Class 2 (2nd Engineer) SC&S 📅 Sep 2018

Exam Question

With respect to the sacrificial anodes fitted to a ship's hull.

(a) State the purpose of fitting anodes to a hull structure.

(b) Describe with the aid of sketch, how anodes may be attached to the hull.

(c) Upon inspection in dry-dock it is found that the anodes have not wasted and areas of hull structure have experienced severe corrosion. Explain possible reasons for this situation

Reference Answer

(a) Purpose of Sacrificial Anodes:
Sacrificial anodes are fitted to a ship's hull to prevent corrosion. Seawater is highly corrosive due to its salt content, which acts as an electrolyte, facilitating the oxidation of iron (mild steel) and the formation of rust. Zinc anodes, being more reactive than steel, act as a sacrificial anode. They corrode preferentially, protecting the steel hull from corrosion. This is a form of cathodic protection.
(b) Attachment of anode to the hull:
(c) Reasons for Unwasted Anodes and Hull Corrosion:

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