Folding prop/ generating electricity?

[Bmorgan562]

Can you have the best of both “worlds”? I was just thinking about how you could benefit from a folding prop to reduce drag but also generate electricity? Seems to me it’s one or the other?

[Tupaia]

Originally Posted by Bmorgan562

Can you have the best of both “worlds”? I was just thinking about how you could benefit from a folding prop to reduce drag but also generate electricity? Seems to me it’s one or the other?

Folding prop no, a feathering prop feathered in reverse will work.

[Bmorgan562]

Argh.!! Thank you. ⛵️

[Pete7]

How do you get a feathering prop to feather in reverse?

Pete

[Bmorgan562]

I don’t know? Isn’t it possible?

[Bmorgan562]

If you could lock it in reverse how could it spin to generate?

[sailorboy1]

Originally Posted by Bmorgan562

Can you have the best of both “worlds”? I was just thinking about how you could benefit from a folding prop to reduce drag but also generate electricity? Seems to me it’s one or the other?

Can not do both. If it is feathering it isn't generating power and if it is generating power it by definition is taking power from your follow progress. A generating prop you drag isn't “free” power like solar, it is taking it from your boat speed.

[Bmorgan562]

Originally Posted by sailorboy1

Can not do both. If it is feathering it isn't generating power and if it is generating power it by definition is taking power from your follow progress. A generating prop you drag isn't “free” power like solar, it is taking it from your boat speed.

So.then do think Generating from a free spinning prop is totally counter productive? Or is it just a function of the components and individual situation. ?

[Tupaia]

Originally Posted by Bmorgan562

If you could lock it in reverse how could it spin to generate?

You put the engine in reverse and switch it off then engage neutral. The forward momentum of the boat will keep it open (un-feathered). I had an arrangement like this the shafts were belt driven from the engines. It did work but the wear on the gearboxes would have been high, requiring some form of clutch. A 2 bladed 12 inch prop was capable of producing about 4 hp at 8 knots, at the cost of 1-2knots of boat speed, a lot of drag and complexity.



A towed generator would be more practical. Unless you are looking at electric motor. IMO still not worth the drag penalty.

[HankOnthewater]

Yes, you can do both with Max prop (classic range). If you run the engine in reverse, then kill the engine (leaving the gearbox in that 'astern' position), when engine has stopped gearbox can be put in neutral. Then the propshaft will turn when you are sailing, and thus can drive an alternator on the propshaft.

If you do not want to drive the alternator, then turn the engine off while the gearbox in 'forward' gear and the blades will feather and the shaft will not turn when you are sailing. When the engine is stopped one can leave the gearbox in forward or neutral, does not really matter as the propshaft is not turning. However I prefer it in neutral just in case I forget when I start the engine next time.

Best of both worlds, but..... not at the same time

Edit: I see that post above wrote something similar, however I think that one can not get 4 HP from such small prop, 4 HP approximates 3 KW and at 12 Volt that is approx 250 Amps (without losses). Hmm not even close to that magnitude, maybe 5 to 10 Amps? and the boat speed loss is less barely measurable, maybe 0.5 knot? I guess all the figures depend on: speed of boat, size and pitch of prop, type of alternator, and the pulleys on shaft and alternator (giving the alternator sufficient RPM).

[DIJ]

Originally Posted by HankOnthewater

Yes, you can do both with Max prop (classic range). If you run the engine in reverse, then kill the engine (leaving the gearbox in that 'astern' position), when engine has stopped gearbox can be put in neutral. Then the propshaft will turn when you are sailing, and thus can drive an alternator on the propshaft.

And presumably lifting the valves to deal with the engine compression to help the engine rotation?


But with the other ways of generating electricity this does seem bottom of the pile.

[etoimene]

Originally Posted by HankOnthewater

Yes, you can do both with Max prop (classic range).

Thanks! I am interested in this subject too. I'll look into details later.

[HankOnthewater]

Originally Posted by DIJ

And presumably lifting the valves to deal with the engine compression to help the engine rotation?


But with the other ways of generating electricity this does seem bottom of the pile.

Not sure if the reference to a valve lifter on the engine is an expression of sarcasm or not understanding what I (possibly poorly) wrote.

When you have a Max feathering prop, and you want a alternator on the propshaft to charge the batteries whilst sailing, then
1. start the engine (with engine in neutral)
2. put gear briefly in reverse (ie 2-4 seconds)
3. when gear is still astern, stop engine
4. put gear in neutral
5. blades are locked in and propshaft will keep turning whilst sailing
6. when an alternator is mounted on propshaft than it will start generating amps (on my boat at approx 4 knots)
7. I can not see a speed reduction on my boat, generating 2 to 10 amps
8. Yes the generation of electricity has to come from somewhere: ie with 5 amps at 1 volts is about 60 watts, less 0.1 of a HP.

Have a look at this how much HP a sail can generate:
https://www.boatdesign.net/threads/h...e-3#post292129
A bit extrapolation: 1 sq ft of sail generates 0.1 HP at 30 knots of wind (yes many variables here).

So, speed reduction is minimal.

If propshaft alternators are the bottom of the pile compared with other ways of producing electricity...... could well be true; definitely not as simple as solar. But it might work for some people, and that was the question of the original poster: if it was possible to have bot a feathering/folding prop and penetrating electricity.

[sengland]

Originally Posted by Bmorgan562

Can you have the best of both “worlds”? I was just thinking about how you could benefit from a folding prop to reduce drag but also generate electricity? Seems to me it’s one or the other?

Hydro generators are the only way to go.
https://www.sailmagazine.com/diy/kno...dro-generators

[stormalong]

Originally Posted by DIJ

And presumably lifting the valves to deal with the engine compression to help the engine rotation?


But with the other ways of generating electricity this does seem bottom of the pile.

You do not leave the engine in gear. Yon need a transmission that can freewheel without damage - some cannot due to lack of lubrication.

Procedure is: put transmission in reverse with engine running. Stop engine, go to neutral. Prop will stay in reverse and spin. You need a pulley on the prop shaft to turn a separate generator. You may need a lay shaft and a second belt to get the prop speed up to the speed needed to produce power. Many people/companies used permanent magnet DC motors as generators. Computer tape drive motors were commonly used.

I used a drag prop generator for many years on passage. In trade wind sailing I could not see any speed reduction. Got about one amp for every knot, above 6 knots. There is a minimum speed that the generator needs to turn to get up to charging voltage output. That is generator design dependent.

Had a friend that had an alternator driven by a lay shaft off his propulsion prop - a big three blade prop and always had a lot of power to spare. This needs a lot of clearance around the prop shaft for the pulley. Many boats don't have that clearance.