Air lubrication for ships
Small air bubbles, ejected under the ship's bottom and migrating backwards, serve to lubricate the air and thus to reduce the friction in the water, known as ship resistance. The aim is to reduce the fuel consumption of ships.
Active method
With the “ microbubbles ” technique, small air bubbles are blown into the water under the ship's bottom . To do this, the corresponding static water pressure and the surface tension of the water for bubble formation of a total of 1.5 to 3 bar must be overcome. With the dynamic pressure, which depends on the air speed as well as the pipe diameter and length, around 4 to 5 bar must be applied. With a correspondingly shaped ship's bottom, these air bubbles bubble from front to back and to the side and reduce the ship's resistance. This means that fuel consumption and thus emissions can be reduced at the same speed.
Practical execution
The method, which is patented and protected by copyright as the “ Mitsubishi Air Lubrication System ” (MALS), has already been tested in practice - with performance savings of over 10%. Extensive investigations were carried out in the model , the results of which were confirmed with the first large-scale ship - the heavy-lift modular transporter Yamatai , built in 2010.
A second heavy-lift modular transporter, the Yamato , has been equipped with MALS. These ships are relatively wide and have a relatively shallow draft ( Yamatai : 6.37 m), which is why the energy expenditure for blowing in the air is lower than with other ships due to the lower hydrostatic pressure on the underside of the ship.
The system was used for the first time on a cruise ship for the Quantum of the Seas , which was delivered in 2014 . The cruise ship Harmony of the Seas , which went into service in May 2016 , also has an air lubrication system. The two Hyperion-class cruise ships built by the Mitsubishi Heavy Industries (MHI) shipyard for AIDA Cruises also received this system. Fuel savings of 5 to 7% are expected.
The currently (2019) largest container ships, the MSC Megamax 24 class , were also equipped with this system. Air lubrication is discussed for inland waterway vessels and used occasionally ( Futura Carrier ).
Passive method
Following the example of nature, a structured, hairy coating on the outer skin of the ships is intended to keep a permanent layer of air on the hull under water.
In nature, numerous plants and animals can be observed that live in water using this method and thus save energy and heat. They have surfaces that are covered by a silvery shimmering layer of air and do not wet when submerged. On closer inspection, fine hair structures become visible in some animal species, which hold the air layer in place even when there is a current. The Salvinia effect (hydrophilic tips on the otherwise superhydrophobic hair) should help prevent air bubbles from becoming detached and keep the air layer stable.
Practical execution
The mechanisms for transferring the passive functional principle to ship technology are currently being investigated at research institutes and technical universities . This work has not yet been completed and ships have not yet been equipped according to this principle.
See also
literature
- I. Zotti, S. Miotto: Study and numerical simulation of the drag reduction on a flat plate lubricated by air injection by micro bubbles , In: Towards Green Marine Technology and Transport , Taylor & Francis, London, 2015, ISBN 978-1- 138-02887-6 , pp. 67-74.
Individual evidence
- ↑ Air carpets for the new AIDA cruise ships , Schiffsjournal, July 9, 2012. Retrieved May 25, 2016.
- ↑ Raising the baseline for ULCV , DNV GL , December 9, 2018 (English)