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Old 12-03-2016, 14:41   #16
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Re: Electric motor for sail boat

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Originally Posted by lonesoldier0408 View Post
Funny you mention that. A DC motor powering an AC generator could be the answer. One battery bank being charged while powering the generator. Swap banks and repeat.


Still surrounded by anchors.
Perpetual motion!!!!!!!!
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Old 12-03-2016, 14:51   #17
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Re: Electric motor for sail boat

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Originally Posted by lonesoldier0408 View Post
Funny you mention that. A DC motor powering an AC generator could be the answer. One battery bank being charged while powering the generator. Swap banks and repeat.


Still surrounded by anchors.
I think that is backward. A Ward Lenard system is the reverse.

At any rate I can see his point for docking. Not me but whatever floats your boat, so to speak.
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Old 12-03-2016, 14:56   #18
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Re: Electric motor for sail boat

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Originally Posted by valhalla360 View Post
Good use of the technology. If you don't need significant range or speed and aren't worried about resale, it's a good solution.
this one
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Old 12-03-2016, 15:08   #19
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Re: Electric motor for sail boat

I have had my electric motor for about ten years now. I bought it without knowing much about it. It runs well on 24 V and gives me about 3.5 knots to my 3 tons salboat. On 36 V it is very strong. I think it was made in the sixties.

My four lead batteries gives me about 40 minutes drive. Thats all, but it is more than enough to take me into the harbour, if the wind makes it difficult to go in by sail.


The first year i used land power to load the batteries, but after that I have just been using a 45 W sun panel to get all the power I need.


Now I will install another 90 W sunpower. That will be more than enough for me. Do you really need a fredge and a freezer? I am not so sure!


Go simple, go cheep and be nice to those who will inhabit the earth after us!
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Old 12-03-2016, 15:17   #20
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Re: Electric motor for sail boat

I have a repower future choice to make, As I look at Electric they promoted use of electric while sailing using small amount of Electric offsetting hull and prop resistance. They boasted increasing hull speed. Also when wind is strong they suggest using prop drag as a recharge method. I sail in area with strong currents and I struggle with the limitations Electric might have. I sail because I love the quite. That part hold most weight. Fair winds
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Old 12-03-2016, 15:26   #21
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Re: Electric motor for sail boat

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Originally Posted by kish View Post



This is incorrect



The appropriate comparison is the energy density of diesel compared to a battery's stored energy.

http://<b>https://en.wikipedia.org/w...gy_density</b>



Diesel / Fuel oil has an Energy density of 48 MJ/kg

Lead Acid battery has an Energy Density of 0.17 MJ/kg



Thus the same mass of diesel produces 282 times more energy than a similar mass of lead acid battery.

This is incorrect as well. LA batteries do not produce energy at all, they merely store it. Compare a diesel genset with solar panels, wind- or water driven generators etc. and all of those can produce energy, which a battery charger can use to store in batteries.

I think I saw another inaccuracy earlier in the thread: when using a generator to power an electric motor, you do not have any losses for charging/discharging batteries. You only have those when you charge and discharge batteries.
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Old 12-03-2016, 15:43   #22
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Re: Electric motor for sail boat

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Originally Posted by s/v Jedi View Post
This is incorrect as well. LA batteries do not produce energy at all, they merely store it. Compare a diesel genset with solar panels, wind- or water driven generators etc. and all of those can produce energy, which a battery charger can use to store in batteries.

I think I saw another inaccuracy earlier in the thread: when using a generator to power an electric motor, you do not have any losses for charging/discharging batteries. You only have those when you charge and discharge batteries.
The only advantage to using a diesel driven DC gen. to power a
dc motor is the ability to control speed and direction. The Staten Island ferries have been powered that way for years. It make the controlled crash on docking better.
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Old 12-03-2016, 15:54   #23
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Re: Electric motor for sail boat

Quote:
Originally Posted by kish View Post

This is incorrect

The appropriate comparison is the energy density of diesel compared to a battery's stored energy.
http://<b>https://en.wikipedia.org/w...gy_density</b>

Diesel / Fuel oil has an Energy density of 48 MJ/kg
Lead Acid battery has an Energy Density of 0.17 MJ/kg

Thus the same mass of diesel produces 282 times more energy than a similar mass of lead acid battery.

