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Old 17-07-2012, 07:24   #31
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Re: Water Generator Concept Thread

I was thinking of making a towed water generator using a small outboard prop welded to a stainless steel rod, connected by line to somethink like this, mounted on the stern rail: Hurricane Cat 4 Mark I Low Wind PMA for Wind Generator

Is there a way to figure out, given a prop's specs, its RPMs when free spinning, based on speed through the water?
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Old 17-07-2012, 07:27   #32
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Re: Water Generator Concept Thread

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Originally Posted by donradcliffe View Post
... Retrieval was fairly easy with the split funnel provided by Ferris.
Our problem with the Ferris was, when the propeller jumped out of the water (we did add lots of weight), the line coiled up to a knot, spun in wild rotations. The split funnel didn't help since it couldn't slide past the knot. The problem started with about 20 knots of wind, sailing at ~6.5-7 knots.

The only way to retrieve the prop and uncoil the line was to stop the boat. Especially downwind, poled out, prevented out, this was a bitch.

The output was less than advertised, but we would have been happy for any 100-120 amp hours per day. But stopping the boat a couple of times per day/night wasn't so great. Later we switched to a propeller with less pitch, it didn't jump anymore, but then produced even less current, like 2-3A at 6knots.

The system worked for less than 5000 miles, then the PM motor failed, salt water got into it. I should have spend the $1000 on something else, burn fuel if needed. I would not recommend any towed generator to a friend

I do like the idea of using an electric trolling motor, or parts of an old outboard.

Dirk
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Old 17-07-2012, 07:35   #33
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Re: Water Generator Concept Thread

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Originally Posted by Triton318 View Post

Is there a way to figure out, given a prop's specs, its RPMs when free spinning, based on speed through the water?
Not sure if this helps: The propeller which comes with the Ferris WP20 tow generator:

Johnson/Evinrude propeller, Part number: 386587. Size 8-1/4x5

I can't tell you how fast it spins under load....
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Old 17-07-2012, 08:47   #34
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Re: Water Generator Concept Thread

We used a home made towgenerator for probably 35,000 miles over the period of owning our old herrshoff "Candlewin" It started out hanging off the stern rail in a juice container to keep it dry then evolved into a beautiful stainless case on gimbals to keep the gen shaft in direct line with the prop.(Important) With the stern of the boat gyrating all over the horizon, there is way too much side pull on the shaft of the generator and power loss without being gimballed.
I used old computer drive motors, the same units the Ferris started with. I think I paid about 25 dollars average for them at surplus shops. You need a diode in the supply line or else it will run backwards if it's output falls off below the voltage of your batteries. I just used a wavebridge rectifier.
Anyways, used about 125 feet of 1/2 nylon line, a 3 foot piece of SS rod with a OMC 9hp outboard prop on backwards. This consistently produced 5 amps at 6 kts, then went up exponentially from there.
With the long length of tow line the shaft/prop is usually deep in the following waves and never flew out to tangle. Never lost a prop to a shark either, I can't imagine anything grabbing that nasty blender when it is spinning. I will definitely be putting one on my new boat.
cheerio, greg
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Old 17-07-2012, 08:51   #35
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Re: Water Generator Concept Thread

Speaking totally out of ignorance here but I will make my comment anyway.

Why would you want water power when you have wind power? My thinking is that a water generator would be nice when anchored in a fast running current. Out at sea when you are actually moving under sail power, could a wind generator not meet your needs?
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Old 17-07-2012, 09:13   #36
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Re: Water Generator Concept Thread

i made a water genny, 24volt permanant magnet motor, the out board propeller with the shaft idea as mentioned.. long rope out the back.. 1.4amps at 14.5volts..at 4 knots.
Got the outboard propeller at the scrap yard the electric motor was $25 at a another scap yard..
I fitted the electric motor(generator) in plastic drainage pipe with ends glued on to weather proof it with just the shaft sticking out..
Not one bit high tec but it works ok..
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Old 17-07-2012, 16:22   #37
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Re: Water Generator Concept Thread

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Originally Posted by Tony B View Post
Speaking totally out of ignorance here but I will make my comment anyway.

Why would you want water power when you have wind power? My thinking is that a water generator would be nice when anchored in a fast running current. Out at sea when you are actually moving under sail power, could a wind generator not meet your needs?
Short answer: no, because when sailing off the wind, which one hopes to be doing much of ones cruising miles, the apparent wind velocity is not sufficient to produce much power from a wind generator.

