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There are two things the women in my crew insist on: Lots of fresh water and hair dryers. Oh, yes, and air conditioning but that's another issue.
RUTU can carry 150 gallons of water but because of the shallow canoe hull there is little room in the bilge for tanks. There are two 50 gallon tanks under the aft bearths and another up forward on the port side but carrying 1,000 pounds of water that far off the center of gravity can have some detrimental effects on sailing ability and trim. I will cover the hair dryer aspect in the electrical system but the fresh water requirement was a perfect excuse to dabble in a mechanicaly oriented do-it-yourselfer's delight. Watermakers! In the original plan a watermaker was near the bottom of the list because they cost so much and eat a lot of electricity. As I began setting the tanks however I started thinking about them again.
The watermaker manufacturers want you to think they are complex and expensive to make but with a little research one can be built for about 20% of the typical retail prices. About 20 years ago watermakers were rocket science but not anymore. All of the basic components are off the shelf standard parts and the membrane makers offer free software to help with the design.
What I came up with is an 800 GPD system with automatic TDS testing and automatic flush and backwash. A system with this capacity and features would retail for about $8,000 from most of the big name manufacturers. I built it for a little more than $2,000 and could have done it for a lot less had I laid out my piping a little more carefully. 2
The Design Process
The first thing I wanted to do is make enough water during the planned one hour per day of charging time to provide for a very generous level of consumption. That means 30 to 35 gallons an hour, .5 gallons a minute or a system capacity of 800 gallons per day. Watermakers convert about 15% of the flow to fresh water so I would need to supply 3.5 gallons per minute and the pressure required to desalinate seawater is about 800 pis. I found the formula for calculating the horsepower for pressure pumps: (GPM*PSI)/1460. I would need about 2 HP to drive the pump. 12VDC pumps don't come much higher than 1HP so the pump would have to be driven either by the engine or a 120VAC motor from the inverter. That ment that the inverter would draw a large percentage of the alternator output that I had carefully balanced to the battery bank for one hour charge sessions and leaves engine drive as the most practical solution.
The Pump
The first job was finding a high pressure pump. Several manufacturers make pumps suitable for watermakers. Two of the most popular are Cat and General. Cat is generally recognized as the best but they are expensive. There are also two different types of high pressure pumps. Piston and plunger pumps. I have been told that plunger pumps are better for watermakers but don't ask me why. The next thing to consider was the material. Seawater under high pressure is very corrosive. Wetted parts must be bronze or stainless steel. There is some controversy here. Many people are afraid of stainless because of crevase corrosion but stainless wears better in pump applications than bronze. The thing is crevase corrosion happens when stainless is in contact with oxygen depleted seawater. If the watermaker is opperated properly; flushed with fresh water after use and pickled for long term storage the pump will never see stagnant seawater so, while bronze will serve well, stainless is the better choice. Unfortunately all stainless pumps cost a lot more than bronze.
Luckily for me I found the perfect pump on eBay. A brand new cat 241 stainless 3.6 GPM plunger pump. The price was unbelievably low because it was attatched to a 100 gallon tank and a big Baldor motor. It cost almost as much to ship from Seattle to macon as I paid for it but after selling off the tank and motor I have about 20% of the retail price of a new Cat 241. There was also a stainless accumulator on the pump when it arrived that smooths out the flow. Not absolutely necessary but nice to have so I added it to the system. I was worried about finding an electric clutch for the pump but found that CAT makes a clutch pulley assembly made just for the 3-frame pump.
 I had already fabricated the mount for the big alternator to be driven off the front end of the engine (see Electrical System) so it was a fairly simple matter to add another mount on the other side for the pump. The belts and pulley ratios were the big question. THere were a number of factors that needed to be balanced. The pump can operate between 1,000 and 1725 RPM but the alternator output curve starts to level out at about 4,000 RPM. For reliable long term service I am using double "AX" belts on the alternator with a 3.75" pulley. The CAT electric clutch pulley is 7". To keep both the alternator and the pump happy at the same engine RPM would require two different pitch diameters on the drive pulley. I made up a little Excel spredsheet and came up with a reasonable compromise of 6" for the pump and 6.9" for the alternator. At an engine speed of 2,200 RPM the pump would be turning at its maximum 1725 RPM and the alternator would be at 4,300 RPM. On the low end, at 1,200 engine RPM the pump would still be putting out 2.2 GPM, enough to keep the membranes happy and at the maximum 3,800 engine RPM the alternator would not exceed its maximum of 8,000 RPM. There was still the problem of keeping the pump form over reving but I will cover that below in the control section.
