Alternator on Prop Shaft

[sailor1924]

My old boat had an offset propellor on a strut. One of the former owners had fit a 13" diameter pulley on the prop shaft that drove a 3.5" pulley on a specially wound alternator. It would give some electric output and as I didn't have a working engine, for several years it was the sole source of power.
It was noisy and, I didn't much like the rumbling of the turning shaft. When I replaced the original engine with an identical unit I kept the alternator installation as a back up.
The last engine I installed would have required a more complicated installation; using a shaft disconnect and thrust bearing. I didn't re-install it after I installed the new engine.

[Mango51]

My Amel mango came with the pulley ,wire, and gauge. But no alternator. It would be nice to have. Master volt or one of those companys offer one that acts as an aux emergency engine besides a alternator.

[Sailmonkey]

Originally Posted by Mango51

My Amel mango came with the pulley ,wire, and gauge. But no alternator. It would be nice to have. Master volt or one of those companys offer one that acts as an aux emergency engine besides a alternator.

The mastervolt unit won't generate power from the motion of the sailboat alone, much too large. A shaft generator needs to be a very small unit, ideally something permanent magnet, only capable of generating a handful of amps to not stop the shaft from turning.

[seabreez]

Originally Posted by brendanmmaher

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??.

This has been tried before... there is not enough speed and power coming out of the prop and shaft under current speed only and there fore will not charge to peak performance...

[Oceanride007]

My boat bought last year has a custom shaft generator. Twas built in 1989, got to remember back then Solar wasn't up to the task and PO had dollars to spend. Yes I think it is a lucas, shaft pulley is about 10" Alternator pulley about 3", its clever enough not to excite when the engine is running. Only tried it out a couple of times, got easy 5 amps. I'd use it at night, as in the day solar is enough to power the AP. Engaging the pulley is tricky and if I had to replace the belt I'd have to figure out how to get it past the shaft. Propellor is fixed, I assume gearbox was selected so it self lubricates. Its a asset. But I'd avoid using it, save it for special occassions.

[davegeorge44]

I had a prop shaft alternator for a few years until I re-engined the boat. There was a guy in Australia at the time who was re-winding alternators to put out at lower RPMs than a car alt would use. It worked great on passage where sailing all night with an electronic autopilot, fridge, etc. Did take off about 1/4 knot from the speed. I gave it up when I changed engines and was sorry.

[topmast]

Back before electric clutches most of my Dad's friends were missing ends of fingers from slipping on and off V belts for pumps, generators compressors .Pretty standard hazard of commercial fishing. I lost a nail once learning the skill.

[HopCar]

"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"


This is a bit of thread drift but has some bearing.
Scot, I'm not sure what harmonic to the flow means but I think you've brought up something interesting. Your description of a falling maple seed is a perfect example of why pilots try to stop freewheeling propellers if they have an engine failure. They can glide farther with a stopped prop.

I'm convinced it doesn't apply to Boat props.

My guess is that the area of the propeller has something to do with it. An airplane propeller has an area that is a tiny fraction of the area of the turning circle.

A boat prop has an area that is a much bigger percentage of the circle. In fact I think some four bladed boat props may have an area bigger than the circle as the blades overlap.

Here is the video that convinced me that boat props create less drag when free wheeling.

https://m.youtube.com/watch?v=jI-UG9RSlJo

[yachtgemini]

Apologies for a further thread drift...

In the late 1990's around Phuket was an Australian cat that had taken an outboard, reversed the prop and removed the engine and replaced it with an alternator. The owner reported excellent amps and that the unit was very easy to deploy and uber reliable. It must have been heavy but it was a Wharam style cat and they reported to be good load carriers.

I know there are much more 'elegant' tow generators available commercially but I liked the fact this was entirely built from the junkyard skip.

And as for Mr Lucas the Prince of Darkness.... in my case, I had a Morris 1100 and an early Mini that suffered at the mere mention of rain and spent much of their life at the auto electricians. However some of the marine gear was very good and in fact, the Lucas motor in my anchor windlass only died after 20 years of hard service.

Ross

[GordMay]

Greetings and welcome aboard the CF, Brendan.

[SeaSon]

Originally Posted by yachtgemini

Apologies for a further thread drift...

In the late 1990's around Phuket was an Australian cat that had taken an outboard, reversed the prop and removed the engine and replaced it with an alternator. The owner reported excellent amps and that the unit was very easy to deploy and uber reliable. It must have been heavy but it was a Wharam style cat and they reported to be good load carriers.

I know there are much more 'elegant' tow generators available commercially but I liked the fact this was entirely built from the junkyard skip.

And as for Mr Lucas the Prince of Darkness.... in my case, I had a Morris 1100 and an early Mini that suffered at the mere mention of rain and spent much of their life at the auto electricians. However some of the marine gear was very good and in fact, the Lucas motor in my anchor windlass only died after 20 years of hard service.

Ross

Hmm, could a cheap electric trolling motor facing backwards...