By the time you take efficiency losses, pto's and what not into account the ratio is better for electric, but not much. The typical number I use is 1lbs diesel:50lbs of FLA batteries.
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Old 12-03-2016, 15:57   #24
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Re: Electric motor for sail boat

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Originally Posted by Cadence View Post
The only advantage to using a diesel driven DC gen. to power a

dc motor is the ability to control speed and direction. The Staten Island ferries have been powered that way for years. It make the controlled crash on docking better.

But we're not ferries. It makes sense to use batteries for short range like in and out of anchorages, marinas etc. and switch to a genset for long distance like powering through calms. In that case, the genset provides range.
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Old 12-03-2016, 17:19   #25
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Re: Electric motor for sail boat

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Originally Posted by suenodelmar View Post
Until we get affordable, higher-capacity batteries, the limiting factor is this:

One pound of diesel oil produces the energy equivalent of about 25 pounds of lead-acid batteries.
To be accurate: Batteries don't produce any energy

They just store energy that has been produced elsewhere by a primary energy source such as diesel, solar, wind or whatever.
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Old 13-03-2016, 10:49   #26
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Re: Electric motor for sail boat

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Originally Posted by s/v Jedi View Post
But we're not ferries. It makes sense to use batteries for short range like in and out of anchorages, marinas etc. and switch to a genset for long distance like powering through calms. In that case, the genset provides range.
No argument there. Twin screw electric is probably great for docking. Even single screw. For long range, to many pieces and parts,and efficiency loses for my taste. I have been wrong before.
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Old 13-03-2016, 12:51   #27
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Re: Electric motor for sail boat

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Originally Posted by s/v Jedi View Post
This is incorrect as well. LA batteries do not produce energy at all, they merely store it. Compare a diesel genset with solar panels, wind- or water driven generators etc. and all of those can produce energy, which a battery charger can use to store in batteries.

I think I saw another inaccuracy earlier in the thread: when using a generator to power an electric motor, you do not have any losses for charging/discharging batteries. You only have those when you charge and discharge batteries.

We must address basic science:
Diesel fuel is stored energy, coming originally from a fossil fuel source.
A Battery is stored energy also, that comes from a charging source, most probably from a fossil fuel source also, if charged from an electrical utility source.

A kilogram of diesel stores 48 MegaJoules of energy.
A kilogram of a charged lead acid battery stores 0.17 MegaJoules of energy.
Comparing like with like; the energy output from these sources gives a ratio of (48/0.17)=282 __ a considerable difference.

Since 1 kg is 2.2 pounds, then 2.2 pounds of diesel would require (2.2 x 282) = 620 pounds of battery capacity for the same energy output.
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Old 13-03-2016, 12:57   #28
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Re: Electric motor for sail boat

Quote:
Originally Posted by kish View Post

We must address basic science:
Diesel fuel is stored energy, coming originally from a fossil fuel source.
A Battery is stored energy also, that comes from a charging source, most probably from a fossil fuel source also, if charged from an electrical utility source.

A kilogram of diesel stores 48 MegaJoules of energy.
A kilogram of a charged lead acid battery stores 0.17 MegaJoules of energy.
Comparing like with like; the energy output from these sources gives a ratio of (48/0.17)=282 __ a considerable difference.

Since 1 kg is 2.2 pounds, then 2.2 pounds of diesel would require (2.2 x 282) = 620 pounds of battery capacity for the same energy output.
Can't help myself, get another kilo of something.

You maybe correct but I doubt anyone will do the math including me. I know where you are coming from. It is not efficient.
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Old 13-03-2016, 14:51   #29
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Re: Electric motor for sail boat

Yep. Fantastic choice. We may too get one further down the track but we will need a small genset too for the longer hauls. I am considering a small Honda then.

Webb Chiles is sailing his rtw now with an electric outboard. He sounds happy with his choice most of the time.

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Old 13-03-2016, 15:06   #30
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Re: Electric motor for sail boat

At the OP:

Can you possibly post the boat displacement / engine power / battery size / type, etc. such details here?

This sure could help other people planning their own electric auxiliaries!

Cheers,
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