The next problem was finding a 3 groove pulley with two different pitch diameters. There ain't no such animal. Even worse, a 7" 3 grove cast iron pulley is a lot of mass to be spinning on the front of the engine. Aluminum would be a much better solution so I decided to turn my own. I found a chunk of 7 1/2" round aluminul at Speedy Metals and, suffering a small brain freeze, proceeded to mount it in my lathe only to realize that while it will swing 10" over the ways it would only clear 6" over the cross slide! A nice simple turning job suddenly bacame a major exercise in imaginative machining. I suppose I could have taken it to a machine shop but where is the fun in that?. .
The Pressure Vessels and Membranes
There are three major manufacturers of RO membranes. All three offer freeware programs on their web sites to help design your system. Osmonics has WinFlows, Saehan has CSMPro and Dow Filmtec has ROSA. I have found ROSA to be the easiest to use and most powerful. Dow FIlmtec is also the major player here in the US. All three make standard 2.5" size membranes in 20" and 40" lengths. They all contain between 27 and 28 sq. ft. of membrane wrapped in a spiral around a central collection tube and have exactly the same dimensions so they are pretty well interchangable. Performance on all three is very close but there are some variations.
When you consider the cost of the plumbing and everything up to the membranes, the difference in cost between a 20" membrane and a 40" membrane is rather small so it makes more sense to go for as much product as you have room for. The 20" membrane only makes sense if you are absolutely out of room and that is very rare. There is always some place you can cram a pressure vessel and once installed you don't need to access it very often. .
 I chose the Filmtec SW30-2540 membranes. Partly because the ROSA program was easiest to use but also because it has slightly better performance than the others. The SW30-2540 requires a minimum of 1 GPM to maintain proper scouring and can produce up to about 30 GPH (700 GPD). The maximum recovery rate is 12% so the supply range can be between 1 and about 4 GPM but the scouring action is best with with close to the maximum flow. Unless the pump capacity is higher than the maximum flow rate it is best to plumb the pressure vessels in series. The CAT 241 produces 3.5 GPM so the logical arangement for my system was a pair of 2540s in series. The recovery rate in the second vessel will be slightly lower because salinity of the brine is slightly higher but the higher flow rate improves total production and maintains the scouring.
Those familiar white tubes with black end fittings are made by A&M Composites and are used by most RO brands. A&M does not sell direct so look around. Prices varry considerably. All the fittings are 1/4"NPT. The seawater input is at one end and the product and brine discharge is at the other. You can buy special mounting brackets for the pressure vessles but I just made a couple from some scrap Starboard and a hole saw. The assembly mounts under the side deck in the aft head in otherwise wasted space.
Pressure Regulator
 This one almost caused me to abandon the project. An electricly driven pump runs at a constant flow rate so the pressure can be regulated with a simple needle valve. Many of the better known watermakers control system pressure this way. The output of my engine driven pump will vary from 2 to 3.6 GPM so a needle valve set for one flow rate will not work. A better way is with a back pressure regulator. When I first started looking for stainless back pressure regulators I was shocked by the prices. Some were over $1,000 and none were less than $500. Then I discovered that a Bypass regulator is the same thing just plumbed slightly different. CAT sells a stainless regulator model # 7070 for $235.00. Normaly this regulator is mounted at the pump of a pressure washer to protect the pump when the washer nozzels are shut off but by mounting it at the far end of the pressure vessels pressure is maintained throughout the system. Real back pressure regulators are specially designed to prevent cycling when fluid is drawn off by other devices on the system but this is not the case with watermakers as all the brine must flow through the regulator.
Prefilters
 I took a hard look at those expensive "marine" filter vessels and then looked at the domestic ones at Lowes. For the life of me I can't figure out why one cost $150 and the other cost $20. This is not rocket science. It is just a plastic container. The filter sizes are standard so you can load them with any quality or mesh filter you want. I did have to bend up and drill a strip of stainless sheet for a mounting bracket but that was about all. In this assembly from left to right is a Y-valve for pickling and a 10 micron followed by a 5 micron filter.At the top of the cross fitting is an SCM digital vacuum guage/switch. It is set for 5" of vacuum and turns on a warning light on the panel when the filters need changing. Below is a check valve and solenoid leading to the pressureized house supply. Not shown is a carbon filter that removes any residual chlorine from the water being used to flush the membranes. The output from the right side of the cross fitting leads to the high pressure pump.
