Alternator attached to propshaft, any views?

[Heckler]

The other day, sailing nicely at 5kts to Pwllheli, SWMBO remarked that she could hear a whining noise. I said its the prop shaft spinning. Anyway I went below, I was bored! I had a look and although Ive seen threads about this before, I put my hand on the shaft and tried to stop it. I couldnt, I was quite surprised. There is a bit of power being generated there. My prop is a 3 blade 16" by 11" I believe.
Question, anybody know how to work out the power being developed by the prop and anybody succeeded in making a prop powered alternator work properly?
Stu

 

[2Tizwoz]

http://www.sailnet.com/forums/miscellaneous/22098-propshaft-alternator.html

The link is to an article describing what's involved and this link http://forum.ssca.org/phpBB3/viewtopic.php?f=4&t=8415 is a description of other people's experience.

Presumably you are sufficiently experienced to take care but there was a report of someone becoming entangled in their propellor shaft.

More difficult with a saildrive however.

 

[Chris_Robb]

I think the main difficulty would be finding the room to put a large enough diameter pulley on the shaft in most AWB types. Solve this and yes, I think it would be worth it. Just remember to grease the shaft seal if a volvo type more regularly if doing big mileages.

 

[mattnj]

The other day, sailing nicely at 5kts to Pwllheli, SWMBO remarked that she could hear a whining noise. I said its the prop shaft spinning. Anyway I went below, I was bored! I had a look and although Ive seen threads about this before, I put my hand on the shaft and tried to stop it. I couldnt, I was quite surprised. There is a bit of power being generated there. My prop is a 3 blade 16" by 11" I believe.
Question, anybody know how to work out the power being developed by the prop and anybody succeeded in making a prop powered alternator work properly?
Stu

what a totally pointless exercise when you can buy an SMDO generator that makes toast for £229!....surely you have better thing to do before you die?

(that attitude ring any bells?)

 

[Heckler]

http://www.sailnet.com/forums/miscellaneous/22098-propshaft-alternator.html

The link is to an article describing what's involved and this link http://forum.ssca.org/phpBB3/viewtopic.php?f=4&t=8415 is a description of other people's experience.

Presumably you are sufficiently experienced to take care but there was a report of someone becoming entangled in their propellor shaft.

More difficult with a saildrive however.

Thanks for the links, am an old time maintenance engineer, quite used to putting a hand on a large spinning shaft to test the temp.
I suppose in this day and age frowned upon, but thats what we did and didnt come to any harm.
Stu

 

[Boo2]

Question, anybody know how to work out the power being developed by the prop and anybody succeeded in making a prop powered alternator work properly?

Dunno what the power would be but it must be substantial if Solomans' regenerative motor sailing products are any guide.

Boo2

 

[TQA]

You can not get something for nothing.

The more amps you generate, the slower the boat will go.

 

[DownWest]

You can not get something for nothing.

The more amps you generate, the slower the boat will go.

Yes,but.. if there is enough wind to reach hull speed or a bit more, would the extra drag matter? And if long distance sailing might the amps be worth the bit of drag?
A
A trailing generator would make more sense, but that wasn't the question.

 

[Leonidas]

The other day, sailing nicely at 5kts to Pwllheli, SWMBO remarked that she could hear a whining noise. I said its the prop shaft spinning. Anyway I went below, I was bored! I had a look and although Ive seen threads about this before, I put my hand on the shaft and tried to stop it. I couldnt, I was quite surprised. There is a bit of power being generated there. My prop is a 3 blade 16" by 11" I believe.
Question, anybody know how to work out the power being developed by the prop and anybody succeeded in making a prop powered alternator work properly?
Stu

On a slightly different issue. My boat manual says that that when sailing one should engage the reverse gear in order to prevent the shaft from turning as it might damage the gearbox (Perkins Prima coupled to Wurth gearbox) Perhaps you could check it out with your maker??

