Propellor for charging batteries using electric motor

[Brewgyver]

I'd love to be able to sail at 125% of hull speed on 10 knots of wind. I haven't been able to pull that off yet, but it's good to have goals!

Of course, it's less frustrating if the goals are actually attainable.

[StuM]

Originally Posted by Brewgyver

I'd love to be able to sail at 125% of hull speed on 10 knots of wind. I haven't been able to pull that off yet, but it's good to have goals!

Of course, it's less frustrating if the goals are actually attainable.

Yep, such claims kind of put the other claims about EP performance into perspective.

[Brewgyver]

Originally Posted by StuM

Yep, such claims kind of put the other claims about EP performance into perspective.

Indeed. I'd also love to move a 40 foot boat (even one as light as the Olson) at for 110 watts per knot... I could ditch the inboard and hang a trolling motor on the stern!
But wait, my puny Minn Kota 30 lb thrust motor uses 360 watts to push my 14 foot plastic kayak at 3 knots???

[u4ea32]

Originally Posted by Brewgyver

I'd love to be able to sail at 125% of hull speed on 10 knots of wind. I haven't been able to pull that off yet, but it's good to have goals!

Of course, it's less frustrating if the goals are actually attainable.

Mine is an Olson 40, but its stiffer than stock (it has an Alan Andrews designed bulb keel), lighter than stock, and has great sails. We hit 10.5 knots under jib and main in steady 15 knots on Sunday inside LA Harbor. We are steady at 9 knots in 9 knots+ wind.

So for my boat, its attainable.

Here we are going 6 knots upwind in 6 knots of breeze.

[u4ea32]

I don't make stuff up. If I say it uses 330 watts to go 3 knots, its because that is what I do observe.

Obviously, power is non-linear with speed, so it takes 5KW to go 6.2 knots, which was identical to the max speed under power with the 3GM30F, same prop, same boat, same owner, same water, same windage.

The boat is lighter now with the electric system: about 600 lbs lighter, on a 10K lbs displacement. 6% is a big reduction in displacement! But still, its really that diesels are not very efficient in fact. They can be if one is at minimum BSFC, but one is never in the sweet spot of low BSFC, so they are not.

[barryglewis]

Propeller charging can be very effective. Ausie succesful racing yacht Solo 57 foot steel cutter was converted to a yawl with electric winches and autopilot in the early 1960s. She completed several circumnavigations her owner Vic Meyers often single handed.
She had a dogclutch system which disengaged the shaft from the gearbox, and engaged a vbelt sytem to drive a 24v generator. At 5k she would generate 5A. (Not an alternator, its predecesor the less efficient generator).
In her cruising mode i had the opportunity to sail her over 3500m, passage making.

I did notice that the propeller pitch was not optimised for motoring, and would cavitate in a strong head wind. At the time i was told the prop pitch had been coarsened to drive the generator, but i cant vouch for this.

I hope you keep us posted with which prop you go for, how you pitch it, and how well the system works

[u4ea32]

Originally Posted by barryglewis

Propeller charging can be very effective. Ausie succesful racing yacht Solo 57 foot steel cutter was converted to a yawl with electric winches and autopilot in the early 1960s. She completed several circumnavigations her owner Vic Meyers often single handed.
She had a dogclutch system which disengaged the shaft from the gearbox, and engaged a vbelt sytem to drive a 24v generator. At 5k she would generate 5A. (Not an alternator, its predecesor the less efficient generator).
In her cruising mode i had the opportunity to sail her over 3500m, passage making.

I did notice that the propeller pitch was not optimised for motoring, and would cavitate in a strong head wind. At the time i was told the prop pitch had been coarsened to drive the generator, but i cant vouch for this.

I hope you keep us posted with which prop you go for, how you pitch it, and how well the system works

Thanks, Barry. This is useful experience. I do think that the pitch of, say, a Maxprop would be set very course (30 degrees!) to improve charging and perhaps make powering a bit worse.

The 5A at 5kts seems reasonable. That would keep my batteries at 100% continuously on a passage.

[zloitapok]

Hi u4ea32,
I'm not sure if regen by main electric engine is a good thing at all. It will slow the boat a bit and if fixed prop installed - you can't totally switch it off. What prop spin speed do you have with current prop? If it exceed a 900-1000 RPM at full power, probably you need a 'heavier' prop to increase prop efficiency. 'Heavier' prop mean primary a larger size prop and secondary - bigger pitch. Propulsion propellers is not suitable for regen, but you can use 'outboard' regeneration unit, which is more effective at regenerating energy and you can choose when you need an energy regeneration and when you need a max speed under sails without drag. Folding props provide a "little convenience" - when you are sailing and prop closed to reduce drag - you will never hook them to a fishing net or some floating rope.

Can you please tell me, what speed at calm weather you got at 400 W of power at electric engine? Just to compare to my results: my small boat (25 ft) move up to 3 knots at 400W.

[Bullshooter]

Hey OP.

Does this sound like anything that would help to optimize prop pitch for your application?

" The software controlled variable pitch sail drive adjusts the pitch of the propeller blades automatically so that the power generation and power output are optimal. Combined with uniquely designed blades it delivers optimal efficiency in both forward, reverse and hydro generation. And with the blades set to the neutral sailing position, the propeller creates extremely low drag similar to the drag of a feathering propeller. "

See this link
https://oceanvolt.com/solutions/syst...op-sail-drive/

[u4ea32]

Originally Posted by zloitapok

Hi u4ea32,
I'm not sure if regen by main electric engine is a good thing at all. It will slow the boat a bit and if fixed prop installed - you can't totally switch it off.

