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Old 09-12-2013, 15:19   #16
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Re: Conversion to Electric Motor

All things being equal, why would not a 35HP diesel require a 35HP electric motor? OK, so you're not using full power from the diesel. But if you estimate say about 1/4 that, then it would seem you would require between 8-10HP.

How do you want to power it remembering 746 watts=1HP which is about 64 amperes at 12 volts. For 10HP you will need a staggering 640 amperes.


Are you getting sucked in with the Volt or the Tesla? Stick around, in a few years you will only find them in history books
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Old 09-12-2013, 15:37   #17
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Re: Conversion to Electric Motor

More to think about-- 1 gallon of fuel oil contains about 140,000 BTUs
1 BTU = about 0.3 watt hour

Therefore 140,000 BTUs = about 42 KWatt hour (42,000)hour now divide that by 12vdc and you have 3500 amperes for 1 hour. Tesla---right on at least until the subsidies end!
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Old 09-12-2013, 16:03   #18
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Re: Conversion to Electric Motor

Quote:
Originally Posted by JRM View Post
OP, please save yourself a bunch of heartache and go to the electric boats group at Yahoo! Discussing electric propulsion here is a waste of time, a la the other threads.
Really. How so? I have carefully followed every thread on electric propulsion in the last couple of years and cannot recall any significant misinformation, bashing, flaming or rude comments. Not saying that there were none at all but from what I recall the overwhelming tone of previous threads was discussing electric options with polite give and take. I have seen honest appraisal of the positive AND negative aspects of going electric.


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Ignore anyone without hard data. People making numbers up doesn't count. That's why the electricboats list is so valuable. Actual experience. You can't compare ICE and electric directly, it's like comparing apples and band saws.
Have seen plenty of hard data. Certainly some occasional opinions without data and plenty of questions and questioning but plenty of real information.


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Originally Posted by JRM View Post
Electric is awesome, if it works for you. But there are some serious drawbacks depending on your intended usage and mindset. It's definitely not for everyone, but it's a decision that should be made based on facts and not fiction.

JRM

-- I'd love to convert our big boat to electric hybrid, but it just doesn't make economic sense at this point. Even as an avowed electric proponent, there are times it just doesn't work.
This is really no different than the conclusions reached on the other electric power threads I recall on this forum. The two main shortcomings for electric are cost and range. Also very few options for higher power off the shelf systems for larger boats.
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Old 09-12-2013, 16:16   #19
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Re: Conversion to Electric Motor

Uh huh, the Fox News: Fair and Balanced way.

"require about 6,000lbs of batteries"
"The manufacture and shipping of all that new stuff (batteries, engines, solar panels) emits a whole lot more CO2 than you'll ever emit using your existing diesel "
"Are you getting sucked in with the Volt"
"Tesla---right on at least until the subsidies end!"

So when the OP says:
"Anyone here who has done this conversion, please let me know about your experience."
Who posting here qualifies?
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Old 09-12-2013, 16:27   #20
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Re: Conversion to Electric Motor

Nimble,

I have had two boats with electric motors as their primary engine. One is old about a year ago, and the other i still use. Does this allow me to comment?One was an Olson 30 racing sailboat boat, the other a dinghy. The Olson I sold the dinghy I still use.

I like electric power, I like the idea of silent running, and I think for a small set of sailors it works great. But despite the advantages there are major drawbacks, and those haven't been readily settled yet.


As for this nonsense that 1kw from electric is more effective than 1kw from diesel... I am prepared to accept that most sailboats have much bigger engines than they need for propulsion, I am prepared to accept that there is a torque curve difference, what I am not prepared to accept is the idea that the prop has any concern over where the power is generated from.

And I stand by that 6k lbs number, I'll go thru the math with you if you like.
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Old 09-12-2013, 16:31   #21
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Re: Conversion to Electric Motor

[QUOTE=skipmac;1411079]Really. How so? I have carefully followed every thread on electric propulsion in the last couple of years and cannot recall any significant misinformation, bashing, flaming or rude comments. Not saying that there were none at all but from what I recall the overwhelming tone of previous threads was discussing electric options with polite give and take. I have seen honest appraisal of the positive AND negative aspects of going electric./QUOTE]

Heh. Came in here to edit my post because I didn't like the tone after I'd thought about it for a while, but too late. Story of my life .

