Alternator

[Manie B]

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/se...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

[michael pierzga]

Seen many tow alternators , but never a home made one. The website Yachtwork has some ideas


http://www.yachtwork.com/report-wind.htm

http://www.yachtwork.com/images/repo...ade%20plan.jpg

The high tec towing alternators that the round the world racers use might be worth study.

http://www.wattandsea.com/

[Manie B]

Michael thanks

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

[Boston]

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.

[CDK]

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!

[michael pierzga]

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

[Manie B]

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

[michael pierzga]

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

[Boston]

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.

[Manie B]

Here is a paper that was written on this kind of installation

very informative

http://web.media.mit.edu/~nathan/nep...lternator.html

it also deals with "low rpm"

[Manie B]

jeez I loved the "steam engine"

the thing "wobbles" like crazy

http://www.windbluepower.com/category_s/56.htm

[Manie B]

You know this is good

Make a break link so the shark doesnt take your whole rig with him.

I have found no other reference to this problem
good one, thanks