 

[pvb]

A trailing generator would make more sense, but that wasn't the question.

Trailing generators typically only produce 3 or 4 amps at 5 knots, and a propshaft alternator would probably produce less. It's not worth considering.

 

[Heckler]

On a slightly different issue. My boat manual says that that when sailing one should engage the reverse gear in order to prevent the shaft from turning as it might damage the gearbox (Perkins Prima coupled to Wurth gearbox) Perhaps you could check it out with your maker??

The MS2 box on mine is fine freewheeling, ref a conversation I had with VP years ago
Stu

 

[Heckler]

Oh, from one of the links above, this chap seems to think it is worth doing:

Once the propshaft gets up speed, tremendous power can be generated by having a large drive pulley (around 10 inches in diameter) on the propshaft, driving a small pulley (around 1.5 to 2-inch diameter) on an adjacent, low speed alternator/generator. This is especially the case once the boat speed gets above 4.5 knots, typically generating eight to11 amps at a cruising speed of 6.5 to 7.5 knots. This output is well in excess of the five or so amps usually obtained from two large solar panels. Most gratifyingly, the eight to 11 amps are generated continuously under sail, irrespective of time, the intensity or angle of sun-rays, or the strength of the wind. The latter two are far from being predictable!

Limited technical information is available to select the optimum propshaft alternator for a given auxiliary engine drive arrangement. There is some guidance in the Australian publication The Marine Electrical & Electronics Bible by John C. Payne (pages 84-85), and in Offshore Cruising Encyclopedia by Steve & Linda Dashew (pages 521-523). Despite the absence of detailed guidance, it is possible for a cruiser with reasonable mechanical and electrical knowledge and skills to undertake a successful installation.


Stu

 

[Heckler]

http://www.sailnet.com/forums/miscellaneous/22098-propshaft-alternator.html

The link is to an article describing what's involved and this link http://forum.ssca.org/phpBB3/viewtopic.php?f=4&t=8415 is a description of other people's experience.

Presumably you are sufficiently experienced to take care but there was a report of someone becoming entangled in their propellor shaft.

More difficult with a saildrive however.

Interesting facts coming out here, one of your links led to this http://strathprints.strath.ac.uk/5670/1/strathprints005670.pdf
Research to answer the question often asked on here about whether to put in gear or not.
Stu

 

[fuss]

You can not get something for nothing.

The more amps you generate, the slower the boat will go.

Trailing generators typically only produce 3 or 4 amps at 5 knots, and a propshaft alternator would probably produce less. It's not worth considering.

The problem is not slowing your boat down. The problem is actually getting it to generate in the first place.
I know this is a stupid example but it makes the point...
if you put one on a 7m boat, it will slow it down and probably wont generate any power, but if you put one on a 30m sailing boat it might generate lots of power and not slow it down at all.


I think propshaft alternators only work if everything is optimised
i have a propshaft alternator and I made it as my boat already satisfied some of the conditions required to make it work well.

The gearbox is hydraulic so spins all the time while sailing, you cannot put it in reverse and stop it.
the prop is 19" 3 blade and the boat 22 tons 50 feet.
The engine is slow revving, that means the alternator works when motoring as well.

I use an alternator not a magnet motor. a magnet motor would be better at lower sailing speeds as it requires no initial amps. The alt needs around 2.5 amps initially for the field coils, so at borderline sailing speeds it might use amps instead of making amps... this is the disadvantage of the alternator... but at higher speeds it generates more amps....
4.5kts is around 5a at 24v
20a at 6.5kts
45a at 8kts.
to work properly it needs...
a clean hull
a clean prop
no cutless bearing play
no water leaks at all at the stern gland
the right ratio which changes for each vessel... mine is around 5:1.
I dont notice any slowing down at all when it is working.
what works on one vessel might not work on another.

