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Old 26-11-2019, 15:03   #16
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Re: Could one use boat propeller to drive el generator?

Depends on what you want... energy transfer always comes with a penalty the more you load the prop the slower you go... so yes its doable but only if you dont have timelines... and I would make it with a disconnect for when you need to move fast
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Old 27-11-2019, 07:55   #17
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Re: Could one use boat propeller to drive el generator?

Let's face it, most boats spend over 95% of the time at the dock. Stealing a small amount of energy when actually under sail is not going to solve any charging problems.

Having said that, the dock where we kept our boat experienced tidal flow up to 4 knots 4 times a day - - - but cheap shore power is much quieter .
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Old 27-11-2019, 09:09   #18
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Re: Could one use boat propeller to drive el generator?

Quote:
Originally Posted by FAST FRED View Post
"I was wondering whether I could not jig up an electric generator to it. Would it un-balance the shaft? Why is it not done? "

It could work in a heavy blow where the boat was near hull speed and you had excess energy to use.

A spinning prop absorbs massive energy , which is why multi engine propeller aircraft feather theirs.

To see the effect simply cut a piece of plywood the same diameter as your current prop rigged as a speed brake . When towed in the water the drag , and speed reduction will be ez to see.

Folks that do not care about the speed reduction can get alternators rewound to produce electric at very low RPM.
Fast Fred, I agree completely with your statement that a stopped airplane propeller creates less drag than a freewheeling propeller. Iíve actually tested it with an ultralight aircraft. Much more drag with a freewheeling prop.

I donít think it holds true for a boat propeller. Iíve seen videos of tests that show that a freewheeling boat prop creates less drag than a fixed prop. Iím not sure why this is true but I think it has to do with the area of the blades vs the area of the swept disc. Here is a video of the boat prop test.

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Old 27-11-2019, 12:39   #19
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Re: Could one use boat propeller to drive el generator?

A free-wheeling prop on a boat under sail is already sapping energy produced by your sails, now you want to hook a electric generator up to the rotating shaft and sap even more from the sails. You must belong to the "Free Lunch Society" Better stock up on plenty of drinking water, this is going to be long voyage.
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Old 27-11-2019, 12:41   #20
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Re: Could one use boat propeller to drive el generator?

Can't remember the details but that test the guy had on this forum was bogus because his test props were not under load.
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Old 27-11-2019, 13:26   #21
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Re: Could one use boat propeller to drive el generator?

As others have said this has been done. Even some production boats have this feature (for example older Amelís and Ovni Ďs). However there are some drawbacks. The rotating propellor creates noise and wear on the stern gear. Adding extra components to the driveshaft increases the risk of problems so the system is incompatible with the desire to keep the drive system as simple and reliable as possible.

To be effective the generator and gearing system are quite bulky and need to be fitted in area of the boat where there is not a great deal of room and access.

Nevertheless, I have seen some very effective systems that can generate useful amounts power on passage.

The system is uncommon in modern cruising boats. Feathering or folding propellors have tended to replace fixed props and when the propellor is feathered or folded it cannot generate power (or drag).

The higher production available from modern solar systems has tended to fill the energy gap.

Ironically, hydrogenerators (with a prop separate from the main drive system) are gaining in popularity, although there have been some significant teething problems.
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Old 27-11-2019, 14:08   #22
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Re: Could one use boat propeller to drive el generator?

It is done. Commercially manufactured slow-speed propeller shaft alternators are available for use when gearbox is in neutral, or when engine is running. However, some gearboxes if spun slowly in neutral do not have adequate oil supplied to some of the bearings, so it may be necessary to modify the gearbox by fitting an oil pump if it does not already have fully pressure fed bearings.
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Old 27-11-2019, 14:13   #23
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Re: Could one use boat propeller to drive el generator?

Quote:
Originally Posted by jmschmidt View Post
A free-wheeling prop on a boat under sail is already sapping energy produced by your sails, now you want to hook a electric generator up to the rotating shaft and sap even more from the sails. You must belong to the "Free Lunch Society" Better stock up on plenty of drinking water, this is going to be long voyage.
Nothing to do with having a "Free Lunch" unless you are sailing below hull speed with full sails.

As soon as you reef (or reach hull speed), then there is surplus power available from the wind/sails. Using it to drive an electric generator will not affect passage times unless the winds are consistently light. If so, simply stop using the generator until the wind strengthens and hull speed is achieved again.
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Old 05-12-2019, 00:36   #24
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Re: Could one use boat propeller to drive el generator?

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Originally Posted by Wotname View Post
Nothing to do with having a "Free Lunch" unless you are sailing below hull speed with full sails.

