Ship Coatings — An overview

Malcolm Latarche
Malcolm Latarche

11 December 2017

Even in the days of wooden ships, protecting the structure of the vessel from attack and degradation was a constant battle. In the modern era, steel is just as prone to problems with biofouling of the hull affecting performance and the need to protect against the elements is still there although today it is corrosion rather than rot and shipworm that is the enemy.

Corrosion is an inevitable factor for all ships as ferrous metals all have a tendency to chemically react to revert to their natural state as iron oxide. The process of turning raw iron ore into steel is an expensive one but preventing reversion is just as costly for the owner. It is not only ferrous metals that can be affected by corrosion; when two different metals are in close contact Galvanic corrosion (also called bimetallic corrosion) can occur.

Externally corrosion, reflects badly upon the ship, its crew and its owner and can provide the reason for Port State Control officials to take an interest in the ship that may well throw up other shortcomings. Internally protection is also needed, and in some very inhospitable areas. The cargo holds of a bulker can suffer badly from both corrosion and physical damage caused by the nature of cargo and loading and discharging operations. Protection against corrosion is also vital in ballast tanks, void spaces and the cargo tanks of crude and chemical tankers.

Coatings are a major weapon but not the only tool in the fight against corrosion. Cathodic protection, chemicals and even the choice of materials are also employed to prevent a ship and its equipment from the inevitable return to iron oxide which is the natural state of the main metal used in ship construction. One day, non-corroding materials may replace steel but while there is progress it is still a long way off and the battle must go on.

With ship efficiency and the need to reduce fuel consumption and exhaust emissions to a minimum having become drivers of marine regulation, biofouling has taken on an even greater significance than it had previously. Ironically, having been forced to abandon the most effective biocides yet developed, shipowners are now facing new regulation that will mandate fouling management.

Until very recently shipowners were more or less free to decide what parts of a ship were coated and with what. But that is changing, and although rusty ships will almost certainly be around for many years to come – and most probably forever – some areas of a ship’s structure are already subject to mandatory coating and to definitive standards under both IMO regulations and the IACS common structural rules.

Things are also shaping up for regulations to be drawn up compelling owners to not only apply anti-fouling or foul release coats but to ensure that they remain in good condition regardless of when the next scheduled drydocking is due to take place.