Friction Resistance of Ship
Drag for Ships Air Drag Form Drag Wave Drag Frictional Drag BC LNG Cont
Friction Drag Active Module to friction drag Micro bubble Polymer Riblet Elasticity modulus Contact angle Negative Module to friction drag Fouling Roughness
Roughness effect Fouling Macro fouling Slime Deterioration of surface Rusting Peeling of paint film Damage of the surface Maintenance work at Afloat under water cleaning Maintenance work at Dock Blasting Coating Blasting deduction of roughness Coating coverage of roughness / propagation of roughness dust spray, contamination
Hull surface condition
Roughness increase by fouling
Proper condition
Laminated layer of aged antifouling film may cause roughness by damage or peeling
Hull roughness by aging CR system by BSRA gauge 900 Hull roughness (μm) 800 700 600 500 400 300 CR AF 50 ships Dry up F/B Dry up V/B Aft coat F/B Aft Coat V/B Average Hull roughness increases by aging. Huge roughness may be caused by peeling of the film. 200 100 0 Ships ages 0 1 2 3 4 5 6 7 8 9 10 11 12
Hull roughness by aging Long life AF by BSRA gauge Hull Roughness (μm) 900 800 700 600 500 400 300 200 100 0 Long life AF 70 ships Dry up F/B Dry up V/B Aft coat F/B Aft Coat V/B Averge Ships ages 0 1 2 3 4 5 6 7 8 9 10 11 12 Hull roughness increases by aging. Tar Epoxy Epoxy system is introduced, which may deduce the film damage and peeling off, and increment of roughness is much less than CR System
Hull roughness by aging Self polishing AF by BSRA gauge Hull roughness (μm) 900 800 700 600 500 400 300 200 100 0 SPC-AF 40 ships Dry up F/B Dry up V/B Aft coat F/B Aft coat V/B Average Ships ages 0 1 2 3 4 5 6 7 8 9 10 11 12 Hull roughness stabilized after 3 years. Tar Epoxy Epoxy system is introduced, which may deduce the film damage and peeling off. Self polishing mechanism may cover increment the roughness by damage??
Active Module Micro bubble Based on the test module, 10% reduction of friction resistance and 4% energy reduction is expected for the vessel 100m length /20m width /DLL 7m. Reduction of friction resistance and energy to form bubble is conflicting * Study started at the Japan Ship Research Association Polymer (Tom s effect) As huge amount of polymer are required, it is not utilized for marine m field. * found and developed by US Navy since 1940 th.
Active Module Riblet generate steady longitudinal vortex to control turbulent flow. The surface will be covered with contamination and effective life is limited. Surface profile like dimple Elasticity modulus Effect is not so clearly reported. Contact angle Effect is not so clearly reported.
Active Module Polymer effect the best elasticity modulus Surface chemical structure by hydrolysis contact angle relation between the contact angle (hydrophilic/hydrophobic mixture) and friction resistance Surface of paint film particle distribution of pigments structure of pigments structure of film
Measurement of friction resistance Comparison of drag owning to surface roughness Sand surface 2 Hydrolysis type AF at smooth surface 1 Si elastomeric AF at smooth surface
Drag Test Velocity 0.5m/sec Velocity 1.5m/sec
Drag test Panel 0.8m X 0.4m Condition of 0.5m/sec Measuring device
3-Dimension Analysis of Paint Film Surface Sand Surface Sand Surface Roughness of BSRA : 169 μm
3-Dimension Analysis of Paint Film Surface Hydrolysis type AF -A Silyl Acrylate with copper Roughness of BSRA : 43 micron
3-Dimension Analysis of Paint Film Surface Hydrolysis type AF-B Metallic Acrylate copper free Roughness of BSRA : 39 micron
3-Dimension Analysis of Paint Film Surface Si-A Foul release coating Roughness of BSRA : 32 micron
Friction resistance depend on the surface structure? 0.1400 Friction to flow rate B A 0.1200 Si-AFB Sand Surface 0.1000 D r a 0.0800 g (k 0.0600 g )Hydrolisis-AF 0.0400 0.0200 BSRA Reduction of Friction μ 2m/sec Sand Surface 170 Hydrolysis-AF A 43 29% Hydrolysis-AF B 39 35% Si-AF B 34 34% 0.0000 0 0.5 1 1.5 2 2.5 flow ate(m/sec) AF-B and Si-B are almost same. AF-A is slightly large. The difference of water-repellent film and hydrophilic film was not acquired.
Roughness of the sample BSRA Ra Rz Pz Wz 43 4.2 13.1 24.8 12.5 170 6.9 46.5 56.7 30.4 39 3.8 11.7 24.6 13.2 34 1.8 12.7 18.6 5.4 Correlation BSRA Ra Rz Pz Wz 0.5 1 1.5 1.8 2 BSRA 1 Ra 0.891189 1 Rz 0.998251 0.863803 1 Pz 0.992941 0.936427 0.984192 1 Wz 0.957783 0.978139 0.939117 0.98512 1 0.5 0.551133 0.862469 0.500983 0.645754 0.766435 1 1 0.897001 0.940786 0.872693 0.936774 0.971393 0.800296 1 1.5 0.875116 0.829556 0.859842 0.897466 0.908341 0.648331 0.966847 1 1.8 0.93458 0.819473 0.928981 0.936727 0.917168 0.548346 0.940224 0.981738 1 2 0.983098 0.876419 0.978425 0.982482 0.957349 0.572026 0.939426 0.946693 0.98367 1
Friction to Surface Roughness The linear relation between friction resistance and surface roughness indicates. Friction Resistance to Surface Roughness measured by BSRA guage 0.14 Friction Resistance (Kg) 0.12 0.1 0.08 0.06 0.04 0.02 0 0 50 100 150 200 0.5 1 1.5 1.8 2 Velocity 2.0m/s Velocity 1.8m/s Velocity 1.5m/s Velocity 1.0m/s Velocity 0.5m/s Surface Roughness (μm)
Conclusion Friction Resistance (1) Surface roughness is the dominant factor to deduce friction resistance more than 30%. (2) BSRA roughness and Friction resistance shows good collation. (3) BSRA Gage may represent Roughness, Profile and Wave (Rz, Pz, Wz). (4) Roughness of hull increases pursuant to age, but self-polishing effect may control the roughness increase. (5) Paint surface property works deduction of friction resistance, and the major cause might be surface roughness or profile. (6) The difference of water-repellent film and hydrophilic film was not acquired.
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Drag increase by slime attachment was reported by many references, as follows. Drag increase by bio-films. Understanding and prevention of drag increase due to marine fouling is as important as drag reduction. Schultz & Swain (1999) compared turbulent boundary layers on natural marine bio-films and a smooth plate. The average increases in Cf for slime film with mean thickness of 160μm and 350μm were 33% and 68%, respectively. Reference: Pro. Fred Stern et al.. The Resistance Committee Final Report and Recommendations to the 23 rd ITTC, page 27.