Having a water-maker onboard a cruising sailboat is becoming more and more popular with long term offshore cruisers, due to the fact that it is much easier to make your own water than having to haul heavy jugs of water back to the boat especially if you want to minimize the cost of having to go into a marina or at the least pick up the anchor, go to the marina fuel pump just to get water, and some countries do charge for water, although not too much. Some boats have ample of water storage capacity but for us it was a matter of choosing between storage for dry goods or installing another two tanks that would not be accessible for cleaning out periodically. We decided to forego the two water tanks for the former.
There are basically three types of water makers that are of any use on an offshore cruising sailboat. 1) DC power,
2) Engine assisted,
3) 110/220 AC volts generator assisted water-makers.
1) The 12 Volts DC powered water-makers come in all shapes and forms, they are very reliable with minimal maintenance and run relatively quite. They do draw a lot of power, for example our first water maker was 12 volts dc and it drew close to 20 amps/hour to make 5 – 6 gallons per hour. Depending on your battery capacity you would have to run the engine while making water or run the engine for a couple of hour after to replenish the batteries. The cost of these units may start at around the $4000 for the smallest model. These would be similar to the Little Wonder at http://www.villagemarine.com, which is now owned by Racor.
Pros: Easy to install; quite; low initial cost; low maintenance cost
Cons: Draws too much power, low production
1b) Another 12 volts system that only draws around 1.4 amps/hour/gallon of water produced or approximately 9 amps/6.3gallons/hour/, is the reciprocating type, similar to Spectra, www.spectrawatermakers.com the drawback is that these machines are more costly, they start at around $5500 and maintenance is more frequent.
Pros: Low power draw; quite; easy to install
Cons: High initial cost; high maintains, low production
2) The next one on the list is 110 – 220 volts AC, several manufacturers including Sea Recovery, HRO, and many more and too numerous to mention. For this type of water-maker you need a generator to suite. If you have already have a generator then this would be the obvious choice in as far as installation and consumption. Dollar wise they do not come cheap, starting in at around $6000 for the cheapest models but cheaper if bought in parts and self installed. The ease of operation makes them also attractive, you do not have to worry about belts slipping, operation is smooth with the 2 hp electric motor running, keeping in mind the generator also has to run so noise level depends on this item. So here is the catch twenty-two, having to have and run a generator, with an output of at least 3.5 KW.
Pros: High production, no battery draw, low maintenance
Cons: High initial cost; fuel consumption (generator); need generator.
3) The next one is the engine driven type. These usually come as modular kits that you will have to assemble them on your own, but they all come with assembly and operating instructions. The biggest draw back for the initial installation is how to mount the high-pressure pump to the engine. The other drawback is that you will have to run the engine to make water but having said that it is good to mention that you will only need to make water every 2 – 3 days depending on the water tank capacity and consumption. Therefore at this point you most likely need to charge the batteries, so running the engine will serve two purposes, make water and charging. The cost for these units starts at around $4000 plus.
Pros: high production; lowest initial cost; no battery draw; low maintenance.
Cons: problematic to install high-pressure pump to main engine.
Therefore we first installed a Village marine 12volts water-maker. In the Caribbean this would only make around 6 gph at best, it drew a lot of power so much so that most of the time we needed to run the engine during or after we filled up our tanks, which hold 65 gallons of water. Therefore after many years of cruising we decided to build our own 20-gph water maker and run it off the engine. Our first choice would have been the 110volt AC but as mentioned earlier we have no space available for the generator. We have the option of increasing capacity to 40 gph if we see fit to do so, for now it has worked fine except for some items that we added or improved upon, we will get to that later.
The reason we chose this application:
1) We had no room to install a diesel generator
2) We need to charge the batteries every other day as we draw a relatively large amount of amps daily.
3) Since most water-makers need to be run often, it would work just right for making water and charging.
Principals of operation: This applies to most marine R.O.’s
Water is pumped through a membrane under high pressure of around 800 psi, controlled by a backpressure regulator valve. Only small molecules can pass through the membrane because it is very tightly woven with special materials. Therefore salt crystals and bacteria are too large to pass and so they are discharged overboard. Only 5% of the seawater being pumped through the membrane turns into potable water, the rest is discharged overboard. You can see from the drawing the flow of the whole system as it applies to our design onboard our vessel. But you can use this drawing and even add or remove parts of it as required.
One can buy everything you need off the shelves from several suppliers. The cost of building our own was $3200 in 2006, which included the high-pressure pump mount that is attached to the engine.
Below you can see the full schematic drawing with all the parts required, some minor fittings might be needed to fit into your configuration. Engine mount bracket is not show as this has to be custom made depending on application you will also need to add the 12 volt magnetic clutch to operate off the engine, Cat Pump PN for clutch is: 34961 to match the 277 pump. I chose the 277 pump because it is a better pump for salt water as it is made of nickel aluminum bronze. You may buy all this from Depco Pumps in Florida, they have a full catalogue and are very helpful, look them up at http://www.depcopump.com/ . plus you can get all the literature on line from them.
High-pressure hoses maybe bought from any hose manufacturer, Aeroquip has one rated at 3000-psi maximum allowable working pressure hose, choose the one with the smallest bend radius as you may need to take it around corners and through some awkward places, I prefer the brass fittings as opposed to the SS fittings, I had failures with the SS fittings after one season in the Caribbean, then it was recommended to me by a water-maker service centre, to use only brass fittings and to stay away from SS because of crevice corrosion. Another thing you should pay attention when installing the hoses is chafe. When the water-maker is running there is a lot of cycling produced by the high-pressure pump therefore areas of hose that are going to be in contact with anything should be protected with rubber hose. To keep pressure drop to a minimum keep the all hose’s diameter as large as possible. I used 3/8” dia hoses for the HP side of the system.
The regular maintenance you need to do with this configuration is to change the 20-micron filter when it gets to dirty and/or the vacuum gauge goes below 5 psi. The 5-micron filter will be clean for a long time but this all depends on where you make water. Change the pump oil as per manufacturer and check belt tension. Pickling instructions also included with the drawing, this only need to be done if you will not be using the water-maker for more than 3 weeks. Three weeks is the maximum interval without making water but only after a fresh water back flash.
Other items to keep in mind when planning to install your own 110 Volt AC or engine driven water-maker are:
- a) You will need a dedicated ¾” seacock
- b) If installation is above the waterline, you will need a booster pump. I would install a booster pump even if the installation were below the water line, as this will give you peace of mind that the HP will not be starved and destroyed.
- c) You will need to make a small control panel, on it mount the flow meter; the pressure gauges, the backpressure regulator and the 3-way valves V1 & V2
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