DIY towed generator

[Jim Cate]

Matt, re tow line: we used 50 feet of half inch double braid dacron. You want rope that is as torsionally stiff as possible, so maybe the torsion line from the luff of a code zero that has blown out could be good! And IMO, 30 meters is too long, prone to tangling and slow to retrieve (and more expensive, too).

I'm also doubtful of the "one amp per knot" estimate. The output of ours was way super-linear... more like speed squared as a factor, just as you might expect.

Finally, I agree that the Gmonster's thoughts were a bit off. As I've told you, our nominal 32 vdc motor was connected directly(via a blocking diode) to the battery. The battery itself acted as a regulator until it reached near full charge, at which point (rarely reached) the voltage would start rising above out absorption target and we would shut it off ... not a big worry!

I'll be very interested in what sorta output you get from the F/P rewire. You might just inspire me to get off my butt and make one myself!

Jim.

[GILow]

Originally Posted by Jim Cate

Matt, re tow line: we used 50 feet of half inch double braid dacron. You want rope that is as torsionally stiff as possible, so maybe the torsion line from the luff of a code zero that has blown out could be good! And IMO, 30 meters is too long, prone to tangling and slow to retrieve (and more expensive, too).

I'm also doubtful of the "one amp per knot" estimate. The output of ours was way super-linear... more like speed squared as a factor, just as you might expect.

Finally, I agree that the Gmonster's thoughts were a bit off. As I've told you, our nominal 32 vdc motor was connected directly(via a blocking diode) to the battery. The battery itself acted as a regulator until it reached near full charge, at which point (rarely reached) the voltage would start rising above out absorption target and we would shut it off ... not a big worry!

I'll be very interested in what sorta output you get from the F/P rewire. You might just inspire me to get off my butt and make one myself!

Jim.

Jim, great stuff, as always, thank you.

Noted about the line length, but I might have to add a couple of feet depending on how I mount the thing. My 1.4 meter freeboard at the stern is a factor in terms of angle, if I have to mount on the rails above the deck I could easily be looking at 6 feet above the water.

I have assumed that I will NOT need a regulator for this thing. I mean, I would be seriously thrilled if it produced enough power to need one, but the 630 AH (12 V) house battery bank is likely going to absorb anything a towed genny that I build can produce. I've already got a warning circuit for the wind generator that sounds an alarm to tell me to tie off the blades, well the same circuit will arc up if the towed genny has filled the batteries, in which case I'll haul in the line. And if I don't, it will just divert the excess power into the dump resistors, soon to become a heating element in my hot water system.

I've assured Newhaul that I will post a thread, with photos, of the final project. He's given me the contact info for someone who is really into this stuff so maybe what comes out of this will be a bit more polished than my usual half-baked solutions.

[smacksman]

Originally Posted by GILow

Smacksman, than you for this post, it constains some terrific metrics and advice.
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You say the amp-air came with a 30 meter tow line. Would you say that was adequate, or if you were making one from scratch (as I will be) would you have made it longer or shorter?

The prop needs to be quite far astern to keep below the surface in the big swells mid ocean. It may have been <30m but it was pretty long from memory. The prop looked more like a big fishing spinner than an outboard prop, if you can visualise what I mean. Putting it in operation was not a big problem - you just had to be quick. Getting it in was easier if you stopped briefly (in more than 30m of water!) or the line would tangle with the prop still turning. Good luck with your project - you are a man after my own heart!

[catsketcher]

Just noticed the thread.

Like Jim, I also had a tape drive DC motor with a rope attached to a prop. The prop was an old 3.3hp prop epoxied onto a 70cm piece of stainless shaft about 15mm thick. A mate welded a u shaped lug on the end opposite the prop.

I mounted the motor into the stern of our cat, which wasn't the best idea, and it would have been better enclosed in a PVC tube end plugs. I got a 30 amp diode and put it in the circuit.

The rope was about 15 metres long. Like Jim said, when we went over about 8 knots it would come out of the water but it didn't really matter.