If your boat is light and shorter then I would think that a permanent magnet solution might be better

 

[Scotty_Tradewind]

Yes,but.. if there is enough wind to reach hull speed or a bit more, would the extra drag matter? And if long distance sailing might the amps be worth the bit of drag?
A
A trailing generator would make more sense, but that wasn't the question.

A trailing genny I like but probably has it's own problems, e.g. when not in use/storage/sharks etc...but would a sideways force on the propshaft be cause for concern...would propshaft bearings suffer at all by the pulley tension after a time?

I reckom Matt amd Stu should 'partner up', they sound as if they would make a fine 'couple'

 

[WindermereColvic]

Prop shaft alt

Somthing i've wondered about a few times, the only flash of enlightenment ive had is to use a chain or toothed belt rather than a v belt, to reduce the amount of sideways (perpendicular to the shaft) force that will be acting on the shaft and bearings.
Alternativle, you could go the whole hog with a diesel - electric conversion. Lynch motor?

 

[Heckler]

Somthing i've wondered about a few times, the only flash of enlightenment ive had is to use a chain or toothed belt rather than a v belt, to reduce the amount of sideways (perpendicular to the shaft) force that will be acting on the shaft and bearings.
Alternativle, you could go the whole hog with a diesel - electric conversion. Lynch motor?

After the info started coming in I thought hmmm, maybe not a bad idea then I thought oh but the sideways pull to tighten the belt will accelerate wear on the Volvo seal. Then I thought ah but, if i made a 1/4" plate to bolt up against the back of the MS2 gearbox, mount the alternator on that and put the drive pulley close up to the flange, most of the load will be taken by the output bearings on the gearbox? Thoughts?
Stu
To the OP the difference between mine and Matts idea is that I wouldnt run a genny whilst sailing, BUT the prop turning whilst sailing gives "free" almost silent power.

 

[fuss]

Somthing i've wondered about a few times, the only flash of enlightenment ive had is to use a chain or toothed belt rather than a v belt, to reduce the amount of sideways (perpendicular to the shaft) force that will be acting on the shaft and bearings.
Alternativle, you could go the whole hog with a diesel - electric conversion. Lynch motor?

I have the pulley right up close to the g/b flange and it says in the manual that the g/b can handle a side load.
If the gearbox cant handle side load then I guess another solution is required. Also if the pulley is near the cutlass bearing then it will put a side load on it which you might discover as a problem far further doen the track as well as maybe stressing the stern gland.
If these problems exist then its probably not worth the effort. I only made it for my boat because the g/b could handle side load, there was room for a big pulley, the pulley was not near the sterngland, the engine was slow revving.... this is a huge advantage incidently, as then the alternator cannot be over revved when the motor is flat out. this then means you have an extra alternator putting out amps when motoring.

For me I am very happy to have 2 alternators working when motoring and one of them acting as a electricity generator when sailing at over 4.5 kts.

 

[Bobobolinsky]

Always assuming the boat is not over or under propped, I saw a guy used a rare earth motor to drive an electric launch on "Boatyard". Why not have a similar unit, with a through shaft, so the alternator is mounted on the shaft, rather than driven by a belt, which would place a load on the seal. The motor was a low speed unit, so gearing would not be required. If the rotation required a reduction, what about a cyclic box.

 

[Ric]

Trailing generators typically only produce 3 or 4 amps at 5 knots, and a propshaft alternator would probably produce less. It's not worth considering.

I disagree. 3-4 Amps is well worth having on a sailing boat.

I have a 32ft AWB, with fixed prop. I have flexible solar panels on the deck (which produce about 2-5 Amps in daylight), a Rutland 913 (another 3-7 Amps), and a permanent magnet alternator fixed directly inline on the propshaft. The combination of all three allows me to run indefinitely a fridge, full complement of electronic instruments (6 x ST60), GPS, Furuno Radar and passage lights without ever having to switch on the engine for charging.

If you just consider capital outlay, I agree it would have been cheaper just to spend the money on one of those poxy plastic generators. But I get more pleasure from running my boat my way.