Could one use boat propeller to drive el generator?

[double u]

& driving a shaft generator is a total different situation from a -theoretically frictionfree - freely rotating prop. Any electric energy has to be produced by the sails & therefore is not available to drive the boat. It isn't going to be much (7A x 16V =112W as an example) so just over 1/7hp

[QuentinC]

Yes you can. Forget using an alternator. Not enough torque for the rpms needed. There was an older post here in the forum.
http://www.cruisersforum.com/forums/f14/permanent-magnet-generator-on-propshaft-22266-5.html
I have read his research on two different sites. His figures are sound vs oceanvolt. If you are not a tinker, an easier way would be to use a 600watt 12 volt PMA from aliexpress.. Takes 600 rpm to achieve max watts. Put a ac clutch on the generator like Harold did and you can run the motor with now worries, just disengage the clutch. A prop for a boat is not the same as for hydro but it will still work. That is how oceanvolt can generate so much power. Their prop adjusts to the correct pitch for thrust and hydro. You lose about 33 percent power generation. Its a compromise without blowing several thousand for a towed array.


https://m.aliexpress.com/item/32879164158.html?trace=wwwdetail2mobilesitedetail& gps-id=storeRecommendH5&scm=1007.18500.139671.0&scm_id =1007.18500.139671.0&scm-url=1007.18500.139671.0&pvid=7f5ee7df-2125-4dc8-ae17-056d0c38eef1&_t=gps-id:storeRecommendH5,scm-url:1007.18500.139671.0,pvid:7f5ee7df-2125-4dc8-ae17-056d0c38eef1&spm=a2g0n.detail-amp.sellerrecommend.32879164158&aff_trace_key=7b03 4378c9c448e5a275d92add2dc408-1575030911156-08131-5dnnyP8k&aff_platform=msite&m_page_id=3354amp-qPXhXz6ttPcQ_DTL-okTqg1575945658888

[Wotname]

Originally Posted by double u

& driving a shaft generator is a total different situation from a -theoretically frictionfree - freely rotating prop. Any electric energy has to be produced by the sails & therefore is not available to drive the boat. It isn't going to be much (7A x 16V =112W as an example) so just over 1/7hp

This is true however the wind (via the sails) will often be supplying more power than the hull can use. This is one of the many reasons why we reef!

[LifePart2]

We did put a prop shaft driven alternator on Life Part 2. It worked great at 6+ knots - until we switched to a folding prop and installed lithium batteries. That put an end to the experiment.

The full account is here: LIFE: Part 2: Prop-Shaft Driven Alternator

Noel

[Seafarer7]

I fabricated and installed two shaft driven generators on my twin engine sailboat. The key concepts that made this very doable were:

1. Fabrication of split pulleys (so I didn’t have to disassemble the shaft from the gear box to install the pulleys). I cut in half standard aluminum pulleys, hollowed out the center to fit my shafts, then coupled them back over the shaft using the shaft-gear bolts.

2. Use of A-link v-belts (again, so I didn’t have to disassemble the shaft to get the v belts on, and also so I can easily tweak the length of the belt to match my install). With A-link belts you first size the belt by removing appropriate number of links, and then re-link the belt around the shaft.

Here’s the link to the belt I used (there are other A-link belts that exist, this is just the one I chose):

Jason Industrial A-LINK-5 Accu-Link V-Belt Belting, 1/2 inch https://www.amazon.com/dp/B00A9ZNE7C..._fG17DbS83JGGF

3. Use of high-voltage low rpm permanent magnet dc motors for generators (so Im generating DC not Ac and didn’t have to use rectifiers which alternators need. I used 72v DC Ametek motors bought off eBay ~ $40)

4. Use of a Solar MPPT controller to regulate and convert the speed dependent high dc voltage output of the PMDC motors down to 12V dc charging voltage. I used a MorningStar MPPT 45 charge controller - same family of charge controllers I use for the 820W solar on same boat. You want a motor that can generate high voltages at low rpm. This high voltage can then be down-converted to excess current at 12v dc via MPPT circuitry. The Morningstar MPPT I used can handle up to 150v dc, though in actual operation at normal speeds I rarely see above 50v dc input.

Attached are photos of the final product. Have two identical installs, one for port engine other for starboard.

Pulleys are 6.6” (split, on prop shaft) to 1.75” (on PMDC motors) for an almost 4:1 ratio.

Props are 3-blade 16”.

System works beautifully. Props start freewheeling at about 3 kts (and stop freewheeling at about 1 to 2 kts). At 3kt 5 amps can be generated. I’ve seen over 15 amps generated (at over 6 ~7 kts of boat speed surfing down waves). Steady state average generation at normal speeds is 10 to 13 amps. This may seem small compared to solar (my solar peak generation is over 40 amps) however over the course of an average day, the props typically generate more than twice the total energy (>200 amp-hours) compared to my solar (100amp-hours).

On a recent CA to HI leg, I was energy-positive (more than enough energy for autopilot, nav instruments, refrigeration, and via inverter a washing machine and electric galley).

[Seafarer7]

These photos show the “split pulley”: a regular aluminum pulley cut in half and reattached around the shaft.

Also shown in one of the photos is the “split belt” (A-link belt in its split state, prior to re-linking around the shaft).

Btw: these A-link belts make a good easy-to-install spare belt for other systems such as engine water pump and regular alternators. I carry some extra onboard as emergency spare.

[Seafarer7]

Final installations : one on port engine the other on starboard engine.

