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Old 27-03-2017, 13:10   #1
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Alternator on Prop Shaft

Hi all. I'm new to the forum.
I am hoping to purchase a 40 /46 Yacht, Centre ( center ) Cockpit. Sailing firstly Mediterranean, Carribean later!!.
Doing initial survey on a yacht I saw a pulley mounted on Prop Shaft.
Pulley driving, by belt, an Alternator mounted on engine above it.
The pulley sizes would have to be "matched" well. Shaft at 8kts, alternator near max rpm too, "presumably" on those lines.
I thought that it is basically a good idea. When yacht is sailing batteries are charging, catering for autopilot, fridge etc.. depending on speed.
I do realise that there a number of issues.
1. The old debate should you lock shaft in gear when sailing.
2. The propeller can't be feathering type. It won't turn.
3. You can't get power from nothing. The boat speed might be decreased because of shaft loading.
4. The spare belts must be mounted on Prop Shaft, hanging clear, when shaft is disconnected.
Point is, I've never seen it before and just wonderef if others saw it or have it installed.
Interesting??.
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Old 27-03-2017, 13:29   #2
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Re: Alternator on Prop Shaft

If I was going to that much trouble I would put the spare alternator on the front of the engine, then at least you can run it at anchor.

Isn't this an old idea before the price of solar and wind became affordable.

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Old 27-03-2017, 13:52   #3
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Re: Alternator on Prop Shaft

I think he's talking about getting advantage of alternator even though engine is NOT running. So here is my take on the OPs questions/issues.


1. It's not a debate, it's what the engine/transmission manufacturer tells you to do...that's the end of the debate right there.
2. true, for your alternator to work.
3. yes it will, but the question is by how much, and that's not a linear equation.
4. also true, but not insurmountable. If you have a universal joint installed on the shaft, you could use that as your break in the shaft instead of pulling the shaft out of the transmission box.






Regarding Propeller drag. A freely spinning propeller is going to create less drag than a propeller locked in gear...UNLESS the propeller ends up turning at a speed that is harmonic to the flow of water passing it. I know that sounds weird, but think of maple seeds when they split and fall of the tree. Once they start spinning, they start to parachute. That is to say the wing engages the whole diameter of the circle they draw. A propeller can do the same thing and cause more drag than a locked propeller because a spinning propeller can "engage" more of the water.


most importantly you want to check with you engine/transmission manufacturer and find out whether they want you to leave the tranny in neutral or put it into gear. That will answer the question right there for you because if you do something else other than what they tell you to do, your engine will not be covered under warranty. Even if you don't have a warranty, it's an indicator that the engine was designed to do it one way and not the other.


I am curious now though, how much drag will an alternator put on the drive shaft? Is it enough drag to cause the propeller to stop spinning? Some propellers don't seem to want to start to spin even when left in neutral, it really depends on how tight everything is in the tranny and the stuffing box, etc etc and how big the prop is and it's pitch. Then again, once the prop is spinning, does it mean it now needs less pressure to keep it spinning? Hmm...Maybe you could fashion some sort of PTO clutch so that the alternator doesn't engage the prop shaft until the prop is spinning.


I'd like to hear what you end up doing and the results.
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Old 27-03-2017, 14:04   #4
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Re: Alternator on Prop Shaft

This sounds like an amel maramu 46 with the 25 amp alternator mounted on the shaft?
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Old 27-03-2017, 15:57   #5
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Re: Alternator on Prop Shaft

Fair Play. Sail monkey.
It was an Amel Maramu. 1980's. Was the Prop Shaft alternator standard on the Amel at that time. Was it worthwhile. Interesting!!.
Scot, I'll try to get the boat first...
It's on my bucket list, always was..
Tks Brendan
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Old 27-03-2017, 16:09   #6
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Re: Alternator on Prop Shaft

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Originally Posted by brendanmmaher View Post
Fair Play. Sail monkey.
It was an Amel Maramu. 1980's. Was the Prop Shaft alternator standard on the Amel at that time. Was it worthwhile. Interesting!!.
Scot, I'll try to get the boat first...
It's on my bucket list, always was..
Tks Brendan


I'm almost positive it was either standard or a common factory option. As to the effectiveness of the alternator....well, if the shaft is turning, why not scavenge a few amps from it. I cannot answer however if it is missing would it be worthwhile to refit. If I was faced with such a dilemma I might put something together out of scrap pile parts.
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Old 27-03-2017, 20:16   #7
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Re: Alternator on Prop Shaft

A man I know who's a fellow cruiser owns a 1936 Gauntlet Cutter named Guiding light. He had a wind generator set up to run off the shaft because he had no where else to mount it properly he said. According to him, it worked ok. As far as drag, he won the Antigua Classic with this boat although I'm certain it was disconnected.
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Old 28-03-2017, 09:25   #8
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Re: Alternator on Prop Shaft

There's a good description of a person that has actually done this and I think answers some of your questions. LIFE: Part 2: Prop-Shaft Driven Alternator

If the link doesn't come through you can google lifepart2 prop-shaft-driven-alternator. It's a good discussion. I have a boat identical to lifepart2 and am contemplating doing the same thing.

