DIY towed generator

[a64pilot]

Silly question, but would an electric trolling motor work? They seem well designed from a drag perspective and I’d assume the prop as well.
Prop is a huge issue, if the prop isn’t right your going to lose a huge amount of power and big increase in drag.
How about cable driving a wind generator?

Me, I’d like to have a seagull to restore, they are very uncommon around here I believe, reason is because I’ve never seen one.

On edit, I found this, don’t know if it helps or not
https://www.fieldlines.com/index.php?topic=130969.0

[a64pilot]

I wonder if an old Scuba scooter, one with the Kort nozzle wouldn’t be better? Large diameter, very well designed prop (supposedly designed with a Cray Supercomputer, way back when) plus very easily, very widely pitch adjustable prop as that was how you adjusted the speed of the old Scooter, motor RPM was a constant.

[Singularity]

Not sure of the transmission on the boat and/or if you normally freewheel your prop under sail, but you could always consider a propshaft generator. Done many times before (normative on some boats like older Amels?) with lots of DIY write-ups on the net.

I researched this heavily before. In summary, in my circumstance, if I could find an old commercial towed generator at a reasonable price I'd bolt it on and go. If I was going to DIY I'd put a PM on the propshaft. I tend to conclude that most others reach a similar conclusion, which is why we don't see so many DIY towed generators...the propshaft approach is just ~easier to install and maintain, and it stays out of the elements with much less to go wrong.

http://www.cruisersforum.com/forums/...aft-67467.html
http://www.cruisersforum.com/forums/...aft-22266.html

[Pete7]

Originally Posted by a64pilot

Silly question, but would an electric trolling motor work? They seem well designed from a drag perspective and I’d assume the prop as well.
Prop is a huge issue, if the prop isn’t right your going to lose a huge amount of power and big increase in drag.

That's an interesting idea.

Pete

[odonnellryan]

I actually have a spare trolling motor, I am interested in this as well. I am sure it would be easy to strap alongside the dinghy and get some readings while using the 2-stroke outboard.

[a64pilot]

Originally Posted by odonnellryan

I actually have a spare trolling motor, I am interested in this as well. I am sure it would be easy to strap alongside the dinghy and get some readings while using the 2-stroke outboard.

It’s the voltage control that would be beyond me I’m afraid, but do you need to control it? So long as it’s in excess of bank voltage won’t the bank control the voltage? Yes you would have to check it now and again, but unless it makes a lot of power I would think it would be tough to overcharge?

Are trolling motors permeant magnet motors, do they have to be if they are connected to a bank?

There has to end a reason it’s not done, it’s too simple to not be used.

[RaymondR]

My go to source for smallish electric motors to use foe various projects has become the motors from electric radiator cooling fans which are readily available from auto parts stores.

You can convert an auto alternator by pressing the rotor apart, removing the coil therein and replacing it with a magnet salvaged from a speaker. Don't know how effective a generator they make. I read it in a book somewhere on DIY wind generators.

[mabowers]

Originally Posted by GILow

Actually, I’ve just remembered that electric wheelchairs have pretty decent DC motors... I wonder how they would behave as generators....

Electric bicycle motor ?

[alctel]

Originally Posted by GILow

Hi all,

I've had the idea to add a small towed generator to my arsenal for a while now. I dabbled with some half-baked concoctions a few years back on the trailer-sailor and I was pretty happy with the results.

But now that I want to make a "real" one, I cannot find a decent low speed generator for sale. There are lots on Ebay that are very cheap, but a bit of digging around and you discover plenty of very disappointed buyers. In short, they are cheap, but they are also mostly garbage.

Can anyone point me in the direction of decent quality low speed generator? Or maybe some web sites where such things are discussed that are not trying to sell me something? (My favourite site here in Australia, the Alternative Technology Association, has been offline for months.)

And just to save people from typing, yes, I do know about the various commercial offerings out there, but they are waaaay out of my budget. This is a cheap and cheerful extra for my charging, to cover running downwind at night when the existing solar and wind generator will not be much use at all and the wind-vane will have to give way to the autopilot.

