The cost of fuel is a significant contributor to naval vessel running costs. Last year the Japanese carrier NYK Line announced it had successfully completed trials of the Mitsubishi Air Lubrication System (MALS) which put quite simply, uses air bubbles to reduce drag. They have reported a not insignificant fuel reduction of 6%. With continuing pressure on Royal Navy operating costs is this something that could be retrofitted to existing ships and designed in to new ones?
NYK used two heavy equipment carriers, the Yamatai and Yamato, both just under 20,000 dwt.
The NYK press release provides more detail
The air-lubrication system effectively reduces the frictional resistance between a vessel’s bottom and the seawater by means of bubbles generated by supplying air to the vessel’s bottom. In fact, this was the world’s first permanent installation of a system using an air-blower. The system was installed on the two vessels when they were built, and the experiments were conducted during actual sea passage. This project has been subsidized through Japan’s Ministry of Land, Infrastructure, Transport and Tourism’s “Support for Technology Development from Marine Vessels for Curtailing CO2” project from fiscal 2009, and has also been supported by the ship classification society Nippon Kaiji Kyokai (ClassNK).
The experiments were designed to verify fuel reduction, examine the behavior of the air bubbles supplied to the vessel bottom under various operational and sea conditions, confirm the relationship between the amount of air supplied and its effect, and validate CO2 reduction.
After reviewing the data obtained by the two vessels for two years under various weather and sea conditions, the optimal control mode of how the bubbles behave in actual sea conditions was confirmed. Compared to the 10 percent reduction measured during sea trials, the reduction of CO2 emissions was confirmed to average 6 percent under various weather and sea conditions. This project was done as a challenge toward the world’s first permanent installation of such a system, and we are proud to have confirmed such meaningful energy savings during actual sea voyages.
The project has been completed, but NYK, MTI, and NYK-Hinode Line will continue to conduct performance analyses on actual vessels and device reviews during dry docks to achieve optimal operation. At the same time, the NYK Group will strive to install the system on other types of vessels for greater energy-saving operations.
Air is discharged through a series of hull bottom vents via a header tank and pressure control system
Both the Yamatai and Yamato have a relatively shallow draft so in order to confirm the systems suitability for use on larger conventional deep draft vessels the Soyo, 91,000 dwt bulk coal carrier has also been fitted.
The German cruise line, Aida, has also ordered the system for its new cruise ships and work is ongoing to create a system that traps the bubble layer so it does not slip up the sides of the hull reducing efficiency.
The conventional wisdom is that frigates and destroyers with their deep V shaped hulls don’t work very well with an air lubrication system but the larger and fatter ships are much better suited.
However, MHI has fitted their system to a ferry owned by the A Line company, the Naminoue is a high speed slender hull design.
MHI and A Line have confirmed a 5% reduction in wave heights of up to 3m
An obvious problem in the naval domain is the hydrodynamic noise that an in use system would make but it would not have to be switched on in high threat environments and this might even be an advantage, masking acoustic signatures.
The DK Group from Denmark has an air lubrication system that can be retrofitted to existing vessels, they claim an installation time of 14 days and a return on investment of between 18 and 30 months.
I expect its not all rosy though, questions remain about its impact on handling, corrosion and maintenance. As with all new technologies, kinks are there to be ironed out.
The Royal Navy has shown great interest in fuel saving measures, from advanced anti fouling coatings to transom flaps, it fully recognising that fuel is going to be an increasingly large factor in running costs.
Could air lubrication play a part in future large Royal Navy and Royal Fleet Auxiliary vessels or is it a system that is limited to flat bottomed vessels, none of which we have now or will have in the future?