Periodic Reporting for period 3 - AIRCOAT (Air Induced friction Reducing ship COATing)
Reporting period: 2021-05-01 to 2022-04-30
The overall goal of AIRCOAT was to develop a disruptive hull coating that reduces the frictional resistance of ships. The AIRCOAT project enhanced a passive air lubrication technology that utilises the biomimetic Salvinia effect. This effect enables trapping air through combination of a hydrophobic micro-structured surface with hydrophilic pins. The project technologically implemented this effect on a self-adhesive foil system. Applying a ship with such an AIRCOAT foil will produce a thin permanent air layer, which reduces the overall frictional resistance while acting as a physical barrier between water and hull surface.
Besides substantially reducing main engine fuel oil consumption and hence exhaust gas emission, the air barrier further inhibits the attachment of fouling, the release of biocide substances (of underlying coatings) to the water and mitigates the radiation of ship noise. As a refit technology, a final product would be immediately applicable to the whole fleet, is independent of the fuel type and can be combined with other efficiency improving technologies. Consequently, the technology creates both an economical and an environmental benefit.
Besides substantially reducing main engine fuel oil consumption and hence exhaust gas emission, the air barrier further inhibits the attachment of fouling, the release of biocide substances (of underlying coatings) to the water and mitigates the radiation of ship noise. As a refit technology, a final product would be immediately applicable to the whole fleet, is independent of the fuel type and can be combined with other efficiency improving technologies. Consequently, the technology creates both an economical and an environmental benefit.
Within the project extensive results have been achieved, selected key results are:
- Novel structuring and replication technologies were developed to reproduce the micro pillar structures required for passive air lubrication. Improved production processes for embossing of microstructures on thermoplastic and silicone material.
- Experimental and numerical investigations revealed possibilities, challenges, and limitations of air retaining surface structures. A complex dependence of air layer durability, drag reduction, biofouling prevention, water depth, flow speed, material composition and industrial manufacturability exists. This indicates that compromises are necessary.
- Geometry and size of surface structure were determined by theoretical calculations and simulations on high performance computer cluster which showed frictional drag reduction of the order of 10% is possible. Depending on ship speed and length, the size of the surface structure has to be adapted.
- Experimental setups were retrofitted with devices for monitoring and controlling dissolved oxygen levels to realise steady conditions.
- Friction force experiments were performed under near-operational at showed a drag reduction of up to 9% at higher speeds. The degassed foil also showed a drag reduction at low speeds.
- Prevention of biofouling were demonstrated for an intact air layer.
- Technologies for air layer monitoring were developed, evaluated and tested.
- Industrial production and application procedures were developed.
- Two real world applications were performed, one on a research vessel and another on a container vessel validating application procedures and operability of the product.
- The environmental benefit to the global fleet was determined by updating the ship emission model STEAM including the effect of friction reduction from AIRCOAT
- A cost benefit analysis performed to determine the potential economic impact of the AIRCOAT technology showing that a monetary advantage will increase with increasing fuel costs.
- Noise emissions reduction was proven with noise dampening increasing with increasing air layer thickness.
- Six key exploitation results were defined leading to a commercialisation plan: AIRCOAT foil itself as a product, a prototype machine to continuously produce foil covered with a sub-micron surface structure, a wall function applicable for CFD calculations, the general model of AIRCOAT that demonstrated passive air lubrication, a semi-industrial production process and the updated STEAM model.
- Novel structuring and replication technologies were developed to reproduce the micro pillar structures required for passive air lubrication. Improved production processes for embossing of microstructures on thermoplastic and silicone material.
- Experimental and numerical investigations revealed possibilities, challenges, and limitations of air retaining surface structures. A complex dependence of air layer durability, drag reduction, biofouling prevention, water depth, flow speed, material composition and industrial manufacturability exists. This indicates that compromises are necessary.
- Geometry and size of surface structure were determined by theoretical calculations and simulations on high performance computer cluster which showed frictional drag reduction of the order of 10% is possible. Depending on ship speed and length, the size of the surface structure has to be adapted.
- Experimental setups were retrofitted with devices for monitoring and controlling dissolved oxygen levels to realise steady conditions.
- Friction force experiments were performed under near-operational at showed a drag reduction of up to 9% at higher speeds. The degassed foil also showed a drag reduction at low speeds.
- Prevention of biofouling were demonstrated for an intact air layer.
- Technologies for air layer monitoring were developed, evaluated and tested.
- Industrial production and application procedures were developed.
- Two real world applications were performed, one on a research vessel and another on a container vessel validating application procedures and operability of the product.
- The environmental benefit to the global fleet was determined by updating the ship emission model STEAM including the effect of friction reduction from AIRCOAT
- A cost benefit analysis performed to determine the potential economic impact of the AIRCOAT technology showing that a monetary advantage will increase with increasing fuel costs.
- Noise emissions reduction was proven with noise dampening increasing with increasing air layer thickness.
- Six key exploitation results were defined leading to a commercialisation plan: AIRCOAT foil itself as a product, a prototype machine to continuously produce foil covered with a sub-micron surface structure, a wall function applicable for CFD calculations, the general model of AIRCOAT that demonstrated passive air lubrication, a semi-industrial production process and the updated STEAM model.
