The aluminum boat has many problems with galvanic corrosion. Also called electrolytic or cathodic, is the deterioration of the material due to an electromechanical reaction, where an anode metal deteriorates generating a flow of ions to another cathode metal, both immersed in an electrolyte.
If we connect them outside the electrolyte, we can see the difference between potential and current between them.
- Painted Surfaces
For there to be galvanic current, both metals must have contact with the electrolyte, that is, water.
It is important not to paint aluminum helmets with copper-based antifouling as it does not insulate and in addition, copper would cause electrolytic corrosion with aluminum.
The cover and cockpit should be insulated with good paint and, if possible, the bilge too. The concept is: any place where you can accumulate rainwater or seawater must be well painted, and isolated.
- Install Sacrificial Anodes
Install zinc anodes for saltwater or magnesium anodes for fresh water.
To know if the sizes and quantities of anodes installed are correct, we should;
Connect the positive of the multimeter to the helmet
Connect the sacrificial anode to the helmet and the positive of the multimeter
Connect the negative of the multimeter to a reference electrode of silver-silver chloride
- Install a Voltmeter
Install a voltmeter on the control panel, connecting one pole to the hull and the other to the reference electrode. A constant reading will be obtained, being able to know if the boat is protected or not.
- Isolate Grounding
The earthing of the alternating current circuit must be very well insulated from the hull, in all metal boats. In this way, we avoid having a connection with the metals of other ships or with the own metals of the navy. You can also place a galvanic isolator, which isolates, by diodes, the ground connection if it detects current.
- Global Isolation
There are two things to isolate in an aluminum boat:
Insulation of Metals: If we decide to isolate the different metals of the ship with respect to the hull then we will simply have to place anode shack in each submerged metal to protect them, and the issue will be solved. This concept is used a lot in fiberglass boats, but in metal boats, it is more difficult: it implies that it will be necessary to isolate the thru-hulls, the legs of the engine, the shaft line, the coupling plug, the rim to the axis of the rudder and other elements.
Isolation of the DC Circuit: To avoid eddy currents from the battery bank, this circuit must be isolated. Eddy currents are electric currents that escape from their conductive circuit to use another as a conductor, for example, the helmet. A simple current of 1 mA can cause a lot of corrosion in a year. The circuit must be isolated from the helmet.