Propellor for charging batteries using electric motor

[a64pilot]

Originally Posted by Pete7

Oh and they have an oil pressure switch linked to the cut out in them so don't like being run at a angle. Might be a bit tricky in a lumpy sea way.

One of the best ways I’ve seen to mount a Honda was on a CC ketch
He hung it from ropes from I believe the aft boom, he did it I’m sure as it transmitted zero vibrations to the hull. But you should be able to mount one with ropes to the handle and it should swing like a stove does, and keep the oil level?
It’s solvable is all I’m saying.

Better plan is of course a built in Diesel gen set.

[a64pilot]

Originally Posted by EWOL Props

at 6.5 knots - 265 W
at 7 knots - 420 W
at 8 knots - 560 W
at 9 knots - 700 W

These are real numbers

I don’t doubt those numbers at all, but what would be interesting to know is what is the speed of the boat that makes 6.5 kts with regen, if you feather the prop?

[EWOL Props]

Originally Posted by a64pilot

I don’t doubt those numbers at all, but what would be interesting to know is what is the speed of the boat that makes 6.5 kts with regen, if you feather the prop?

The impact on the speed of boat in Regen compared to Feathering position is variable and depending on the speed, low impact at low speed, higher impact at high speed. Let's say a reduction of about 0.3 knots up to 4-5 knots, a reduction of 0.6-0.8 knots above 7.5 knots.

Surely it would be better not to have a reduction of speed but this is for a limited time, with that charging power you will need a regen of a couple of hours max from time to time to keep your batteries full, or you can use regen only in case you need to turn on the fridge.
Also once you have finished charging you can switch back to feathering to gain back the speed. all this is feasible while keeping the helm.

A speed loss of average 0.5 knots for 2 hours is nothing except if you are racing.
For full electric boats you will need more than one source of energy and for longer time to recharge batteries enough; infact the boats we supplied were equipped with our prop + wind mill and solar panels, but that has been enough to make the World tour and pass the Panama channel without endothermic engine !!!

[wingssail]

Originally Posted by EWOL Props

The impact on the speed of boat in Regen compared to Feathering position is variable and depending on the speed, low impact at low speed, higher impact at high speed. Let's say a reduction of about 0.3 knots up to 4-5 knots, a reduction of 0.6-0.8 knots above 7.5 knots.

Surely it would be better not to have a reduction of speed but this is for a limited time, with that charging power you will need a regen of a couple of hours max from time to time to keep your batteries full, or you can use regen only in case you need to turn on the fridge.
Also once you have finished charging you can switch back to feathering to gain back the speed. all this is feasible while keeping the helm.

A speed loss of average 0.5 knots for 2 hours is nothing except if you are racing.
For full electric boats you will need more than one source of energy and for longer time to recharge batteries enough; infact the boats we supplied were equipped with our prop + wind mill and solar panels, but that has been enough to make the World tour and pass the Panama channel without endothermic engine !!!

The question is not whether or not you can run a fridge on regen power, it is: Can regen provide power to run an electric propulsion motor?

The answer is clearly, it cannot.

If you wish to keep your fridge on, regen can be an answer. So can solar, (possibly wind).

But of you want to run your 20KW propulsion motor for 4 hours, you need much more than regen.

[john61ct]

I do not think anyone is thinking regen power would contribute any significant proportion of the energy required for propulsion.

Similarly with solar input,

both would require either

a purpose-designed custom boat as a technology demo / PR stunt, unsuitable for most of our needs, or

an owner who had zero schedule, was happy to wait for days and weeks gathering enough electrickery for a few miles propulsion at a time.

Ideally both.

[EWOL Props]

Originally Posted by wingssail

The question is not whether or not you can run a fridge on regen power, it is: Can regen provide power to run an electric propulsion motor?

The answer is clearly, it cannot.

If you wish to keep your fridge on, regen can be an answer. So can solar, (possibly wind).

But of you want to run your 20KW propulsion motor for 4 hours, you need much more than regen.

Hi Wingssail,

maybe my message was not enough clear, we have some few fully 100% electric sailboats out in the mediterreanean sea and one having made the World tour. They have been equipped with propeller regen, windmill and solar panels and they work regularly, so the answer to the question "Can regen provide power to run an electric propulsion motor?" is Yes it can and it has been done already

[kevinjilliana]

perhaps if you can solve the problem of perpetual motion you will be a hero in this new green world. Just stick to plugging into the marina power or use solar or wind to charge the batteries. Good luck with that.

[EWOL Props]

My aim is not to convince anybody, honestly I don't care too much if somebody believes that or not, just telling you what has been done by us and other companies together....in reality, not theory

[KTP]

If you are in a sailboat you already have a flexible schedule. If you want to go around the world fast, take a airplane, it is much much cheaper.

[wingssail]

Originally Posted by EWOL Props

Hi Wingssail,

maybe my message was not enough clear, we have some few fully 100% electric sailboats out in the mediterreanean sea and one having made the World tour. They have been equipped with propeller regen, windmill and solar panels and they work regularly, so the answer to the question "Can regen provide power to run an electric propulsion motor?" is Yes it can and it has been done already

I am not doubting you, but I'd like to see the numbers.

