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Old 11-10-2013, 19:14   #1
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Sea water evaporation system

Does anyone have input for this style fresh water maker? Is the weight saved compared to the weight gained worth it? Is this practical?

Having a full tank on the 46' DeVries sloop emptied by the rich kid who was too sea sick to bother shutting off the tap four days out to Hawaii from SF forced me to come up with a very rudimentary still. Thanks to the almighty the idiot didn't empty the propane too. Now, I carry more than enough one gallon jugs if I am the captain and I am way too freaked out to rely on a water tank">fresh water tank.

I am also thinking it would be far safer than having to chlorinate and filter water from not so clean sources.

A water maker is expensive, runs on electricity, possibly not reliable, and would never pay for itself after a few years use if you were to sell the cat.

Your thoughts please...

http://www.google.com/url?sa=t&rct=j...53899372,d.cGE
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Old 11-10-2013, 20:37   #2
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Re: Sea water evaporation system

Seems to me that it still takes energy to make water with a still!! Weather it's electicity, or heat from propane it still takes power! Of all of man inventions, a still is one of the most dangerous!! They take constance tending! I used them in the navy,and they are a bear to keep working right! Believe me the amount of cost saved from a New style water maker to a still is nothing like the danger of a distilling unit!! Much rather have something that works pretty much on it's own compared to useing a still and constanty watching it to keep it safe ! Just my 2 cents
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Old 11-10-2013, 21:55   #3
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Re: Sea water evaporation system

bobconnie, I'm sure you are correct about stills being a bad idea as a fresh water source for a small boat but have you ever tried to make gin with an RO unit?

Seriously though, RO is the current preferred method to produce fresh water from salt because of it's lower energy consumption than stills. The manual RO units sold for use in life rafts are much more effective than the old solar stills sold for the same purpose. I bet a clever person could drive an RO unit with a windmill or drag prop.
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Old 11-10-2013, 22:17   #4
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Re: Sea water evaporation system

BobConnie I think the USN versions use a low and high pressure side to increase efficiency at the cost of complexity and safety. Also they are fueled which is a cost to consider.

I think the kind the OP used was unpressurized which would decrease the risk but increase the fuel costs. Also, based on the link he/she provided I think the OP was wanting to develop a solar system.

To the OP, I also have been considering a solar still. Since I don't currently have a boat, I am not pursuing it. In the interests of creating a low cost system I was only interested in using off the shelf parts, to wit a skylight with an already built in drip rim to catch the product. The brine tub would be 1" foam insulation with a fiberglass liner, with black felt or polyester fleece to keep the brine from sloshing. All painted black. The question I have is whether to go with a domed skylight which will drip some of the product back onto the brine but will not need to be tended, or to use a flat plate skylight that will need to be tended to ensure there is always a slope towards one edge or the other so the product will not drip back when the unit is level in a calm or at the dock. See attached sketch.

Another thought is to use a pyramid skylight with significant slope, but this make the unit less off the shelf and perhaps higher profile on the cabintop which is where I thought it should be located.
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Old 11-10-2013, 22:18   #5
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Re: Sea water evaporation system

Quote:
Originally Posted by bobconnie View Post
Seems to me that it still takes energy to make water with a still!! Weather it's electicity, or heat from propane it still takes power! Of all of man inventions, a still is one of the most dangerous!! They take constance tending! I used them in the navy,and they are a bear to keep working right! Believe me the amount of cost saved from a New style water maker to a still is nothing like the danger of a distilling unit!! Much rather have something that works pretty much on it's own compared to useing a still and constanty watching it to keep it safe ! Just my 2 cents
No! The still was an emergency measure. Please check out the link. This is total solar.
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Old 11-10-2013, 22:26   #6
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Re: Sea water evaporation system

Quote:
Originally Posted by Adelie View Post
BobConnie I think the USN versions use a low and high pressure side to increase efficiency at the cost of complexity and safety. Also they are fueled which is a cost to consider.

I think the kind the OP used was unpressurized which would decrease the risk but increase the fuel costs. Also, based on the link he/she provided I think the OP was wanting to develop a solar system.

To the OP, I also have been considering a solar still. Since I don't currently have a boat, I am not pursuing it. In the interests of creating a low cost system I was only interested in using off the shelf parts, to wit a skylight with an already built in drip rim to catch the product. The brine tub would be 1" foam insulation with a fiberglass liner, with black felt or polyester fleece to keep the brine from sloshing. All painted black. The question I have is whether to go with a domed skylight which will drip some of the product back onto the brine but will not need to be tended, or to use a flat plate skylight that will need to be tended to ensure there is always a slope towards one edge or the other so the product will not drip back when the unit is level in a calm or at the dock. See attached sketch.

