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HANSA 05-2019

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Schiffstechnik | Ship

Schiffstechnik | Ship Technology Performance tests for antifouling coatings Current performance testing of antifouling products is mainly based on static raft exposure tests (according to ASTM D3623/ D6990) or polishing tests in seawater (ASTM D4938). Such methods give only indirect measurement of friction drag properties of hull coatings Major function of antifouling coatings is to keep added friction drag due to biofouling accumulation on a ship hull at a minimum. There are three test methods that do give direct data on friction drag properties of coatings (with and without fouling) and as such can be used in product comparison and selection of suitable products. Whereas for registration of antifouling products manufacturers need to provide efficacy data from (simulated) field tests, a short description of this standardised method is given as well. Efficacy tests for registration of antifouling products Endures has long lasting experience in static raft exposure tests of antifouling paints. These tests are carried out according to the BPR Guidance Document Vol. II – Efficacy (version 3, ECHA, April 2018). As an independent contract laboratory Endures can make direct comparison of the performance of paint products from different suppliers under the same exposure conditions. Our exposure site in the harbour of Den Helder, the major naval base in The Netherlands, is representative for North Sea coastal water with high fouling pressure during a fouling season lasting from March till November. Seawater parameters such as temperature, pH, salinity and oxygen concentration are continuously monitored at the lab. The methodology to evaluate the efficacy of antifouling paints is based on methods described in ASTM D3623/ D6990. Regular inspections and photographs are made during the fouling season, percentage coverage of fouling on panels is estimated and from these data a Fouling Resistance (FR) rate is derived: FR 100 means no fouling and with F 0 a panel is fully covered. Product performance is evaluated on pass/fail criteria described in the BPR Guidance document. This test will only show the ability of a coating to resist or prevent the settlement of fouling organisms. Endures raft in the harbour of Den Helder and raft exposure rack with different hull coatings Drag performance testing of ship hull coatings The principle of this test is to carry out comparative measurements of friction resistance of coated disks with and without fouling. In addition to static raft exposure tests this test gives relevant information on fouling adherence and release properties of hull coatings. This test is carried out with the Friction Disk Machine available at the laboratory. Paints under investigation need to be applied on circular disks. The coated disks are first measured in clean condition, then exposed for a specific time period in the harbour of Den Helder where they get fouled and then retrieved to the laboratory for a second drag measurement. The difference in friction drag between fouled and clean condition gives quantitative data on the drag penalty that a certain fouling pattern may give. This way different paint products can be compared on friction drag properties. The test method is suitable for both self-polishing paints (SPC) as well as for fouling release coatings (FRC). Minimal speed foul release test for hull coatings The purpose of this test is to establish the minimal speed for self-cleaning of hull coatings with marine fouling. The test protocol involves two different steps: Static exposure of coated panels to marine fouling for periods of 1 – 4 months, followed by rotating drum testing in seawater at increasing speed (4 – 30 knots) for several rotation times. After static exposure the panels are inspected on fouling condition, mounted onto the rotor drum and subjected to a rotation protocol with incremental speed steps of two knots up to the speed where all fouling is removed. At each speed several rota- Friction Disk machine for drag measurements on coated disks with and without marine fouling © Endures 52 HANSA International Maritime Journal 05 | 2019

Schiffstechnik | Ship Technology Scheme of static/dynamic ageing protocol that will reveal foul release properties of hull coatings © Endures tion times can be investigated. Results that are obtained are twofold: 1) what is the minimal speed at which fouling starts to be washed off and 2) what speed/rotation regime is required to get a fully cleaned coating surface. This way different coating products can be compared on foul release properties at various sailing speeds and after various idle times. Idle day’s tolerance test for hull coatings As an extension of the method described above we have developed a cyclic test protocol in which hull coatings can be subjected to repeated static/dynamic ageing periods and tested on fouling release after each raft exposure period. The test cycle can start with a dynamic phase (simulating vessel operation at certain speed) followed by a static idle time or the other way around. Repeating the cycle several times may reveal the long term drag performance of hull coatings. Authors Job Klijnstra & Mark Bakker Endures BV, Den Helder, The Netherlands WANT TO SAVE COSTS IN SHIPPING? Proper Antifouling reduces fuel consumption and maintenance costs! Endures can help you with performance testing and selection of suitable coating systems. HANSA International Maritime Journal 05 | 2019 Independent contract laboratory R&D and Consultancy on Corrosion Protection and Antifouling. www.endures.co.uk 53

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