Electrolysis on aluminium and steel boats in the harbour

    Electrolysis on boats or yachts

    As yacht surveyors we regularly get questions about electrolysis on yachts, sailboats and powerboats.

    Especially owners of aluminium or steel boats fear electrolysis. However, this can also be a problem with other boats or yachts. However, there are many stories about this subject, which makes it difficult for ship owners to distinguish between myth and truth.

    This article lists a number of facts and tells you what you can do to protect your ship in port against electrolysis.

    Read also: BYSC is specialized in inspection and surveys of steel boats.

    How does electrolysis occur in a port?

    Electrolysis occurs when two metals are electrically connected and those two metals are immersed in a conductive liquid. If these two conditions are met, current can flow between the two metals and cause corrosion by electrolysis. The metal that is the ‘least noble’ will then corrode.

    Is there a problem when an aluminium boat is lying next to a steel boat?

    No, as long as they’re not electrically connected. Not being connected means no current and therefore no electrolysis. Maybe now you think it’s quite unlikely that the two ships are electrically connected. However, it is important to take into account that if you are connected to shore power, you will (probably) be connected to your neighbour via the grounding (the yellow green wire) of that shore power.

    What can we do to prevent electrolysis in the harbor?

    1. Don’t take shore power.

    This is good for the climate (if you don’t use your generator of course) and you have nothing to fear from electrolysis. The owner of an aluminium boat in this case has nothing to fear from a steel boat.

    If you go ‘rafting’, as is quite common in summer in busy marinas, there is no reason to panic when a steel ship moors next to your aluminium ship. As soon as you both hang on shore power, the picture naturally changes.

    2. Do not connect the grounding of shore power to the grounding of the boat.

    However, this may be illegal in certain countries. Moreover, if it is carried out in this way (i.e. without earthing), it can be dangerous. Your leakage current switch will not work in this case if there is a leak from a cable to the hull. Be careful, grounding the boat to the mains is not always safe either.

    I personally experienced a deadly potential difference between the grounding wire of the yacht club’s power supply and the ground (the steel pontoon, the water,…). This happened in a marina in Brazil. Our battery charger and that of all the neighbours on the pontoon burned out completely. There are certain battery chargers that are protected against this.

    3. Set up an isolation transformer.

    This is by far the best solution: you have a safe installation, the leakage current switch works and you have nothing to fear from electrolysis. Let your neighbour know as well, he will thank you for it.

    Owners of aluminium boats should certainly have such a transformer, so they never have to fear steel neighbours, poles or steel ladders in the quay, as they are never electrically connected to it.

    Detail drawing of an isolation transformer. Source: victronenergy.nl

    Other situations where electrolysis occurs on boats, yachts or ships

    There are still possibilities where electrolysis can make your life miserable. A good example is the propeller (made of bronze) and the propeller shaft (made of stainless steel). They are connected and are located in the water. This creates current and therefore electrolysis.

    This is dissolved by attaching a zinc, aluminium or magnesium anode (the choice depends on a number of elements) in contact with these metals. Then this anode is first sacrificed. The same applies to other elements that are in the water: passages in bronze or brass, for example.

    Anode tegen elektrolyse
    Picture of an aluminium anode. Source: kokwatersport.nl

    Problems also arise when on a metal ship the hull is used as a negative pole to connect other devices (e.g. lights) with only a positive wire (the negative is then the connection to the hull. This is done in cars for example. Then there is also a small current flowing through the boat if these devices are functioning, so electrolysis is done here as well. This is easily solved by making all electrical connections two-pole (negative -black- and positive-red cable).

    Electricity is and remains dangerous on the water. However, you can see that certain problems are easy to solve with a number of minor interventions. Check it out or call in the inexpensive expertise of Belgian Yacht Service & Consult for this.