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Old 03-08-2010
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Question Emergency Water Desalination

Hi there-
I'm on a team of junior level engineering students who, as a design project have been tasked with creating an emergency water desalinator. It is our understanding that very few smaller vessels carry any sort of device like this - largely because of cost. We have a conceptual design, however, none of us have any real experience sailing. From those willing, we would greatly appreciate some input.

Here's the basics:
1. Remove salt through evaporation instead of expensive RO filters or through FO filters that require a sugar-like solution.

2. Total weight 15-25lbs

3. APPROX Dimensions of: 2.5ft*1ft*1ft

4.Production of 1-2 gallons/day should be very easy

5.Total cost to produce >30USD

6.We are attempting to make this work only requiring hand-power($$), but may require electrical input (similar to that of car battery) to achieve 1-2 gal/day. (Evaporating water is very energy intensive)

Are there any thoughts given that much? Anything you would or would not like to see in this type of device? Do you realistically seeing something like this being included in your emergency supplies? How many consecutive days would you want to be able to count on this device providing water?

Any thoughts that you have would be very much appreciated and seriously considered.

Thanks much,
David
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Old 03-08-2010
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"1. Remove salt through evaporation"
There's nothing new about that. Survival training has taught how to use a piece of plastic for solar evaporative desalination for ages. Replicating something so well documented would be pointless, unless you can add something new to it.
And it is no trick doing this on a small boat--except of course when the sea is not calm. If your setup can work, say, on the roof of a car while four big guys are jumping up and down rocking it on the shocks, now you've got conditions similar to what might be found on a sailboat.
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The advantage we see in creating a machine, is that it would produce a much larger quanitity of water than using just solar energy - especially if there's no sun.
We are considering conditons in using this, we've wanted some insight on just how rough the sea is - particularly in a small boat.
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A solar still is not hard to create, and given sunlight in the tropics, quite effective. One way to improve on it is to use a Pelletier effect chiller to increase the rate of condensation.
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If you out to sea (offshore) and there is any kind of wind the big issue would be a unit that would hold up to the normal waves/wind that beat up most anything on deck

Things get torn off sailboats all the time in bad weather
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Thoughts:

You're going to need quite a few BTU's in order to evaporate enough water to meet your goals. The first thing I can think of is using some sort of hand operated heat pump in order to accomplish the energy transfer...

Sea Roughness? Standing up while below is like trying to stand up inside a pickup camper while driving down a washed out forest road that throws you side to side and just happens to take you over 8-10 foot high rolling hills at the same time. Not impossible, but not that easy at first either, and you better have something to hold on to.
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If you could develop a device capable of a
gallon or two of fresh water a day, you would
definitely be on to something.
There are emergency hand pump
water makers that require a lot of hard labor
to yield a gallon of water. Solar stills require
a bit of manipulation to eek out a mere trickle of water.
I envision a device that could sit on deck and
passively, yet slowly, produce drinking water from
sea water all day long. You might consider
incorperating a solar powered fan to hasten
evaporation. Two gallons a day sounds optimistic,
but I hope you prove it is not impossible.
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You should have 2 quarts per day per crew member as a minimum objective. I think some kind of piston pump (hand operated) and membrane is likely better than evaporation. If it's dark & stormy the hand pump should still be viable.
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Hand powered RO watermakers, like the Survivor 35/40e series are well known. They're also high-maintenance and expensive.

Solar stills are low-maintenance, low cost, and low output. Hell, you can make one from a big ziploc bag, a bowl and a piece of black plexiglass.

I think the OP is looking to design something between the two.
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Quote:
Originally Posted by NeverSailed View Post
Hi there-
I'm on a team of junior level engineering students who, as a design project have been tasked with creating an emergency water desalinator. It is our understanding that very few smaller vessels carry any sort of device like this - largely because of cost. We have a conceptual design, however, none of us have any real experience sailing. From those willing, we would greatly appreciate some input.

Here's the basics:
1. Remove salt through evaporation instead of expensive RO filters or through FO filters that require a sugar-like solution.

2. Total weight 15-25lbs

3. APPROX Dimensions of: 2.5ft*1ft*1ft

4.Production of 1-2 gallons/day should be very easy

5.Total cost to produce >30USD

6.We are attempting to make this work only requiring hand-power($$), but may require electrical input (similar to that of car battery) to achieve 1-2 gal/day. (Evaporating water is very energy intensive)

Are there any thoughts given that much? Anything you would or would not like to see in this type of device? Do you realistically seeing something like this being included in your emergency supplies? How many consecutive days would you want to be able to count on this device providing water?

Any thoughts that you have would be very much appreciated and seriously considered.

Thanks much,
David
I don't get it! One would think if you are going to need a emergency water desalinator you are going to need it in a life raft and not on board the vessel.

I can't see packing a car battery in my ditch bag. How would a person recharge it so you make more water? The 4 x 8 foot solar panel or the gen-set in the ditch bag.

The cost of 30 dollars? You can't buy the car battery for that. There is a reason that there are hand pump water makers on the market.

I don't see the need or the practicality of it.
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