Watermakers

Tips on using and winterizing
Having chilled (and fresh) water at one’s disposal is a dream for long distance cruising and a lot less weight on board for speed freaks. Although many multihulls, including in charter fleets, are equipped with a watermaker on board, for some, this hi-tech equipment may seem complex to use. Here we explain how to use one (properly) and how to maintain it. And since you are not always on board, we have included a winterization procedure for you.
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Olivier Barret
Publié le 01/12/2022
Par Olivier Barret
Numéro : 187
Parution : Jan. / Feb. 2023
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Multihulls World #187
Most watermakers work on the principle of reverse osmosis. Put simply, the sea water is sucked in by a low-pressure pump and passes through a 40-micron pre-filter which blocks the bigger particles. It then passes through a 5-micron filter which retains the smaller impurities. A high-pressure pump then sends the seawater through a tube containing semi-permeable membranes
The pressurized seawater (above osmotic pressure: 30 bar/435 psi in the Atlantic and 35 bar/500 psi in the Mediterranean) is forced to pass through these membranes, which only allow water molecules to pass through while retaining the molecules of salt and other minerals. At the end of the process, one liter of fresh water is obtained for every 10 liters of salt water absorbed, the excess brine water being pumped back into the sea. As the low-pressure seawater pump has to operate continuously, it is advisable to ensure the level of charge of the batteries, and preferably to operate the watermaker while recharging under engine or when connected to shore power. Nevertheless, there is a constraint linked mainly to the frequency of use. Composite membranes are vulnerable to fouling. It is therefore advisable to run the watermaker on a regular basis (even for short periods of time) in order not to let seawater stagnate in the system. If this happens, bacteria can flourish and eventually clog the pores of the membranes. After a shutdown of less than three days in tropical waters, or one week in temperate waters, the unit can be restarted straight away. After that and up to one or two months, depending on the sailing area, you’ll need to rinse the unit with water from the tanks in order to evacuate any residual seawater and leave only fresh water in the watermaker.
However, after this time period, in addition to rinsing, you must run clear water mixed with chemical solutions, first alkaline and then acidic through the unit, followed by a final rinse before reuse. This operation is sufficiently demanding to motivate the user to run their equipment with a simple rinse every two months. In some cases, such as winterization, time constraints mean that this is not always possible. In this case, you need to prepare for a long shutdown. After the chemical cleaning, a biocide is injected into the circuit (this is usually provided in the maintenance kits). These products prevent the bacterial fauna from developing, and the device can remain non-operational for a year. After one year, you will have to restart it by rinsing the tanks with water. Apart from these precautions, routine maintenance consists of cleaning the strainer (when your boat is out of the water for bottom paint), the 40-micron pre-filter and finally the 5-micron filter, which should be replaced when it is dirty. Avoid drawing from water containing hydrocarbons - these may damage the membrane. We cannot recommend this maintenance enough, as the replacement cost of used membranes is prohibitive.
We have monitored the winterization of an Aqua-Base ES model with a capacity of 105 liters/hour (27 US gal/h). It is a model which uses energy recovery to increase the high pressure. Only the low-pressure pump works electrically to transfer the sea water. Winterization is done after the standard maintenance of rinsing and cleaning. We will go through all the steps of this process to detail the sequencing of these operations. We would like to thank Philippe Bauer from Tendance Voile for his time and his explanations.
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The 105 liter/hour (27 US gal/h) Aqua Base ES watermaker is modular. In our case, it is mounted under a forward bunk and the freshwater tank is located next to it, which facilitates servicing. Watermakers and their peripherals are sometimes installed in places that are not easily accessible and the attached elements are scattered, hence the advantage of this type of model that adapts to the surrounding configuration.

1 - Preparation

The manufacturer’s manual is essential for locating the various parts and components of the system. It should be meticulously followed, as the circuits and procedures can be complex - and each model is different. Note the pressure gauges on the right to check low pressure (bottom) and high pressure (top).
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On this manufacturer’s exploded diagram, all the circuits are identifiable: the seawater intake, the various filters, the high-pressure pump, the membranes, the seawater discharge and the tank filling can all be identified. Several junctions are equipped with three-way valves to divert the circuit for rinsing and cleaning operations.
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The chemical cleaning products, on the right, are in powder form. Each bottle must be diluted in 10 liters (just over 10 quarts) of water, which is equivalent to a big bucketful. The winterization product, on the left, is liquid, and this is mixed with twenty liters (5¼ US gal) of water.
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Watermakers have their control system next to the device (gray housing). A control system can also be installed at the chart table for daily use.
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2 – Cleaning the filters

First, we check the first 40-micron filter, and clean it if necessary. Note that to avoid any harmful oxidation, all the circuit valves are made of PVC.
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Next, check the condition of the 20- and 5-micron filters (in this case). If they are too clogged, they must be changed. This should be done at least once a year, or more often if use is intensive.
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The active carbon filter is located at the outlet from the fresh water tank, on the return pipe to the fresh water rinse circuit. It should be checked regularly during any maintenance operation, as the membranes do not easily cope with the chlorine that the tanks may contain.
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3 – Rinsing with fresh water (after not using it for one or two weeks)

To begin with, fresh water is redirected from the tank to the desalination circuit intake instead of the seawater intake.
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We start a 15-minute continuous cycle. The water in the tank will pass through the membranes and gradually remove the salt. The red light indicates that the water is not drinkable, which is normal at this stage of the maintenance.
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4 – Cleaning the salinity probe

The salinity probe automatically determines the freshness of the water. Salt deposits could have accumulated on it, and if this is the case, it should be cleaned.
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If the water is safe, it is directed through the bottom pipe to the tanks. On the other hand, if the water is not fit for consumption, it goes through the top pipe to the discharge with the brine.
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5 – Restarting the unit

Before restarting, close the purge valve, which must be opened for any maintenance operation.
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When restarting, the green light comes on and indicates that the water is suitable for consumption.
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To ensure that the water is perfectly clean, there is a sampling valve before the connection to the tanks. You just have to open the valve and fill up a glass from the end of the pipe.
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6 - Chemical cleaning

(Following step 3 if the shutdown is longer than one month). Then go back to step 3 with a fresh rinse and restart as in step 5.
In order to run a continuous cycle, close the saltwater discharge valve and direct the discharge circuit (black pipe) to a bucket.
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The bucket is filled with 10 liters of water and the contents of the alkaline bottle, and a 15-minute cycle is run in a loop. A new 15-minute rinse (step 3) follows, and then a further 15-minute cycle with the acid solution. Then a final 15-minute rinse before restarting (step 5).
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In the bucket where the black discharge pipe arrives, the circuit supply pipe is installed, replacing the seawater pipe, thanks to the three-way valve at the beginning of the circuit.
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7 - Winterization

(Following step 6, if the unit is to be shut down for a period of several months)
This involves injecting a liquid solution that will stagnate in the circuit and prevent bacteria from proliferating. We proceed as for step 6, except that the mixture is made using twenty liters of water. The system is run in a loop, stopped and the inlet and outlet valves are closed to trap the liquid in the circuit. At the end of the winter period, the maintenance and restart cycle from step 3 is repeated with two consecutive flushes.
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After a season of sailing, signs of oxidation can appear. A good clean with soapy water and a thorough wipe with a cloth soaked in WD40 is the bare minimum. In temperate regions, it’s not a bad idea to run a dehumidifier in the bilge the during the winter.
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Tags : watermaker

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