Are you AC, DC or belt?
by Bobby Schenk
Since the revolutionary development of the first Reverse Osmosis membranes by DuPont some 40 years ago,
millions of tons of potable water have been produced from salt water by RO desalination plants. They have saved lives, made the desert fertile and even produce the water necessary for the ice rink to get the Saudi royalty skating.
Some of the smaller units have reached such a degree of reliability and affordability that more and more yacht owners cruising the seven seas consider a watermaker the best option to provide themselves with the priceless commodity 'fresh water'.
All watermakers available for yachts follow the same reverse osmosis principle, where highly pressurized seawater flows along a rolled up, semi permeable membrane, which allows a certain amount of freshwater to pass. This freshwater is collected and directed into the tanks, while the rest of the seawater flows back into the sea as brine.
The first question to ask before the installation of a watermaker should be:
How do I drive my high-pressure pump? AC, DC or belt?
AC driven systems make perfect sense if you run a generator regularly. Various manufacturers offer a multitude of models. Be aware that electronics in combination with watermakers have a tendency to create problems, which normally cannot be fixed without spending a lot of money and the help of a manufacturer approved service station. One drop of saltwater in the wrong place is all it needs to get you carrying jerry cans again.
A non-computerized version costs less to begin with and is much more reliable.
Main engine belt driven systems can produce huge amounts of fresh water even on a smaller yacht without a generator and without putting any extra strain on your battery system. Their only disadvantage is that they are not so easy to install and sometimes there is just not enough space around the engine to accommodate the really quite small high pressure pump. Once in place though they are pure joy, especially if they are equipped with an automatic regulating valve. This will grant a constant pressure regardless of the engine RPMs, thus adding safety, ease of operation and longevity.
12 or 24 Volt DC systems are the most versatile, as batteries can be charged by alternators, generators, solar panels, wind-, water- or shaft generators or shore power. There are two versions on the market:
1) systems with energy-recovery, its commonly known representatives being: Schenker, Katadyn/Power Survivor (PUR), Spectra, Livol and
2) systems without energy recovery using fast single plunger pumps or slow and cool running triplex plunger pumps like the ECHOTec.
Both approaches have their advantages.
Some Energy-Recovery systems use only 60% of the amps to produce a given amount of water, therefore putting less strain on your energy budget. The Venture 200 for example, claiming to be the most energy efficient watermaker in the world, produces up to 8 gallons of freshwater using 10 Amps @ 12 Volt, provided it is used in warm waters. A breakthrough compared to older designs like the Katadyn/PUR.
So why buy a system without energy-recovery and use more Amps? Lots of reasons again! Modular versions like the ECHOTec cost some $2,000.00 less to start with. They are also easier to install, cheaper to maintain, more robust and longer lasting which reflects in a longer warranty period. Depending on how many hours a day you run them, a small solar panel or a higher output alternator takes care of the difference in consumption.
Once you have decided on the power supply, the number of showers and washing machines on board has to be discussed with admiral and crew. Typically AC and belt driven units produce between 20 to 60 gallons per hour, while 12 Volt units are limited at about 13 gallons per hour.
Make sure that all wetted metal components of your watermaker of choice including the high pressure pump are made of high quality stainless steel and you should be good to go and enjoy sailing wherever safe water supply is an issue.
Anyway, the times are over where a watermaker was a pure survival instrument,
luxury is on!