Energy recovery from freewheeling prop

[GordMay]

Originally Posted by markxengineerin

... It sounds like the numbers need to be run. I don't know much about prop calculations and have too many other projects at the moment, but will add this to the list.

When you do, see:
“The Propeller Handbook” ~ by Dave Gerr ➥ https://www.cruisersforum.com/forums...do=file&id=109

[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.

[CarlF]

Yanmar issued a bulletin in 2008 (MSA08-003) saying that NO Yanmar transmissions should be locked in gear while sailing. Doing so would void the warranty. This bulletin reversed the recommendation to sail with it in reverse in some earlier manuals. People persist in saying that it depends on what engine or transmission you have - IT DOESN’T. It is OK to briefly put a folding prop into reverse to cause it to fold but you then must go back to neutral..

And as Jedi says above, a locked prop has much more drag than a freewheeling one. You will sail slower.

Using the propeller shaft to generate electricity will also create more drag and reduce sailing speed. Solar panels don't slow the boat down.

Here is a good discussion of both issues.

https://www.catamaransite.com/refere...ler_drag_test/

[markxengineerin]

From that last link:

This is an advisory which pretty much ends the debate on whether or not to free wheel propellers while under sail with Yanmar diesels installed… don’t you think?

No, I want to know why, so that I can judge the risk and make my own decision. The transmission is from 1994, warranty/what Yanmar demands is no longer relevant. Just waiting for someone to say they've done it for years with no consequence, hopefully someone has.

I understand that a free-wheeling prop is more efficient, as are the folding/feathering.
I may end up there.

But today my 660 watt solar panels generated 3kw-hrs of electricity, south of Canaries. It was mostly sunny. On a normal day I'll use somewhere near 2.5 kw-hrs, so that's fine. But in the winter, in the English Channel, I was getting between 0.4-1, for weeks on end. To double the solar on a 37' boat is definitely going to affect something. Weight, complexity, windage.

If I can get 10 amps (number not verified, just a guess) , 24 hours a day, from a prop that's already there, and already spinning, that's a bonus 3kw-hrs. I don't understand the opposition to doing this. It would be optional to use- turn it on when you're already going hull-speed and it's is "free".

[markxengineerin]

Question on the max-prop- could it be used to regenerate, if you wanted to, ie can it be locked "open"? I am not familiar with how they work, but that would be the best of all worlds. Sail efficiently with it feathered, and regenerate when beneficial.

[s/v Jedi]

Originally Posted by markxengineerin

Question on the max-prop- could it be used to regenerate, if you wanted to, ie can it be locked "open"? I am not familiar with how they work, but that would be the best of all worlds. Sail efficiently with it feathered, and regenerate when beneficial.

Regen with the prop is a path of hurt, don’t do it (repeating it in case you didn’t see it before). Install extra panels, 660W is nothing, similar boats to yours have 2-3 times that.

Complex? Not more than coupling chains or belts to a prop shaft and zero maintenance instead of a path of hurt.

Windage? Nothing compared to the drag of a prop doing regen. It will take 2 knots of your speed. For us, the difference between free turning, what you do, and feathering is more than a knot so imagine when you load the spinning shaft!

Weight? Less than regen.

[markxengineerin]

You're probably right, I have some solar ideas too. Love to see those 37' monohulls with 1000w +, don't think I've ever come across one. My panels are already an eyesore vs. the rest of the boat and can't imagine how to triple it.

[Fuss]

I started a thread on this maybe 5 years ago. Mines still going and it 10 years old.
Ideally you need low revving motor 2300rpm
5x prop speed, mines 250rpm at 4 kts , so 250 x 5 = 1250 at alt.
Hydraulic gb
10a at 4.5kts 24v
Bmv 700 gets confused and doesn’t register amps going in at this low speed.
Great in strong winds…40a in storms!!

It’s a spare alt and can be used while motoring.
No noticeable drag on 28 t Mono.

The negatives are…
Don’t get it wet…but hey, you guys tell me you don’t get your fancy all singing and dancing electronically everything controlled lifepo4 wet so should be no problem right.
Needs the setup above to get the most out of it.
This is an alternator so uses 3a when switched on so you need to not have it on under 4 kts.

[Pete7]

There are a couple of things against you using a prop to generate electrical power. Firstly the blade shape of most props whilst good for propulsion isn't great for generation. Think Jimmy Cornell tried different props on his cat but it didn't work well.

The other things is you need is speed and big props. Below 5 knots forget it. Above 7 knots then lots of power. On a 37ft yacht you may be able to achieve these.

