Roughest hour – approaches to ship hull fouling management

Doctoral thesis, 2019

Submerged surfaces at sea are colonized by a high diversity of sessile (i.e. attached) life forms. As the merchant fleet capacity increases, responding to growth in demand for seaborne transport, so does the hull wetted surface area that is prone to colonization by these sessile organisms, i.e. marine biofouling. Such colonization leads to increased ship hull surface roughness, which results in both environmental and economic issues, namely fuel penalties and increased emissions to air. Improved maintenance of the hull would not only reduce these penalties, but also reduce emission of antifoulants and other paint components to the marine environment, as well as risks related to the transport of non-indigenous species on fouled hulls.

The work presented in this thesis aimed at improving current approaches to the management of ship hull fouling, which typically rely on a combination of fouling-control coatings and an in-water cleaning scheme. Knowledge on the adhesive strength of fouling to minimize cleaning forces, on the one hand, and evaluation of the hull condition and hull roughness penalties, on the other hand, are therefore central to the aim of this thesis.

The outcome of performed work supports a preventive approach to hull maintenance, e.g. gentle and frequent cleanings (hull grooming), or an alternative predictive approach, based on vessel performance and condition monitoring for detecting early forms of fouling. Tools are provided with potential to improve hull maintenance practices. These include minimizing cleaning forces applied during in-water hull cleaning through knowledge on adhesion strength of fouling (Papers I, III and IV), and more-accurate determination of the impact of fouling on vessel performance, namely by accounting for hull form effects (Papers II) or using a novel performance indicator that would be applicable in wider comparisons between vessels (Paper V). Seen as a whole, results indicate that the goal of minimizing the environmental and economic risks involved in hull fouling management can only be achieved through continued collaboration between different industry stakeholders, researchers, technology developers, authorities and policymakers, leading to an optimal path in development.