My project to build an electric boat

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Deker
Posts: 104
Joined: Fri Jul 21, 2006 2:40 am
Location: Borehamwood

Electric boat !

Postby Deker » Wed May 28, 2008 2:27 am

Hi Deddly.

Mike says that a starter motor may do, I think not, starter motors are NOT designed for continuous running, they are inefficient for any form of traction use.
They are designed to pull loads of current from batteries to rotate an ICE rapidly to get it started.

As Mike says "Alternatively, you go onto eBay and buy yourself an electric scooter or disability wagon. You'll have the motor, the controller, the batteries and the charger, all in one go."
That sounds good to me.
And loads of nuts & bolts too.

From my past, small boating on the cheap, I would suggest nothing less than about 8 horse power = 6 kilowatts and 24 volts as the minimum battery voltage.

If you see a motor rated at x volts and at x amps, if you are not sure how to calculate the watts, simply multiply the two, for example a motor label shows 24 V, 30 A.
Sounds a lot, but would only equal 720 watts, less than 1 horse power ! or PS in the modern style of power output.

I could go on about propellor thrust angles in terms of theoretical distance per propellor revolution, but, only if you want to get involved that subject.
It is important when considering electric power for boating applications.

For a boat of the size you are making, personally I would not consider electric power on a flowing or tidal river - - unless I had a huge budget for batteries and suitable motor.

Hopefully you may prove me to be wrong, (For I am a great fan of electric power) if so, please tell me how you did it.

Deker

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Peter Eggleston
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Location: Tyne Valley Northumberland

Postby Peter Eggleston » Wed May 28, 2008 12:53 pm

Considering that milk float motors are only rated at 7.5 horse power I would not have thought you would need anything near 8 horse power for a small boat.
Peter

Deddly
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Joined: Fri Dec 21, 2007 4:31 pm
Location: Södermanland, Sweden

Postby Deddly » Fri Jun 20, 2008 5:16 pm

Peter Eggleston wrote:Considering that milk float motors are only rated at 7.5 horse power I would not have thought you would need anything near 8 horse power for a small boat.
Peter


I would aggree, I don't think I need that kind of power for what I'm looking for. Mind you, any ideas where I can get an old milk float motor from? :D

I'm still not convinced that a starter motor won't work...ok it's not the perfect solution but nothing I've used on the boat so far has been disigned for how I'm using it... overheating is a concern with a starter motor, what if I get a 24v starter and run it at 12v? If I run it at only half its rated input surely it wouldn't pack in?

--
Ed

Deker
Posts: 104
Joined: Fri Jul 21, 2006 2:40 am
Location: Borehamwood

Motor

Postby Deker » Sat Jun 21, 2008 1:18 am

Ed, if you must use a starter motor, I strongly advise against it, but use the permanent magnet type.

If you overheat it the magnets will become unstuck.

Any starter will run down your batteries rapidly.

And of course a field wound starter is not reversible, except the permanent magnet types.

Other disadvantages with starters -

The bearings are of the bush type, except the more expensive modern types.
The bushes are not designed to run continuously.

They want to rev to infinity, various losses prevent them from actually doing so.
The result is, you are trying to do gentle adjustments to docking your boat, the water current works in favour of the boat, the starter sees less load and will rev faster, accelerating your boat. Not really desired !!!

This still applies even if you use a resistor type controller.

I like making electric toys that people can ride on. I have never considered starter motors as a suitable motive scource.

Deker.

Deddly
Posts: 31
Joined: Fri Dec 21, 2007 4:31 pm
Location: Södermanland, Sweden

Re: Motor

Postby Deddly » Sun Jun 22, 2008 5:38 pm

Deker wrote:Ed, if you must use a starter motor, I strongly advise against it...
...If you overheat it ...
...run down your batteries...
...not reversible...
...bearings...
...want to rev to infinity...

I like making electric toys that people can ride on. I have never considered starter motors as a suitable motive scource.

Deker.


OK guys I'm convinced, I reluctantly concede that starter motors are a bad idea, which stuffs my whole plan.

That leaves me with the problem of finding a motor again. I've been thinking a lot and since a powerful 4-10hp electric motor (and the batteries) are seemingly out of my reach I can probably make do with a 800-1000W motor - it is a VERY slow moving river, and I just found out they close the sluice gate when it's not rained for a while.

My thinking is that I can use it to get around slowly when there's no wind, and rely on sails when I want to go faster. In the long run I can buy more batteries and keep my eyes open for more powerful motors. I'm just finding it hard to come by anything that fits the bill.

I haven't even managed to find an old outboard at the scrapyard yet, feeling a little bit depressed about the whole thing but I'm sure I'll find something eventually...

Would be nice to have the budget to buy everything I needed new :roll:

--
Ed

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Peter Eggleston
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Location: Tyne Valley Northumberland

Postby Peter Eggleston » Sun Jun 22, 2008 9:04 pm

I don't know how well this would work, but you could try using an old style car dynamo as an electric motor, as unlike the starter motor, it is designed to run all the time.
It is worth watching out on ebay regularly for the stuff you need as things crop up all the time. I bought a brand new Advanced DC motor normally priced at £400 for £80 and have since bought virtually all the parts I need for my trike off ebay at knock down prices.
You could probably find your outboard motor here as well.
Peter

Deddly
Posts: 31
Joined: Fri Dec 21, 2007 4:31 pm
Location: Södermanland, Sweden

Postby Deddly » Mon Jun 23, 2008 1:09 pm

Ebay is a wonderful place, unfortunately for me the Swedish version of Ebay doesn't have the wonderful variety that the UK one does, and people don't like putting their stuff on at a low starting price, because they might get only one bid.

I'll keep my eyes open though, that's for sure. The dynamo sounds like a good idea, would that definitely work? Is it a stupid idea to use a 230v motor with some kind of inverter?

--
Ed
Last edited by Deddly on Mon Jun 23, 2008 1:20 pm, edited 1 time in total.

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geekygrilli
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Postby geekygrilli » Mon Jun 23, 2008 1:17 pm

I've still got this, somewhere....you're more than welcome to it.

http://www.batteryvehiclesociety.org.uk ... .php?t=795

Deddly
Posts: 31
Joined: Fri Dec 21, 2007 4:31 pm
Location: Södermanland, Sweden

Postby Deddly » Mon Jun 23, 2008 1:26 pm

geekygrilli wrote:I've still got this, somewhere....you're more than welcome to it.


That looks very promising, I've sent you a PM, thanks for mentioning that one!

--
Ed

Deker
Posts: 104
Joined: Fri Jul 21, 2006 2:40 am
Location: Borehamwood

Boat motor

Postby Deker » Tue Jun 24, 2008 1:59 am

Hi Deddly.

A dynamo can be used as a motor, but you may shed loads of tears trying to get any power from them.

Now this is far better.
geekygrilli wrote:I've still got this, somewhere....you're more than welcome to it.

Geeky, I have one similar to yours, it is series wound, is the one you have series wound ?
If it is, then reversing would be a problem, probably impossible.

Ed. Do you have what we call in England "Fairgrounds" = travelling show people who have electric fun rides ?

I am asking this to give you some advice on how to find an economical method of controlling the motor Geekygrilli has, assuming you have his motor.

Deker


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