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Old 30-07-2015, 09:40   #31
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Re: Upgrading My Electric Propulsion System

All this machination about swivels, bicarb coating etc....?
Gee guys, just put in a smaller bank of lithiums and be done with it.
80% discharge, no memory, no spills, lighter weight.

My boat is not electric drive, but IS electric everything else except cooking and I never use the engine for charging or hot water.
I have posted a list of "stuff" onboard on other threads, but let's just say, we're independent except for growing food.

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Old 30-07-2015, 11:50   #32
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Re: Upgrading My Electric Propulsion System

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I think your setup is perfect for moving up to a few miles very fast, or maybe 10-20 miles at 2-3 knots if you have about 8 batteries. Maybe this what you wanted? You will get better range the first few years though, but once the batteries are old this is all you can really expect.

For me I would install a 30 inch propeller that turns at 200 rpm using only 400 watts to push the boat at 4 knots. Pushing 300 amps at 48 volts will make the boat jump around but I don't see how it's really useful unless you are going to be acting as a tug boat.

Alternately I would like to see an efficient mechanical system for driving a sculling oar from an electric motor. I believe it's possible and it has a lot of advantages. This system if designed properly I would expect to move 2 knots using 100 watts of power input.
I actually dont think 400 watts would push my boat at 4kt, no matter what prop I use. If you can find someone with actual experience pushing a 7600lb boat at 4kt using only 400 watts, or even mathematical and scientific proof that it is possible, I would be greatly interested. But I can't mount a 30" prop, anyway. The hull is in the way. Stupid hull!

You realize, of course, that it takes I believe 741 watts to equal just one horsepower? It is unrealistic to expect 1/2hp to do the work commonly done by a 4hp outboard. Outboards are inefficient but not THAT inneficient, I am guessing.

But the sculling oar idea could work with a Stirling Engine, or something similar, I think. Why not give it a try?
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Old 30-07-2015, 11:59   #33
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Re: Upgrading My Electric Propulsion System

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Is there any concern using welding wire vs marine tinned wire?
Yes, but I haven't seen 2/0 ga marine tinned wire. The voltage drop is way less with really big stuff, even though I could probably go as small as 4ga and not risk an electrical fire. And there is a lot of contact area with wire this big. So it is an issue but IMHO not a tremendously humongous issue.
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Old 30-07-2015, 12:34   #34
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Re: Upgrading My Electric Propulsion System

If the wallet permitted, I certainly would go lithium; though they too have safety drawbacks. I'm seriously considering no engine at all, saving a whole lot of money, weight, space and aggravation. The attraction of electric is mighty powerful though, so I'll be building with a shaft tube whether or not the engine goes in. I guess I'll have to overcome the limitations of spillable acid one way or another. A seawater battery using the ocean as electrolyte, now that'd be a nifty thing...
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Old 03-08-2015, 09:26   #35
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Re: Upgrading My Electric Propulsion System

Well, sea trials dodn't go so well. The 12kw motor used more current and got less speed than with the 5kw motor.

BUT... our diver took a quick peek and my bottom is really dirty (the BOAT bottom that is) and he says I only have a 2 blade prop. Well, I seem to recall that last year it was a 3 blade folder. Which would account for the increased vibration. Hmmm.... Im going under the boat this weekend myself, and our guy will scrub the hull for $70 so thats a date. One more trial with the big motor and if it is unsat then I will crunch some numbers and decide whether to change to a 3:1 gear or what. My top speed was only 3.7kt at 100a, and last year I got 4.7kt from only 65a. I think my folding prop shed a blade while I was horsing aroud with it tied to the dock.
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Old 03-08-2015, 10:13   #36
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Re: Upgrading My Electric Propulsion System

From what I've read of electric conversions, the owners usually go up a prop-size or three. If I do go with an engine, it'll be diesel electric, with a large variable pitch prop.
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Old 28-10-2015, 14:51   #37
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Re: Upgrading My Electric Propulsion System

Hi Growley Monster, sorry to revive an old thread, but you left us hanging. Did you ever get your prop checked and see the performance you'd expect from your new motor?

I'm dreaming about boats again, and I am interested in all aspects of electric propulsion.
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Old 02-11-2015, 09:30   #38
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Re: Upgrading My Electric Propulsion System

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Hi Growley Monster, sorry to revive an old thread, but you left us hanging. Did you ever get your prop checked and see the performance you'd expect from your new motor?

I'm dreaming about boats again, and I am interested in all aspects of electric propulsion.
I have not got around to the prop change or the bottom job. Been busy with my e-bike and my straight razors and other projects. The only boat project I got done is the new throttle control. One knob on the tiller to control fwd/rev and speed. Fully clockwise is full ahead. Center is stop. Fully CCW is full astern. Works great and it is so convenient and intuitive. Plus it mystifies bystanders when I dock with no obvious means of propulsion or control. You cant see the itty bitty knob from a distance, especially with my steering and engine bell hand covering it.
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Old 03-11-2015, 12:59   #39
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Re: Upgrading My Electric Propulsion System

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Originally Posted by GrowleyMonster View Post
I actually dont think 400 watts would push my boat at 4kt, no matter what prop I use. If you can find someone with actual experience pushing a 7600lb boat at 4kt using only 400 watts, or even mathematical and scientific proof that it is possible, I would be greatly interested. But I can't mount a 30" prop, anyway. The hull is in the way. Stupid hull!

You realize, of course, that it takes I believe 741 watts to equal just one horsepower? It is unrealistic to expect 1/2hp to do the work commonly done by a 4hp outboard. Outboards are inefficient but not THAT inneficient, I am guessing.

But the sculling oar idea could work with a Stirling Engine, or something similar, I think. Why not give it a try?
I think it is possible to design a efficient boat that could be propelled to 4kts at only 400W, but one decides to depart from conventional thinking to achive that.

I mean if I was to design a 36ft boat with displacement of 8,200 lbs, I would make its LBR very high, say 6.00 and not the more traditional 2.50.

Then one can see what speed can be realistically achieves with 400W - that would be 4.5 kts!

See attached model made in FreeSh!p

The trade is to end-up with a narrow hull that may not be suitable to certain requirements.

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Attached Files
File Type: pdf calc.pdf (49.6 KB, 20 views)
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