Have a look a the graphs Watt and Sea publish for the their systems to see what difference speed make as an example.

https://www.wattandsea.com/en/hydrogenerators/

There is a German system which is smaller and generates 5A at 5knots. About 2000 Euros.

https://www.youtube.com/watch?v=gfAf...channel=MJambo

If you go down the propshaft route, you need a big pulley on the shaft to ge the alternator up to a higher speed as already mentioned. There used to be split pulleys to do this, don't know if they are still readily available. Oh and you need the space under the shaft to spin it. With one of todays external regulators to control the alternator Sterling or the NZ one.

https://nordkyndesign.com/product/no...ce-controller/


Pete

[skipperpete]

I mentioned earlier that I’d had a flirtation with a propshaft alternator with limited success the install was easy because the engine (5LW Gardner) was hard mounted so the alternator drive belt and pulley load didn’t affect the engine alignment, (on a soft mounted engine the alternator ideally has to sit atop the gearbox) and I had the advantage of being able to vary the pitch of the propeller (Hundested) for optimal power under sail….. it worked, but at the time my cruising was coastal, not passage making so running the engine frequently was normal and from that alone I generated enough power for my needs.
The interesting thing was how easily the prop could rotate the engine under sail if not feathered , this was annoying but not bad for the engine because it was keel cooled with a dry exhaust so no risk of flooding the exhaust with raw water from a jabsco pump ( I did have an engine mounted jabsco as a deck wash pump)
So here’s the point, if you lock your gearbox in astern while sailing fast there is a distinct possibility that even with the average 2:1 multiplication effect reversed a propeller can STILL turn over a shut down engine (Maxprop warn about this for vessels capable of high sailing speeds) ….and here’s the real life instance to sort of support this…. I do a lot of engine alignments and jobs where I need to either rotate the engine or simply undo the coupling bolts so I just move the shift lever to either ahead or astern depending on whether I want to release the coupling bolts or just turn the shaft a bit to access the next bolt…. I can easily rotate the prop shaft in gear in one direction with just a socket and breaker bar but can turn the crankshaft against compression in the other direction, often fairly easily but harder on a newer engines and more so with the 3:1 reduction boxes. (1:3 if turning the coupling). An old perkins 4-108 with a 1.5:1 mechanical reversing gear turns very easily so this needs to be considered by anyone who sails over , say, 8 knots. Oh, other considerations if you’re still awake…..yes the engine won’t start in opposite rotation and the water pump">raw water pump flow is reversed as is the lube oil pump.

[s/v Jedi]

Originally Posted by markxengineerin

You're probably right, I have some solar ideas too. Love to see those 37' monohulls with 1000w +, don't think I've ever come across one. My panels are already an eyesore vs. the rest of the boat and can't imagine how to triple it.

You can double that without even needing more space with sliding panels like we did

[Fuss]

I think that solar install above does not look suitable for bad weather, it looks to have not enough lateral support…perhaps a closeup would help.
When I look at some of these transom installs in marinas, I can only assume these have never been in heavy weather.
It’s sort of like splayed fork anchor swivels in the marinas, they’re everywhere.

[HankOnthewater]

Here is some info on the subject, but unfortunately does not answer the original question of Engineering Mark.
https://lifepart2.info/equipment/pro...ven-alternator
Even though the article is now nearly 10 years old, it says the same as Jedi did upthread several times: installing more solar may be easier and cheaper.

I do the same as Jedi in post #17, although with a different gearbox.

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.

I am removing the small alternator on my engine, and replacing that with a small propshaft mounted alternator, big enough to charge the starter battery with 5-10 amps net ..... I hope.
The 2nd much bigger alternator remains for the ship's battery bank.

I can report later this winter when I plan doing a long trip.

[Sailorichiban]

Hello All,
The best of my recollection, based on my reading of the Yanmar manual many years ago, was to keep it in neutral. This instruction I always followed, except when someone accidentally engaged the gear. Never had any problems, in neutral when sailing. The gearbox would heat up, but to a lesser degree than during extended motoring.

As far as operating an alternator from the prop shaft, looks like too much complexity is involved, though possible. Thoughts to consider; a means to disconnect or a variable speed drive to compensate for the much higher level of rpms during motor operation. A very intriguing concept though! Seriously was considered, the concussion was too much time in install, then too much time to test and fine tune.

Fair winds and gentle following seas, to All

[argonauta1]

I did not mess with energy recovery but I was concerned about wear on the gear box/shaft bearings and also reducing drag. So I traded out the three bladed fixed prop for a feathering Max Prop. In light air cruising we picked up at least half a knot. Read 12 Nm per day. It was one of the best mods we did before heading out bluewater. To set the Max Prop to feather, one had to but the transmission briefly in reverse then back to neutral. We were always reminded if we forgot by the whirring noise of the shaft and transmission.

Vessel was a 44 Ft Beneteau.