Energy recovery from freewheeling prop

[markxengineerin]

I think that solar install above does not look suitable for bad weather

The pictured setup has survived 60 knots (actual sailing), from various wind angles, and over 100 knots on a mooring. No problems. It does sway side to side depending on the heel angle and wind pressure, but it's stopped after about 1/2" by the backstay, because clearance is so minimal. I'm happy with they way it has been working, never makes any noise and you'd never notice it moving unless looking out for it.

Sliding panels- Very heavy, and high effort to design and build. I'm thinking more about lots of small cells in various locations, with lots of DIY charge controllers. But this is just an un-researched idea at this stage.

When my boat was new, it had a prop shaft alternator, just about to re-install that again, alternator is a 20Amp Motorola, with a serpentine belt and a 1:5 pulley system to the propshaft. When sailing I have then the option to feather the prop, or drive the alternator.

This sounds pretty ideal to me. But I'd also want to disconnect the transmission entirely when "alternating" because clearly it is a big source of friction loss, based on temperature rise. I wonder if freewheeling the prop, no trans connected, no alternating, and counting RPM could also be used to estimate speed thru water as well as those silly little paddle wheels. I would guess yes, might be another side-benefit of a well designed system. I am most likely going to try this, but lower on the priority list vs. a lot of other things.

[deltaten]

TANSTAAFL !

Issues considered, I'd sooner have electrical problems than mechanical. A panel goes down; or controller goes on the fritz, just disconnect and re-set the panels and keep on....
Toast a trans, break something involved, screw up the prop? Can you still move...without lotsa time/money/inconvenience?

The K.I.S.S principle applies.
Figure your costs in time/money/aggravation; installation and maint. for both systems and efficiency/repairs.

HTH

[caffel]

I sailed the Indian ocean with a motorbike alternator belted off of the shaft at threee times prop speed on a Volvo Md2. Complete sucess, saving abt two hours of engine charging per day.

[Jimmyhenry]

An interesting experiment is to tow a dinghy with the outboard down. Out of gear it remain in the water with the prop spinning. But if you put the OB in gear it immediately pops up.
Go figure which has the lesser resistance.
Pete

[argonauta1]

Larger drag vector on the dinghy rear pops the bow.

[Jimmyhenry]

Pops the outboard. Not the bow.

[LifePart2]

My personal experience of harnessing the free wheeling prop energy is recorded on my blog here: https://lifepart2.info/equipment/pro...ven-alternator

It worked well when boat speed was above 6kts.

But then when I switched to a folding prop it was game over, as the drag of the alternator just caused to prop to fold up.

But I did gain at least a half knot of speed by replacing the fixed prop with the folding one!

Noel

[SailingHarmonie]

Originally Posted by markxengineerin

The fancy props do seem like the best choice if ignoring the desire to generate electricity.

Actually, a MaxProp gives you the choice. If you stop the engine while it is turning FORWARD the prop feathers as normal. If you stop the engine running in REVERSE the prop does not feather, and you CAN use it to drive an alternator.

For many years prop shaft alternators were a popular option on Amel boats. I have seen many of these. They work fine on boats with MaxProps. A typical prop shaft alternator generates enough power to fully run house loads while underway, on most boats, under most conditions. Very few cruising boats spend a large enough fraction of their time underway to justify the expense and wear and tear on expensive parts, IMO.

Those people who imagine a shaft alternaor will charge a battery bank sufficient to actually power a drive engine are not in the real world.

[markxengineerin]

How many boats have tried disconnecting the transmission entirely, when generating? It requires a separate shaft bearing to be engaged when doing so, but I think the transmission losses are significant, based on temperature rise.

Very few cruising boats spend a large enough fraction of their time underway to justify the expense and wear and tear on expensive parts, IMO.

It's true, I would only have used it twice this year. But it would be easy enough to turn "off" and eliminate wear. I am thinking of a really cheap setup using a bicycle chain and sprockets.

[GrowleyMonster]

It is essentially the same as an e-boat sailing in regen mode. Any resistance to the prop turning, creates drag and slows the boat a certain small amount. EXCEPT when the boat is already at or exceeding hull speed and operating in an inefficient zone where there is excess energy from the sails that cannot be properly utilized. In this case, you can put quite a large load on the shaft and the drag of the prop will have only an extremely small effect on boat speed.

BUT, with the shaft locked, the load is, for purposes of computing drag, practically infinite. The only way to have higher drag would be to actually TURN the prop in REVERSE. So, taking power from the shaft robs you of less speed than locking the shaft. Taking LESS power robs LESS speed. Freewheeling with zero load takes still less speed off the boat. Keep in mind we are talking a fraction of a knot. Some e-boaters actually turn the prop with minimum power to take even the freewheel drag off the boat, running a hundred watts or so, just "helping" the prop to spin as the boat sails ahead.

So, locking the shaft, ever so slightly bad for speed, except when the wind is really up and you are climbing your own bow wave, but in many if not most cases it is good for the transmission. Obviously, then, you wouldn't want to make a habit of freewheeling if your transmission can be damaged by doing so. That quarter knot or so isn't worth it. If you were REALLY in a hurry, you would have a big express cruiser and be burning 100gph.