As to the threads and info, I counted a quick 4 posts in this thread alone filled with mis-information and that was in the minute I poked through. I'm in the middle of digging a trench, so I don't have time to go back through the other threads, but as an electric boater, they're pretty much similar.

Post #5: A 20 gallon fuel tank is 6,000 lbs of batteries. I tend to like math, but just doing random math for math's sake isn't helpful. What chemistry is this? Massive assumptions about energy efficiency and storage and usage. Again, apples and band saws.

Post #7: Another misapplication of arithmetic. Again, HP in an ICE and KW in an electric propulsion system isn't a 1:1 correlation. We can do all the fancy multiplication we want, but when the underlying assumptions are so false it's pointless. Additionally, wild speculation about costs based on the previously mentioned wild speculations about power. I know of several electric conversion that varied in cost from less than to more than a diesel repower. But a 50% premium just isn't reality.

Post #9: I'll give this one a bit of leeway, but "greenhouse" emmisions isn't generally why inland lakes ban ICE engines. It more has to do with petrol products ending up in the water, which is significantly less likely in a hybrid system.

Post #12: Some more bad numbers. They just keep hammering away with these ludicrous power conversion misapplications. I have spec'ed out a sweet electric hybrid system for my 40', 28,000 lbs (on the scale) cruising boat and I can assure you it doesn't require a 35KW, or even 30KW generator. More like a third of that for the Cadillac plan.

This place is great, and I have learned huge amounts here, but it isn't a place to come for information on electric boat conversions. I wouldn't go to the electric boat list and ask questions about long term cruising. It doesn't make this a bad place, just not one that's good in this specific application. When one of these threads pop up, I generally make the referral. I've never had a mod tell me that it's inappropriate, and if one does so I'll be happy to cease referring people to a specialized list for this topic.

I'd love to have a measured discussion on this topic here, but it's hard to put out good information amongst all the wild speculation. Some of the numbers presented in this thread and others, while having no basis in reality, *seem* logical. That's what makes them so frustrating to deal with. Especially because I'm not an expert in the field, just a guy who did some research before putting my money up, and who only has a few years of electric auxiliary sailing experience.

JRM
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Old 09-12-2013, 16:47   #22
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Re: Conversion to Electric Motor

JRM--- Electric anything not energized with a commercial power line is suspect to compromise. Some will accept sacrifices others will not. Think about some basics such as how an electric car gets energy for heat and AC. Also consider what those basic comfort factors translate into lost range.

Not sure about the 6000 batteries but I am sure that a gallon of fuel oil has about 140,000 BTUs. Also sure about 1 BTU = about .3 watt hours. The rest is simple math and of course efficiency losses also count which I did not include in my earlier post.

If you are happy with auxiliary electric propulsion that is all that matters!
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Old 09-12-2013, 17:02   #23
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Re: Conversion to Electric Motor

Here are some facts after being in the electric propulsion business for awhile:
1. The column of water that the propeller moves is what moves the boat. We call that thrust.
2. Thrust is a function of torque applied.
3. Electric motors provide significant torque as soon as they start rotating.
4. ICE (gas, diesel, propane, natural gas, etc.) have a relatively flat torque curve that peaks at a relatively high RPM.
5. Trial and error has shown that there is a 3:1 correlation for torque at the prop, and therefore thrust. A 12kW electric motor with a properly pitched prop and operating at the correct RPM will generate about the same torque (thrust) as a 32 to 36hp ICE.
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Old 09-12-2013, 17:26   #24
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Re: Conversion to Electric Motor

Electric Yacht | CLEAN, GREEN & QUIET Marine Propulsion Systems!

