The challenge of supplying antifouling coatings to reduce emission of greenhouse gases Erik Risberg Jotun A/S
Outline The complex technology situation Boundary layers and their influence on frictional resistance Influence of hull roughness Importance of performance over time How to monitor the performance of a vessel Examples of the monitoring of real vessels
Fuel savings Compared to what?
Development of crude oil prices
Influence of fouling on drag resistance Description of conditions Average coating roughness (μm) Increase in drag resistance (15 knots) Hydraulically smooth surface 0 0% Typical as applied AF coating 150 2% Deteriorated coating or light slime 300 11% Heavy slime 600 20% Small calcareous fouling or weed 1000 34% Medium calcareous fouling 3000 52% Heavy calcareous fouling 10.000 78% Schultz, M. P. Biofouling, 2007, 23, 331-341
Drag resistance caused by fouling Type of fouling Increase in the hulls frictional resistance Source Slime 5% Conn et al. (1953) Slime 8-14% Watanabe et al. (1969) Slime 18% Lewkowicz and Das (1986) Slime 10-20% Loeb et al. (1984) Slime 25%* Lewthwaite et al. (1985) Slime 8-18%* Bohlander (1991) Shell and weed 85% Kempf (1937) 75% covarage shell 4.5 mm * Also some hard fouling and/or macroalgea Munk T., Kane D. and Yebra D. M. In Advances in marine antifouling coatings and technologies Hellio C. and Yebra D. Ed.; Woodhead Publishing Limited: Cambridge, 2009, p 156.
Technologies prior to and after TBT ban Approximate market share prior to TBT ban Approximate market share in volume as of 2010 Hydrolysing 75,0 % Hydrating 55,0 % Hydrating 25,0 % Hydrating Hydrolysing Misc 7,0 % FRC 2,0 % FRC Misc Hydrolysing 36,0 % Hydrating Hydrolysing
The complexity of technologies FRC Hydrating Hydrolyzing FRC Non real Hydrating hydrolysing Hybrid Ion exchange Silyl acrylate What really matters is performance, not the technology! How do we measure performance?
Does AF impact GHG emissions? Potential - Estimated annual bunker consumption for the world fleet is 400 mill metric tons - Estimated overconsumption due to hull conditions (fouling!) around 15 to 30% [MARINTEK, Propulsion Dynamics] CO 2 saving potential of around 190 million metric tons from AF! How to realize potential? - Reduce fuel consumption by minimizing frictional resistance of vessel Presentation will explain background in order to understand potential
AF impact on GHG emissions? Answer: reduce fuel consumption by minimizing frictional resistance of vessel speed fuel environment (wind and weather) resistance hull wave making (hull shape) frictional (hull surface) Thrust Propeller Shaftpower Engine GHG
Skin frictional resistance boundary layer v ext = 0 v ship = 0
Skin frictional resistance boundary layer v ext = 0 boundary layer V ship
Skin frictional resistance boundary layer v ext = 0 V ship v ext,0 = v ship v ship Boundary layer: - No slip condition (v ext,0 = v ship ) - Velocity gradient v ext,0 v ext = 0
Skin frictional resistance boundary layer v ext = 0 0.01 v ext,0 V ship δ v ext,0 = v ship v ship,1 Boundary layer: - No slip condition (v ext,0 = v ship ) - Velocity gradient v ext,0 v ext = 0 - Boundary layer thickness δ (v = 0.01 v ship )
Skin frictional resistance boundary layer v ext = 0 0.01 v ext,0 V ship δ v ext,0 = v ship v ship,1 Main factors influencing boundary layer thickness for given hull: 1) Flow characteristics (laminar, turbulent) 2) Ship speed 3) Surface roughness 4) Water viscosity (temperature, salinity, )
Skin frictional resistance boundary layer flow characteristics δ 1 δ 2 v ship v ship Laminar boundary layer - Regular layer structure - Shear forces from molecular action only (viscosity) - Quick velocity decay, thin boundary layer - At low Reynolds numbers (very low speed, «short» bodies) Turbulent boundary layer - Regular layer structure breaks down (turbulence) - Shear forces from molecular action (viscosity) and larger scale mass movement (turbulence) - Slower velocity decay, thicker boundary layer - Substructure - Common in real life (ships)