Water driven generators continue to work whilst sailing downwind because the boatspeed is still adequate.

One will never be voluntarily anchored in a tidal stream of sufficient speed to produce much power from a towed generator, since it takes on the order of 4-5 knots for most of them to become very productive.

Cheers,

JIm
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Old 17-07-2012, 18:15   #38
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Re: Water Generator Concept Thread

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Short answer: no, because when sailing off the wind, which one hopes to be doing much of ones cruising miles, the apparent wind velocity is not sufficient to produce much power from a wind generator.

Water driven generators continue to work whilst sailing downwind because the boatspeed is still adequate.

One will never be voluntarily anchored in a tidal stream of sufficient speed to produce much power from a towed generator, since it takes on the order of 4-5 knots for most of them to become very productive.

Cheers,

JIm
It depends a lot on where you sail. Windy places are great for wind generators, and there are plenty of places where it's windy in a lot of the anchorages as well. I've only had two offshore passages, and both had plenty of wind over the deck, even when heading downwind, so we got lots of power out of the wind generator.

On the other hand, a wind generator would be useless in the Pacific Northwest in the summer.

I also shy away from slowing the boat down by half a knot to make power. Half a knot on a one week passage is 84 miles, or most of an extra day at sea. My boat's slow enough as it is. That said, if you're bumping up against hull speed, then you have lots of power available from the sails, and the extra drag won't slow you down at all (though in those circumstances, you probably have enough wind over the deck to use the wind genny which is also useful at anchor...)
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Old 17-07-2012, 21:15   #39
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Re: Water Generator Concept Thread

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It depends a lot on where you sail. Windy places are great for wind generators, and there are plenty of places where it's windy in a lot of the anchorages as well. I've only had two offshore passages, and both had plenty of wind over the deck, even when heading downwind, so we got lots of power out of the wind generator.

On the other hand, a wind generator would be useless in the Pacific Northwest in the summer.

I also shy away from slowing the boat down by half a knot to make power. Half a knot on a one week passage is 84 miles, or most of an extra day at sea. My boat's slow enough as it is. That said, if you're bumping up against hull speed, then you have lots of power available from the sails, and the extra drag won't slow you down at all (though in those circumstances, you probably have enough wind over the deck to use the wind genny which is also useful at anchor...)
G'Day CW,

Well, in the absolute sense you are correct -- your location does matter. But for us it seems that we try to organize our passages around sailing off the wind in moderate conditions. Sometimes it even works out like that! So, there we are in the trades, which in our part of the world tend to blow in the 20 +/- 5 knot region most of the time. So, let us say 22 knots true for arguments sake. In our boat (now) this gives average downwind speeds of around 8-9 knots, which in turn mean apparent winds of around 13-14 knots. Our Air-X is only good for 4 or 5 amps at these velocities, and with rolling about this is often not continuous. Useful, yes, but not enough to keep up with all our loads at sea. So, assuming that one develops a drag generator that stays in the water at those speeds (and our old one would definitely not do so) outputs of 10+ amps should be easy to attain... visions of ice cubes dance through my head!

Getting back to the real world of our previous boat and its troller, our lower energy needs of the time meant that we only needed to run it a few hours a day, and the loss of speed, while annoying, wasn't all that bad. And as you said, when nearing hull speed the drag becomes less of an issue.

Incidentally, that old homebrew troller also had a big wooden air prop that a fellow cruiser carved for us in La Paz. When at anchor we would hang it up in the foretriangle with a web of lines securing it and it did yeoman duty as a wind generator. Getting that 5 foot diameter baloney slicer down in squalls was a near-death experience that would not pass an OSHA review!

Obviously, having all the systems:solar, wind and water give one the most options, and that is what I'm striving towards... 2 out of 3 so far!

Cheers,

Jim
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Old 18-07-2012, 14:04   #40
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Re: Water Generator Concept Thread

Hello to all,
I sail a 47' monohull....
I am I BIG fan of solar!!!
I've been using solar on-board boats for 15+ years, and on-shore, in remote/off-grid locales for almost 30 years....
And, I have a 520 watt solar array on my current boat, or the past 6 years and 12,000+ offshore miles...
Here are details / photos of my solar install...

Solar Panels

BUT....

But, I also have had a Ferris Towed-Water-Gen now for about 6 years....and I love it...