On a typical 45' medium weight cruising yacht, what size electric motor and battery bank would be needed to provide four hours of motoring at 75% of hull speed?

For four hour's motor operation at 75% hull speed, how much power is consumed?

What is the contribution, in terms of watts and time, of each power source required to supply that motoring energy?

What wind speed assumptions?

[wingssail]

Originally Posted by KTP

If you are in a sailboat you already have a flexible schedule. If you want to go around the world fast, take a airplane, it is much much cheaper.

Your comment is rather flip. I know very few sailors, and I doubt if you do either, who are content to sit still on a windless day and wait for enough wind to sail. That wait can often be measured in days.

The truth of the matter is that most cruisers, off shore, coastal, or day sailors, depend on using the engine to move their vessel when the wind does not blow, and that does not include the vast majority who simply cannot be bothered sailing except in the most favorable circumstances anyhow.

[KTP]

Originally Posted by wingssail

Your comment is rather flip. I know very few sailors, and I doubt if you do either, who are content to sit still on a windless day and wait for enough wind to sail. That wait can often be measured in days.

The truth of the matter is that most cruisers, off shore, coastal, or day sailors, depend on using the engine to move their vessel when the wind does not blow, and that does not include the vast majority who simply cannot be bothered sailing except in the most favorable circumstances anyhow.

I know very few people who have climbed Everest but that doesn't mean it isn't viable or doesn't happen. I don't know why they take the risk to do it but they do.

I guess what I am trying to say is that just because something is more difficult, that does not make it wrong for that person if they want the challenge.

There are many people who would not want the slow speed of a sailboat with a diesel engine....it takes hours to get anywhere even at 8 knots.

[GrowleyMonster]

Regen for charging an EP bank is practical when:
1. Boat speed is in the double digits
2. At those times when the boat is at hull speed and has excess power available from the sails.
3. Speed is unimportant and electrical load is near zero.
4. Variable pitch propellor is used.

Regen is not magic. It must obey the laws of physics. There are circumstances when regen can provide lots of power and circumstances when it can provide only token amounts of power. For most small boats, assume that most of the time the needle points more toward the latter.


Solar is practical if you can mount enough panels. Can be hard to put up more than a kw on most sailboats. Full rated power you only get under ideal conditions, maybe three hours per day in cool weather with zero shading from rigging. Those panels can be a severe inconvenience or even a danger, in foul weather. For some owners of some boats in some conditions, they can be well worth their price. The nice thing about solar is if you bulk charge your bank with a diesel (or portable generator) which is reasonably efficient, you can then rely on solar for absorption and float charging, which is very inefficient to do with an IC engine.


Wind generators typically provide only a token charge for a big propulsion bank. They don't stop running when the sun sets, though. Myself I don't care for them. They usually create more problems than they solve.


For cruising, you have to accept a lot of tradeoffs with pure EP. A well designed hybrid system is another thing, though it comes with increased cost and complexity. Having the diesel gives the boat much longer legs. Having the electric gives you fantastic maneuverability when required, instant power when needed, near silent running, and justifies a large bank which can be useful for running otherwise frivolous electrical appliances. Regen implemented by driving the electric motor incidentally to driving the prop shaft can be adjusted to keep the diesel at its most efficient power and speed, even if demands for power at the prop are low. A diesel has a certain amount of overhead from simply turning the engine regardless of load. So getting the biggest bang for the buck while it is running is a good thing. You may have a diesel that drives your boat to hull speed at half throttle in calm conditions. Maybe it is at its most efficient at 70% output, lets just say. So you would like to run it there but the extra power beyond what is needed to reach a significant fraction of hull speed is just wasted. Well, then put it to work by increasing the load, making electricity. This is probably the closest to a win/win situation with electric propulsion on a cruising boat. The advantages of a diesel. The advantages of EP. Flexibility. Redundancy. Whether all this is better than a straight diesel drive is a matter for the individual owner to decide.


Best use for EP is to get a day sailer in and out of berth, with shore power charging. Then it is very much win/win. A small gas outboard engine, or a portable "get home" generator, is good insurance but not needed by most boaters, or seldom needed, but still a nice backup. In this case, regen is NOT needed, and a folding prop is perfectly okay though you can use a fixed prop and simply turn it with the electric motor with just enough power to make the drag insignificant, probably around 30 to 50 watts. Meanwhile you have electric power instantly available for tacking and stuff, and it is ready for docking. No smell, no noise. No hassle.


Regen, then, is almost a mythical thing, significant only under limited circumstances, and a big selling point in EP sales pitches. I say "almost" because under those limited circumstances it could make a significant contribution due to its 24/7 nature, and use of equipment that is already in place.

[fred4936]

We have a Thunderstruck kit on our boat, and it has been great. The prop is a three bladed fixed. I am sure it slows the boat when sailing, and the regen is not very effective. We get a few amps when sailing above 4 kts, but not many. It is a bonus, but not to be counted on.

[skenn_ie]

A propeller isn't the right shape for generation, though it will work. A turbine is a mirror image of a prop, the camber of the blades is reversed.