1. Density of the current:

The electrochemical and mechanical conditions have a large influence on the design of the cathode protection system.

Other conditions to bear in mind are: temperature, salinity, resistance to the dissolving of oxygen, etc.

The specifications of a cathode protection system are normally expressed by the density of the electrical current required to give the surface which has to be protected a sufficient potential.

The normal density of the current for ship hulls varies from 10 m A/m2 to 30 m A/m2, although it can be increased in special cases.

2. Life of the Anode:

With anodes, you can usually calculate a life from one to for years while for Aluminum Anodes you can expect them to last for approximately five years.

3. The number of Anodes:

The total current needed is calculated by the following formula:

The total weight of the anodes:

The number and type of Anodes to compensate for the total of the current and the weight required:

Current required Number of Anodes = Current leaving each anode Calculated weight Number of Anodes = Weight of each anode

4. The position of the Anodes:

The anodes must be distributed conveniently around the wet surface of the hull, near, above and below the balance keels, increasing in number in the zone of the stern due to the high density of current originating from the propeller. We also recommend the installation of anodes in the sea valves, tuyeres, propellers, etc.

This normal practice can be varied depending on the geometry of the ship, its system of painting or also on the expected use of the vessel.

5. Recommended practice for the installation:

ZINETI Zinc or Aluminum anodes for the protection of ballast tanks and ballast and cargo tanks.

Since the Second World War, the classic anode used for the protection of ballast tanks was Magnesium. This metal was extraordinarily well suited, having an electronegative force of 700mV over that of polarized steel.

The greatest advantage was its rapid power of polarization. Its problem was an overproduction caused by the emission of hidrogen and its electrochemical power, approximately 55%.

Today this metal is rarely used due to the restrictions imposed on it by the classification associations. However it is still used in tanks with platforms.

Zinc and Aluminum show a relatively low potential, the condition voltage being in the order of 230 to 300 mW over Polarized Steel; however they have an efficiency of 80%. Experience shows us that with regards to Zinc Anodes that the importante of contamination of the steel is very small.

The result of the Aluminum Anode depends largely on the additives (Indium and Zinc), which immunize the tendency of the steel to form a film of paciflying rust.

Aluminum, as much as Zinc, has a large and satisfactory history as a cathode protection material. One of the advantages of Aluminum is that, in its installation, only a third of the weight is used compared with Zinc, which is important when considering the dead weight of the ship, and also taking into consideration that the cost of the installation is calculated by the shipyard according to the installed weight. One disadvantage, in agreement with the classification associations, is the possibility of sparks, which gives rise to the situation whereby the aforementioned associations impose certain restrictions on the use of Aluminum Anodes, but not those made from Zinc. The distribution of these Aluminum Anodes, due to the possibility of sparks, must be studied so that the they are placed in low areas of the tanks.

Precise data needed to make a calculation for the protection of ships: