Propeller shaft alternator

[la7qz]

Hi

I'm thinking about installing a propeller shaft alternator on our 36 foot 10 ton Cheoy Lee Clipper Ketch, but have some questions.

A lot of people have tried installing a standard marine or automotive engine alternator as a shaft alternator and I already know this is doomed unless the alternator is rewound since the alternator never spins fast enough to really produce anything. However, we have a spare 400Watt three phase permanent magnet wind generator alternator (from a Duogen). We are flying an identical alternator as a wind generator with blades from a Four Winds, and this works very well. Cutin is at around 300 RPM, producing (from memory) around 5 A at 400 RPM and maybe 10A at 500 RPM. (Not sure about these numbers, but pretty close). The most I've seen is 34A at 1170 RPM in a big gust.

Magic's engine is a Yanmar 3GM30F (24hp), and she normally cruises happily at 5 - 5.5 knots at 1500RPM under power. I believe the gearbox is 3-1?

My goal is for the shaft alternator to produce 5A when sailing at 6 knots. More will be welcome of course, but 5A would make me happy. In other words, the alternator needs to spin at around 400 RPM (or more). Does anyone have an educated guess what propshaft RPM I can expect at 6 knots with a load of 5A (approximately 65W) on the alternator? Sizing the pulleys right is probably more important with a permanent magnet alternator since I can not control the field.

BTW, the solar panels and wind generator are regulated by a Morning Star Tristar 60 configured as a dump load regulator with a 600W 12V heating element in the hot water tank. This works very well and we even sometimes produce hot water from wind and sun. Since the regulator is connected direct to the batteries with a set point of 14.4V, it will automatically take care of any excess energy from a shaft alternator, so overcharging is not an issue and any hot water produced would be most welcome.

Owen, Donna and Sparky
Yacht Magic
St Maarten

[stormalong]

I do not have a prop shaft alternator. A friend of mine had one on a 44 ft steel sloop. He drove the alternator faster by placing a lay shaft next to the engine so that he could increase the alternator speed by using a large pulley on the lay shaft and a small one on the alternator. He used a standard automotive alternator and produced a lot of power. If you have that kind of room you might consider that. He also had a big three blade prop driving it. Be sure your transmission can freewheel without damage and expect to replace your cutless bearing pretty regularly.

[Jack Tyler]

Among the many considerations to think through is what MAGIC's future plans are. If you are expecting daysails and overnights up & down the islands and are only wishing to arrive at an anchorage with more amps in the house bank, perhaps a free-wheeling prop and the noise it generates won't bother a crew that's mostly in the cockpit. With a 36' CL Clipper, I'm guessing the noise is going to be close enough to a resting crew that living with it on longer offshore runs would be quite a nuisance. What is your current experience with your free wheeling prop?

The shaft alley on a Belgium 46' aluminum cutter we cruised with could accommodate a large enough shaft pulley, bolted together from two halves, to turn the boat into a power company on their long runs. Lacking all the other AE sources you mention, they inevitably had to power down the boat when they arrived at a destination. So depending on the boat's geometry in the drivetrain area, it can certainly be electrically productive.

BTW there have been some other threads here on this same topic so be sure to use 'Search' if you haven't already...

Jack

[FAST FRED]

I suggest you first tow a pail that has the same diameter as your propeller.

The speed reduction will be about the same while charging.

FF

[ka4wja]

Owen,
I have personal experience with both a propeller shaft alternator, AND a towed-propeller-permanant-magnet-dc-generator.....
Perhaps I can add some real world info that would be of help.....

1) First off, my experiences (both with prop-shaft alt. and towed-gen) on 2 different boats, is completely different than that of Fast Fred's......

I suggest you first tow a pail that has the same diameter as your propeller.
The speed reduction will be about the same while charging.

I've found the drag, in either set-up, to be of little consequence.......

Yes, the drag from a spinning prop, driving a small alternator, is more than that of a free-spinning prop.......But is substanially less than that of the same prop "locked" and not spinning at all......but even this is less drag than you'd measure towing a bucket/drogue the same size as your prop.....


2) Some specifics on my experiences with a prop-shaft alternator....

