The Enemy Below - Adhesion and Friction of Ship Hull Fouling

Licentiate thesis, 2017

Below the waterline, commercial ships are good targets for marine organisms to attach and proliferate, a problem commonly known as biofouling. A fouled hull means higher hydrodynamic resistance, which can result in significant fuel penalties. In a fossil-fuel thirsty maritime sector, this means disadvantages in economic, societal and environmental terms. This thesis presents tools for improving current practices related to hull performance management, focusing on the adhesion strength of marine organisms on different coatings (Paper I) and estimation of fouled-hull penalties (Paper II). In Paper I, knowledge gaps that hinder better matching of cleaning forces to adhesion strength of marine organisms are identified, and conclusions are derived from published adhesion strength data. From this adhesion-strength perspective, it is arguably better to invest in combating early stages of fouling, e.g. during idle periods, than using aggressive methods against advanced stages of fouling after an idle period. Regarding estimation of benefits of hull cleaning from a fuel-saving perspective, Paper II demonstrates that the hull form might be an important parameter to consider at low speeds and for less slender vessels. This thesis further applies a rapid calculation method (Granville method) in estimating the hull condition from vessel monitored data (noon reports). The estimated roughness height can be used as an indicator of the hull condition, with the advantage of being independent from vessel speed, which is not the case for other indicators, such as percentage speed loss.