Bubbles make headway for shipping industry

Introduction

Almost 90% of goods around the world are transported by ship, as shipping is still the most economical mode of transport. Given the size of this industry, it is no surprise that it is a large contributor to greenhouse gas emissions. According to a 2014 study on greenhouse gases conducted by the International Maritime Organisation (IMO), ocean-going vessels released 938 million metric tonnes of carbon dioxide in 2012 – 2.6% of total global emissions. By 2050 carbon dioxide emissions from international shipping could increase by between 50% and 250%, depending on economic growth and developments in energy-saving technologies.

What steps have been taken to make this industry more energy efficient?

Shipping companies have taken various measures to tackle gas emissions, mainly by reducing fuel consumption. This has environmental as well as financial benefits, as fuel comprises nearly 50% of a ship’s operating costs. Rising fuel prices and stringent environmental regulations have led to the development of various technologies to achieve emission targets and create more fuel-efficient ships.

Technology to improve fuel efficiency and/or reduce gas emissions include:

• air lubrication systems;
• dual fuel engines (LNG and diesel);
• rotor sails;
• modifications to ships’ bulbous bows;
• on-board DC grid systems; and
• energy-saving propeller attachments.

The last decade has seen the implementation of air lubrication technology, which reduces the frictional drag on a ship’s hull, thereby improving its fuel efficiency. It works by creating air bubbles beneath the hull, which form a layer of air that reduces the resistance between the ship and the water. The idea of using air to reduce friction in ships has been around for more than a century, with a sustainable solution first being developed by Mitsubishi – the Mitsubishi Air Lubrication System. Since then many other companies have followed suit with their own technologies. These include SAVER AIR from Samsung Heavy Industries and the Silverstream System from Silverstream technologies.

A considerable number of patents were filed in this field before 2000, but since 2010 there has been a significant growth in patent registration. The major innovation hubs are in the United States, France, Korea, Japan and China, as well as across Europe. The major players for this technology are as follows:

• Mitsubishi heavy industry (Japan);
• Samsung heavy industry (Korea);
• Hyundai heavy industry (Japan);
• Silverstream technology; and
• IHI corporation (Japan).

Although this technology has significant advantage in terms of cost and fuel efficiency, it still has its limitations. For example, air lubrication systems can only be used on flat-bottomed ships. Further, air bubbles flowing from the hull surface can enter the propeller, which affects its efficiency, as well as creating excess noise and vibration. While experiments conducted by Mitsubishi suggest that air bubbles have only a negligible effect on the propeller, rough seas and changes in fluid density can produce unfavourable results.

In addition, it remains to be seen how this technology will apply to ships without flat bottoms (eg, cruise ships with V-shaped hulls).

As the date for the IMO 2020 Fuel Sulphur Regulation to come into force approaches, more energy-efficient technologies are needed to offset the high cost of very low sulphur fuel oils and scrubber technologies. Since no single technology can achieve the necessary economic savings, it seems likely that different technologies will have to be combined – however, it remains to be seen precisely how this will be achieved. There are also hopes for new technologies to help to make the industry more eco-friendly.