Back in the 1970's sailing a 35,000 lb modified-fin keel with sked-hung rudder, with a 21" fixed 3-blade prop, we had a small (35-amp) Motorola alternator mounted above and just aft of the transmission, driven by the prop shaft while spinning freely under sail......
This was rigged with a ext regulator, mounted directly to the case of the alternator, with the field wire run to a cut-off switch on the electrical panel, allowing an easy way to switch it on/off....
If you use the right alternator (small) and set-up is designed / installed correctly, it DOES work, even without having a custom-wound alt.....
(Using this switch, we found VERY little difference in boat speed at all....
Please remember that this was way back in the pre-GPS days, and was also many years before 1/10 kt reslotution digital boat speed indicators.......but if there was decent wind, there was NO loss in boat speed, and if the wind was light, we saw maybe 1/4 kt loss at most.....in complete honesty, it was ~30 years ago, so my memory isn't perfect, but that's my best recollection....)

This set-up worked well, and in addition to a few years in the Bahamas and Caribbean, it sailed across the Atlantic twice, and a few years in the Med, etc...and it survived just fine......15+ years and 15,000+ miles......
And although I don't know the exact charge current at different speeds, it did keep up with the 12 vdc frig/freezer, and misc sailing instruments......but did NOT have enough output left over to keep up with 24/7 use of the power-hungry Wood Freeman autopilot......
(Using my best recollection of our power used and generated, we had about 1 - 1.5 amps per knot of boat speed, at 5 - 8 kts....giving us 5 - 10 amps......but did NOT have an amp meter on it.......)
There was a big pulley on the shaft, allowing the alt to spin at a usable speed.....and there was a Big, Heavy clutch on the shaft, between this pulley and the transmission (Not my idea, but rather the idea of the builder, Hinckley) which allowed all the power of the shaft to go into turning the alternator, rather than the big transmission.....
To this day, I understand Hinckley doing it this way, but I still think the clutch was unecessary.....
{ Don't forget to slide a few V-Belts over the shaft when insatlling this (we had 10), so that you don't have to unbolt the shaft and slide it back to put on a new belt!!! }
Sometime in the mid to late 1980's, new motor mounts were needed, the shaft was pulled, etc....and the yard doing the work suggested removing the clutch and alternator.....and installed a new shaft.....
At this time, there wasn't a big need on board for this, since it was now mostly ocassional cruising.....and island hoping.....

And FYI, I still have this exact 35-amp Motorola Alternator, now 35 years old, mounted on my 327 cu in Chevy V-8 engine in my '23-T Roadster (in storage in my garage in Florida)....I cleaned it up quite a bit and put a few coats of hi-temp engine paint on it....and it is still working fine.....


3) And for some specifics on my towed-propeller-generator.....

A few years ago, I installed a Hamilton Ferris WP-200 towed-generator on my 1999 Catalina 470, a decent performance, approx. ~29,000 lb sloop....with 6' deep fin keel (9550 lb fin/wing) and spade rudder......
I suppose most would call her a light displacement performance cruiser, with a D/L of ~165 and S/D of 16.8.....but she makes a fine entry and with rounded bilges forward, she's a very nice offshore cruiser......
I've used the Hamiton Ferris WP-200 on both of my Atlantic crossings and found it to work just fine.....
(Since I have 520 watts of solar panels w/ MPPT controllers, I don't have too much need for this towed-gen, unless on LONG passages...and even then, if the skies are clear, I make most all of my power from solar, including that needed by 24/7 use of autopilot.....but, when skies are cloudy/rainy, it really helps!!!)

I find about 1.3 to 1.6 amps, per knot of boat speed, from 4 to 8 kts......which is a bit less than their specs......but I've used it mainly in heavy following seas (cloudy skies!) where the "pull" isn't always constant, so the reults I got aren't an absolute of everyone's results....

The drag I've found is slight.....
Testing in light airs, show a very slight loss of speed.... ~1/4 kt. at most.......
And when sailing in decent wind, I've found little, if any, loss in boat speed.....

I've sailed with this Hamilton Ferris WP-200 (perm. mag. dc motor/generator) for a few years now....across the Atlantic twice, etc..........approx. 9,000 - 10,000 miles...and can tell you it works very well.....
(see my posts on this in the "energy" forum...also see photos of my intial install at http://www.c470.jerodisys.com/470pix/47074.htm )

4) As for what speed your shaft will be truning at, and what pulley ratios you'll need......
I'd be making a guess....but I suspect that you'd need at least 2:1 ratio......

5) Just wondering if you've considered relagating the Tri-Star to just the wind gen, and using a MPPT controller on your solar?????
This will cost some $$$, but might be worth it.......since your prop-shaft generator will of course be of use only when underway......and you may end up spending those same $$$ on pulleys, brackets, etc......
Just a thought.......

