Maxim Candries

The Measurement of the Drag Characteristics of Tin-free Self-polishing Co-polymers and Fouling Release Coatings Using a Rotor Apparatus

An experimental study was carried out to compare the drag characteristics of a tin-free self-polishing co-polymer (SPC) and a foul release coating. Rotor measurements were carried out using different cylinders coated with both paint types. The experiments showed that the frictional resistance for the foul release test cylinders was lower than for the tin-free SPC cylinders. The drag characteristics were related to the roughness parameters of the tested surfaces measured with an optical measurement system. The measurements indicated that the texture of the foul release surface was significantly different from SPC systems. The findings show that the drag of a foul release coating will only correlate with a characteristic roughness measure that takes both the amplitude and the texture of the surface into account, and that is calculated at bandwidth parameters which depend on the degree of roughness.

Experimental Investigation of the Turbulent Boundary Layer of Surfaces Coated With Marine Antifoulings

Turbulent boundary-layer measurements have been carried out on flat surfaces coated with two different new generation marine antifoulings. The coatings were applied on 1-m-long test sections that were fitted in a 2.1-m-long flat plate setup. The measurements were carried out in two different recirculating water tunnels by means of two-component laser Doppler velocimetry and were compared with measurements of a smooth steel reference surface and a surface covered with sand grit. Both coatings exhibited an increase in frictional resistance compared to the reference surface, but the increase was significantly smaller for the Foul(ing) Release coatings than for the Tin-free SPC coating. The coatings did not significantly affect the boundary-layer thickness. When expressed in inner variables, the coatings did not have an effect on the turbulence intensity profiles, but when expressed in outer variables, the coatings affected the near-wall turbulence intensities.

Estimating the Impact of New-generation Antifoulings on Ship Performance: The Presence of Slime

Due to the phase-out of TBT-SPCs imposed by the International Maritime Organization, new-generation antifoulings are set to replace 80% of the existing antifouling market. Two types of coatings are claimed to offer satisfactory performance over five years: tin-free SPCs and foul-release coatings, which were both commercially introduced in the mid 1990s. This paper gives an overview of the research at the University of Newcastle upon Tyne which compares the drag, boundary-layer and roughness characteristics of both coatings when newly applied. It was found that foul-release coatings offer less drag than tin-free SPC, by an amount which depends on the quality of application and which has been related to the respective differences in roughness characteristics. Assessments have shown that foul-release surfaces are very effective against macrofouling organisms, but that the surface is covered by slime films when the vessel returns to drydock. A literature review on the effect of slime films on ship resistance shows that slime films have a significant effect on drag, but in turbulent flows the effect is likely to remain limited because of detachment processes. Further research is underway to investigate this.

LOWER FRICTIONAL RESISTANCE CHARACTERISTICS OF FOUL RELEASE SYSTEMS

This paper discusses how a systematic investigation of the resistance and roughness of two state-of-the-art alternatives to TBT-SPC was undertaken. The roughness and drag characteristics of two antifouling paint systems are investigated: a state-of-the-art (Tributyl) tin-free Self-Polishing Co-Polymer (SPC) and a non-toxic Foul Release system. Towing tank experiments have confirmed that the total resistance of 6.3-m plate coated wit the Foul Release coating system was on average 1.4% lower than when it was coated with both a stylus instrument and an optical measurement system. Correlation with the measured drag has shown that the roughness of the Foul Release cannot be characterized by a height parameter. The texture of the Foul Release surface is significantly different from SPC systems as is evident from parameters such as the average absolute slope Sa and the correlation length of the roughness profile. Roughness and drag seem to correlate well when the parameter is used to characterize the roughness.