‘Bubbles’ – taste that word – and think soda, soap, play and well-being. But did you know that air bubbles can also reduce fuel consumption and emissions from oceangoing vessels?

By Kari Williamson - Published 09.09.2025
More than 80 percent of the world's goods, measured by volume, are transported by ship. This transport accounts for three percent of global greenhouse gas emissions, according to the UN Trade and Development (UNCTAD).

“A lot of people probably think that we can simply switch fuel types or perhaps completely electrify these large ships, but as of today, the technology has not come that far. The battery packs alone would have to take the place of all the goods that would otherwise be transported,” says Kourosh Koushan, a special adviser at SINTEF.

“The fastest way to reduce emissions from ocean freight traffic is to make ships as energy efficient as possible,” he says.

This is where air bubbles come into play. And penguins, for that matter.

“Lubricating” with air
Any child who has played with a boat in a bathtub or pond can tell you that it’s tricky to get a toy boat to go fast. You have to use a little force, and if you stop applying force, the boat stops relatively quickly. This is because the boat encounters resistance in the water.

This phenomenon applies to large ships as well. Seventy to eighty percent of a ship’s resistance comes from the encounter between the hull and the water. This resistance can be counteracted by bubbles, which can lower drag by 10-20 percent. This idea comes from the natural world, where penguins release small bubbles from their feathers to move faster through the water.

By pressing air down under the hull with compressors, a thin layer of air is created so that the ship does not have as much direct contact with the water. The goal is to create a ‘bubble layer’ that envelops as much of the flat bottom part of the hull as possible.

But everyone who has blown soap bubbles knows that bubbles burst sooner or later. When a big bubble bursts, many small ones are formed. But even these can have a positive effect.

The big question is how the air will behave under the hull. Will the air create bubbles? Will air pockets be created? How do they behave? These partially unanswered questions make it difficult to accurately calculate resistance.

“Although we know that air lubrication leads to a reduction in fuel consumption, it’s really difficult to predict how effective an air lubrication system will be before it is put into operation,” says Koushan.

“Studying the behaviour of the bubbles at full scale in an operational ship is also challenging. That’s why laboratory tests are still very important to better understand how these systems work,” explains senior research scientist Luca Savio.

How can we study bubbles underwater?
To better understand about how air lubrication works, the researchers use both experiments in laboratories and numerical tools to analyse the bubbles. How do they move, when and where do they burst, and what effects does this have?

Over the years, researchers have developed methods to measure how much resistance can be prevented with air lubrication. They can also follow a single bubble using advanced high-speed cameras, making it possible to study the fundamental physics behind it.

Advanced mathematical tools are used to analyse the effect of air lubrication systems on different types of ships and their interaction with the propeller. This makes it possible to improve the systems.

Simplifying somewhat, we can say that algorithms count the bubbles: How many are there, how big are they, how fast are they moving, and how far are they from the hull? At the same time, researchers measure the friction between the hull and the water with and without air to note the differences. This is influenced by the properties of the bubbles.

A lot that has to work in unison
The interactions between hull design, air lubrication and propeller selection are thus intricate and require working in unison. Everything has to work together for air lubrication to function optimally. If calculations are off, the result could be an increase in energy consumption.

Energy is required for the compressors that pump air under the hull. The energy calculation can end up in the red if all parts of the system are not optimized.

The interaction with the propeller is also important. The bubbles should not find their way there, because this too can reduce efficiency. The propeller design needs to be adapted to bubble lubrication.

Great potential
So far, only a few hundred of the world’s 50 000 ships use or have ordered air lubrication systems.

“Air lubrication systems have traditionally been installed on existing ships, which means that the ship's hull, propeller and machinery are not optimally configured to exploit the full potential of the systems,” says Savio.

Several new ships have been built with air lubrication. But there are still no clear guidelines for how such ships should be designed, and therefore we risk not achieving the desired savings.

“Including the climate impact of air lubrication in the regulations would provide incentives for companies that use air lubrication systems. It could also help convince more shipping companies to use them,” Savio says.

Some air lubrication facts:
Air lubrication trials are taking place in the Cavitation Tunnel at SINTEF. The cavitation tunnel was originally built in 1967 and upgraded in 2019. It is much smaller than a ship, but large enough to test air lubrication systems, and it can achieve water flow levels as strong as ships are exposed to at sea.

Windows along the tunnel allow air bubbles to be counted, measured and tracked.

Air lubrication was one of the topics discussed when more than 60 industry representatives and researchers gathered for the first international conference on Air Lubrication, at SINTEF’s Norwegian Ocean Technology Centre in Trondheim in June.

Most suppliers of air lubrication systems were represented at the conference (Alfa Laval, DAMEN, Foreship, Hyundai, Mitsubishi, Samsung and Silverstream), in addition to shipping companies, shipyards, propeller suppliers, classification societies and other related industries.
Contact Kourosh Koushan