Matt

I had the exact same thoughts last year for pretty much the identical use case.

They don't really make new ones anymore - but keep asking around and you'll find someone who has one in a garage or something. I bought an old tow genny last year for 250 USD that needed a bit of refurbishment.

[cyan]

Since efficiency and low-friction is key for a low-speed generator, you cannot do better than with a direct-drive synchronous permanent magnent generator. No gears, no brushes. The recently affordable rare earth magnets like Neodymium make these things easily exceed 90% efficiency. There is a lot of DIY info out there, or you can find small Chinese units for around a couple hundred bucks. A prop on a short shaft with a rope may not be the perfect solution for the wet end, but that can work just fine.

[Jim Cate]

Hi Matt,

Just noticed this thread...

Years ago i made a towing generator from a surplus 32 V perm mag tape drive motor. These were commonly available then as reel to reel tape drives were retired from service and replaced with more modern bulk storage devices. I used a 6 hp Johnson o/b prop on a s/s shaft about a meter long and some hard lay 1/2 inch double braid line. Output was ~1 A @ 4kts, ~4 A @ 5 kts and ~10 A @ 6kts. At greater speeds the output went up dramatically, but the damn thijg kept jumping out of the water and tying huge knots in the line. Various attempts to keep it submerged failed. It slowed the boat some, estimated at around one half knot at our normal cruising speeds around 6 kts, but that was only subjective. We found that output to be very helpful then, long before we had solar or underway wind power.

I think that any perm mag DC motor will work as a generator, and the battery bank itself works as a regulator... we just hooked it motor up through a blocking diode and let 'er rip. In the rare event that the SOC got high, as evidenced by the voltage climbing to the high 14s, we would shut it down.

Another source might be someone's retired Air-X. When the internal reg goes out, some folks abandon them, and they would make a useful towed array by substituting a bridge rectifier for the reg.

Good luck, and i'll be watching for your solution.

Jim

[GILow]

Originally Posted by cyan

, or you can find small Chinese units for around a couple hundred bucks...

And there is the very problem. There are plenty of small Chinese units available, but nearly without fail they appear to be total crap. I am trying to find a good quality device.

[GILow]

Originally Posted by mabowers

Electric bicycle motor ?

Excellent out-of-the-box thinking, thank you. I will see if that's an option.

[GILow]

Originally Posted by GILow

... One of the members here got good results with an old mainframe tape drive motor...

Originally Posted by Jim Cate

Hi Matt,

Just noticed this thread...

Years ago i made a towing generator from a surplus 32 V perm mag tape drive motor.

You may have noticed the thread, but the thread had already noticed YOU.

Yep, I am trying to recreate your old setup. Based on your numbers it would be perfect for my boat, I rarely see over 6 knots for a start.

Some clever ideas coming through from the CF'ers, I have some homework to do.

I looked high and low for the old tape drive motors, no luck at all so far. The wind-generator mob loved them, but apparently the bearings did not last long with those sorts of loads.

[GILow]

Originally Posted by a64pilot

Silly question, but would an electric trolling motor work? They seem well designed from a drag perspective and I’d assume the prop as well.
Prop is a huge issue, if the prop isn’t right your going to lose a huge amount of power and big increase in drag.
How about cable driving a wind generator?

Me, I’d like to have a seagull to restore, they are very uncommon around here I believe, reason is because I’ve never seen one.

On edit, I found this, don’t know if it helps or not
https://www.fieldlines.com/index.php?topic=130969.0

There are no silly questions... though, there sure are some utterly mindless answers.

The cable driven wind generator is actually a good one, there's even a conversion kit for the smaller version of my wind generator. I looked at it for my boat, but my wind gen is something like 3 meters above the deck, which is 1.4 meters above the water. The angles and access would be a nightmare, not to mention removing the blade every time I wanted to convert. I am keeping an eye open for an affordable little Aerogen 4, but they hold their value, dammit!

The trolling motor thread was interesting. In short, it failed, and there would be so many other problems with installing one that I wouldn't know where to start.

But keep thinking of other approaches please.