MARIN: Air Cavities Reduce Ship Resistance

Evert-Jan Foeth, MARIN
Monday, December 19, 2011
The air supply system of the air cavity ship was reproduced faithfully on model scale.

It is now proven that air lubrication leads to a reduction in power and consequently, leads to fuel savings thanks to the Joint Industry Projects PELS and SMOOTH. The projects have shown that air lubrication makes it possible to reduce power by 15% for an inland ship travelling at normal operational speeds. 

Although it is possible to optimise the wave pattern and the hull, skin friction is almost a constant. Reducing friction by injecting air has been tried before but actually accomplishing a power reduction has proven more difficult. The beneficial effect of air bubbles on the drag for boundary layers is well known but two important effects block its application for displacement ships. Small microbubbles  are effective at reducing drag but are challenging to produce in a laboratory, let alone aboard a ship. Large bubbles that can be produced easily only remain in the boundary layer briefly and their beneficial effect dissipates quickly. This is difficult to verify at model scale when air bubbles do not have sufficient time to escape the boundary layer. Trials with a ship fitted with blowers supplying air through porous plates in the side and bottom plating showed a resistance reduction of only 1% to 2%.
 
A series of cavities in the hull filled with air, whereby the boundary layer is removed altogether, proved to be far more effective. However, a poorly designed cavity can increase resistance and some hull forms are not suited. Together with DST and DAMEN Shipyards Group, a series of model tests and trials with the modified inland ship Kraichgau were performed and results showed net power savings as high as 15%. The ship performed equally well in both deep and shallow water. Tests where Kraichgau sailed unnervingly close to passing ships, bridge pylons and riverbanks confirmed that the cavities remained filled with air and continued to operate as intended. Addressing questions such as how we can get bubbles to work and how much we really gain from air cavities, MARIN will continue its research on air lubrication.
 
About the Author
Evert-Jan Foeth is project manager Ships at MARIN, the Maritime Research Institute Netherlands. MARIN offers simulation, model testing, full-scale measurements and training programs, to the shipbuilding and offshore industry and governments.  For more information:e.j.foeth@marin.nl.
 
 
(As published in the December 2011 edition of Maritime Reporter & Engineering News - www.marinelink.com)

Technology

Scorpene Submarine Data Leak: Setback to Indian Navy

India has began multiple investigations to determine the extent of damage caused by the reported massive leak of secret data detailing the combat and stealth capabilities

NOAA Engineers a Better Current Sensor for Mariners

Navigating into seaports is now safer and more efficient for mariners thanks to improved NOAA technology that ships rely on to give them information about currents.

SMM 2016: World Premieres from around the Globe

Some 50,000 trade visitors from the whole of the world are expected in Hamburg for the start of SMM in less than two weeks. And once again, it is fully booked – with a total of more than 2,

Environmental

NParks, Keppel in S$2.08 mln Partnership for Restoring Singapore Forest Wetlands

The National Parks Board (NParks) and Keppel Corporation today unveiled plans for a partnership to restore the freshwater forest wetland ecosystem historically

C-Job Designs Flettner Freighter for Switijnk

The Dutch shipping company family Switijnk has contracted C-Job Naval Architects to develop a Rotor Sail-equipped design to meet their specific loading and sailing profile.

Vitol's Malaysia Terminal Suspends Ops after Spill

VTTI, the storage unit of world's largest oil trader Vitol, has suspended operations at its terminal in southern Malaysia following an oil spill, two industry sources said on Friday.

Marine Power

MN100: R.W. Fernstrum & Company

The Company: R.W. Fernstrum & Company set the standard in marine heat exchangers over 65 years ago, building a reputation focused on innovation. Today, its commitment is to continual improvement,

US Navy Ships Conduct Astern Replenishment-at-sea

“While replenishments-at-sea are routine, astern refueling is unique and requires precise navigation and coordination,” said Lt. Cmdr. Jason Ileto, fleet replenishment scheduler for Commander,

Better Turbocharger Performance, Proven Tech

Engineer wisdom: Nothing is worse as the right idea at the wrong time. But with the new ECOCHARGE Two-Stage Turbocharging System MAN D&T has reached both goals.

Marine Materials

MN100: R.W. Fernstrum & Company

The Company: R.W. Fernstrum & Company set the standard in marine heat exchangers over 65 years ago, building a reputation focused on innovation. Today, its commitment is to continual improvement,

Alfa Laval Launches DuroShell LPG/E Cargo Condenser

With the new Alfa Laval DuroShell plate-and-shell heat exchanger, Alfa Laval aims to strengthen its offering in LPG/E cargo reliquefaction with a construction that

Five Minutes with Paul Switzer

Five minutes with Paul Switzer - Manager, Shipbuilding & Offshore, Viega   For readers not familiar with Viega, please give a ‘birds eye’ view, putting the company

Marine Equipment

MV WERFTEN, Foreship Sign Design Agreements

MV WERFTEN signed a letter of intent with the engineering company Foreship in Stralsund today. The agreement includes parts of the basic design as well as design,

Zumaia Offshore Acqires MPP Workboat Aitana B

In April 2016 Zumaia Offshore, S.L., leading workboat owner and operator based in the Basque Country, took delivery of the Cummins-powered MPP workboat “Aitana

Maersk Line's Innovative Smart Reefers

Have you heard about Maersk Line's smart reefers that can listen and talk? Cutting edge technology that reduces risk in customer supply chain, claims Maersk Line.

 
 
Maritime Careers / Shipboard Positions Maritime Contracts Maritime Standards Naval Architecture Navigation Offshore Oil Pipelines Port Authority Salvage Ship Electronics
rss | archive | history | articles | privacy | contributors | top maritime news | about us | copyright | maritime magazines
maritime security news | shipbuilding news | maritime industry | shipping news | maritime reporting | workboats news | ship design | maritime business

Time taken: 0.0911 sec (11 req/sec)