Not shown is the Water Puppy boost pump that is feed from the sea chest that supplies seawater to all onboard systems.
Plumbing
Reverse Osmosis is all about pressure so sizing the plumbing must be done with some care. IF the lines are to small the pressure drop reduces efficiency and cuts the product output. This is particularly important with engine driven pumps where runs from the pump to the membranes can be long. Hoses also have to be protected and reisitant to abrasion. An 800 PSI spray of seawater can cause quite a mess. I had to run through the engine compartment and bilge, under the aft head sole and up to the membranes so I chose 1/2" stainless braided hose rated at 2800 PSI. Not cheap but close to bullet proof and caused only about 2 PSI of pressure drop. There is a similar problem on the product side of the membrane. The planned output of 40 GPH is 3 quarts a minute. Pushing that much water through 1/4" tubing and many fittings produces a considerable back pressure. Each pound of back pressure in the product plumbing increases the amount of pressure the pump must deliver the seawater at. Some things I could not avoid. The pressure vessle output, flow meter and selector valve were all 1/4" but I increased the tubing to 3/8 to minimize the back pressure.
Fittings and high pressure hose can add up to a significant part of the costs. I haunted Ebay for stainless Swagelock 1/4" NPT to 3/8" tube fittings, Tees, three way valves and some others but had to resort to McMaster for the braided high pressure hose, end fittings. I also found some nice plastic quick connects for the product tubing. The Yor-Lok fitting s at McMaster are considerably cheaper than Swagelocks and seem to be interchangable.
The Control Panel
The control panel has to hold a lot of stuff. Besides the various switches, flow meters and pressure regulator, I added a Hanna TDS meter, solenoid valves to automate the basic functions and a manual test outlet. It will be mounted in the aft head in front of the membranes. I wanted it to look "professional" and explored having a laminated plastic face engraved to cover the aluminum mounting plate. I took a design to a sign shop and was not happy with the price I got considering the amount of work I would still have to do making the backing plate. Then I discovered Front Panel Express on the web. A DIYer dream! These folks have a freeware program that you can download, design your panel, specify the holes, material, colors and text, price it out instantly and send the file back to their shop in Seattle. Ten days later I had a professionally made gold annodized aluminum panel.
 Is that cool or what??
Because the pump speed can vay I needed to monitor both the product and the brine output so there are two Dwyer flow meters. The brine meter reads to 5 GPM and the product meter reads to 60 GPH. Although not by design, the product scale is exactly 1/5 of the brine scale so that when the indicators are even the recovery rate is the optimum 20%. That makes it easier to adjust the pressure for any flow rate. This brings up one disadvantage of engine driven systems. Because the pump output can vary from 2 GPM to 3.6 GPM the pressure needs to be adjusted between about 675 PSI and 820 PSI to maintain the proper recovery rate. The lower pressure also raises TDS about 60 PPM so it will be best to run the engine close to 2,000 RPM when ever possible. If it will be run below 1800 RPM for any length of time the pressure will have to be adjusted down to maintain the recovery rate at 20%.
The brown box is a Hanna TDS meter. I found it on an aquarium supply web site of all places for$130. I called Hanna tec support to see if it would be suitable for an RO system. It seems that Hanna TDS meters are used in several well known RO systems. The meter's output switch controls a 3-way solenoid that diverts the product to waste until the TDS gets below 250 ppm. Just in case there is a manual override valve with a test spigot.
Operation is very simple. The control buttons are wired to some very simple logic curcuits that control relays. The Green button engages the pump clutch if the engine RPM is between 1200 and 2200. The clutch remaine ingaged until the red button is pressed, the engine RPM or pressure get out of the correct range. The yellow button opens a solenoid to bypass the back pressure regulator and another that changes the feed water from seawater to fresh anf flushes the membranes for about a minute. Then it closes the output solenoid so that the pressure then backwashes the pre-filters for another 20 seconds.
