Electrical Propulsion vs Diesel Propulsion

[deckofficer]

Originally Posted by Sand crab

I was hoping this thread would die but no, It's like a zombie, it lives forever! Actually, I like zombies. They are like my first ex, dead in bed.
On the torquedos and other inboard motors do they run backwards so you don't have to have a tranny? Likewise do they spin really slow?

Yes, all within the controller, so no gears. And 10 rpm if you want. The most efficient props are large and slow turning with a pitch that will allow your desired speed at the low rpm. The container ships I sailed on were diesel direct drive at a cruise speed set for 113 rpm. MacG, I know for the small scale of my future system, you would be onboard. I have no net weight gain over a conventional system.

[roverhi]

If a boat needs a 40hp diesel to power into a head sea and wind, it will need 40hp electric to do the same. Running an electric motor that large at full power will eat batteries so fast it will make your alternator spin. Electric power is fine for getting in and out of the slip and occasional short term light air powering with a small electric motor. For the real world of long distance cruising, electric power just doesn't work unless you carry a gen set. If you have to carry a gen set, why not just put in a diesel that will power the boat in all conditions and be done with it??

[MacG]

For small craft that will be the only solution. But if your boat is a bit bigger, like Jedi' s Sundeer f.e., it may become a good idea.

[Oliver L.]

Guys,

let's do the math:

I have nice big batteries. 1000 Ah at 12 Volts = 12 kWh of Energy (out of which I probably never should draw more than 50%). This will run a 25 kW electrical engine for 30 minutes.

They weigh 480 kg or around 1,000 lbs. The equivalent in Diesel fuel is around 2 kg (10 kWh of thermal x efficiency).

The other option - a genset with electric motors - fares better, but still takes two conversions more: In the generator to electrical, and then in the motor again to mechanical. Net effect - less propulsion per liter of fuel. Couple that with the fact that this technology simply has not been refined to the same reliability as a diesel engine (admittedly, only hearsay on my part) and you have twice the trouble for half the fun.

...and did I mention that I love the redundancy of my two engines? Except when that redundant drive has brought me back to port - in there it is really virtually impossible to bring in the boat with just one engine...

Oliver

[sailstoo]

The real question here is whether you should carry a short-barreled shotgun or a 9mm with an extended mag on your diesel/electric genertor driven electric/non-electric day sailer cruiser?

[44'cruisingcat]

Originally Posted by Sand crab

On the torquedos and other inboard motors do they run backwards so you don't have to have a tranny? Likewise do they spin really slow?

The torqueedo's have a planetary gearbox, so while the prop spins slowly, the actual motor spins pretty fast. About 10,000 rpm at full throttle I believe.

[AuroraGH]

Originally Posted by roverhi

If a boat needs a 40hp diesel to power into a head sea and wind, it will need 40hp electric to do the same. Running an electric motor that large at full power will eat batteries so fast it will make your alternator spin. Electric power is fine for getting in and out of the slip and occasional short term light air powering with a small electric motor. For the real world of long distance cruising, electric power just doesn't work unless you carry a gen set. If you have to carry a gen set, why not just put in a diesel that will power the boat in all conditions and be done with it??

I don't understand why the assumption is always that the electric motor runs off of batteries. Perhaps, like the diesel electric ships and locomotives, it runs directly off of the genset.

Diesel engines have wonky power curves. They have narrow RPM ranges that produce optimal power. Outside that range and they're inefficient. Given the other power demands (electronic nav, lights, house power, etc)... lots of boats are running expensive giant diesel engines to charge house battery banks.

Should a compact diesel genset arise that can power a 40hp electric motor, it seems a no-brainer to replace the diesel with the a genset and motor. From what I've seen, most of these electric wonders will simply sit in the space that my gear/transmission box sits. They are about the same size. Now if I can replace the engine with a genset of the same size with adequate power output to run the motor, I don't really care about the battery capacity. Automating the genset to start up on demand based on load/battery capacity and adding an inverter and now I have AC house power, just like at the dock.

The problem is I haven't seen a genset with an output capacity that can physically fit into the space of my engine (and my engine is very space inefficient - VW Pathfinder marinized with a "kit" - looks very steam-punk compared to a modern Yanmar).