Electric Seas - A Resource For The Electric Boating Community

Check it out, I'm thinking about it.
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Old 09-12-2013, 18:06   #25
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Re: Conversion to Electric Motor

Quote:
Originally Posted by CharlieJ View Post
Here are some facts after being in the electric propulsion business for awhile:
1. The column of water that the propeller moves is what moves the boat. We call that thrust.
2. Thrust is a function of torque applied.
3. Electric motors provide significant torque as soon as they start rotating.
4. ICE (gas, diesel, propane, natural gas, etc.) have a relatively flat torque curve that peaks at a relatively high RPM.
5. Trial and error has shown that there is a 3:1 correlation for torque at the prop, and therefore thrust. A 12kW electric motor with a properly pitched prop and operating at the correct RPM will generate about the same torque (thrust) as a 32 to 36hp ICE.
Thanks Charlie,

Good information from someone that knows the subject. One other detail to consider comparing electric vs ICE. The electric doesn't have many the parasitic losses the ICE has to drive like water pumps (raw and fresh), alternators, etc. so more of the power goes into driving the boat.
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Old 09-12-2013, 18:48   #26
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Re: Conversion to Electric Motor

Quote:
Originally Posted by CharlieJ View Post
Here are some facts after being in the electric propulsion business for awhile:
1. The column of water that the propeller moves is what moves the boat. We call that thrust.
2. Thrust is a function of torque applied.
3. Electric motors provide significant torque as soon as they start rotating.
4. ICE (gas, diesel, propane, natural gas, etc.) have a relatively flat torque curve that peaks at a relatively high RPM.
5. Trial and error has shown that there is a 3:1 correlation for torque at the prop, and therefore thrust. A 12kW electric motor with a properly pitched prop and operating at the correct RPM will generate about the same torque (thrust) as a 32 to 36hp ICE.
REALLY???

First torque by itself is meaningless. It is a force, not power. Now lets examine some of your above numbers and I'll start with your 12KW motor.

1HP= 746 watts so 12KW/746 = 16HP

And torque's relationship to HP is HP= (torque)(RPM)/5252

Certainly 16HP electric motor is a far cry from a 36HP diesel or gas or for that matter another electric motor.

Yes one can rate an engine's or motor's torque but it is only in relationship to a particular RPM and the HP needed to develop that RPM
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Old 09-12-2013, 19:25   #27
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Re: Conversion to Electric Motor

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Originally Posted by SkiprJohn View Post
Here's the one I'm familiar with:
Electric Propulsion
Still doesn't have the range of a diesel.
You mean diesel range is finite where as electric is not?
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Old 09-12-2013, 20:09   #28
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Re: Conversion to Electric Motor

So let's talk about energy density for a moment. There are two ways to rate it, energy per weight, or energy by volume.

..................by weight...........by volume (1)
Diesel----------45.4mj/kilo -----38.6mj/liter
Li ion battery-----.75mj/kilo. ---2.33mj/liter
Lead acid battery .17mj/kilo ----.34mj/liter

Oh the surface then diesel is roughly 60times more energy dense by weight than lithium ion, and 267 times more dense than lead acid batteries.

Diesel engines are roughly 50% efficient(3), while electric motors in this size are between 85 and 88% (2) efficient. So battery power makes up a little hit here, but not nearly enough to make up for the difference.


(1) Energy density - Wikipedia, the free encyclopedia
(2) Electrical Motor Efficiency
(3) Diesel engine - Wikipedia, the free encyclopedia
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Old 09-12-2013, 20:32   #29
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Re: Conversion to Electric Motor

I haven't made a conversion as the OP asked for. But I've been in the Marine industry for a long time and know a lot of the big guys who do this type of work on cruising boats. Just in my limited world and you can take it for what it's worth but I know I see a lot more conversion to diesel from electric than the other way around. I've listened to owners who swear by it and those that swear at it. I've talked to a few of the people that will do electric conversions. They may not be too vocal about it but the general consensus is that they are in business and will give the customer what he ultimately wants, even if they shake their heads while doing it. Put me in the camp of do what you feel is best but electric drive is just not there yet for most cruisers.
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Old 09-12-2013, 21:34   #30
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Re: Conversion to Electric Motor

I don't see why this is such a difficult topic. After spending three weeks driving a Neon leaf all over Oahu with zero issues with recharging and spending zero dollars on gas, I am totally sold on electric cars. Guess what, the technology works.

Often I find that it is the people linked to the oil business that argue against electric cars and global warming, oddly enough.

Like I said, I plan on sailing my boat. Engine is for getting in/out of the marina and situations that require it. I suspect I will be able to accommodate a reasonably sized battery supply for my needs.

Thanks to everyone who replied.
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