 The small light below Flush is wired to a vacuum switch that closes if the pump supply line pressure drops indicating that the pre-filters need cleaning.
The back side of the panel requires a little explanation. Brine from the membranes enters the controp circuit through the cross fitting at the bottom. In this picture a black cap protects the inlet. To the right is the pressure guage and to the left is the pressure regulator. Above is the pressure relief solenoid used in flushing the membranes. From the pressure regulator the brine passes through the flow meter and then through the white hose to the overboard discharge fitting at the bottom center.
The product water enters through the orange and white quick connect at the lower right and passes over the TDS sensor before entering the product flow meter. On leaving the flow meter there is a 3-way valve for manual testing and a 3-way solenoid. This solenoid discharges the product overboard until the TDS meter (the white box) detects that the salt content is below 200 ppm. When water quality is acceptable, the solenoid opens and the product water is sent to the tank selector manifold.
The overall layout is a bit messier than would have wanted but I had to make some last minute changes in the solenoids after I haf ordered the front panel.
The Electronics
All that logic sounds expensive and intimidating but it is actually just 3 simple circuits that I found on the web and some standard 12VDC automotive relays. Total cost about $30. The on/off function is a DPDT relay with one of the poles wired back to the coil through an interlock circuit. When the on button is pressed the coil is energized. As long as the interlock circuit is complete the coil remains energized. The interlock circuit consist of the normally closed off button, the engine speed sensor to prevent over reving, a Hobbs oil pressure switch and a system pressure switch. The engine speed sensor was the next problem.
The pump cannot be run much faster than 1750 RPM and the membranes should not be operated below 2 GPM. That measn that the system cannot be running when the engine RPM is below 1200 or above 2100. It would be very easy for someone to goose the engine without turning off the watermaker so some method of protecting the system was required. RPM switches are common in the hot rod world for things like shift indicators and Nitrous Oxide boosters and cost under $75. Unfortunately they get the speed signal from the ignition. No help with a diesel. Industrial units cost upwards of $200. Fortunately I got a look at the innards of an industrial unit before planking out any money. It was just a LM2917 frequency to voltage converter and a LM339 voltage comparator with some trimmer pots and capacitors. THese are standard automotive chips that work fine on battery voltages. A little research on the web revealed the circuitry and I bought all the components for less than $6.00. The project was completed when I found an Omron magnetic proximity sensor on eBay for another $8. It senses the bolt holes in the Aquadrive adaptor plate.
The automatic flush/backwash circuit was another challange that turned out to be fairly simple. It is just a 555 timer chip and a couple of transistors with a couple of trimmer pots to adjust the delays. A starting pulse from the push button starts the timer which opens the pressure bypass and fresh water supply solenoids and turns on the high pressure pump. After about 40 seconds of flushing the membranes with fresh water the timer shuts down turning off the high pressure pump and closing the pressure bypass solenoid. A 1N4002 and a 2N2222 transistor set up as a common emmitter delayed off curcuit keeps the house pressure solenoid open for another 20 seconds to back flush the prefilters. The flushing consumes about 3 gallons of fresh water
The most expensive part was the printed circuit board. I have made my own in the past but professionally made boards are always much better so I laid out the board using Eagle PCB design shareware and combined it with a group of boards that I was building for my smart lighting control system. The set of 8 boards was then converted to Gerber files and sent to a prototype board maker. Two weeks and $100 later I simply bandsawed the boards apart and started soldering.
For the more electronically obsessed, you can check out the circuit diagrams and PCB layouts here.
The Layout
Below is a schematic of the watermaker layout. You will notice that several components require 120VAC. Hanna strongly recommended that the TDS meter be AC powered to avoid any problems from fluxuating battery voltages. Also the high pressure solenoid is not available in 12VDC. The flush solenoid could have been 12VDC but the AC versions are available on ebay for 10% of the retail price.
YOu will also notice the remote panel. As the controls are all low voltage momentary push buttons with simple wiring, it was a natural progression to add a way to turn the system on from the cockpit. I mean, once you have poured your morning cup of coffee, stared teh engine for the morning charging session and settled into the cockpit to enjoy the sunrise, why go below just to start the water maker? Also, shutting down is a lot easier. Just hit stop and then flush a minute or so before killing the engine. OK, so I am a cockpit potato in the mornings.
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