Key corrosion weak points for superyachts revealed by PECA CMAP surveys

The Lab at Brookes Bell, the materials testing division of UK maritime services provider Brookes Bell, has identified key corrosion weaknesses in superyachts with the help of its corrosion mapping (CMAP) service using Pulsed Eddy Current Array (PECA) technology. This technology allows inspectors to ‘see through’ up to 300 mm of thick coatings, teak, insulation, or fairing to map exact metal loss and calculate remaining plate thickness before a yacht enters refit.

Caroline Young of The Lab at Brookes Bell says that superyachts feature heavy fairing, paint, and cosmetic layers, meaning that underlying structural corrosion is often concealed until significant damage has already occurred.

The Lab started development of the CMAP technique using PECA in 2020. The technique was validated by Lloyd’s Register for use on naval vessels, and later on commercial vessels in 2022. Since then, Young estimates that The Lab has conducted scans on approximately 30 superyachts of various sizes, ranging from targeted scans to full vessel scans.

Scanners at using The Lab's CMAP with PECA technology, which can ‘see through’ up to 300 mm coatings

The method highlights the condition of the steel, the remaining wall thickness, and material loss without the need to prepare surfaces, or remove thick coatings or insulation material. The PECA system works by measuring the feedback from magnetic pulses generated by a coil just above the surface being scanned.

The Lab’s marine corrosion mapping, analytics, and modelling software takes the digital output collected from the probe and converts it into usable data for the asset owner and shipyard involved in overhaul, refit, and repair. The global overview model consists of many scan zones, each overlaid onto a 2D or 3D mesh naval architect’s design/construction model.

Scan results overlaid on a car ferry photo showing corrosion 

Results gathered over the past few years show that teak and composite decks are among the most prevalent areas for hidden corrosion in superyachts. Failing seams or fasteners in teak can let water in and trap moisture against underlying steel or aluminium deck plating. Corrosion can also occur under insulation due to condensation and small leaks around internal structural bulkheads and machinery spaces, according to The Lab.

Another major area of concern is hull antifouling. Micro-failures or application errors in underwater hull coatings allow saltwater to penetrate beneath the paint film, creating localised ‘scabs’ of under-film corrosion that degrade hull plating. Up top, thick layers of fairing compound can also develop micro-cracks that let in and trap moisture.

Internal tanks and wet spaces are also identified as key weak points in PECA surveys. Tank tops, internal seams, and the lowest suction points within these tanks are prone to localised pitting and microbial corrosion from stagnant water or residue. Plating beneath the flooring in bathrooms, showers, or galleys is another weak point, as micro-fissures in tile or sealed floors allow greywater to pool on structural floor plates.

Finally, machinery and piping systems, such as seawater and exhaust pipework, can be sources of corrosion due to constant exposure to corrosive electrolytes and hot gases. Fire systems can also suffer due to internal stagnation.

The Lab notes that surveys can be conducted on superyachts ahead of refit projects, providing advance knowledge of corrosion locations, weak points, and the quantities of steel that need replacing.