Another thought is to use a pyramid skylight with significant slope, but this make the unit less off the shelf and perhaps higher profile on the cabintop which is where I thought it should be located.
The link had the idea that glass was far more efficient at moving the condensate droplets faster and hence allowing more sunlight to further speed up the evaporation process by allowing more light into the system. Maybe a c
dome would be difficult to fabricate out of glass and expensive?

The sloshing would limit this system for certain but can it be compensated by design? This stuff just intrigues me!

I think many here know about the emergency solar condensate collectors on life rafts.
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Old 11-10-2013, 22:38   #7
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Re: Sea water evaporation system

Catamarans are far less apt to slosh and heel. I am thinking more in terms of smooth sailing anyways. Certainly at anchor, you could replenish fresh water supplies. Certainly when the sun is blazing and the seas are relatively calm... Hmm?
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Old 12-10-2013, 20:18   #8
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Re: Sea water evaporation system

In Boy Scouts we dug a shallow hole in the damp sand, placed a cup in the center of the hole, covered the hole with a sheet of plastic film sealing it around the edges with sand on top, then placed a small rock on the center of the plastic film to make a low spot over the cup. In a day we could get a half cup of water from a 3 foot diameter hole as water evaporated from the sand, condensed on the plastic, ran to the low spot and dripped into the cup. Some scratched up the bottom surface of the plastic with sand to help the water droplets run down to the low spot better.

I'd go with RO.
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Old 12-10-2013, 20:25   #9
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Re: Sea water evaporation system

The Navy aircraft survival packs had plastic solar stills in them. Used to be available surplus though it's been years since I've seen them. Probably rig one up but they are very inefficient at creating fresh water.

The easiest way to not have happen what happened to you on your TransPac is turn off the pressure water system. Install foot pumps if you don't already have them. Will cut your water consumption to a fraction. Pressure water systems are gross water wasters.
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Old 12-10-2013, 20:47   #10
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I helped test several water purification systems for the military a few years ago. These were for disaster relief scenarios, and one was a plastic solar still. The unit was very simple--just a plastic bag with a semipermeable membrane dividing it into two compartments. I had high hopes for that system because of the elegant simplicity of the design, but it proved ineffective in our testing. Under ideal conditions a few of them together might have made enough water to sustain one person. The concept is scalable, though--just not worth the effort when there are tried and true alternatives, IMO. YMMV.
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Old 13-10-2013, 00:16   #11
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Re: Sea water evaporation system

I am finding stills that are far more efficient and way less costly, both in materials and energy consumption, than anything posted yet.

The Solar Water Still Challenge | Technical Education Magazine
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Old 19-10-2013, 05:15   #12
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Re: Sea water evaporation system

Once upon a time, there was a paperback book "Farming the Sea", don't remember the author, about ways to live off of the sea while in a boat. One particular article was about making a plastic, roll up, hang on the rail in the sun, solar still. You put seawater in one section, and thru evaporation into a drip tray, got drinking water out. It had to be monitored every few hours to keep salt water out of the fresh water. Seems like it was a polyethelene and black felt sewn and sealed unit where the brine was pooled in the bottom and thru evaporation to the top, it condensed onto a drip trough into a container The book is no longer published but there seems to be copies floating around. Think there was a downloadable pdf copy on one of the forums years ago.
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Old 19-10-2013, 07:11   #13
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Our water fouled 5 days out of Molokai for oregon. Out army surplus solar stills (X2 ) created water thief tasted so badly of plastic that it was undrinkable.

Answer = place bucket at the junction of the mast and boom. Raise the boom 2' with the topping lift. Lower the sail to create a belly fold directed at the bucket. Steer for a squall & drink up.

And always have 15 -20 gallons in jugs before you leave.

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Old 19-10-2013, 07:15   #14
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Re: Sea water evaporation system

I wonder if the plastic tasting water had been filtered through an activated charcoal filter would it have then been drinkable?? Activated charcoal is available from most aquarium shops in 1 lb bags... as well as filter material to keep it in its container.
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Old 19-10-2013, 11:05   #15
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Actually ran the water through a katadyn back packing filter and it helped but still was too rugged to drink. Capturing rain water from squalls came in over five gallon increments and tasted great.
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