I am not sure if it will work either, which is the point of the thread: what have people actually experienced for regen using the main prop, shaft, and electric motor?

My current folding prop does not work at all. As soon as power is no longer being added to the shaft, the prop immediately folds. No way to spin it, and keep it spinning as it absorbs energy from the water. That energy is drag, and drag folds the prop. And sure enough, that is in fact exactly what always immediately happens.

Perhaps a feathering prop, like a MaxProp, FeatherStream, Kiwi Prop, AutoStream, Variprofile, EWOL, etc. These might work. Maybe. I have only seen claims by vendors, no comments by users yet.

But of course, some vendors do claim folding props can work, and they absolutely do not, and I can't imagine how they possibly could.

Originally Posted by zloitapok

What prop spin speed do you have with current prop? If it exceed a 900-1000 RPM at full power, probably you need a 'heavier' prop to increase prop efficiency. 'Heavier' prop mean primary a larger size prop and secondary - bigger pitch.

I do think I can easily go with a increase in pitch, as electric torque is immediate.

Originally Posted by zloitapok

Propulsion propellers is not suitable for regen, but you can use 'outboard' regeneration unit, which is more effective at regenerating energy and you can choose when you need an energy regeneration and when you need a max speed under sails without drag.

I have been investigating the hydro generators, and they have clear advantages. But also obvious disadvantages: duplication of something I already have, at the same cost I already paid.

I might well go with one of those units, but first I am trying to simply utilize what I already have. Simple is almost always better.

Originally Posted by zloitapok

Folding props provide a "little convenience" - when you are sailing and prop closed to reduce drag - you will never hook them to a fishing net or some floating rope.

No kidding! I will certainly not go with a high drag prop in any event.

Originally Posted by zloitapok

Can you please tell me, what speed at calm weather you got at 400 W of power at electric engine? Just to compare to my results: my small boat (25 ft) move up to 3 knots at 400W.

I'll take some more data this weekend when we go out (if I remember, which I may not).

[u4ea32]

Originally Posted by Bullshooter

Hey OP.

Does this sound like anything that would help to optimize prop pitch for your application?

" The software controlled variable pitch sail drive adjusts the pitch of the propeller blades automatically so that the power generation and power output are optimal. Combined with uniquely designed blades it delivers optimal efficiency in both forward, reverse and hydro generation. And with the blades set to the neutral sailing position, the propeller creates extremely low drag similar to the drag of a feathering propeller. "

See this link
https://oceanvolt.com/solutions/syst...op-sail-drive/

This is a claim by a vendor, backed up by video, that just does not make sense: I do not believe it. If I can find **independent** claims that this works, I will be intrigued.

I am not saying OceanVolt is lying or unscrupulous. But I don't think that when they eventually actually install one of these things in an actual real boat, that it will actually work like they claim. I can be wrong! I often am! But the forces at play don't allow that system to do what they suggest: drag folds folding props, and regeneration requires drag.

[seandepagnier]

What you want is a repeller, not a propellor.

If you want to also use this to power the boat then you can not achieve efficiency. In other words, if you use your propeller to generate you will get less watts for the same amount of drag.

It's not possible to have the most efficient turbine for both propulsion and generation unless the blades themselves can change shape (not just rotate like variable pitch, but also reverse their camber)


It would be interesting and possible to design a propeller/repeller with neutral camber. This is what is used also by sculling oar blades.

It would not give as good efficiency under power, or generating, but would be a compromise between the two.

Otherwise, a better bet is to keep your propeller for thrust, and use a tow gen with a repeller for generation.

[seandepagnier]

Originally Posted by wingssail

Query to EWOL:

This is nonsense, because people who "travel under power" are foolish.

For this use case, a free trolling motor and a couple deep cycle batteries is fairly inexpensive compared to any other options.

[quote
Fossil fuels provide orders of magnitude more power per kg or cu ft than the best battery technology available today.

Nuclear power provides orders of magnitude more power than fossil fuels. Fossel fuels should not be allowed for the same reason nuclear isn't. They pose a significant danger to all.

[seandepagnier]

Originally Posted by wingssail

Query to EWOL:
Conclusion:
Electric power is not suitable for even minimal use case on a cruising yacht. Yes, it works, but the cruiser will have to compromise considerably about travelling under power, either by speed or distance, generally both.

This is nonsense, because people who "travel under power" are already foolish. The engine is intended for harbors and tight areas, and even then it can be avoided.

For day sailing, leaving and entering the marina, and short return trips under power, electric may be useful, but it will still be expensive.

For this use case, a trolling motor and a couple deep cycle batteries can be obtained free, but you can just sail. Propellors were never needed to go cruising.

Fossil fuels provide orders of magnitude more power per kg or cu ft than the best battery technology available today.

Nuclear power provides orders of magnitude more power than fossil fuels, and we have the technology to make it possible to power small craft.

Fossel fuels should not be allowed if nuclear isn't, for the same reason. They both pose a significant danger.

[a64pilot]

Whatever it’s worth it’s very likely that a prop being driven will need its blades to be much flatter pitch than when used to propel the boat, not increased pitch, increasing pitch will greatly slow the Prop RPM.
If you have ever autorotated a helicopter you’ll understand immediately.

But look at a wind generator for example, the blades pitch is almost flat, course pitch won’t harvest as much power from the fluid flow.