[deckofficer]

Originally Posted by roverhi

If a boat needs a 40hp diesel to power into a head sea and wind, it will need 40hp electric to do the same. Running an electric motor that large at full power will eat batteries so fast it will make your alternator spin. Electric power is fine for getting in and out of the slip and occasional short term light air powering with a small electric motor. For the real world of long distance cruising, electric power just doesn't work unless you carry a gen set. If you have to carry a gen set, why not just put in a diesel that will power the boat in all conditions and be done with it??

Not quite. An electric motor might have a cont rating of 5 hp, but will produced 30 hp for a thermal determined time frame. I built an electric scooter that does just that, so my small 0.77 Kw 48 volt battery bank will allow acceleration that beats my Corvette to 40 mph, and can cruise 6.5 miles. It fits into the dinghy quite nicely.


On a 8500 lb PDQ 36, where (2) 9.9 outboards do a fine job, two 4000 watt electrics will do at least as well. Modern lithium batteries would not be a weight penalty when the same 48 volt propulsion bank is also the house bank.

If it wasn't for me being the caregiver to my 92 year old dad, I would be showing all of you just how well this would work now. This whole debate feels like deja vue for me because I just went through all this on the engine I built for my hot rod. Everyone on the hot rod forum (except for a few) were telling me the only way to build an engine for performance was to accept that it will only return 5 mpg. My ride breaks 30 mpg, does a 10.8 @ 132 in the 1/4, and because I went to the extreme in mounting the engine and transmission as low in the frame rails as possible, it can pull 1.04G in the corners. It is my Swiss Army knife of hot rods. I always relish the challenge when popular belief says "it can't be done".

[deckofficer]

Originally Posted by AuroraGH

I don't understand why the assumption is always that the electric motor runs off of batteries. Perhaps, like the diesel electric ships and locomotives, it runs directly off of the genset.

Diesel engines have wonky power curves. They have narrow RPM ranges that produce optimal power. Outside that range and they're inefficient. Given the other power demands (electronic nav, lights, house power, etc)... lots of boats are running expensive giant diesel engines to charge house battery banks.

Should a compact diesel genset arise that can power a 40hp electric motor, it seems a no-brainer to replace the diesel with the a genset and motor. From what I've seen, most of these electric wonders will simply sit in the space that my gear/transmission box sits. They are about the same size. Now if I can replace the engine with a genset of the same size with adequate power output to run the motor, I don't really care about the battery capacity. Automating the genset to start up on demand based on load/battery capacity and adding an inverter and now I have AC house power, just like at the dock.

The problem is I haven't seen a genset with an output capacity that can physically fit into the space of my engine (and my engine is very space inefficient - VW Pathfinder marinized with a "kit" - looks very steam-punk compared to a modern Yanmar).

They have just what you and I need. 5Kw through 50Kw at whatever charging voltages you need. Since we all run inverters, we don't need a heavy gen set for 120/240 60 hertz that has to run at some rpm /60.
http://www.propulsionmarine.com/wp-c...r-Brochure.pdf

Check out the weight (or lack there of) of these DC gen sets.
8 KW Polar DC Marine Generator | Propulsion Marine

[deckofficer]

For you folks that have the big heavy boats up to 15 meters, this one will work just fine for your needs.....
http://www.propulsionmarine.com/wp-c...e-Brochure.pdf

User configurable for 8 different voltages (DC) from 48 volts @ 416 amps up to 320 volts @ 62.5 amps.

[44'cruisingcat]

Originally Posted by AuroraGH

I don't understand why the assumption is always that the electric motor runs off of batteries. Perhaps, like the diesel electric ships and locomotives, it runs directly off of the genset.

Diesel engines have wonky power curves. They have narrow RPM ranges that produce optimal power. Outside that range and they're inefficient. Given the other power demands (electronic nav, lights, house power, etc)... lots of boats are running expensive giant diesel engines to charge house battery banks.

Should a compact diesel genset arise that can power a 40hp electric motor, it seems a no-brainer to replace the diesel with the a genset and motor. From what I've seen, most of these electric wonders will simply sit in the space that my gear/transmission box sits. They are about the same size. Now if I can replace the engine with a genset of the same size with adequate power output to run the motor, I don't really care about the battery capacity. Automating the genset to start up on demand based on load/battery capacity and adding an inverter and now I have AC house power, just like at the dock.