Wind Powered Generators

Here are details / photos of my towed-water-gen install...
Towed-Water-Generator

I've used it on 2 Atlantic crossings, and on a couple passages to/from the US and Carib...and on a few shorter passages to/thru Bahamas....
All-in-all, about 12,000+ miles offshore....
Never had a problem using Ferris' "split-funnel", except when I dropped it and it flew overboard in a full-gale, at night of course!!! (I made my own "spare", and ordered a replacement when I got to port...)

{Please note that while it is a real pain, and it takes some strength, while sailing at about 7.5 kts with a building wind....I, myself, have persoanlly pulled in the entire 75' towline, with prop and shaft attached AND spinning, and with the line twisting/tangling, without using the funnel (dropped overboard minutes earlier!).....just arm strength and good sailing gloves....and yes it was at o'dark thirty with 30+ kts of wind....it IS do-able, as I did it in Dec 2007 when 400 - 500 miles east of Anegada, BVI, approaching / sailing thru TS Olga....}


(Intially I did have some line chafe caused by MY improper mounting angle, but after I modified my mounting arrangement, no problems!!)


I found about 1 to 1.5 amps, per knot of boat speed....starting at about 3.5 kts....
Here are my avg. results:
4 - 5amps @ 4kts
6 - 7 amps @ 5kts
7 - 9 amps @ 6kts
10 - 12 amps @ 7kts
12 - 14 amps @ 8kts (with some prop skipping, until I added the HEAVY weigths)

My results, at speeds of 6 kts or higher is less than the factory specs....but my results for speeds 5 kts and below is almost within spec...

To be clear a water-gen isn't for everyone....and solar is still (and probably always will be) king!!!
But, for long passages (especially downwind and/or thru cloudy skies / ITCZ, etc.) nothing beats the 24/7 charging of a water-gen....



And, for ME, on MY boat, with MY application, here is what I found:

a) prop-shaft gen....(back in the 70's, my parent's old Hinckley had one that worked great!!).....but doesn't work for me, with feathering AutoProp and no room inside the boat near the shaft/transmission, even if I had a fixed-prop...
b) fixed / hinged-water-gens....WAY to EXPENSIVE....and poor quality, hi-maintenance, etc....
c) Towed-water-gens...."reasonably" priced...proper mounting is neccesary to prevent line chafe....and either Hamilton Ferris or AmpAir/AquaAir works well....

I chose the Hamilton Ferris WP-200....and have been very happy with it....

Oh, and Ham Ferris and his guys are all super nice and a real pleasure to do business with.....


I hope some find my personal, first-hand results, from multiple offshore passages (and my photos/details) to be helpful....

Fair winds...

John
s/v Annie Laurie
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Old 19-07-2012, 06:30   #41
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Re: Water Generator Concept Thread

Thanks everybody for the great ideas!
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Old 19-07-2012, 06:48   #42
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Personally, I would try first to meet my power needs with things that don't slow the boat down. Every fraction of a knot is precious on a sail boat, and dragging a form of sea anchor to make power strikes me as a high cost to pay. I can see doing it as a last resort when solar and wind can't meet needs, but I'd view it as the tool of last resort.
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Old 19-07-2012, 06:50   #43
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Re: Water Generator Concept Thread

Hopefully, in a few years, the innovation at MIT of a new filter will make this a very easy and energy efficient task.

A new approach to water desalination - MIT News Office
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Old 19-07-2012, 08:54   #44
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Re: Water Generator Concept Thread

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Personally, I would try first to meet my power needs with things that don't slow the boat down. Every fraction of a knot is precious on a sail boat, and dragging a form of sea anchor to make power strikes me as a high cost to pay. I can see doing it as a last resort when solar and wind can't meet needs, but I'd view it as the tool of last resort.
You need to go cruising and learn that racing is not the only way to sail. It took me a while, but I learned that reefing at night, not using the spinnaker, towing the dinghy, and using the towing generator all slow the boat down but are not the end of the world. Another thing I have learned is that all boats are more comfortable when they are slowed down.

The towing generator had an insignificant effect on boat speed when the winds were above 12 knots, but it slowed me down 0.5k when the wind was light.
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Old 19-07-2012, 10:09   #45
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Re: Water Generator Concept Thread

I towed one for awhile.Made plenty of juice but it was freaking dangerous.Gawd help anyone who fell overboard and grabbed the towline.It would be a scene from a horror movie.What a pita to tame and get back aboard.
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