Skin frictional resistance boundary layer flow characteristics 0.01 v ext,1 0.01 v ext,2 δ 2 δ 1 v ext,1 = v ship,1 v ext,2 = v ship,2 v ship,1 v ship,2
Skin frictional resistance boundary layer flow characteristics Roughness increases boundary layer thickness, by increasing turbulence (reducing effectivness of viscosity as mechanism for transfer of moment [=velocity reduction])
Roughness A B average height Ra 3.24 µm highest peak to lowest valley height Rt 19.6 µm 3.28 µm 18.9 µm Candries, M. Atlar, M. Mesbahi, E. & Pazouki, K. Biofouling, 2003, 19:S1, 27-36
Roughness A B A B smooth 3.28 µm 18.9 µm Candries, M. Atlar, M. Mesbahi, E. & Pazouki, K. Biofouling, 2003, 19:S1, 27-36
Marintek study Towing tank basin (250m long «swimmingpool») 10m long plates towed through tank Rough application 15% higher friction Different AF coatings, good application <2% difference
Role of hull coatings Frictional resistance ~ fuel consumption Task of hull coatings (outest layer) Ensure low friction (smooth) surface over the whole docking-cycle of a vessel: -Out of dock: set friction level -Docking period (5 years): keep friction level ( anti-fouling) Long time performance decisive as out of dock differences in resistance due to different coatings is modest Accumulated consumption A B good initial poor long time poorer initial good long time time consumption savings for B time
Role of hull coatings Documenting impact of AF for fuel consumption: Document out/in of Dry Dock (DD) AND over docking period Only measuring performance out of and into DD results in substantial uncertainty Hull Performance DD1 actual? actual? DD2 Time
Proposal - components Data logging unit GPS Aft draft sensor Doppler log Fwd draft sensor Shaft Power Anemometer
Proposal process performance indicator Good Hull Performance indicator % speed deviation from speed-power design curve
Proposal Data measurement and logging on board Shaft Power [kw] Tausende 18 16 14 12 10 8 6 4 2 Speed-power design curve Shaft Power versus Speed - Vessel Design Curve 0 6 8 10 12 14 16 18 Speed Through Water [knots] Long trend analysis of speed deviation 10% Deviation from SHP / Speed curve over time 0% Hull performance information Ship Speed Deviation -10% -20% -30% -40% -50% 01.01.2008 31.12.2008 31.12.2009 31.12.2010
Bulker 51k DWT performance analysis of three periods Dry dock 1 Dry dock 2 Dry dock 3 Green and blue period: TBTcontaining AF Yellow: TBT-free SPC Black: TBT-free SPC Speed dev. of 1% ~ Power dev. of 3%
Bulker 51k DWT effect of docking on performance -3.6% -2.8% -11.7% (6 months averages) Differences out of dock very minor, major difference is pre-paint work (substrate)! Differences over docking periods are considerably +3.0% +4.8% +10.1% newbuild after DD after DD after DD before DD before DD before DD
VLCC Coatings: Unknown SPC before DD FRC/FFR after DD Very regular trade (explains regular fluctations) 3 sister vessels Small difference in speed deviation, equals a huge differences in fuel consumption: 1% difference equivalent to ~3% increase in fuel consumption! Challenging to compare sister vessels Vessel FRC/FFR Unknown SPC Av. annual Av. annual A -2.0% -1.0% B -2.1% -0.2% C -1.5% -2.3%
Conclusion Technology is not important Performance is! Several different approaches to monitor frictional resistance Difficult to upscale laboratory measurements to real life Important to monitor changes throughout DD intervals Evaluate long time trends Question the results and reports presented Transparent method needed When ship owners trust performance data, they can also trust the effect of applying the optimal coating