As soon as you reef (or reach hull speed), then there is surplus power available from the wind/sails. Using it to drive an electric generator will not affect passage times unless the winds are consistently light. If so, simply stop using the generator until the wind strengthens and hull speed is achieved again.

That's right.



HOWEVER, few people do it in exactly this way, and there is a good reason -- no one wants to listen to the shaft turning, or to put wear on gearbox, shaft seal, cutless bearing. That's why nearly all serious ocean sailors have folding or feathering props, and you can't drive a generator with one of those.



So you use a separate hydro generator, like this: https://www.wattandsea.com/en/produc...ydrogenerators


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Old 05-12-2019, 01:12   #25
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Re: Could one use boat propeller to drive el generator?

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Originally Posted by jmschmidt View Post
Can't remember the details but that test the guy had on this forum was bogus because his test props were not under load.
Ahh I see, Maine Sail is bogus, Hmmm
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Old 05-12-2019, 05:09   #26
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Re: Could one use boat propeller to drive el generator?

Quote from post #24 HOWEVER, few people do it in exactly this way, and there is a good reason -- no one wants to listen to the shaft turning, or to put wear on gearbox, shaft seal, cutless bearing. That's why nearly all serious ocean sailors have folding or feathering props, and you can't drive a generator with one of those.


Correct me if I am wrong, but a feathering Max-Prop, can be used to drive a prop shaft alternator. I believe if you run the engine in reverse, then kill engine (without putting gear in neutral), then the blades are angled and not featuring so that it can drive a the propshaft.
BTW, to have the blades feather, one kills the engine while the gearbox is in foreward.
I have such prop, but I must say never tried to stop in reverse to check that claim out, will do so this weekend, will report back.
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Old 05-12-2019, 19:11   #27
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Re: Could one use boat propeller to drive el generator?

I can't say - my Autoprop certainly doesn't work that way.

But even if the Maxprop does work that way - do you really want to use your shaft and gearbox that way? I wouldn't.
Quote:
Originally Posted by HankOnthewater View Post
Quote from post #24 HOWEVER, few people do it in exactly this way, and there is a good reason -- no one wants to listen to the shaft turning, or to put wear on gearbox, shaft seal, cutless bearing. That's why nearly all serious ocean sailors have folding or feathering props, and you can't drive a generator with one of those.


Correct me if I am wrong, but a feathering Max-Prop, can be used to drive a prop shaft alternator. I believe if you run the engine in reverse, then kill engine (without putting gear in neutral), then the blades are angled and not featuring so that it can drive a the propshaft.
BTW, to have the blades feather, one kills the engine while the gearbox is in foreward.
I have such prop, but I must say never tried to stop in reverse to check that claim out, will do so this weekend, will report back.
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Old 05-12-2019, 19:19   #28
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Re: Could one use boat propeller to drive el generator?

Several feathering props can be made to stay out of feather and can drive a generator.
However we have another issue, and that is a prop that is intended to be a driving force is very inefficient when itís driven. Itís exactly the reason why props just donít produce much force in reverse, that is actual well designed props with an aerodynamic profile and an obvious leading and trailing edge.
Autoprop gets around this by flipping the blade over so the leading edge remains the leading edge, but unfortunately without some kind of redesign there is no way to keep it from feathering that I know of.

So while you can use your propulsion prop to make electricity, you will make much more electricity with less drag with a propeller that is designed to be a turbine and not a propulsion prop.

Then your using a tool that was designed for the purpose itís being used.

An aircraft propeller would make a horrible boat prop and vise versa as a ridiculous comparison, thatís of course more obvious.
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Old 05-12-2019, 19:22   #29
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Could one use boat propeller to drive el generator?

We have a member that nugged this out I believe, but I may be mistaking him coming to a design for an electric driven propulsion prop.
Anyway I believe his screen name is boat Alexander. Ask him to explain.

However on the spinning prop, I was absolutely certain that a fixed prop was les drag, itís easily demonstrated in an airplane.
But a boat prop is different, I theorize itís because of what is known as the swept area being so different.
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Old 05-12-2019, 22:02   #30
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Re: Could one use boat propeller to drive el generator?

Keep in mind that the propeller shaft is kept in position with a THRUST bearing, usually in the transmission, that the shaft pushes on to move the boat.

When rotating while the transmission is in neutral you will be PULLING on the bearings which are not intended for this mode and may be subject to excessive wear.

WARNING, IN particular, when the engine is not driving the transmission there is no forced lubrication which can result in excessive deterioration of the rotating parts.
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