How Penguin’s Air Tricks Help the Shipping Industry

Over 80% of the world’s goods measured by volume are transported by ship. According to the United Nations Trade Development (UNCTAD), the transport accounts for 3% of the world’s greenhouse gas emissions.

“Many people think they can probably simply switch fuel types or maybe even fully electrify these larger vessels, but as of today, technology isn’t too far away. Battery packs alone must replace all the goods that would otherwise be transported.”

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

This is where air bubbles come out. And Penguin, about that.

“Lubrication” with air

Any child who played with a boat in a bathtub or pond can say that it is difficult to make a toy boat faster. You need to use a little force. If you stop applying forces, the boat will stop relatively quickly. This is because the boat encounters resistance in the water.

This phenomenon applies to large ships as well. 70-80% of the ship’s resistance comes from the encounter between the hull and the water. This resistance can be counteracted by bubbles that can reduce the bubbles by 10%-20%. This idea comes from nature, where penguins release small bubbles from their wings, moving through the water faster.

Pushing air under the hull using a compressor creates a thin layer of air so that the ship does not come into contact with the water very directly. The goal is to create a “bubble layer” that envelops as much of the flat bottom of the hull as possible.

But everyone who blows the bubbles knows that the bubbles burst sooner or later. When a large bubble bursts, many small bubbles form. But even these can have positive effects.

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

“We know that air lubrication leads to reduced fuel consumption, but it’s really hard to predict how effective an air lubrication system will be before it works,” says Koushan.

“It is also difficult to study the full-scale foam behavior on operational vessels, so clinical testing is extremely important to better understand how these systems work,” explains senior research scientist Luca Savio.

How can I study bubbles underwater?

To better understand how air lubrication works, researchers analyzed the bubbles using both laboratory experiments and numerical tools. How do they move, when and where do they burst, and what impact will this have?

For many years, researchers have developed methods to measure resistance that can be measured by air lubrication. It also allows you to follow a single bubble using advanced high-speed cameras and study the basic physics behind it.

Advanced mathematical tools are used to analyze the effects of air lubrication systems and their interactions with propellers on different types of vessels. This will improve the system.

To simplify it a little, the algorithm counts bubbles. You can say how many bubbles are, how big they are, how fast they are moving, how far they are from the hull. At the same time, researchers measure friction between the hull and water with or without air and pay attention to the differences. This is affected by the properties of the bubble.

Working at once

Therefore, the interaction with hull design, air lubrication, and propeller selection is complicated and requires working together. To function optimally, everything must work together for air lubrication. If the calculation is off, the result can be an increase in energy consumption.

A compressor that pumps air under the hull requires energy. If all parts of the system are not optimized, energy calculations can end in red.

Interaction with the propeller is also important. The bubble should not find a way there. This can also reduce efficiency. The propeller design must adapt to bubble lubrication.

Great possibilities

So far, only a few hundred people have used or ordered lubrication systems in the world.

“Air lubrication systems have traditionally been installed on existing vessels, meaning that the ship’s hulls, propellers and machines are not optimally configured to take advantage of the system’s full potential,” says Savio.

Several new ships were built with air lubricant. However, there are no clear guidelines yet as to how such a ship should be designed. Therefore, we risk not achieving the desired savings.

“Including the climate impact of air lubrication in regulations provides incentives for businesses using lubrication systems and could also help persuade more shipping companies to use them,” Savio said.

Air lubrication testing is being conducted at Sintef’s cavitation tunnel. The cavitation tunnel was originally built in 1967 and upgraded in 2019. Much smaller than a ship, but large enough to test a lubrication system, allowing the vessel to achieve water flow levels as strong as it is exposed to sea.

The windows along the tunnel allow you to count, measure and track air bubbles.

Air lubrication was one of the topics discussed in June when more than 60 industry officials and researchers gathered at the first international conference on air lubrication at the Norwegian Ocean Technology Centre in Sintef, Trondheim.

Most suppliers of air lubrication systems participated in the meeting (Alfa Laval, Damen, Foreship, Hundai, Mitsubishi, Samsung, Silverstream).