I really liked the setup when we had fewer solar panels. It would generate 5-7 amps at up to 8 knots which covered the autopilot and other stuff. When the motor died due to water ingress we upgraded the solar from 120 to 400 watts so I didn't replace the motor. But I have good feelings about the setup. It cost me the diode because I didn't have to buy the tape drive motor. I would consider getting a geared motor. The guys at Motion Dynamics have heaps of motors. I have this one

https://www.motiondynamics.com.au/un...r-400-rpm.html

but haven't used it. With the gearing it may do well, but it may not turn enough.

It is a good project to get you some amps for night sailing.

cheers

Phil

[GILow]

Originally Posted by catsketcher

Just noticed the thread.

Like Jim, I also had a tape drive DC motor

So... you are one of the culprits who used up all the tape drive motors... right...



with a rope attached to a prop. The prop was an old 3.3hp prop epoxied onto a 70cm piece of stainless shaft about 15mm thick. A mate welded a u shaped lug on the end opposite the prop.

Jim had a 6 HP prop, you used a 3.3 HP prop. Aside from what this tells us about Jim it is interesting because it indicates that the prop can probably be a bit smaller than I expected. Up until your post I was actually thinking of using a 8 HP prop (what does that say about me I wonder) but clearly not needed. Your cat would have been significantly faster than my boat (the best I've ever managed was 8.5 knots through the water) so maybe I should go a LITTLE larger than the 3.3...?

....


I would consider getting a geared motor. The guys at Motion Dynamics have heaps of motors. I have this one

https://www.motiondynamics.com.au/un...r-400-rpm.html

but haven't used it. With the gearing it may do well, but it may not turn enough.

I would have been tempted by that one too, and that was exactly the sort of answer I was looking for when I started the thread.
But I've kinda moved on from then and now I have the F&P motor in the shed ready to go. Just spinning it with a car wheel brace is enough to power a car headlight globe so I am optimistic it will work well.


It is a good project to get you some amps for night sailing.

Thanks for the input Phil. You've added some really useful data. Looking forward to a chance to test some of these ideas in the water.

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[wsmurdoch]

In addition to choosing your propeller, one thing that you will have to deal with is finding the optimum amount of energy to draw from your spinning propeller. Think of it this way. Spinning freely, the propeller turns its fastest, but you get no energy and your batteries get no charge. Stopped completely, the propeller extracts no energy from the moving water, and again your batteries get no charge. The propeller rotational speed (for a given boat speed) that produces the greatest amount of current into your batteries at a given voltage is somewhere between the propeller's free spinning speed and zero. (Theory points toward 59%.)

With a tape drive motor (or similar) you can change the gearing (or belting). With your Fisher and Paykel motor you can change configuration of the stator coils. With a re-wound automotive alternator you can change the number of poles, wire diameter, and number of turns in the stator.

So, don't stay locked on with a particular F&P pole wiring configuration, and be prepared to experiment to find the best configuration for your propeller and sailing speed.

Bill

[GILow]

Originally Posted by wsmurdoch

In addition to choosing your propeller, one thing that you will have to deal with is finding the optimum amount of energy to draw from your spinning propeller.

......

So, don't stay locked on with a particular F&P pole wiring configuration, and be prepared to experiment to find the best configuration for your propeller and sailing speed.

Bill

Bill, that's a great summary of the challenge.

I did look at the feasibility of running the wires from the F&P coils to a switch block so that I could easily switch between coil configurations and compare outputs before permanently soldering anything. I even wondered if in doing so I would discover that different modes worked better at different speeds and that the switch would become a permanent addition.

I spent twenty minutes comparing the various suggested wiring layouts for some kind of commonality that would make doing so anything but the biggest darn wiring headache I had ever seen since the day a guy put an angle grinder through a 1000 pair inter-building telco cable and put most of the Victorian state government internal telephone network out of commission for a week.

Then I went inside and lay down until the headache cleared.

After which I said "F -- k it!" And chose the wiring layout that was labelled "general purpose".

You are correct, of course. But I am already known for making things over complicated, I probably shouldn't make it worse.

[Boatguy30]

What about a starter/generator from a golf cart? Seem to be basically permanent magnet motors? This is very similar to what Hamilton Ferris sells.

Downwind in the Pacific the sails shade the solar panels after mid day. Hoping to find one in Georgetown or cobble something together between Bahamas and Panama

[GILow]

Yes, any permanent magnet DC motor should work.

Interesting point about the problem with the downwind run. A towed generator would be a good solution.