Daily Journal

03 August, 2005

Delivery of fresh produce from Guaymas Engineers reminiscing of distant ports of call As a courtesy, all ships fly the flag of the country that are visited; in our case, Mexico. The evaporator or water maker onboard

How does a ship provide enough water for the crew?  Following is an explanation on how the ship makes its own water.  It was provided by Ron Wheatley, the Chief Engineer of the R/V New Horizon.  The New Horizon’s Engineering Department operates, repairs, and maintains a distillation plant for the production of fresh water from the sea.

This machinery is similar in principal and construction to distillation plants in industry that produce many products, including distilled water and distilled spirits (alcohol).  It is an older technology that has been used for many decades.

Simply stated, sea water is boiled in a vacuum chamber.  The resulting steam vapor is then condensed on cooling coils and collected for transfer to our fresh water tanks.  The chamber is under a near-perfect vacuum to increase the efficiency of the process, since sea water will boil at a much lower temperature in a vacuum (115-130° F).  The chamber is designed to allow only pure water vapor to enter the collector area, thus preventing sea salt and other contaminants from entering.  As the newly-produced fresh water leaves the collector, it passes through an electrical conductivity sensor to detect chemical impurities.  The New Horizon’s product water is very pure- a typical measurement of total dissolved solids is 1.5 to 2.5 parts per million.  Additionally, before transfer to our tanks, the water is passed through an ultraviolet light chamber for biological disinfection.

Under ideal conditions, the New Horizon’s distillation plant is capable of producing 960 gallons of water every 24 hours.  Several external factors can affect this amount, the greatest of which is the temperature of sea water- colder sea water helps us maintain a better vacuum and therefore, greater efficiency and production.  Current sea water temperatures in the Gulf of California are in the 85 - 92° F range which causes us to produce less.

960 gallons may seem like a fair amount, but with 31 people onboard, we would have less than 31 gallons per day per person.  The galley (kitchen) is the single biggest consumer of water, with the clothes washer and personal showers following.

The R/V New Horizon has a storage capacity of nearly 8600 gallons in three separate tanks.  This provides a margin of safety in the event we have an evaporator failure.

On land, each person in the USA uses between 55–70 gallons of water per day.  Most of that is used up flushing toilets.  We take military showers on the ship.  That means you turn the water off before you soap up and then turn it back on to rinse off.  We’re careful about doing laundry, too.  And our toilets on the ship are flushed with salt water straight from the sea.

Math Problem:

How many gallons of fresh water are produced per hour onboard the New Horizon?

Trivia Tidbit of the Day:

More than half of the world's fish catch comes from the Pacific Ocean.  The northern Pacific is the most productive fishing area in the world.