[Seafarer7]

Results
These are actual “in-use” data, (solar and hydro generator snapshots) taken from two different scenarios
(A) Captured in daytime, cloudy, with boat near hull speed, estimated to be going 6 - 7 knots.
(B) Also daytime, sunny near solar noon, boat speed estimated at 3-4 knots.



To understand the displayed data and photos (which are screenshot of the onboard energy-monitoring computer) one needs to know these are the outputs of 3 MorningStar MPPT Solar Controllers:
- 2 dedicated to solar panels (a 300w bank of panels and a separate 520w bank of panels) and
- the third dedicated to the two hydro-shaft generators combined (in parallel, with blocking diodes to prevent one hydro-generator from discharging into the other).


Case A: Cloudy, Boat was at or near hull speed:

MPPT#1 (300-watt solar) Output:
- 10.24 amps @ 13.5v (charge voltage) = 138.5 watts

MPPT#2 (520-watt solar) Output:
- 5.29 amps @ 13.47v = 71.3 watts
(This group of panels gets somewhat shaded by the sails)

MPPT#3 (the 2 hydro-generators) Output:
- 14.11 amps @ 13.5v = 190.83 watts

Total charge power into the combined 1225-AH battery bank (solar + hydro):
29.65 amps = 400.67 watts





Case B: Sunny, Not much wind, Boat speed estimated at 3 to 4 knots:

MPPT#1 (300-watt solar) Output:
- 21.46 amps @ 13.22v (charge voltage) = 284.11 watts

MPPT#2 (520-watt solar) Output:
- 16.16 amps @ 13.19v = 213.35 watts
(This group of panels gets somewhat shaded by the sails)

MPPT#3 (the 2 hydro-generators) Output:
- 6.21 amps @ 13.19v = 81.96 watts

Total charge power into the combined 1225-AH battery bank (solar + hydro):
43.83 amps = 579.42 watts

[ozepool]

Originally Posted by suiramor

When my boat is under sail, my (fixed) propeller is rotating (I did read the fascinating thread somewhere here whether to put it into gear, reverse or leave in neutral - I leave mine in neutral). However, I was wondering whether I could not jig up an electric generator to it. Would it un-balance the shaft? Why is it not done? (like the dynamos in the old fashioned bikes)

It depends, our Ampopetta had a Stewart Turner 10hp with a 3 to 1 reduction driving a 20x18 prop, max 500rpm. This was done with the engine backwards under the cockpit, to one side, 4 "V" belts drove the largish shaft mounted pulley! Got that? now if you dropped off the belts and ran on one to a generator it would maybe charge the battery. The wind/boat speed needed to be getting up designed hull speed to free wheel, SOO if you had a puny little prop forget it, get some solar panels as the drag is not worth it anyway IMO These days with LEDs the battery may be much smaller than what was needed in the 1960s. The Stewart had a v pulley on the flywheel we just used that to drive our generator as we did not do long trips, just harbour sailing with friends. Alternators may charge at car idle but a flat battery you may need 5-10 HP, you can see this idea is problematic, I guess our shaft speed freewheeling may have been 300 rpm, the large pulley giving you 900+ in a generator but I doubt the prop would have enough umph, you may have to use larger/smaller pulleys to make it work at all!

[skenn_ie]

A propeller is the mirror image of a turbine rotor, so is not effective for power generation, As others have said, it you are sailing close to hull speed anyway, you won't be particularly concerned with drag or efficiency. At other times, it will slow you down considerably. You would be better with a folding/furling prop and trail an old fashioned log connected to a low-speed permanent magnet alternator/brushless motor

[CaptainRivet]

@seafarer:Great info and awesome solution. Thank you so much for sharing.

Found some info on the Ametek Motors you used:
https://greenterrafirma.com/permanen...et-motors.html

Also a direct replacement for the 99V version, which they say is the best for windturbines:
"Ametek Motor Generator Replacement PMA Boss99 - TLG WindPower"

Hope that helps you

[CaptainRivet]

What do you think as about this PMA ?
https://www.ebay.de/itm/Freedom-PMG-...gAAOSwJQdXC9S6

My shaft turns at around 200RPM with 3kn of speed.

Rectifying AC to DC it is cheap and not a problem.

[skenn_ie]

Yes, but not very efficiently. The drag : output power ratio will be quite high. The blade profile is all wrong (mirror image) for use as a turbine.

[CaptainRivet]

Originally Posted by skenn_ie

Yes, but not very efficiently. The drag : output power ratio will be quite high. The blade profile is all wrong (mirror image) for use as a turbine.

This is very boat specific... On mine with a huge prop for a 40ft boat with 21x15 a fixed versus an folding prop is only 0.25kn in best and nearly not noticeable the faster i go. Forget to stop the freewheeling prop by hand, loads of force there. So the added drag a small shaft gen adds won't be noticeable. Also long keeler seem to help here... Most conditions in my case cirumnavigation downwind sailing with the big Parasailor out i am around 6 average, surfing waves in the 9-10kn range the additional drag of the shaft gen is negelectable/not noticeable.

Different on other boats eg my friends 50.5 Bennetau looses nearly 2kn with a fixed compare to a folding prop.

In General what i found out in my research that motorsailors have the most favorable/sufficient setup for a shaft gen. Because they have bigger engines and bigger props. So reduce drag they took measures during conception/construction. the better a motorsailor sails, the better they took care in construction about drag.

[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.