Hi Gardner,
Your questions certainly are not idiotic, but designing an "efficient" water maker is complex - the molecular interactions between air, water and salt at the evaporating surface get into areas of molecular kinetics that are not totally understood by anyone, and building efficient heat exchangers has been making engineers go quietly insane since the steam engine was invented.
However "efficiency" in this context may be overrated - you don't pay for sun light, and making a solar distillation water maker that does work is really simple, no vacuum required. If you haven't already, I suggest you research solar stills online.
Adding the vacuum section reduces the temperature required for a given rate of evaporation but doesn't reduce the energy input required to evaporate a given amount of water. The reduced temperature could reduce the heat loss from the system (and increase efficiency), but by creating the vacuum with a long length of tube you increase the surface area, and hence increase heat losses which may defeat the purpose.
I suspect the added complexity doesn't pay off in increased yield.
Reverse osmosis systems are pretty simple and reliable provided you do the proper maintenance, and as long as the sea water is not polluted or muddy.
If you just want lots of fresh water on board then RO is probably the way to go. If you want a small but reliable supply of water for emergencies/becalmings etc then a solar still with no moving parts is probably good. For most sailors simply carrying enough water is the easiest solution, although not ideally suited to light boats like proas.
To actually answer your questions:
Running a tube up and down a mast over 10m tall would create the vacuum you see in the google link.
A circular mast would almost certainly be strong enough to take a full vacuum (disclaimer - consult your naval architect), but it would be hard to seal around the halyards and wiring that goes up most masts, and I wouldn't think filling the mast with water was a good idea, at anchor or no.
Cheers,
George
On Saturday, 31 October 2015, 14:55, "Rob Denney harryproa@gmail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
On Sat, Oct 31, 2015 at 1:26 PM, Gardner Pomper gardner@networknow.org [harryproa] <harryproa@yahoogroups.com.au> wrote:
Well, I was thinking that you may not have to pump it. You could just haul the tube up the mast with a halyard.I have never had a water maker, but all that I read about them makes them sound like a lot of maintenance and a lot of money. I would love a simpler way to produce fresh water. I just thought that maybe this hadn't been developed because it would only apply to sailboats.
On Friday, October 30, 2015, taladorwood@yahoo.com.au [harryproa] <harryproa@yahoogroups.com.au> wrote:Sure a vacuum will work to boil water and then the salt free condensate can be collected.The question is whether pumping the water 60 feet in the air is more efficient than pumping the water through a filter (reverse osmosis). My money is on pumping the water through a filter is more energy efficient.There are lots of ways of getting fresh water.Talador
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Posted by: George Brettingham-Moore <gbrettin@yahoo.com.au>
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