Water is essential for life. Although humans can survive longer without food, we cannot last much more than three days without water. Naval submarine deployments generally last from three to six months, the majority of which submarines spend submerged. Meanwhile, naval surface ships can remain at sea for periods of up to nine months. Moreover, massive cargo ships that journey across the globe (often with relatively slow speeds to minimize fuel consumption and emissions) can be out in open waters for several weeks, depending on their destination.
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Cruise ships, on the other hand, typically spend shorter durations at sea; however, they deal with a high passenger volume, as the average capacity of a cruise ship is about 3,000 passengers, with many accommodating even more. So how do they manage to supply the necessary clean drinking water for both crew and passengers while surrounded by saltwater? Some cruise ships (rubber ducks included) can store water in enormous tanks, with capacities of up to 500,000 gallons, but other vessels lack such extensive storage facilities.
For instance, submarines, which operate with a crew of just 130, have limited storage and utilize every available inch for supplies. Consequently, they cannot feasibly carry the required amount of water. Instead, they rely entirely on onboard desalination and distillation plants that intake seawater, extract the salt, and produce potable water.
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Water as far as the eye can see
Ships and submarines employ several methods to extract salt from seawater, but advanced reverse osmosis is generally the most dependable method. This process uses a pressurized membrane that forces seawater through, filtering out the salt and transforming it into fresh water. It mirrors the technology used in many residential filtration systems, like the Waterdrop Filter reverse osmosis systems. Additionally, it operates more efficiently by substituting the conventional pump-and-motor setup with a mechanism that harnesses energy from the high-pressure discharge water produced during the process. Furthermore, most reverse osmosis units are smaller than those utilized in the distillation method referred to as steam evaporation.
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Steam evaporation often utilizes the heat from the ship’s engines, passing water over them, which causes the water to boil and vaporize. A plastic sheet positioned above the steam collects the purified water, which then runs through a pipe into storage tanks. In other scenarios, a separate distillation apparatus heats seawater, and the resulting desalinated steam condenses into fresh water within a collection tank.
Inside a submarine, this desalination technique can generate up to 40,000 gallons of fresh water per day, while systems aboard surface ships can produce around 100,000 gallons daily. All this water is essential for cooling computers and navigation systems, as well as for drinking, cooking, and personal hygiene.
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