Building a watermaker

A watermaker is an expensive piece of gear for a voyaging sailboat. By no means do you need one to take off into the world on your sailboat, but in my case, it is becoming more and more of a necessity. The more time I spend away from the dock in remote areas, the more independent I must become. I’m also getting older. Hauling 5 gallon jugs of water to the dinghy from a river or some far off spigot, rowing them out to Splendid, and lifting them over my head and pouring them into the tank on a regular basis is getting old. I’ve been doing it for a decade and this chapter in my life is finally coming to an end.

But a watermaker just doesn’t make our life easier, it makes it healthier. Drinking from a foreign water source demands a bit of trust. In my case I refuse to add chlorine bleach to my drinking water. So I’m finally doing it, building a watermaker, we’ll have endless clean drinking water soon.

About a year ago my buddy Roger traded me this old Sea Recovery 110v watermaker for a few days work. It was installed on a boat in 1981 (32 years old) and was not of much use to him after he purchased the boat.

I wanted it for the hi-pressure pump (Cat pump) seen below which was driven by a 110v electric motor. Cat pumps are incredibly well built and should last a lifetime. They are expensive (around $2,500 new) however rebuild kits are available from the manufacturer.

The cat pump is the heart and soul of many watermaker systems and I plan to have mine in service for many years.

I never planned to use the electric bits of the watermaker as you don’t need them. What you need is a lift pump on the low-pressure side (before the cat pump) if the system is installed above the water line. You also need to pre-filter your sea water through a sea strainer and filter it down to 5 microns. Once you have clean sea water you will run it through a hi-pressure pump capable of pumping the sea water at 1000 psi and run it to the pressure vessel which houses the reverse-osmosis membrane.

The pressure vessel has 3 ports. hi-pressure sea water in, hi-pressure sea water out, and product water (drinking water).

Your hi-pressure sea water out will go to a pressure regulating needle valve, and then overboard. All in all it’s a pretty simple system.

Powering the hi-pressure pump is another consideration. I don’t like 12v watermakers as they don’t produce enough water, need to be powered (charged) by the main engine or generator anyway (not cost effective), and are harder on the membranes.

I prefer engine driven systems as they are capable of making large amounts of water quickly. I fitted my cat pump with a 12v clutch so I can engage the pump with a push of a button. I had to build a platform in the engine room next to the engine so I could run a belt to it.

As you can see from the picture I have it mounted on a platform where I can wrench it to increase the distance between the pump pulley, and the engine pulley, therefor tightening the belt.

The biggest issue with engine driven systems is the mounting of the pump. Most want to mount the pump on the main engine so it vibrates in tune with the engine. I’ve decided to mount it off the engine for numerous reasons. Primarily being, if it leeks I don’t want it leaking on my engine. Secondly I wanted to mount it next to the 110v electric motor so I could choose to power it by 110v (generator), or the main engine simply by changing the belt. It’s kind of hard to see but I’ve fabricated the mount with a closed-cell foam core. The top platform is bolted to the bottom platform and foam is sandwiched between the two. It’s my hope that this design will absorb the engine vibration and save the wear on the pump, we’ll see?

I also purchased a new pressure vessel and membrane. The pressure vessel is Spectra part number FT-PV-SPSW25X40 ($570.00), and the membrane is made by Dow ($187.50) . The pressure vessel is made of fiberglass and capable of working at 1000 psi. I chose to go with a fiberglass pressure vessel as stainless and aluminum ones don’t last as long. If they start to corrode on the inside they will quickly knacker your expensive membrane. Fiberglass is the preferred material.

I got to tinkering with the old Sea Recovery controller and electric bits. The electric end consists of a hi-pressure safety switch, a low-pressure safety switch, a salinity tester, and an automatic 3-way diverter valve that diverts the product water to your tank after the salinity probe deems the water salt-free. I got my multi-meter out, tested everything, and it all worked just fine.

Man I wish electronics were build like they were in the 70’s & early 80’s. The inside of the controller is a burly piece of circuit-board with hand soldering, and substantial parts built to last a life-time. So I decided to install it all in the galley.

The only hurdle I had with using the old controller is the whole point of it is to protect your system from pressure too high or low. It was designed to turn off the 110v electric motor in case of potential damage. Well I found a work-around. I purchased a 10 amp AC-DC converter on eBay and wired it into the system. Now if the hi or low pressure switches engage, the controller will discontinue supplying the 12v clutch with power and save the system from damage. I live restoring old stuff!

I have to make a trip to Panama city to buy a new hi-pressure gauge and some plumbing. But upon my return I should be making around 25 gallons of fresh water an hour. When I have some extra cash I’m going to plumb another membrane into the system increasing production to about 40 GPH.

I wont have to be so hard on my guests about conserving water now.

Speaking of which I’m bidding a bunch of charters these days and I’d like to say a few things.

You wont find much information online about the San Blas Islands as nobody publicizes them. Panama doesn’t make tourist money here and the Kuna Indians don’t know about advertising (yet). This is what makes it so special here, you can really get away from it all!

I must also say visiting Panama and the San Blas islands is completely safe, not to mention the most beautiful place I’ve ever seen.

Well that’s it for today guys. I need to get back to boat work!

Peace, Love, and Coconuts!

– alex

Published in Alex Dorsey