Guarding against the invisible enemy

Corrosion is a silent yet formidable threat to superyachts. Only through constant vigilance, regular inspections, and targeted interventions can its effects be contained before they lead to significant repairs or compromise a vessel’s structural integrity. 

Often dismissed as merely a cosmetic flaw, corrosion is in fact a major technical concern in many refit projects. If left unchecked, it can undermine a yacht’s structure, reduce its value, pose safety risks, and generate substantial repair costs. In this interview, François Gautier, Manager of the Coatings Department at MB92 La Ciotat, sheds light on the most common types of corrosion, the areas on board most at risk, and the best practices for managing the issue effectively and over the long term.

What are the most common types of corrosion found on superyachts? 

Two forms of corrosion are particularly prevalent on board superyachts. The first, known as galvanic corrosion, occurs when an electrochemical current forms between dissimilar metals in contact within a moist environment. The imbalance in electrical potential leads to accelerated degradation of the less noble metal. This typically affects fasteners, portholes, and certain deck fittings made from stainless steel—especially when proper insulation between materials has not been ensured. 

The second type, known as general corrosion, results from prolonged exposure of bare metal to moisture, often due to insufficient surface preparation. Salt residues or other contaminants left on the substrate can hinder the adhesion of the coating system and compromise its long-term performance. This form of corrosion often develops discreetly, with early signs concealed beneath the paint and difficult to detect visually. 

Where does corrosion typically take hold on a superyacht? 

Some areas are particularly susceptible due to their function or layout. Tanks, which are exposed to varying chemical environments, require constant monitoring. Poorly ventilated compartments or areas where water tends to stagnate, especially near deck hardware, are also at risk. Appendages such as rudders and propeller shafts are subject to abrasion and therefore demand special attention. Additionally, if the hull is inadequately protected or the antifouling system has deteriorated, accelerated corrosion may occur, particularly if cathodic protection is lacking or improperly installed. 

When do the first signs of corrosion typically appear? 

During the initial years of operation, the risk of corrosion remains low (provided the vessel has been well designed, built, and maintained…). However, after around five years, increased vigilance becomes necessary. The first signs are often subtle: blistering, hairline cracks, or localised coating failures. If these warning signs are not promptly addressed, they can evolve into deeper damage, potentially affecting the vessel’s structural integrity. That’s why a preventive inspection policy is essential to ensure the longevity of onboard systems. 

Which technical shortcomings can undermine corrosion control systems? 

Several issues can undermine corrosion protection efforts. At the design stage, poorly drained or hard-to-reach areas may make it difficult to apply protective coatings properly. Failing to adhere to fundamental principles such as the quality of welds, thorough surface preparation, appropriate coating system selection, and high-standard application, will inevitably compromise the performance of anti-corrosion measures. The use of incompatible metals or lack of adequate ventilation are also recurring issues. 

From a maintenance perspective, the main pitfall lies in delayed or poorly executed repairs. It’s not uncommon to see hasty patch-ups carried out under pressure, with little regard for the prescribed systems. Every surface type presents unique challenges: a freshwater tank, for instance, requires a very different approach to that of a ballast tank or an exterior area exposed to the elements. Ensuring proper surface preparation, selecting the right coating system, applying it correctly, and achieving the recommended film thicknesses are all critical to the treatment’s durability. 

What advice would you give for effectively preventing corrosion? 

Acting quickly is key. As soon as any sign of corrosion appears, it’s vital to determine the root cause—not just treat the symptom. Prevention is equally important. Sensitive areas, such as tanks, should be checked annually, even if no issues are visible. A proactive, well-structured maintenance plan not only extends the lifespan of onboard equipment but also helps control long-term operating costs.