May 26, 2004

Cruise Training

Water water everywhere, but not a drop to drink.  Since the beginning of people going to sea in ships, water has been a primary concern.  First and foremost, the sailor needs water to drink.  As ships became mechanical, water was needed for the boiler and other vessel operations.  On long sea voyages, it was difficult to carry enough water to live comfortably, and the water that was carried would go bad after long periods of time.  Catching rain and finding islands to replace used water was, in the early days, an important part of the navigators job.

Today, we use evaporator systems to make fresh water out of salt water.  This is very expensive if you just use fuel or electricity to heat the water, but we are able in most cases to use waste heat from the ships main engine to make water.

We use between 30 and 40 tons of fresh water a day on the ship.  This is about 8000 to 10000 gals. per day.  With 244 people on board, this is between 30 and 40 gallons per person per day.  It sounds like a lot to drink, or like a really long shower, but most  of this water is used by the galley, or in the washing machines, or cleaning on deck. 

We have two flash type evaporators on the ship, each capable of producing about 35 tons of water a day.  When we are full, we use one evaporator to keep up, and when we are low, we use both evaporators to catch up.  We can only make water at sea, as the sea water in port has too many pollutants in it and the temperature of the evaporator does not kill bacteria. 

The evaporators us the engine cooling water to turn the salt water into steam, and then use sea water in condenser tubes, to turn the steam back into fresh water.  The condenser reduces the pressure in the system and allows the salt water to flash into steam at a lower temperature than the normal boiling point.  After some of the salt water is boiled and steam removed, the super salty, brine is washed overboard with more salt water and the process starts again. 

Thus, we are now able to go to sea with little or no worries about fresh water to drink.