Options are a folding prop, a feathering prop, an adjustable pitch prop, or for long passages, removing the prop. Or one you don't see very often, a clutch of some sort, maybe a splined sleeve, and a thrust bearing, so the shaft can spin merrily away and the stub on the transmission be just sitting there shrugging its little bronze shoulders. Being able to decouple the shaft would cure any worries about the transmission, but allow you to run a shaft generator. You could also use the break in the shaft to install or replace belts when needed, or change pulleys while experimenting on the best reduction or multiplying ratio. For an alternator, you could even use a BLDC/PMAC motor, which could give you an instant maneuvering push when needed, without starting Dorothy. Power tacking, for instance, while on watch alone, with a boat that is stubborn to tack for whatever reason. Of course that would mean a 48V system, but 48V stuff is getting more and more common, and cheaper, as eboats become more common. The motor's controller handles the regen function, sending relatively clean DC to the batteries.

[GrowleyMonster]

Originally Posted by markxengineerin

How many boats have tried disconnecting the transmission entirely, when generating? It requires a separate shaft bearing to be engaged when doing so, but I think the transmission losses are significant, based on temperature rise.

A thrust bearing, actually. You need to stabilize the shaft in the fore/aft direction while still allowing rotation.

[derfy]

Originally Posted by s/v Jedi

I have one of those Kanzaki gearboxes but also a MaxProp, so after engine shutdown I move it to reverse, which causes the prop to feather, then switch it back to neutral and the prop stays feathered and doesn’t spin. Also, 1 knot extra speed.

I got rid of my maxprop as it was a continual maintenance headache, and put on a hefty three blade fixed prop, and let the shaft spin free under sail. Yanmar mandates this for my transmission.

Sailing performance degradation was not perceptible with wind > 10 kts. Anywhere near hull speed and there is zero difference. I suspect the performance difference is greater when sailing in light air well below hull speed, a situation I do not often encounter when cruising. I have not seen excessive wear on the cutlass bearing or stuffing box. If anything, I might kept them in better shape.

Having said that, for racing, a feathering or folding prop is mandatory. A folding prop and full keel would be really nice in Maine with all those lobster traps. You could sail right thru'em.

I would never put an alternator on a prop shaft. It is hard enough to get them into good alignment and balance. Once you are there, you want to keep it there. When the shaft in balance, there is minimal noise and no vibration.

How about the old-fashioned towable taffrail generator? Somebody used to make a wind generator that converted to a towable unit for long downwind crossings. Probably does not generate much power, but it might keep the autohelm running.

[s/v Jedi]

Originally Posted by derfy

I got rid of my maxprop as it was a continual maintenance headache, and put on a hefty three blade fixed prop, and let the shaft spin free under sail. Yanmar mandates this for my transmission.

Sailing performance degradation was not perceptible with wind > 10 kts. Anywhere near hull speed and there is zero difference. I suspect the performance difference is greater when sailing in light air well below hull speed, a situation I do not often encounter when cruising. I have not seen excessive wear on the cutlass bearing or stuffing box. If anything, I might kept them in better shape.

Having said that, for racing, a feathering or folding prop is mandatory. A folding prop and full keel would be really nice in Maine with all those lobster traps. You could sail right thru'em.

I would never put an alternator on a prop shaft. It is hard enough to get them into good alignment and balance. Once you are there, you want to keep it there. When the shaft in balance, there is minimal noise and no vibration.

How about the old-fashioned towable taffrail generator? Somebody used to make a wind generator that converted to a towable unit for long downwind crossings. Probably does not generate much power, but it might keep the autohelm running.

All boats are different. On mine, there is zero prop maintenance apart from using a grease gun now and then. Also, feathering the prop wins more than one knot boat speed vs free spinning it. Our hull design is known for being easily driven so I guess that also means easily slowed down by a prop that isn’t feathered.

[markxengineerin]

Soliciting ideas for shaft de-coupling, or any data on regeneration power with/without a decoupling feature... Anyone?

Here is a simple version for brainstorming, where the shaft coupling has to be unbolted from the transmission manually. Shaft gets slide back 1/2" (pick a number) which engages the supplemental shaft support bearing. The manual process isn't ideal, but would keep things simple.

I think the toughest part about this would be figuring out how to mount the blue support structure labelled "hull" to the hull. I imagine it being made of G10 and just heavily glassed in, in a way that would not be very beautiful. But with every hull being different, I don't have a better idea.

If decoupling the transmission turns out to be unnecessary, and if the transmission output bearing can support a small radial load (I haven't looked at it, but it probably can) that makes the design much simpler.

(base sketch borrowed from the SigmaDrive brochure)

"Alternator" would be something like this:
https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

Lower KV value would be best, anyone know of any good "motor" sources?

[derfy]

Originally Posted by markxengineerin

Soliciting ideas for shaft de-coupling, or any data on regeneration power with/without a decoupling feature... Anyone?

Here is a simple version for brainstorming, where the shaft coupling has to be unbolted from the transmission manually. Shaft gets slide back 1/2" (pick a number) which engages the supplemental shaft support bearing. The manual process isn't ideal, but would keep things simple.

I think the toughest part about this would be figuring out how to mount the blue support structure labelled "hull" to the hull. I imagine it being made of G10 and just heavily glassed in, in a way that would not be very beautiful. But with every hull being different, I don't have a better idea.

If decoupling the transmission turns out to be unnecessary, and if the transmission output bearing can support a small radial load (I haven't looked at it, but it probably can) that makes the design much simpler.


(base sketch borrowed from the SigmaDrive brochure)

"Alternator" would be something like this:
https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

Lower KV value would be best, anyone know of any good "motor" sources?

I'm an electrical engineer, so please excuse me for venturing a comment on mechanical issues.

Have you not just described a clutch? They used to be on old cars.