6) Steve and Lind Dashew have a great deal about prop-shaft generators in their Offshore Cruising Encyclopedia......if you don't have a copy, pick one up....it's a great reference book......
You may find some info on their website as well......setsail.com (???)

7) Lastly, I agree with Jack.....looking to how/where you'll be sailing, will be a big factor here.....


I realize this doesn't give you exact answers to your questions......but I wanted to clear up any mis-conceptions.....
And, I do hope I helped....

Fair winds....

John

[Brilliant]

Here is an excellent article about a Propshaft Alternator. http://www.sailnet.com/forums/miscellaneous/22098-propshaft-alternator.html

I have always wanted to add one on "Brilliant" but the more I looked at it, the more expensive it seemed to get. The biggest stumbling blocks were where do you find a 10" pulley and where do I find space in the engine compartment to hard mount the alternator.

It's a great idea, let us know if you have success.

Pete
s/y "Brilliant"
Moody 425
Waiting on parts, Sadler Point Marina, Jacksonville, FL
http://www.sailblogs.com/member/brilliant/

[la7qz]

Hi

The biggest stumbling blocks were where do you find a 10" pulley and where do I find space in the engine compartment to hard mount the alternator.

This is why I'm using a wind turbine permanent magnet alternator. A wind turbine is built to charge at much lower revs than a car/boat engine alternator, so there is no need for a huge pulley.

I'm just trying to determine before I start what the pulley ratio should be between the shaft and the alternator I'm using. I'm actually leaning towards starting out with 1:1, My thinking is that if the propshaft spins at 500 rpm when the engine is driving the boat, then it might well end up around 400 rpm (5A at 12V) with the load of the shaft alternator. If anything, I may well end up having to gear this alternator up.

And as for the thoughts on drag and wear. I always have the option to put the engine in gear when the shaft alternator is not needed. (It's a scientifically proven fact that there is less drag from a locked prop than from a freewheeling spinning one.)

Owen, Donna and Sparky
Yacht Magic
St Maarten
Netherlands Antilles

[Sven_G]

(It's a scientifically proven fact that there is less drag from a locked prop than from a freewheeling spinning one.)

No, it is the other way around (for fixed props).

In the drag tests Volvo did a few years ago only two-bladed props locked vertically behind a keel or skeg had less drag than freewheeling 2 or 3 bladed propellers. I'm told that YM just recently did a similar drag test article with the same results but I have not seen that article. For an academic paper showing that locked produces about twice as much drag in most cases go to eprints.cdlr.strath.ac.uk/5670/ and download the paper.

I suspect racers who want others to be slower are the ones who keep perpetuating this myth about locked props having less drag


-Sven

[Tony Bullard]

I have a propeller shaft alternator on my Mariner 39 CC. It produces up to 6 amps at 5.5 knots. I have a 3 to 1 pulley to drive a standard alternator. I turn it on and off with a spring loaded pull cord which engages and tensions the drive belt.

I loose no more than a quarter knot, at worse and since I am cruising, not racing, it means very little. Its a very nice system, especially if your using LED lighting, add 230 watts of solar panels and I can sail many days before I have to use some other source to charge my batteries full up. Before sailing at night really drew the batteries down and I lost a little bit of ground every day using just the solar panels.

I really don't understand more people don't use this system.

Tony
s/v Columbine

[FAST FRED]

"I really don't understand more people don't use this system."

Some trannys can not be freewheeled , and there is a huge difference in the prop size fitted to many sailboats.

The bigger the prop diameter (we use 19inch) the bigger the drag in a hard working unit providing power.

A small 15 inch or less unit will be about 1/3 the drag at 100 to 200 rpm so some folks find the drag acceptable.

The style of stuffing box and perhaps the use of an outside cutlass also add shaft drag , slowing the boat , but not producing power.

WE use a combo stuffing box with stern bearing (18 wraps of stuffing creates the bearing)that is good for cruisers.

The packing can be changed out in the water if spare packing is aboard.

We have changed over to the new Gore style packing and it seems far superior to the flax or tefflon .

No lube is required to stop a required drip for cooling , as the new material does not have the friction and can be tighter with no warming of the stuffing box.

Installed , and after a first few hours another adjustment and it seems to last season after season.

This is impressive as the side loads from our wide blade 2 blade 19inch prop are high as it comes out from behind the deadwood , 700 times a min at cruise.

FF

FF