Alternator

Discussion in 'Boatbuilding' started by Manie B, Dec 5, 2011.

  1. Manie B
    Joined: Sep 2006
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    Manie B Senior Member

    Gents the question is

    has anybody tried to build their own "towing alternator"

    http://www.ampair.com/
    Rory McDougall used one successfully on "Cookie" in the last Jester Challenge
    http://roryandcookie.blogspot.com/s...dated-max=2011-01-01T00:00:00Z&max-results=50

    YouTube has dozens of videos of a lawnmower engine driving an alternator via a belt, and they work well
    but I cant find ANY example of someone trying to drive it by towing a propellor on a long shaft
    the lawnmower systems are cheap and do the job, why not try to tow it?

    here is the PDF of Ampair brochure
    see page 7 and 8
     

    Attached Files:

  2. michael pierzga
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    michael pierzga Senior Member

  3. Manie B
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    Manie B Senior Member

    Michael thanks

    the first link actually has plans on how to build one - great stuff thanks
     
  4. Boston

    Boston Previous Member

    they use a slightly modified alternator in many of the available wind turbines, works like a charm. so no reason at all you couldn't do exactly what your talking about. Except I'd only want to throw it out once I was parked and let the current drive the prop. That way your no burning fuel to drive the thing. Also someone came up with a wave powered generator. Was a number of hinged sections geared to a drive unit. Every time they flexed the energy was converted into driving a shaft that drove the alternator. They just rewound the rotor, or was it the stator, can't remember but one of them was rewound and presto. Worked like a charm.
     
  5. CDK
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    CDK retired engineer

    Most people want to reduce drag to a minimum and use folding props, self polishing anti-fouling etc. to achieve that. If that is not your concern, install an alternator that is belt driven from the prop shaft, it is more reliable than something towed behind the boat.

    If you want to experiment without spending a lot of time: there are propulsion devices for swimmers and divers, employing a permanent magnet motor in a torpedo shapes housing. Mostly cheap stuff made in Asia.

    Remove the batteries, make a watertight cable connection and tow the thing behind your boat. They are small in size, so do not expect fast charging!
     
  6. michael pierzga
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    michael pierzga Senior Member

    The problem with shaft alternators is that Manies boat is so small. Ive used dc alternators, belted off free wheeling prop shafts , my whole life. They work very well.

    A very low friction stern tube is needed . This implies an oil bath, roller bearing , thrust bearing, shaft tube. Expensive . Also investigate whether your gearbox can free wheel without damage. Twin disc works fine. I dont know id Volvo style legs can be used with an alternator.

    Additionaly the physical space between gearbox shaft coupling and stuffing box must be big enough to get the alternator in.

    On bigger boats the free wheeling prop shaft geerates DC and when fitted with a additional belted hydraulic pump...hydraulic pressure to power the auto pilot rams. A very robust system

    If you have the space , its well worth exploring the shaft alternator idea. They are durable because they are protected from the elements and effective when shaft free wheeling or motorsailing
     
  7. Manie B
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    Manie B Senior Member

    The plus point of the towbehind is that it is easy stowable, easy de-ployable and when stowed, no friction.
    I read a piece on towing at 6 amps all night long
    that is fantastic because the lights etc. has very little drain on the batteries

    for me it is a very valuable backup
    6 amps is plenty for me
    my solars will only deliver 2x2amps x 5 hours = 20amps per day on a good day
    12 hours of towing could give a huge 72 amp/ hours
    and thats pretty cool for 15kg pull
    I bought a 55 amp 12v alternator new for ZAR587 = US$73
    a 2 amp 35w solar panel was ZAR773 = US$96 EACH
    prices includes VAT14%

    small new 5hp fourstroke engines are around ZAR1400 = US$ 175

    so I got the motor and alternator and will build it as soon as I have the boat on the trailer
    will keep you guys posted

    I will definately experiment with towing as well
     
  8. michael pierzga
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    michael pierzga Senior Member

    Just like a tafrail log, big Fish will bite the towed prop. Make a break link so the shark doesnt take your whole rig with him.

    You might investigate the shape and efficiency of a walker log type towed prop
     
  9. Boston

    Boston Previous Member

    There is a company called Windblue that makes alternator stators for low speed conversions of alternators

    http://www.windbluepower.com/

    you might find some useful stuff there.
     
  10. Manie B
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    Manie B Senior Member

  11. Manie B
    Joined: Sep 2006
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    Location: Cape Town South Africa

    Manie B Senior Member

  12. Manie B
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    Manie B Senior Member

    You know this is good

    I have found no other reference to this problem
    good one, thanks
     
  13. petit bateau
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    petit bateau Junior Member

    I came across this thread whilst looking for a picture of Rory & Cookie who of course we helped. If you read the Ampair manual for the Aquair (which is where I work) you will find that the need for a weak link is discussed. The Aquair is not perfect but nothing is, and we think the Aquair is a pretty good all round balance of performance (i.e. max amps, min drag, max reliability) and cost (i.e. min). Sticking electrics in the water is fraught with difficulty and cost, and shaft generators are tricky for smaller boats as discussed. Hence the Aquair towed generator design.
     
  14. gonzo
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    gonzo Senior Member

    I think the system that looks like an outboard is a good setup. The alternator is in the pod like on an electric trolling motor, and it can be tilted/lifted off the water.
     

  15. petit bateau
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    petit bateau Junior Member

    You might want to check the price, as that is a substantial part of what makes something 'good'.
     
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