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  #51  
Old 10-13-2012
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Re: Optimal propulsion system

OK..This sounds like something I've been daydreaming about. I have a 15 Kw/55 amp propane 4 cyl Onan gen set. Total weigh w/o gas is #850. There is no out shaft, as the gen and motor are interconnected. I'd like ta see what it would take, motorwise??? .75 X 15 formula comes up to 11.25 hp. Size a boat to that hp and see if it could handle the weight of motor and gen set as ballast????? Figger mebbe 1200# with a couple batts and motor controller. If ya could mount the weight low enuff...........
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  #52  
Old 10-14-2012
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Re: Optimal propulsion system

delta, propane has a very low energy density compared to diesel. Which is why ships and submarines and even locomotives use diesel-electric propulsion very successfully, but never use propane-electric.

Propane will work if you can get it very frequently, very conveniently, very cheaply, and you've got lots of storage space. But unless you've got a rare boat operating n a rare environment, forget about it.
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Old 10-14-2012
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Re: Optimal propulsion system

How about a trimaran where the two amas are propane tanks???

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Re: Optimal propulsion system

Won't work. You load down the amas, and that makes it harder to keep one out of the water at all times. Now you've got a tri-ma-barge instead of a trimaran.
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Old 10-15-2012
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Re: Optimal propulsion system

Hellosailor;
re: density/BTU; Yes, too true. The only advantage to propane is that it stores indefinitely. My musings were more about the drive-train issues and the other applications you mentioned. Since a freight train uses diesel to run gens to power electric motors; would the same reasons/logic/engineering apply? I suppose not,; as a sailboat does not need to shift hundreds of tons of weight.
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Old 10-15-2012
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Re: Optimal propulsion system

In the automotive world, Tesla seems to be on the cutting edge of battery technology. Their cars run about 300 miles before needing a charge and, if my memory serves me correctly, requires only an hour or so to recharge, maybe even less. And their cars are lightning fast! But their cars aren't cheap.

But how would the best battery technology we have today work in a marine environment, propelling a much heavier object through a much denser media? Would it reduce the load on the generator? Would it burn the batteries out? Would they need constant recharging? Maybe Tesla can answer that.

When I see what Tesla is doing, I have to ask myself why the major auto companies aren't doing the same thing. I think the Chevy Volt is only good for about 35 miles on battery power alone. Why don't the big three make a more expensive model that can compete with Tesla? We gotta get the Tesla guy to work on marine propulsion. He'd figure it out.
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Re: Optimal propulsion system

Julie,

Tesla is using lithium ion batteries last I looked. Figure an energy density on them of about 2% by weight compared to gas. So to replace a gallon of gas you would need roughly 325lbs of batteries. The Tesla battery pack weighs around 900lbs, so figure the energy equivalent of 3 gallons of diesel. And they aren't cheap, the battery pack which is good for a nominal 4 years cost roughly $36,000. So even assuming electricity is free it's going to cost you $8,500 a year in battery packs.

At today's fuel prices you would have to be doing a lot of motoring to come anywhere close to justifying it from a cost advantage.
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Re: Optimal propulsion system

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Originally Posted by Stumble View Post
Julie,

Tesla is using lithium ion batteries last I looked. Figure an energy density on them of about 2% by weight compared to gas. So to replace a gallon of gas you would need roughly 325lbs of batteries. The Tesla battery pack weighs around 900lbs, so figure the energy equivalent of 3 gallons of diesel. And they aren't cheap, the battery pack which is good for a nominal 4 years cost roughly $36,000. So even assuming electricity is free it's going to cost you $8,500 a year in battery packs.

At today's fuel prices you would have to be doing a lot of motoring to come anywhere close to justifying it from a cost advantage.
To you good sir, I concede that you win this argument, and you will win for a LONG time to come. This isn't about just energy density and cost though. The cheapest way to get from point A to B on the water is by ferry. Next best, is powerboat. We can't possibly justify all the design and space losses of our sailboat hulls, the weight of our keels, and the massive expense of our rigs and sails compared with a simple small engine that can push us at displacement speed.

In fact, most of us already have that engine aboard but prefer to use our cost-ineffective method of propulsion (sails) even though they usually make us go slower, we can't pick our direction and they require constant attention. Curious isn't it? We crazy sailor types must like things in our propulsion systems besides cost and efficiency then. See my post a page back or so on motor-sailing and why we like electric.

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  #59  
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Re: Optimal propulsion system

"We gotta get the Tesla guy to work on marine propulsion. He'd figure it out. "
Someone hasn't read up on what the Tesla cars are. It would be very easy to build a boat the same way. Make it a two seater, tack an extra fifty grand on the price to cover the battery system, and Bob's your uncle.

There's no magic in the Tesla cars, just a lot of EXPENSIVE stuff.

They were supposed to be partnering with Toyota for the RAV4 EV this year, but Toyota has also made some major quite announcement about getting out of the EV market (except for a handful of pre-committed cars as a test) completely now. They see it as being totally uneconomical.

Got a boat? Get a diesel, Mr. Herr Professor Doktor whatever Diesel designed them to run on peanut oil, not petroleum products. Of course, he had no idea the particulates in the exhaust would cause asthma and cancers, but the fuel (vegetable oil, unprocessed) is certainly cheap enough.
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Re: Optimal propulsion system

Lithium, on a boat, now that's a great idea!
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