like. For example, running an EV-1, plugging into the grid for recharge costs something in the neighborhood of 1/10 the amount per mile as using gasoline, with gasoline at something like $2.50 per gallon, assuming we use CAFE standards as a guide. Since there are far far fewer things to break in an EV-1 than in a regular car, it is also cheaper to maintain (by far) which, by the way, is one of the big reasons the electric car thing has been being dragged out. Dealers would stand to lose a huge amount of their revenue base in maintainence.

The trick here is to get our energy from a commoditized source, and to allow it to come through in a transparent way, thus increasing competition amongst power plant producers. Right now, ICE plants have the clear margin and only a very few companies are able to produce them since they are so bloody complicated. But Electric motors are dead simple, albeit precise, to produce.. AC especially easy since there don't have to be permanent magnets involved.

That being said, since we have a totally interchangeable backend (which we choose to use ICE to power for the moment, since it is the most convenient) we are no longer constricted. We no longer have to commit to a very expensive refit to change motive power. With the ridiculously high MBTF on electric motors we have much less worry that they will fail, and so we can concentrate on getting the best bang for our buck on the back end. Once fuel cells become feasible, we can just drop the thing in with a bit of installation hassle, some cabling and regulator tweaking. If we are in Timbuktu and our plant fails, we can swap in a gasoline generator. When some amazing Lithium compound batteries come by that promise to be safe AND store gobs of power, we can toss some of those into the mix, mixing up our storage and generation needs ad hoc as the situation demands.

We cannot both be totally green and do this sort of thing. If so, we would change totally to sails and have our auxillary entirely on battery used only in harbor. What I believe needs to be done is think about putting pressure on the marketplace and force out these innovations through competition. To some extent the hybrid electric plant helps in that mission. I sympathize with 'greening' things up, but the total amount of pollution and energy useage for ocean shipping is so miniscule compared to power generation and autos it need not concern us so much, and carbon neutrality can be gotten closer to by using biodiesel or alcohol (depending on your plant)whenever it is available. Far more important is, I believe, the forcing of competitiveness onto the energy market, allowing us to use whatever fuels we wish to use in order to power our plants. We should not be slaves to the fuels distribution systems set in place by the oil companies.. rather we should have multiple sources from which to draw our fuels. Hydrogen is a bugaboo in this regard, as they want to send it out in teh same distribution network that they control.

Essentially, we need more freedom as to from where we get our fuel.. literally. From water, sun, crops, algae, wind, whatever! That would give us a real market for energy, and we would be less constrained by a few princes in arabia and a few billionaires in suits. The start of that is making it really easy and relatively cheap to switch to new types.

[TimothyB]

Altair Nanotechnologies has a new fast recharge lithium battery they are putting in cars and trucks
http://finance.yahoo.com/q/h?s=ALTI

read the news on the company. Perhaps someday we will see an all electric boat running off fast charge lithium batteries.
They recharge in just a few minutes.

Just a quick comment...

It is true there are large Lithium batteries being prototyped for use on cars and trucks. The issue is they are VERY DANGEROUS. They require complicated charge equalization and management circuitry that prevents them from blowing up or bursting into flame if overcharged or overtaxed. I would be very reluctant to use these things on a boat with salt air and all that. I can't imagine the delicate circuitry would last that long, and given the consequences for failure I think it will be a bit before these sorts of batteries are used in consumer applications. They will need to address these stability problems before they can start installing them into electric vehicles.

That being said, there is a guy who has spent 30k on retrofitting his car with such batteries (plus all the other gear including motor, inverter, etc). Every battery (he has about 50 of them I believe) has a circuit board and tall heat sink on it, and the whole battery bay is criss crossed with wires. He is an EE and knows what he is doing, but even he has emergency cutoffs and fire suppression right there in the car.

[htom]

I used to be a big fan of the H* economy until someone pointed out that hydrogen was really only a way of moving energy about -- and that in some ways gasoline, et al, were better ways.

It seems (at least to me) that for "optimum efficiency", that both the propeller pitch and propeller RPM have to vary. If the prop pitch is fixed, varying only the RPM, how much -- if any -- improvement would result from changing to a variable pitch prop that was adjusted with the RPM? 1% (tiny)? 10% (some)? Huge? (Asking for guesses, not proofs.)

[TimothyB]

Variable pitch props are used this way all the time in commercial applications. It is just that it is more expensive to fit one of those than a fixed prop, so the yacht market, not anywhere near so concerned about fuel useage (think about how much those powerboats guzzle down) as they are about 'performance' tends to stick with fixed.

One really cool thing about variable pitch props is that you don't need a reverse gear at all. You just pitch the props backwards. There are also automagic units that match hull speed with prop angle/RPM for you, giving you the best efficiency all the time. Also, on sailboats you can pitch them at 90 degrees, so the blades present minimal resistance to the flow of water past the hull.

On the other hand, it is one more thing to break and they do need to be well maintained to be useful. Having them freeze up midocean would completely suck. :-)

[P.I. Stazzer-Newt]

http://www.bruntons-propellers.com/products/variable/autoprop/

[Dan McCosh]

Yesterday I was looking at a small electric car sporting a removeable windmill. The windmill was supposed to charge the batteries while the car was parked, then stored while the car was driving. This led to some interesting conversation about what you would expect with the windmill still operating while the car was running, particularly with a wind blowing. Windmill-powered boats have been built, with one benefit being they can sail directly upwind.

[Hesp]

http://marine-hybrid.co.uk/index.html

[72rdstr]

Was reading this earlier this morning. Lots of good info on fossil / electric hybrids.

Relative to a commercially available set up on yachts. What part do you think the added cost/complexity of have on the availabilty? Seems like you'd effectively be doubling the # of powerplants having a significant impact on maintenance and upkeep.

JMHO

[Sailor]

Maybe I should be a bit more specific. Weight is not a problem as the vessel in question is quite large. She's 57 feet on deck and is a sailing vessel. Lead batteries down low are not a bad thing in a sailboat. A larger battery supply is simply offset by using less lead in the keel for ballast. I also like the idea of quiet running in a calm anchorage at night. Getting underway without a sound in the middle of the night to make a tide or take advantage of a beautiful full moon withough waking the entire anchorage. I don't want to pay for diesel. the regenerative capability of solar, wind and freewheeling will ensure efficient use of mother nature when cruising offshore. The vessel in question is Peterson's 57 foot coaster. Fritha was built to her plans. She's a big heavy cruising boat that would not be set back by the installation of a heavy powerplant. Battery technology is advancing as well and by the time I actually build her the weight may no longer be an issue. I would like to be able to set up her interior any way I like. By installing an electric drive motor I can seal it away as there are next to no moving parts and I will have to deal with that part of the system much less frequently than the genset and batteries. just a thought