Tuesday, August 23, 2011

Watermakers 101

Last year I started researching reverse-osmosis watermakers.  Since we plan to spend a lot of time in the Sea of Cortez and considering that my wife isn't really thrilled about salt-water showers I decided I'd better put one on the boat. 

However, buying one of these units for a small boat can put a big dent in the cruising kitty.  The concept is pretty straight-forward and most parts can be purchased online or at your local hardware store so why not  build it yourself?  With an internet connection and a little time you can dig up everything you need to know to put a system together. 

Essentially, you use a high-pressure pump to push salt water through a reverse-osmosis membrane.  Most of the water is discarded as brine while some is pushed through the membrane as fresh water.  I was looking primarily for a system that I could run every 2-3 days which would produce enough water for two people and use a minimal amount of battery power to operate. 

There are essentially two ways to go:  AC-powered or DC-powered.  Both require a significant about of power to operate.  AC systems produce a lot of water and can be powered by a generator and high-output inverter or run directly off the main diesel engine through an additional pulley.  For larger boats with an engine room you can put together a very modular AC system for a few thousand dollars. 

On Jean Marie space is a luxury we simply don't have.  So, I decided to go with a DC solution and created a spreadsheet comparing current DC-powered watermakers in terms of amps per gallons (that is, the number of amps required to produce one gallon of fresh water).  In this comparison Spectra Watermakers with their patented Clark pump came out well ahead.  Two problems: (1) Spectra watermakers are very expensive and (2) they don't sell the Clark pump separately. 

I went back and forth on the pros and cons of building versus buying until the annual boat show in Oakland.  After about twenty minutes with the sales rep I pulled the trigger on a new Spectra Cape Horn.  Their boat show price was just too good to pass up. 

The Cape Horn is perfect for our needs, producing up to 14 gallons per hour at 18 amps.  It comes with two feed pumps to the Clark pump and has the option of running on one pump or both as needed.  Installation was challenging due to space constraints but, after some effort, I got the system up and running. 

I was so impressed with the product and the company that I signed up for their roving rep program.  Roving reps are cruisers who are trained and authorized to provide maintenance and support for Spectra watermakers.  I spent a week at their office in San Rafael learning all about watermaker design and the Clark pump and am now an authorized Spectra Roving Rep.  I have no idea what that means for us yet.
Questions or comments? We'd like to hear from you. Click the link below to respond.