The problem is I haven't seen a genset with an output capacity that can physically fit into the space of my engine (and my engine is very space inefficient - VW Pathfinder marinized with a "kit" - looks very steam-punk compared to a modern Yanmar).

To power your 40 hp electric motor you'd need a bigger than 40 hp genset.

But the OP did mention refuelling with a power cord, which does suggest running off batteries...

While diesel torque curves may be "wonky" they work quite well in boats, where they can be set up to run in their most efficient rev range almost all the time. IC engines are pretty well suited to displacement boats. Much more so than to cars, which is why cars need multi-ratio gearboxes.

[deckofficer]

Originally Posted by 44'cruisingcat

Much more so than to cars, which is why cars need multi-ratio gearboxes.

Now that is a whole new subject, IMHO cars need to be electric. I have a stake bed truck I converted to electric and bought a container full of a China knock offs of the Smart Car, fully electric. When I'm at my place in SoCal, that is all I drive. Since I have a solar charged large bank of batteries for power outages, I just charge these two vehicles from that so the solar charge controller never has to back off the charge rate. Free driving except for insurance and windshield wiper fluid.

[Tropic Cat]

Originally Posted by deckofficer

....
On a 8500 lb PDQ 36, where (2) 9.9 outboards do a fine job,....

Wait.... who told you this? Those motors are perfect for no winds and no waves, getting to and from the dock. For cruising, PDQ made the same boat as a LRC with twin diesels. Those 9.9's can't maintain boat speed into any kind of a head wind. Anyone who has them should tell you this.

Look, you've already made up your mind. I'm not going to wade in here. Let me just say that this is a great idea that just is not ready for prime time.

Remember, when you're out 'there' and the weather kicks up and things go bad...they go bad real fast and all at once. You need motors you can depend on for more than 30 minutes or you endanger your boat and crew.

[downunder]

Originally Posted by deckofficer

MacG, my dear friend, I beg to differ. I have finally settled on which boat will be my final and last boat, and that is the little PDQ 36. I'll sell those two 9.9's and replace them with two Torqeedo 4.0's. For power generation, should I need to motor more than the 50 miles the 48 volt battery bank can take me, instead of a heavy, 120/240 60 hertz diesel genset, I'll use a diesel gen set that can run any rpm because it's output will be only DC at the charging voltage for the propulsion/house bank of batteries. 48 volt inverters if you have heavy 120 volt, 60 cycle loads are the best way to go because when you turn on that 1200 watt appliance, instead of 100 amps on the DC side, it is only 25 amps. I'll admit, both the DC genset and electric outboards are more expensive (but a lot lighter) than conventional. I will enjoy quiet motoring with gobs of torque and a fully electric galley all the way down to my 1500 watt electric BBQ on the railing, and pulling all the propane tanks, lines, regulators, alarms, and appliances out of the boat.

Very doable and not that expensive.

Deck Officer I wish you well In your future conversion.

However, it is fair to say that you are at the cutting edge of the technology with your bike and car conversions and I think the Torguedos you are talking about are only about to hit the marketplace not yet proven in the application.

There was a similar weight vessel in Australia (Oram) that went in the water with Torquedos and I think they gave up and went down another route. Others know more about this vessel than I.

Unfortunately at present the implementation of electric propulsion systems on crusing vessels for long distance crusing is still at the cutting edge of development and not yet mature technology nor yet price competetive.

If you are prepared to pioneer technology and accept all that comes with it that is your choice.

It is simply pushing the envelope at present to widely recomend electric drive systems for cruisers, generally.

cheers

[44'cruisingcat]

Originally Posted by downunder

Deck Officer I wish you well In your future conversion.

However, it is fair to say that you are at the cutting edge of the technology with your bike and car conversions and I think the Torguedos you are talking about are only about to hit the marketplace not yet proven in the application.

There was a similar weight vessel in Australia (Oram) that went in the water with Torquedos and I think they gave up and went down another route. Others know more about this vessel than I.


cheers

Actually that boat was launched with E-power pods. They proved to be very poorly made and totally lacking in customer support, so were quickly replaced with Torqueedo's.

Unfortunately the Torqueedo's had several reliability issues also, and were replaced several times under warranty, until finally being replaced permanently by outboard power.