Fir was never fit with water filters or a watermaker because she had enough tanks to last for the length of her Coast Guard assignments.   She returned to base often where she had access to an unlimited supply of clean, fresh water.  With a crew of 75, water was continually rotating through the system, Regular turnover eliminated the development bacteria and algae in the tanks.

Our plan to repurpose Fir will include little time in a marina.  The ability to make clean, fresh water is mandatory.  We will keep our fresh water tanks full for ballast.  However, stored water will not remain fresh without treatment. 

Initial Treatment

It is critical that we begin with water that is relatively clean. Water with excess debris will clog our membranes and add to the wear on pumps.  Under initial water filtration see how we purpose to manage this issue.  

A large watermaker from Dometic as presented at the 2017 Ft. Lauderdale Boat Show.  Smaller systems in the foreground.

A large watermaker from Dometic as presented at the 2017 Ft. Lauderdale Boat Show.  Smaller systems in the foreground.


Most desalination plants are based on reverse osmosis ("RO").  Reverse osmosis s a technology that is used to remove a large majority of contaminants from water by pushing the water under pressure through a semi-permeable membrane.  Salt water, under high pressure (think 800 psi), is presented on one side of a semi-permeable membrane. The water molecules are small enough to pass through the membrane. yet salt, and just about everything else is too large.  About 10% of the water taken into a watermaker is converted to clean, fresh water. The balance is salt water and minerals expelled from the system as waste. The result is near pure water.

RO systems require regular maintenance and cleaning that begins with a backflush system after each use.  The backwash passes fresh water along the saltwater side of the membrane and flushes contaminants. "Pickling" is a slang term used when preparing a system for inactivity.  It refers to filling the system with a biocide, like sodium metabisulfite, to breakdown small organic compounds wedged in the membrane while preventing other organics from growing.

We have a few requirements of our system  First, since Fir has plenty of room, we want the watermaker fully assembled by the manufacturer, and built into a frame.  In contrast, modular systems on smaller boats often have components spread out and connected by hoses due to space constraints.  Second, we prefer an automated system where the unit initiates a fresh water flush after each use.  This will keep the membrane in the best condition.  Finally, in an effort to reduce crew requirements. we insist on remote display and controls for communicating with the Wheelhouse.  

We are looking for a system that produces 3,500 to 4,000 gallons per day. 

FCI's Atlas System. Picture from their website.

FCI's Atlas System. Picture from their website.


RO systems are so effective that they remove nearly everything, including beneficial minerals from water.  One problem in storing RO water is that it absorbs carbon dioxide from the surrounding air.  As a result, RO water can quickly become acidic with a Ph between 5.5 and 6.5.  With our tanks are made from mild steel,  storing acidic water would be a corrosive disaster.

The solution is a mineralizing filter.  This is a simple filter filled with crushed marble as media.  When acidic water is passed over the marble, minerals are released into the water, and the Ph is made neutral.  This process stabilizes the water, reducing Ph fluctuation.  


The Fir's domestic water system is split between the Engine Room and the Auxiliary Engine Room. After some study, we have decided to maintain this general arrangement.  The watermaker and filtration systems will go in the Auxiliary Engine Room.  The domestic hot water system and domestic water manifold will go on the starboard side of the Engine Room.  

To accommodate the new systems, we will have to remove an old sink, water fountain, and phone booth from the Auxiliary Engine Room. In its place, we will build a sled to house the domestic water system.  The sled will include our watermaker, initial filtration and pumps.


The Ft. Lauderdale International Boat Show had a dozen or more vendors selling watermakers. Most of these companies assemble parts made by others.  Only a few companies actually manufacture/design watermakers. 

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We have narrowed our selection to FCI and Dometic.  Both companies produce large, mission critical water makers as well as smaller, lighter systems designed for yachts. Our demand is relatively low. yet we have a greater need for reliability.  Consequently, we want a watermaker built from heavy duty components usually associated with larger systems.  Key elements include a high pressure pump, and connecting lines to various components. Dometic is a large company, with exceptional products that provide solutions in multiple areas.  FCI is a smaller company, with an equally impressive product, compact in size, but great in production.  


Check back to see how we made the final decision.