Electric motor/generator ?

Bill Roosa · Aug 6, 2014

Not really, you still need the motor to turn the generator so that is a wash weight wise. the generator and electric motor are big hunks of metal and weigh a LOT more than a transmission. a transmission is 98% efficient at converting high speed rotation to low speed rotation and providing reverse. generators and electric motors are around 90% efficient so the combination is only 81% efficient vs 98% for a transmission. They also take up a lot more space than a transmission.
The reason they use engine-generator-electric motor on big ships is that they are actually cheaper than making a transmission that large and they allow the engine to operate at a constant (best efficiency) speed while the prop can turn at whatever speed you want.

Sailm8 · Aug 6, 2014

It appears to be efficient only on a large scale. You don't see any diesel electric semis on the highway but you do see trains running along side. Maybe when super batteries appear it would have a chance.

Bill Roosa · Aug 6, 2014

And for the "why not use a battery......" question, pound for pound and volume for volume diesel fuel has a lot more energy in it than any battery.

Terry in Naples · Aug 6, 2014

There is a new lithium battery discovery from WSU that triples the capacity of the battery. This type of innovative breakthru may indeed be the catalyst to newer electric motors in cars, boats ..well everything. So hold on to your hat.. It may be closer than you think.

Dave Groshong · Aug 6, 2014

The guy who purchased my 37ft IOR design boat took out the diesel and installed an electric motor, coupled with lots of solar panels, he motored it from Seattle to SF Bay

http://www.electricyacht.com/

Bob McL · Aug 6, 2014

Another reason for electric on ships is that the electric driven prop can rotate 360-degrees. In one harbor our cruise ship could not anchor but the motors held the ship in place even with the turning tides. They just put the GPS on "hold position" and we were told that it would automatically stay within five feet of the designated spot. The ship could also move completely sideways making parking way better than auto park on cars. Pretty slick!

rtshinn · Aug 7, 2014

Running a small diesel at its most efficeint speed to charge a bank of batteries , combined with solar panels does make some sense. The engine only runs when the batteries need charged, instead of idling whether or not you want to move. But yeah, there is a loss with every conversion from one form of power to another.

Battery technology is still the Achilles' heel.

Bill Roosa · Aug 7, 2014

The reason diesel-electric (that is the correct technical term) is not that useful for boats is there is a constant load. I would note that I've never seen a boat with a "gas peddle" , they have a throttel that is not designed for constant changes in load like a car engine. Soooooo
in an auto application the motor can be down sized to meet the agerage demand (75is MPH cursing) and the batteries take care of the accelerating. On a boat you always operate at the average and are not accelerating the boat so adding a system to charge the batteries all the time while the electric motor consumes the generated power is kinda dumb. You don't need a battery in this situation and so cannot down size your motor and gain efficiency....
Bottom line is until you can store as much energy as your diesel tank can in a battery there is really no sense in "going electric"

Gunni · Aug 7, 2014

Electric propulsion works great on the Gunboat cats! www.Moonwave-systems.com

Bottom line - there are more ways to generate steady electricity on a boat than an internal combustion engine, and there is a completely independent alternative propulsion system - the sail plan. Propellers become generators.

Bill Roosa · Aug 7, 2014

So in a pinch when you need more than 4 hours of engine life you turn on the (you guessed it) diesel engine!!!!!
I'm impressed with the tech but it just is not there. I gota believe that the money invested is going to keep me in diesel fuel for quite some time.

capta · Aug 7, 2014

What you are describing is, as mentioned above, a diesel electric drive system. It is most popular in trains, but was used to operate cargo, military and Coast Guard vessels for many years.
However you are not talking about a simple 110 volt or even 220 volt ac system. Most are 380 volt, 3 phase systems, or more, and the weights involved are quite a bit more, for the same hp, than a diesel engine alone. The advantage of instant full torque, is not a priority for an auxiliary engine on a sailboat. I have researched this several times, thinking a continuous speed generator running an electric motor might be more economical to purchase, install and operate than a variable speed diesel auxiliary, but it just does not work out that way. Considering a 50 hp electric motor consumes 37.3 kW of electricity, this means you would need at least a 40 KW generator ( 40.5 kW. in actuality, if the efficiency of the electric motor is 92%), a bit of a beast for a smaller yacht. Even with solar, wind and generator charging, 37.3 kW is a lot of electricity to manufacture. It would triple your maintenance, as well.
I'm afraid until Dr. Emmett Brown invents the flux capacitor, we are pretty much stuck with the internal combustion engine to power our boats.

Gunni · Aug 7, 2014

capta said:
What you are describing is, as mentioned above, a diesel electric drive system. It is most popular in trains, but was used to operate cargo, military and Coast Guard vessels for many years.
However you are not talking about a simple 110 volt or even 220 volt ac system. Most are 380 volt, 3 phase systems, or more, and the weights involved are quite a bit more, for the same hp, than a diesel engine alone. The advantage of instant full torque, is not a priority for an auxiliary engine on a sailboat. I have researched this several times, thinking a continuous speed generator running an electric motor might be more economical to purchase, install and operate than a variable speed diesel auxiliary, but it just does not work out that way. Considering a 50 hp electric motor consumes 37.3 kW of electricity, this means you would need at least a 40 KW generator ( 40.5 kW. in actuality, if the efficiency of the electric motor is 92%), a bit of a beast for a smaller yacht. Even with solar, wind and generator charging, 37.3 kW is a lot of electricity to manufacture. It would triple your maintenance, as well.
I'm afraid until Dr. Emmett Brown invents the flux capacitor, we are pretty much stuck with the internal combustion engine to power our boats.

