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Dealing with Corrosion

All vessels if not protected from the elements, will suffer corrosion of some form, in their life time. Types of construction and material use will not change this as boats are subjected to the harsh outside environment. Corrosion types are subject to material types. Wooden vessels can develop rot, steel can develop rust, fibreglass can develop crazing and “chalking” of the gel coat. There are many variations of these corrosion types, some of which create other problems within the vessel.

Unless too extreme, most corrosion can be dealt with if managed correctly. The best approach is to remove the corroded areas completely and replace with like material. For example, if a wooden coaming on a yacht is rotten, completely remove. Treat the underlying substrate and replace with a new coaming. If a steel frame in a steel vessel is rusted, cut out, treat the surrounding area, and replace with a new frame. Often repairs are carried out on corrosion with extra material added, but complete removal and replacement is the optimum solution.

Corrosion can be formed in various ways. But often in all vessels a lack of ventilation, water ingress, and a lack of material protection is the main cause of corrosion. A nice dry, ventilated interior with ample substrate protection is the best way to prevent corrosion. On any vessel any damaged or missing paint work should be dried, repaired and repainted as soon as possible. This describes mainly the affects from biological corrosion. Other forms of corrosion are galvanic corrosion, stray current corrosion, crevice corrosion and pitting, and corrosion resulting from stress.

Because corrosion is a very involved and in-depth subject, a brief summary of design features that will reduce corrosion follows:

– Selection of materials should balance corrosion resistance with cost. Modern plastics  have allowed hulls and components to be isolated to inhibit corrosion.

– Avoid similar galvanic couples.

– When materials are not galvanically matched, fastenings should be more cathodic than surrounding metals.

– Sacrificial anodes should be used liberally.

– Component design should reduce the number of areas that can hold moisture or allow crevice corrosion. Silicon sealants are highly effective in preventing moisture from entering components or fittings.

As always, prevention is better than cure, especially when dealing with all types of corrosion in the marine environment.