In summary, the AIRCOAT project was the first of its kind to produce sets of a biomimetic self-adhesive ship hull coating with fouling-release and air retention properties incorporating microscopic structures validating its operability on macroscopic structures. The large-scale experiment was the first to experimentally demonstrate the drag reduction effect of air-retaining coatings in large scales within a near-operational environment.
Within the project, challenges were identified which have to be overcome before an industrial application:
- Degradation of air layer: three mechanisms have been observed: diffusion in case of unsaturated water, mechanical stress at the water and air interface, and hydrostatic pressure at higher water depth
- Long-time fouling resistance: Sea trials of with foil over several months showed growth of marine organisms on the surface possibly due to the degradation of air by diffusion.
- Conservation of hydrophobic property over long times, which is a challenge not only known in this field.
- Industrial production and application procedures require large investments for industrial equipment and automatic application procedures to cut dry-dock time short.
Within the project, remarkable progress was made in different fields:
- Production: A continuous casting machine for micro-structured surfaces was developed with a wide application range of micropatterned products creating a solid foundation for future research and developments applicable in many sectors; thus, providing a significant societal impact as energy efficiency measures are sought after in many sectors to counteract climate change.
- Simulation: A numerical model (wall function) was developed to estimate the influence of rough surfaces in CFD simulations at lower fidelity and hence with lower computational effort. The model paves the way for further research around micro-structured surfaces such as AIRCOAT, or riblets, as well as a better understanding of the impact of fouling or surface contamination. It can thus be used to provide information to operators of ships and potentially other transportation means as well as policy makers on the impact of surface condition on energy efficiency and potentially influence surface condition monitoring and treatment schedules and associated legislation.
- Methodologies: Tools and methods have been developed to determine the economic and environmental benefits of energy efficiency measures by linking results from the microscopic level with a macroscopic view. E.g. with the extension of FMI’s STEAM model there now is the possibility to consider the effect of changes in friction from either friction reduction measures or biofouling in emission modelling of the global shipping fleet. This can provide more precise information on shipping related emissions to policy makers impacting future legislation and thus creating benefit for the society.
- Experiments: Hydrodynamic test under near-operational conditions showed drag reduction at high velocities and indicated drag reduction for micro-structured AIRCOAT surfaces even without air coverage. As a test patch was successfully applied to a commercial vessel, fully intact after several weeks, this paves the road to full hull application to minimise drag and prevent biofouling without the use of highly toxic paint. With expected fee increase for CO2 emissions and fuel prices the still cost-intensive production and application of foil the AIRCOAT technology becomes more and more attractive for merchants, ship owners and shipping companies. The preservation of natural resources like fossil fuel, the sea and the atmosphere are of great advantage to the society.
Within the project, challenges were identified which have to be overcome before an industrial application:
- Degradation of air layer: three mechanisms have been observed: diffusion in case of unsaturated water, mechanical stress at the water and air interface, and hydrostatic pressure at higher water depth
- Long-time fouling resistance: Sea trials of with foil over several months showed growth of marine organisms on the surface possibly due to the degradation of air by diffusion.
- Conservation of hydrophobic property over long times, which is a challenge not only known in this field.
- Industrial production and application procedures require large investments for industrial equipment and automatic application procedures to cut dry-dock time short.
Within the project, remarkable progress was made in different fields:
- Production: A continuous casting machine for micro-structured surfaces was developed with a wide application range of micropatterned products creating a solid foundation for future research and developments applicable in many sectors; thus, providing a significant societal impact as energy efficiency measures are sought after in many sectors to counteract climate change.
- Simulation: A numerical model (wall function) was developed to estimate the influence of rough surfaces in CFD simulations at lower fidelity and hence with lower computational effort. The model paves the way for further research around micro-structured surfaces such as AIRCOAT, or riblets, as well as a better understanding of the impact of fouling or surface contamination. It can thus be used to provide information to operators of ships and potentially other transportation means as well as policy makers on the impact of surface condition on energy efficiency and potentially influence surface condition monitoring and treatment schedules and associated legislation.
- Methodologies: Tools and methods have been developed to determine the economic and environmental benefits of energy efficiency measures by linking results from the microscopic level with a macroscopic view. E.g. with the extension of FMI’s STEAM model there now is the possibility to consider the effect of changes in friction from either friction reduction measures or biofouling in emission modelling of the global shipping fleet. This can provide more precise information on shipping related emissions to policy makers impacting future legislation and thus creating benefit for the society.
- Experiments: Hydrodynamic test under near-operational conditions showed drag reduction at high velocities and indicated drag reduction for micro-structured AIRCOAT surfaces even without air coverage. As a test patch was successfully applied to a commercial vessel, fully intact after several weeks, this paves the road to full hull application to minimise drag and prevent biofouling without the use of highly toxic paint. With expected fee increase for CO2 emissions and fuel prices the still cost-intensive production and application of foil the AIRCOAT technology becomes more and more attractive for merchants, ship owners and shipping companies. The preservation of natural resources like fossil fuel, the sea and the atmosphere are of great advantage to the society.