Fitting a watermaker

 

This is a technical blog post, if your eyes glaze over, it's not you it's me; stop reading and go and do something more interesting.

I recently fitted a Schenker Zen 50 desalinator to our Boréal 47, Vagrant. A fellow Boréal owner asked me to write up the experience, so I thought I may as well do so here. I'm not a professional marine engineer, please treat what follows accordingly.

Choosing a watermaker

Watermakers or "desalinators" are commonly found on cruising yachts. They take electricity and seawater as inputs, force the brine at pressure through a fine membrane and, through the magic of reverse osmosis, produce potable water of a higher purity than most tap water.

Sara and I live on Vagrant full time, rarely have a huge crew, and can survive easily for a couple of weeks at anchor on our 600L water tanks. We wanted to fit a watermaker to give us more freedom. Strangely, we had no problems finding water in Scotland this summer. However, we're heading to sunnier climes where water can be pricey (particularly if you need to put the boat in a marina), might only be available from a restaurant tap and require multiple dinghy trips, or might not be available at all.

There's a large choice of watermakers suitable for yachts. You need to choose between a 12/24V DC or 110V/220V AC pump, and the size/capacity of the machine. Vagrant doesn't have a generator (but does have a LiFePo battery bank, 600W of solar, a 600W hydrogenerator, and a 350W wind generator). I chose a DC pump that we can use without having to run our AC inverter. A DC pump requires larger power cables, but is simpler and slightly more efficient. The capacity choice was driven by cost and available space. There's also a benefit for choosing a smaller capacity: the watermaker is used more regularly, which keeps the membranes cleaner and reduces the need for artificial flushing and cleaning. I was looking for a model that produced somewhere around 50L an hour.

Schenker is an Italian company that makes a range of watermakers. Like many modern watermakers, these use hydraulic energy recovery techniques to maximise the use of the high pressure produced by the pump. One of the reasons I settled on the Schenker range is the reputation of the UK dealer, Mactra Marine. There were two obvious choices from the Schenker range: the Smart 60 and the Zen 50. Jim at Mactra was helpful in steering me towards the Zen 50, and ensuring we had all the right parts for the plumbing. We also purchased the Mactra cleaning loop kit — essentially additional valves and pipes to allow cleaning solution to be pumped through the system.

The pre-installation

When we ordered Vagrant, we specified the watermaker pre-installation option. This cost less than a thousand euros, far cheaper than the factory-fitted watermaker (€13 000 ex VAT at the time, for reference we spent about half of that on this installation). The pre-installation included:

• A salt water inlet and standpipe. All of Vagrant's seacocks are mounted on standpipes above the waterline. This means the boat won't sink if the seacock fails.
• A pipe to the pressurised freshwater, for flushing the watermaker.
• Pipes to our two water tanks, for fresh water (the useful output).
• A tube welded to one of the daggerboard casings for the waste saltwater output. Boréal also uses the casings to vent the gas locker and the diesel tank.

The pre-installation didn't include the waste water pipe, or any electrical wiring.

The pre-installation determined that the water maker should be fitted between the two after cabins. This space is accessible from both sides, through a hinged panel and a removable bookshelf in each cabin.

Connecting the waste water pipe

To reach the daggerboard case, the waste pipe needed to be routed through a channel in the lazarette bulkhead. The channel was full of silicone to make the bulkhead watertight.

The silicone took two hours to pick it out with various tools. My most productive move was to cut the cable ties and yank on the existing cables.

Building the shelves

The Zen 50 system is comprised of various parts including the watermaker itself, an external pair of pumps, a box of electronics, various filters, and a control panel. The water maker and the pump are quite heavy (about 25Kg and 10Kg respectively), and need vibration dampening mounts.

I built a shelf for the watermaker using aluminium angle I bought off the shelf at a local store. The aluminium had various pre-drilled holes which reduced the work. I bolted it to the central hull stringer and a rib. I used a wooden cleat to attach the aft support to the side of the cabinet. The shelf was positioned as low as I could get it, in the aft half of the cabinet for easy access via the hinged panels, but with a few inches behind to allow easy access to the mounting points.

This photograph is looking aft in the boat. It shows the shelf (to the right), and the watermaker temporarily suspended by a block and tackle. In the foreground, you can see the standpipe for the seawater inlet. The yellow paste around the bolts is Duralac, to reduce corrosion.

The watermaker bolts to the shelf using Schenker-supplied brackets with rubber washers to reduce vibration. There's a bit of flex to the shelf, but the watermaker itself provides enough stiffness when it is bolted in the four lower corners.

I built a wooden shelf to mount the pump group. The pump group comes pre-mounted on an aluminium frame, with the pumps on suitable rubber mounts. I decided it would be easier install/remove using two large self-tapping screws into the wooden shelf. 

 

The white box contains the electronics. This was mounted on the side of the pump group. To make it fit, and also so it is more easily accessible, I added a bracket to raise the box above the pump group.

Plumbing

By this stage in the game, I thought I was nearly done. How wrong I was. I had to lay out and plumb ancillary components including:

• An active carbon filter for the fresh water.
• A 50 micro filter and accumulator before the pump group.
• A mesh filter and one-way valve for the saltwater intake.
• Two valves for the cleaning loop.
• Valves to allow the product water to be diverted to a sampling pipe or to one of the tanks.

This photograph shows, tracing the pipework from left to right, the active carbon filter on the fresh water input, an electovalve, the one-way valve with sea water coming up from the bottom via the mesh filter, the input diverter valve for the cleaning loop, and the input to the pump group. You can also see the output diverter valve for the cleaning loop. I've used standard water hose connectors to allow cleaning loop pipes to be connected as required. 

Here's the 5 micron filter and accumulator, mounted on a backing board above the watermaker. Also note the steering cables (in the blue conduit) and engine control cables. I was very careful not to impede these. 

And finally, the output plumbing. It can be diverted to a pipe for sampling to check the water is good, or to one of the two water tanks. You can see the resulting access to the watermaker through the hinged panels is very good.

The plumbing required rubber reinforced hose for the high-pressure connections. This was one of the few things not included in the kit, but I managed to source some at the very-well stocked Sopromar chandlery in Lagos. The downside was the Sopromar price of €48 a metre. Sopromar also did well by selling quality hose clamps one at time. With every connection double-clamped, the system ate these up at an incredible rate.

Wiring

The wiring involved running 16mm² cables from the house battery switch to the pump group, a data cable for the control panel, and a cable to the electro valve.

The 16mm² cable was connected to the house battery switch with a fuse holder and a suitable mega fuse. There wasn't enough room in the control box to directly connect 16mm² cables (my only real criticism of the design), so I had to step down to 10mm² cable for the last foot or so. I abused another fuse holder to provide suitable terminals for the connections. Running cables was as fun as it always is.

I installed the control panel in the centreboard cupboard. 

The mistakes

Inevitably, I learned a few lessons.

Lesson one: when the manual says "don't exceed with the torque", it means it. I managed to shear the hose barb for the seawater output, leaving the other end in the watermaker. Fortunately our friend Trevor had a set of larger screw extractors. The correct torque for these PVC fittings is not much more than hand-tight. 

Lesson two: don't drive screws into an aluminium frame using a rattle gun.

Lesson three: read the effing manual. When we first tested the watermaker, all the lights came on, the initial flushing cycle worked fine, but it refused to come up to pressure and produce water. I was half-way through an email to Jim at Mactra when I double-checked the manual and had to dope-slap myself: … the non-return valve has to be installed under the seawater level… Solving this required a bit of rework to the pipe layout (the pictures above are the final, working version).