Could one use boat propeller to drive el generator?

[skenn_ie]

For efficiency, a propeller or a turbine needs to have the flatter or undercambered side and the blunt edge of the blade towards the relative flow, On a propeller the flat(er) side faces aft. For a turbine, it faces forward. Even if a windmilling prop only reduces speed by 1/2 knot, that is quite a bit of power when compared to the size of the boat. If you start generating power from that "turbine", it will probably be 20% efficient as opposed to a dedicated turbine, probably 60 - 70%. Putting you hand against a flange or pully is no guide. 1/4HP would easily overcome hand friction.

[CaptainRivet]

Originally Posted by QuentinC

Take a look at this one.
https://m.aliexpress.com/item/328791...1-7a6a35d7458b

This is in the rpm range that you are looking for. The ac clutch is a great idea to disable the generator when the engine is running.
Also search YouTube for John Daniels. He has a lot of info on these types of generators.
I would not use the f&p generator unless you really like to tinker.

Thank you.

Did you see the PMA i posted above from Missouri?
250 til 900RPM range for 12 till 48V output (so ratio 1:1 till 1:2 needed) and compared to the one you posted sealed for marine use and 1600W instead 650W so this one will put out more amps and have bigger coils.

Yes the f&p looks like its not sealed and with sll the sensors a more complex solution then needed here. Simple, as basic as possible and working...

Like to use a tried out and prooven solution here, don't have to re-invent the wheel here.

[GarthGregory]

I have just built one - very straight forward - not expensive , uses a PMA alternator - just can't test due to lockdown - will post results ,when tested .

[CaptainRivet]

Originally Posted by GarthGregory

I have just built one - very straight forward - not expensive , uses a PMA alternator - just can't test due to lockdown - will post results ,when tested .

Great, looking forward to see more about your solution.

How did you solve the issue when motoring that the PMA generator is disengaged.

Also do you solve the issue when your batteries are full and voltage spikes high and kills the MPPT controller?
What batteries do you have, lead or Lithium?
Big difference as lead limits the current naturally while with Lithium the Alternator tries to deliver max current possible => can stall the propeller as the initial higher resistence to drive the PMA is much higher

[GarthGregory]

I have 6 x lead Acid batteries and Solar on the boat , so I only intend to use Propellor Alternator on longer sails and so will disengage the alternator ,when not in use . The PMA 's are bi-directional , so motoring or sailing makes no difference . My controller has a dump load feature , so I will wire the excess to my water heater unit .Electronics are not my strong point at all , but PMA's use rectifiers , not regulators , so it is not possible to just switch it on or off. I certainly have plenty of power when sailing and have built a 3 to 1 pulley ratio which will give me a 1200 to 1500 rpm at 5 to 6 knots . The PMA should produce about 15 Amps at 1500rpm and 12 Volts from as low as 150 rpm .The power consumed should be about .75 H/P and less as the boat speed increases . Also power is 24 hrs a day - wind dependent . When we all get over this virus and are sailing , I will try to post some actual numbers . These prop/alternator systems were a standard fitting on the Amel boats for 20 to 30 years , so not a new solution at all .

[Mike Banks]

Yes you can--but it is not great at doing it. However there is a special propeller available that when driven by the motion of the sea changes its pitch to become a more efficient turbine.

[skenn_ie]

Get an electric outboard motor (make sure it has a permanent-magnet motor) and turn the prop around so that the undercambered side faces forward.
I am not certain about water propellers, but aircraft propellers produce less drag when stationary than when "windmilling", so I suspect, on a sailing vessel, your main propeller is better with a brake.