Blowing bubbles to lower emissions

Air lubrication systems work by coating the flat bottom of the vessel with a layer of micro-bubbles. The improved frictional resistance reduces the fuel consumed and, in turn, emissions produced.

We spoke to Noah Silberschmidt from Silverstream Technologies to gain a better understanding of how their air lubrication system works.

Q. How does your air lubrication system work?

A. The Silverstream® System operates by deploying a uniform carpet of air to lower the frictional resistance between the hull of a vessel and the water. A natural phenomenon called ‘shearing’, where the interaction of water and air in the air release units (ARUs) generates a carpet of microbubbles that covers the full length of the flat bottom of a vessel. These microbubbles are uniform in size and do not merge or collect.

Q. How much can CO2 emissions be reduced?

A. Fuel consumption and associated CO2 emissions can be reduced by 5-10% net, depending on vessel type.

Q. Do the air bubbles have an influence of noise or vibration at the propeller?

A. The bubbles are small in diameter (1-3mm) and emerge at hydrostatic pressure, eliminating the tendency to escape up the vertical sides of the hull. This means we can coat the entire flat bottom of the vessel and maximise savings.

Research is ongoing into the positive consequential outcomes our systems on the operation of the vessel. This includes a reduction in hull fouling, dampening of noise and vibrations as well as the suppression of a vessel’s underwater radiated noise (URN) signature. Anecdotal reports have suggested that there is a decrease in vibrations on passenger ships when the Silverstream® System is in operation, but this needs further scientific study to verify.

Q. Tell us more about the air release units (ARUs)?

A. The Silverstream® System works by installing 10-12 ARUs in an arrowhead formation along the flat bottom of a vessel, inside the double hull. The system is designed for a small footprint. The oil free compressors are energy efficient and compact enough to fit in bespoke engineering spaces. The system is flexible and modular to work for newbuilds and retrofits alike.

Q. How long does it take to retrofit your system?

A. Retrofits of the Silverstream® System are usually carried out within a two week dry-docking. In some cases, it can be achieved within one week. Riding squads are often used during commissioning to prevent any commercial issues arising, such as off hire and time out of service. Co-operation with owners, operators and relevant experts is important whether a retrofit or installing on a new build vessel.

Q. What are the maintenance requirements?

A. Compressors can be maintained in service and ARUs can be inspected at routine dry-docking intervals. Note that if the system is out of service, there are no adverse effects of drag as the ARU plates are flat and are set flush with the hull. Maintenance requirements have been reduced thanks to relatively few moving parts. Training is provided to operators so that maintenance frequency is prolonged.

Q. What is the power demand of this system?

A. Power demand varies between each installation, but it is kept low because the natural energy of the vessel moving through the water is used to shear air onto the flat bottom as opposed to expelling at pressure. This is the same phenomenon that causes white caps on waves. To accurately assess savings in operation it’s always calculated as net of energy used.

Find out more
Learn more about reducing shipping’s greenhouse gas emissions via our ‘Navigating Decarbonisation’ area.

More details about Silverstream Technologies can be found on their website.