Seems like this won't work on sail drives and some transmissions require placing the transmission in gear while sailing. The transmission on my boat indicates to leave it in neutral which works great for placing the alternator on the prop shaft.

On our last multi-day crossing we had to run the engine to charge the batteries. Would have been really nice to have an alternator on the prop shaft!
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Old 28-03-2017, 09:28   #9
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Re: Alternator on Prop Shaft

These were standard on early Amels and were a great bit of kit. They had some nice features like you had to take your engine start key out and use it to turn the excite current on for the alternator. Since the alternator was configured for low shaft RPM using the alternator and engine at the time was potentially terminal.

I had a shaft alternator on an earlier boat ( specially rewired Lucas sold for that purpose) and it was simply brilliant. However, it really depended upon having the right gearbox, pulleys and safety circuits etc. . But in reality, I would not like to give up my folding prop or go back to maintaining that belt or dealing with the additional cutlass bearing wear when solar panels are so damn good and reliable.

I now use a towed water generator for long crossings and enjoy many of the benefits.

If I was going to do some serious ocean miles again or if I bought a boat with an existing working system in place I would have a shaft alternator again but otherwise, it will be more solar panels.

Ross
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Old 28-03-2017, 09:36   #10
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Re: Alternator on Prop Shaft

Passing Cloud had a shaft generator Worked very well on ocean passages. A secondary clutch on the shaft disconnected tranny (synchro from a logging truck trans) belt idler too. Swung a huge 3 blade And at 68' ,lots of room to build all this stuff. Smaller vessel might look at taff rail type or a Thai long tail shaft as a matter of scale.
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Old 28-03-2017, 09:59   #11
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Re: Alternator on Prop Shaft

Max Prop in the past has listed as a feature that a shaft driven alternator will work with their prop. If you stop the engine with the transmission in forward the Max Prop will feather and the shaft won't turn. However if you stop the engine with the transmission in reverse the Max Prop will not feather and continue to drive the shaft and turn the pulley on the shaft.
Tom
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Old 28-03-2017, 10:15   #12
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Re: Alternator on Prop Shaft

Quote:
Originally Posted by brendanmmaher View Post
Hi all. I'm new to the forum.
I am hoping to purchase a 40 /46 Yacht, Centre ( center ) Cockpit. Sailing firstly Mediterranean, Carribean later!!.
Doing initial survey on a yacht I saw a pulley mounted on Prop Shaft.
Pulley driving, by belt, an Alternator mounted on engine above it.
The pulley sizes would have to be "matched" well. Shaft at 8kts, alternator near max rpm too, "presumably" on those lines.
I thought that it is basically a good idea. When yacht is sailing batteries are charging, catering for autopilot, fridge etc.. depending on speed.
I do realise that there a number of issues.
1. The old debate should you lock shaft in gear when sailing.
2. The propeller can't be feathering type. It won't turn.
3. You can't get power from nothing. The boat speed might be decreased because of shaft loading.
4. The spare belts must be mounted on Prop Shaft, hanging clear, when shaft is disconnected.
Point is, I've never seen it before and just wonderef if others saw it or have it installed.
Interesting??.
Probably take a 4' dia. pulley on the prop. shaft to even come close to enough RPM at the alternator?
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Old 28-03-2017, 11:04   #13
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Re: Alternator on Prop Shaft

Quote:
Originally Posted by yachtgemini View Post
.... I had a shaft alternator on an earlier boat
(specially rewired Lucas sold for that purpose) and it was simply brilliant. .... Ross
As an old British car owner and driver, I want to remind all that Lucas was known as, "The Prince of Darkness." In fact, somewhere in an old box I have metal badge that I once proudly wore on my helmet that said, "Lucas, Prince of Darkness." It was an title that was earned, not inherited. Go forth with caution as that light may suddenly fail.
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Old 28-03-2017, 11:28   #14
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Re: Alternator on Prop Shaft

That helps to explain why the English do not eat Ice Cream....They all have Lucas Refrigerators !!!!
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Old 28-03-2017, 11:49   #15
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Re: Alternator on Prop Shaft

Hiya. Had a shaft alternator on a 40 ft Amel.absolutely fantastic for Ocean crossing. 5 knots plus 8 to 10 amps. Autopilot and radar on all night no issues.did lose a bit of boat speed. If I had one again I would combine it with a max prop and just use it at night when solar is down. Aparrently max prop can feather or not if you chuck in reverse before stopping the engine.
Simon
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