Bodewes Binnenvaart, part of the Damen Shipyards Group, believes it had found a unique way of meeting increasingly strict environmental standards while simultaneously saving on fuel costs by means of a technology called air chamber energy saving (ACES).
Even though transporting a tonne of cargo long distance by water is already more energy-efficient than any other transport mode, boosting the energy efficiency of shipping remains a key goal for the industry.
Moving a single tonne of cargo over a distance of one kilometre by container shipping barge results in the production of some 33 grams of carbon dioxide emissions. Road transport of the same cargo weight more than triples such emissions to 105 grams, according to CE Delft Stream.
Further reducing hull resistance, and thereby fuel consumption, was the challenge Damen faced in its bid to contribute to the greatest possible energy efficiency of a vessel for the benefit of both shippers and shipping companies. According to Damen, optimising the vessel's propulsion system plays an important role in this but optimising its hull shape certainly does too.
Resistance components as a function of vessel speed
Broadly speaking, the resistance of a vessel in water can be subdivided into the following components: friction resistance, form resistance and wave-making resistance, of which the friction resistance at the key speeds for transport vessels makes up some 60-70 percent of total resistance.
The Energy-saving Air-lubricated Ships Project (commonly referred to by its Dutch acronym PELS) instigated by Damen Shipyards is geared to reducing the frictional drag on ships by inserting air between the ship's hull and the water. Research undertaken together with research institutes Marin in Wageningen and DST in Duisburg, Germany, and others, investigated the nature of the physical mechanisms, how these could best be incorporated into the design of a vessel and which energy savings then become possible.
This research showed that the air chamber concept, whereby air is blown into specially formed recesses in the bottom of the ship, resulted in the greatest efficiency.
Bodewes Binnenvaart subsequently submitted an existing, conventional inland shipping barge for the validation of the research on the scale of a model.
After comparing and analysing the data collected during the model tests and test ride, project members decided on the definitive form the conversion of the conventional tanker into an air chamber vessel would take.
In 2009 and 2010 various measurements were executed on this ship in different conditions on Dutch inland shipping routes to build up a representative picture of the average sailing profile for a similar vessel.
Subsequently the data acquired during the test sailings were minutely compared with the data collected during the model tests conducted at the facilities of the two research institutes Marin and DST, so resulting in a reliable and workable mathematical model being made available.
The outcome of these readings was a reduction in resistance of some 10 to 20 percent at typical operational speeds for this ship. Applied to a standard Damen River Liner this resulted in fuel savings as represented in the figure below:
Application of the ACES concept yields annual fuel savings for users of around 15 percent on average.
For a conventional vessel with a usage of 400 cubic metres a year, application of ACES would thus save the owner some 60 cubic metres a year.
Alongside attractive savings on a ship's operating expenditure (OPEX) the system thus also yields a reduction in carbon dioxide emissions of some 15 percent.
Because the system is not linked to a particular type of engine or specific number of revolutions and its workings are not influenced by the use of follow-up techniques for exhaust fumes, Damen said its application represents a welcome addition to the options currently available to ship owners.
After completion of the PELS 2 project, additional research was carried out with the support of the European Commission within the Framework Programme for Research and Development.
The development of the air chamber energy saving (ACES) system has now been completed, and the system may easily be fitted in dry bulk goods vessels as well as the tankers of Bodewes Binnenvaart. Vessels fitted with this construction will be registered by Bureau Veritas according to the Class Notation: "Air Lubricated Vessel".
The system will also be brought onto the market for vessel types other than the standard DRLs and DRTs, so that it will be as widely applicable as possible for all inland shipping.
