Where do large navy ships, at sea for weeks or months at a time, acquire their fresh water? Do they have huge resevoirs built in, or do they have a way to disstill sea water to make it potable?
IIRC, they have desalinization units aboard.
They have desalinization equipment, which is used to not only produce the drinking water/laundry/cooking water, but in the case of oil and nuclear-powered steam ships, to create the water used in the boilers. (Salt water tends to corrode the piping; in fact the water going into the boilers is as pure or purer than the drinking water.)
Even a respectable size yacht will have its own desalinization unit.
The most common set up on surface ships is to use multiple stage flash-type distilling units. Seawater is heated to approximately 170 degF and then sprayed into a chamber that is under vacuum. A portion of the water flashes into vapor and is collected, the remaining brine is pumped to the next stage and the process repeats. The collected fresh water is then directed to either potable water tanks (and is brominated in route to prevent bacteria growth) or feed water tanks for the boilers/reactors. Prior to being used in the boiler/reactor it is sent through a demineralization unit to further purify it.
My last ship had two units which combined could produce 200,000 gallons of fresh water per day.
The navy is now starting to replace the flash-type units with reverse osmosis units, but I do not have any experience working with those.
MM1(SW) (Retired)
Good answer Grit. The techno-geek part of me loves the fact that they use a low pressure environment to lower the boiling point of the seawater. I got a chance to see the layout of one of these boilers in a Navy repair manual.
BTW: I’ve heard that the largest consumer of fresh water by far on an aircraft carrier is the steam catapult. True or no?
Thanks, one and all for the info. I guess the nuclear subs use the same system?
To be honest I don’t have the carrier experience to give an informed answer.
I was recently assigned to a large amphibious assault ship with Harrier and helicopter squadrons attached. I can tell you that they used an obscene amount of water in corrosion control, the daily washing of the aircraft. We always cringed when the air wing asked us to open the flight deck fresh water riser. If left unchecked they would use a 2-1/2 inch hose, running constantly, and we could watch the level indicators for the storage tanks dropping at a steady rate. It usually took communication at the department head level to keep it under control.
The vacuum not only reduces the boiling point of the water, it also reduces the free oxygen in the freshwater which reduces corrosion.
That’s amazing Grit. I did two westpacs, one on the Constellation and one on the Ranger and don’t remmeber freshwater firehoses being used to wash aircraft like that.
Padeye
I won’t say it was a common occurrence but it did happen too frequently for comfort. As I said it usually took intervention at the Dept. Head level to get it straightened out. These were Marine aircrews/support personnel by the way so maybe they just didn’t understand how critical water conservation was.
On preview of my previous post I have a correction, that would be 1-1/2 inch hoses not 2-1/2 inch. THAT would have definitely used a lot of water :smack: .
There were many times that we caught people using water foolishly, even though there were almost weekly notices in the POD. One that jumps to mind is when our Engineer caught 1st Division using a garden hose to wash down their head (bathroom/shower area for all the non-squids). We had several of them standing “watch” on the evaps for about a week after that. This was on a Knox class frigate where the average temperature in the engineroom hovered around 100degf.