On Wed, 22 Aug 2007 07:40:38 -0500, Vic Smith
wrote:

On Wed, 22 Aug 2007 08:06:46 -0400, "Roger Long"
wrote:


"Larry" wrote

Distilled water has none of these problems. What I can't figure out,
especially on power yachts, is why all that waste engine heat going up
the stacks isn't running engine-room-mounted distillers for fresh water
to drink.

You are spot on with this comment. When I was working at Woods Hole, in the
days before reverse osmosis, they had an engineer who knew how to tweak the
waste heat vacuum distillation units to the point that they got a gallon of
fresh water for every gallon of fuel burned; that's after the fuel had
pushed the ship or made electricity.

Take a look at the power draw for a reverse osmosis unit and then figure out
how much "fresh water" you have to carry in the form of fuel.

It a size/expense issue as much as anything else. Navy boilers
commonly used "economizers" to preheat boiler feed water, but
they were fairly massive units sitting in the stacks.
Evaporators aren't exactly mini me's either.
I think a look at the heat exchangers used to provide heated water
might give some idea on what's involved.
Heck, you already don't have space to use your engine crank.
It sure would be fun to tinker with. For a sailboat I'd probably look
at rain collectors, solar stills, and bottled water first.
I've sometimes wondered why IC engine designers haven't yet come
up with an engine that can't better utilize the BTU's in the fuel
instead of throwing it away via heat. Think of those millions of
engines out there wasting all of that energy from radiators, hoses,
heads and blocks.

The only distillation unit I've seen was one that used the engine to
heat the water also used the engine to drive a vacuum pump to lower
the pressure in the distillation chamber. and I suspect that is how
you would have to do it on a smallish boat. I wasn't primarily
responsible for maintenance on the damned thing but got lumbered with
working on it as I seemed to be the only one at the site that would
admit to understanding its theory of operation. Either I was the only
smart one or the only dumb one (for admitting I understood the beast).
When I left the project water was still a problem at that site.





Bruce in Bangkok
(brucepaigeATgmailDOTcom)