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Cathodic protection

Katodiskt skydd under vattenlinjen (fartygsskrov)

In this post we’ll do a “deep dive” into cathodic protection below the waterline . Primarily regarding the hull of ships and vessels.

It would be almost impossible to cathodically protect a hull that is uncoated, due to the protection current requirement and current distribution.

In addition to this, there must be an electrically insulating layer between the steel wall and the antifouling coating in order to stifle the electrochemical reduction of toxic metal compounds.

There is a clear difference btween complete and partial protection of a under water area, which is depending on the extent of the protected object.

Partial protection is usually described as protecting the stern of the boat. This is particulary endangered due to the fact of the high flow rate and aeration and formation of cells on attachments. ( such as the propeller and rudder ) .

Partial protection can also be extended to the bow, which also is subject to high rates of flow.

Complete protection of ships with galvanic anodes or impressed current is becoming more and more important since more damage to the coating due to mechanical damage are becoming more frequent.

In all cases of partial or total hulls of aluminium or stainless steel must be protected by cathodic protection. High alloy steels with over 20% chromium and 3 % molybdenum are not any exceptions, since they are very prone to corrode beneith the coatings.

I hope this made some things much more clear!

Ps. We are experiencing more and more customers stating that they’ve been recomended to use Aluminium anodes more often. We want to put out an friendly reminder that : The choice of anodes are not only based on what type of anode is more durable or not. Several factors come into play like : Type of water, total surface of the hull and so on.

Please get in touch if you want to know more.