Propellor for charging batteries using electric motor

[a64pilot]

20% of the prop diameter in clearance
https://www.miwheel.com/resources/faq/inboard/#33692


a Lot of money but I believe you will best get what your after by getting an adjustable pitch prop and get an increase in charging by flattening out the pitch.
I'd assume ideal is a prop that could have different pitch setting for forward and reverse and be able to be locked into one or the other when under sail.

A Max Prop may can do this?

Of course then you also get a feathering prop for when sailing speed is more important than charging

[KTP]

Thanks for the link and suggestion, will look them over.

I really don't see the need for a feathering prop with a electric propulsion system. If I don't need the regen and just need the fastest sailing speed, I can simply push the throttle forward more such that the controller starts sending a couple of amps to the motor and spins the prop. This should eliminate any drag effects? 2 amps on a 350AH bank isn't going to hurt much.

[a64pilot]

you would need to overcome friction of course, I don't think 2 amps would even come close assuming a bank of 48V max. Lets say it would take 200 Watts just for argument, 200W 24 hours a day, seven days a week is a lot of power, a whole lot.
Assumption is you want to do this to cruise, if only day sailing, why bother?
Bank size is sort of irrelevant here, 100AH or 1000AH, the power you pull out is going to have to be more than replaced, charging is not 100% efficient.

I'm pretty certain that best pitch for propulsion is going to differ greatly from best pitch for regen, and that best pitch for regen is going to be too much drag, so You'll end up picking a happy medium.

To do that your going to have to have a prop with two different pitches, and unless your incredibly lucky or very good at calculating pitch settings, your going to need an adjustable prop.

[KTP]

Originally Posted by a64pilot

you would need to overcome friction of course, I don't think 2 amps would even come close assuming a bank of 48V max. Lets say it would take 200 Watts just for argument, 200W 24 hours a day, seven days a week is a lot of power, a whole lot.

You make a good pro regen argument here considering most people say regen is not worth considering. If one is passage making and generating 200 watts of regen 24 hours a day that is a a lot of power.

[a64pilot]

Originally Posted by KTP

You make a good pro regen argument here considering most people say regen is not worth considering. If one is passage making and generating 200 watts of regen 24 hours a day that is a a lot of power.

I'm not saying you can, Not saying it's viable.
My belief is maybe it is if you have a very fast lightweight boat, not so much if you have a typical cruiser.
But all that is just a gut feeling, maybe I'm wrong?


However I don't see how a prop meant for propulsion is also going to be a good prop for generating power.

There has to be a good reason why you don't see many towed generators, cause they would be far better for generating power as everything can be optimized for generating power as opposed to trying to use a big propulsion system as a generator.

It would seem to be far more logical to tow a generator and have a folding propulsion prop

[KTP]

I can think of a few reasons why we don't see towed generators.

1) The generator electrics are immersed in salt water constantly, unless the thing is on the end of some long pole contraption which means you have to have room to stow it when it isn't needed.

2) It is an extra expense (unlike the "free" regen option you get just by having electric propulsion)

3) It is extra wiring where the electric propulsion is already wired for regen.

[jmh2002]

Maybe a simpler solution (if not the most cost effective one) is a folding / feathering prop optimised for propulsion combined with a watt & sea optimised for regen and also retractable for no drag if no regen is required?

[wingssail]

Originally Posted by KTP

Actually passage making is probably the area where we would least likely need an electric motor. If you figure a 3000 mile passage, you are going to run out of fuel on a diesel with 2500 miles to go...if you carry a massive fuel tank.

It is coastal cruising where I see the need to carry a small generator for emergency....the eu2200i will do perfectly and is 47 pounds....not really "massive".

Well, you know, 11kw electric drive is roughly equal to 15 hp, barely marginal for a 40' boat in my opinion.

That 11kw is used each hour of operation.

Your Honda, driving an AC battery charger capable of charging at 50amps, which is 600watts, will have to run 18hrs to get one hour of motor operation.

Did I do the calculation incorrectly? Because, if not, it does not seem like electric power is very practical for cruising offshore or coastal.

Regen is even further from practicality, I see numbers like 40watt, 70watt, and some people imagine 200watts. Even if that were possible it means 55 hours of 200watt regen to get one hour of motor operation. 55 hours of high winds and all the while you are suffering from heavy drag and reduced speeds. By the way, these are much more pronounced on a light weight boat which has low drag in the first place.

Tell me how I'm wrong in this.

[Pete7]

If there is enough wind to move the hull at a decent speed, wouldn't it be simpler to fit a wind mill to generate some amps ?

Pete

[Pete7]

Originally Posted by wingssail

Your Honda, driving an AC battery charger capable of charging at 50amps, which is 600watts, will have to run 18hrs to get one hour of motor operation.

Our Honda 20i didn't even move out of snail mode running a 40AH charger. Even switching on the 1kw water heater didn't faze it. The latest 22i are what about 2kw at 230v, still not enough to drive a yacht directly though.

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.

[Oceanride007]

I have a shaft driven alternator, on a 41 footer 11000kg, My Engine is 50HP. Best I've seen is maybe 6 amps at 13v.
RPM free spinning roughly half the idle revs. Dia ratio of V belt off take about 10"Dia to 2"dia. Don't really use it now as got plenty of solar. Just a few helpful (hopefully) thoughts.

[KTP]

Our battery charger is a Magnum Energy MS4048 inverter/charger. It puts out 60 amps at 48 volts, which is 3000 watts, much more than your 600 watt example. It would however take two of the EU2200i running in companion mode to fully supply the shore power input to our charger. We can get 1800 watts out of one EU2200i though.

There is not huge drag from regen, at least not that I see in our boat with 10 foot beam and 13,500 pound displacement. I actually did not see any difference in speed when cycling the regen on and off at 4 to 4.5 knots but it obviously is hard to tell since I was only doing 50 watts of regen. I'll see in further testing...I would love to get a good day on a 6.5 knot beam reach and see what cycling in and out of regen does.

[JimsCAL]

Low drag and regeneration are mutually exclusive. Pick one.

[EWOL Props]

We have some experience on regen on electric propulsion for boating. One of our EWOL props has made the World tour on a full electric propulsion and other boats are still running fine after quite a good number of years in operation.
The prop can be easily positioned on the feathering position (increase of sailing speed) or normal propusion or regen (reverse position).
In Regen position the resulting power generated is linear to the boat speed and strongly depends on the model of electric engine installed, prop size, hull shape and other variables. However the results are always quite good, I give you one example here...
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

[a64pilot]

My little Honda 2000 will run my charger at 90 to 100 amps and pull 13.3 amps, it’s continuous power limit.
The 90 to 100 amps difference is based on output voltage, I normally run it when the batteries are low and output voltage is only 12.5 to 13 or so, that’s when it can handle 100 amps, but if voltage gets up to absorption levels 14.3 volts, of course amperage comes down.
A 2200 Honda ought to of course charge at 20% higher, up to 110 - 120 amps.