Are you dismissing any hydro, wind, solar generation and assuming no storage? Beyond that, you already have +60kW generation capability onboard, and you have it in two diesel engines. Right? You also have a propane energy system, and a gasoline engine system. Maintenance indeed. The question becomes should I retrofit, and that is where the cost/benefit evaluation meets the existing investment, and the answer is most likely a NO. This is new boat technology.

capta · Aug 7, 2014

Gunni said:
Are you dismissing any hydro, wind, solar generation and assuming no storage? Beyond that, you already have +60kW generation capability onboard, and you have it in two diesel engines. Right? You also have a propane energy system, and a gasoline engine system. Maintenance indeed. The question becomes should I retrofit, and that is where the cost/benefit evaluation meets the existing investment, and the answer is most likely a NO. This is new boat technology.

I don't understand what you are asking? Where are you getting 60kw? I was assuming the OP had a fairly small vessel. Where did you come up with two diesels? What has propane have to do with the viability of a diesel electric system on a small craft? Who in their right mind would built a gasoline electric system? I really do not understand anything you are saying?

Gunni · Aug 8, 2014

capta said:
I don't understand what you are asking? Where are you getting 60kw? I was assuming the OP had a fairly small vessel. Where did you come up with two diesels? What has propane have to do with the viability of a diesel electric system on a small craft? Who in their right mind would built a gasoline electric system? I really do not understand anything you are saying?

Your auxiliary diesel and genset diesel give you somewhere around 60kW of power generation. I have +40kW in my smaller boat. The OP was simply asking why hybrid systems aren't done. They are. The Moon-Wave system in the GunboatG4 includes replacement of the propane system by all electric cooking, and because they own Torqueedo electric outboards they include a charging dock at the davits to charge the dink outboard - no gasoline. But overall your estimates for total power requirements don't appear to factor the ability to store motive power in a battery pack, or regenerate energy while under sail. There is 5kW of photovoltaics on the cabin top alone. Once you have energy in a battery, you can power very powerful electric motors, or run your reverse cycle in silence.

Bill Roosa · Aug 8, 2014

I think that if you go to the moonwave web site you will see that they are talking about some very big systems running high voltages and intended for a rather largish sail boat.
but their fall back solution is a diesel engine burning diesel fuel. From an investment standpoint that is a lot of electric motors, inverters, and a massively expensive battery bank that could (IMHO) be better spent on diesel fuel and beer.
So ask yourself, can you afford to buy this setup if your engine and tranny went south for some reason? I'm thinking that the answer would be buy another diesel cause it is much cheaper.

Bill Roosa · Aug 8, 2014

and for completness there are 37kWh/gal in diesel fuel so my 40 gal tank is 1.5 MegaWh of energy, show me the battery bank that can compare and not sink the boat due to its weight.

kloudie1 · Aug 8, 2014

Yep.. and can be recharged. inside of ten minutes.

capta · Aug 8, 2014

Gunni said:
Your auxiliary diesel and genset diesel give you somewhere around 60kW of power generation. I have +40kW in my smaller boat. The OP was simply asking why hybrid systems aren't done. They are. The Moon-Wave system in the GunboatG4 includes replacement of the propane system by all electric cooking, and because they own Torqueedo electric outboards they include a charging dock at the davits to charge the dink outboard - no gasoline. But overall your estimates for total power requirements don't appear to factor the ability to store motive power in a battery pack, or regenerate energy while under sail. There is 5kW of photovoltaics on the cabin top alone. Once you have energy in a battery, you can power very powerful electric motors, or run your reverse cycle in silence.

My genset is 8kw. My ME has an 110 amp alternator, a far cry from 60kw. I sure do not see where in the world you can get 60 kw without 60 kw of gensets, enough solar panels to cover half a football field, and or one gigantic windgen for a massive battery bank which would weigh more than the genset and ME.
A solar array that takes up 128 square feet, can produce about 1400 watts, or 1.4 kw. You must have a GIGANTIC cabin top if you really get 5kw from them. I do believe, if you check again, you have more like 500 watts of solar on your cabin top, not 5kw, or 5000 watts
I must be missing something here, or I'm just no good at math. Just so you and I are talking about the same thing; 60,000 watts, not 6,000 watts, right?

alexco38 · Aug 9, 2014

They said about regenerative when on sail. That means go slower as more drag caused by the generator that the sail has to overcome.

One guy in our club converted to electric a few years ago. He regretted that ever since. This year, the motor cant even turn by hand due to corrosion seized up. Expensive to repair. He cant even sell the boat. Sad story.

Electric motor/generator ?

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