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Old 02-09-2011, 22:48   #1
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Generator on Prop Shaft ?

My boat has a 4108 Perkins with a v_drive , and doesn't have a feathering prop. Been thinking about try to mount a pulley and a belt that would drive a small automotive alternator when i am sailing , the prop shaft spins quite fast kinda worried me that it might be tough on the vdrive and the tranny. An ac deco thirty amp with an internal voltage regulator would be simple to wire..........have never tried to stop the shaft with any kind of brake , but when you are sailing at eight or ten knots , that thing really spins. Anybody ever tried that before ? I can't be the first person that thought of this.......any experience with this experiment would be gladly received
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Old 03-09-2011, 06:43   #2
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Re: Generator on Prop Shaft ?

this is one i built a few years ago on a 53 ft yacht
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Old 03-09-2011, 06:46   #3
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Re: Generator on Prop Shaft ?

Atol, how did it work? Did it make very much current? Did it slow the boat very muck?
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Old 03-09-2011, 07:03   #4
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Re: Generator on Prop Shaft ?

I had some very limited experience with this on a friend’s 44 Jeanneau. The PO had mounted a generator on the engine block that turned with the spinning shaft. He wired a voltage-sensitive relay on the generator output that picked up at around 7 knots boat speed and placed the generator online. There was a light on the cockpit engine panel showing the relay status so you could tell when the generator was producing power. There was also an interlock to disable the relay when the engine was running. Seemed to work OK as long as the boat maintained a sustained speed over 7 knots, otherwise it just kept dropping out.

Can’t speculate on the effects on the drive train, I guess there are various schools of thought on that topic.
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Old 03-09-2011, 08:41   #5
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Re: Generator on Prop Shaft ?

Quote:
Originally Posted by Cowboy Sailer View Post
Atol, how did it work? Did it make very much current? Did it slow the boat very muck?
it was a standard 80amp 24v alternator,with a 30 cm pully on the shaft and 5cm on the alt spindle,worked after 5.5 knots boat speed with no appreciable drag.

would have used a 35-40 cm pully if space had allowed to be able to charge at lower boat speed.

on /off control on the field wire,unit was machine sensed so would keep the batteries at 13.8 volts,and vary output depending what was switched on,ie fridge ,freezer,auto pilot,nav gear.

alternator needs 1000+ rpm at the spindle before it will excite and produce any current,so pully ratios are critical,as is shaft rpm.

this one had a 6:1 ratio so about 180 rpm at the prop shaft taking into account the slip on the propellor itself of about 80% ie(if the engine was turning under power rpm would be about 300rpm to achive 5.5 knots of boat speed)

calculations are very critical ,as is a large enough pully on the prop shaft to get the right ratio at the alternator.
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Old 03-09-2011, 08:55   #6
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Re: Generator on Prop Shaft ?

How was the noise when it was charging? Acceptable?
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Old 03-09-2011, 10:09   #7
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Re: Generator on Prop Shaft ?

no change from the normal prop shaft noise.the shaft was allways free to spin
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Old 04-09-2011, 09:23   #8
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Wow , that is awesome. I wasn't thinking of getting anywhere near that fancy with the field energize . Just a toggle switch , and maybe a bracket , to engage the belt while under sail only. Wasnt thinking I would need to do anything more fancy than just wire the output directly to the house bank either. Dont have any solar controller or anything else wired in yet.
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Old 04-09-2011, 09:39   #9
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Re: Generator on Prop Shaft ?

with the field wire switch there is no need to disengage belts,so they can be left tight all the time as will freewheel till energised.

a 30a alternator would be fine as whilst underway it produces power 24/7.

the most critical is getting the right size pully,this can go directly on the flange/gearbox coupling to the propshaft,so no bearing,alignment issues if the alternator is attached by a plate to the gearbox housing.

the rpm at the alternator is not important as long as it is above 1200 rpm as they can spin at up to 7-8000 rpm,what is critical is the pully ratios;ie bigger pully=lower boat speed needed for it to start working.
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Old 12-09-2011, 00:27   #10
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Re: Generator on Prop Shaft ?

Very nice set up you built . IM glad i kept searching for this topic good pics there Thank You. Ive done quiet a bit of research on this and as you have said do the math calculations carefully.You can get low RPM alternators so that is not really a problem .Cheers
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Old 12-09-2011, 02:32   #11
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Re: Generator on Prop Shaft ?

be good if you could post any links on low rpm alternators,ie pricing and output specs.
cheers atoll
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Old 12-09-2011, 03:18   #12
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Re: Generator on Prop Shaft ?

Here are a couple links

Arco High-Amp, Low RPM 12 Volt Alternator

http://www.windandsolar.com/alternat...10408&type=pla
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Old 12-09-2011, 04:21   #13
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Re: Generator on Prop Shaft ?

found these that look like they may do the trick with a regulator on the voltage side of things

Permanent Magnet Alternators
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