The efficacy of capture - In-water Cleaning

B Watermann, A Thomsen, J Wallis, B Daehne

B.Watermann, A. Thomsen, J. Wallis & B. Daehne. 2022. Ship&Offshore - Special Greentech. Hamburg: DVV Media Group GmbH

In-water cleaning of ship hulls is widely carried out to increase ship performance, and is under intense discussion regarding regulations, quality improvement and technologies in use [2]. One critical aspect is the common practice of cleaning biocidal antifouling paints, which is incompatible with national and EU water legislation, and the impact of abrasion on antifouling coatings that are not designed for cleaning.

Additionally, the majority of cleaning operations do not filter or capture the fouled material. Furthermore, there is usually no control or verification of the quality of the cleaning technology applied. Fluorometric technologies are used to control the efficacy of capture. Ideally, the removed fouling should be captured and sucked up by the cleaning machine using a vacuum system.

In waters with high visibility, optical methods like front and aft cameras can be used. Dyes can be injected to control the efficacy photometrically [9]. Unfortunately, in ports along the North Sea and most ports of the Baltic Sea, the visibility is low and optical control methods cannot be applied, requiring other verification methods.

One option is to use the relation between fouling stage and weight of fouling as an indicator of the amount of fouling which has to be captured. Taking samples of the fouling accumulation prior to cleaning may provide a guide to the volume of fouling present on the hull and the amount to be captured.

In this way, the captured material can be compared with the earlier estimate and may provide a reasonable estimation of efficacy. To explore the validity of the relationship between fouling stage and fouling weight, data from previous fouling studies were compiled and scrutinised regarding their usefulness for such an estimation.