Modes of Transport - Maritime Shipping

The Green Ship of the Future
The Green Ship of the Future

Maritime shipping is a particularly environmentally friendly and efficient mode of transport. In comparison to land and air traffic, it produces less emissions in terms of the load and distance transported, and is substantially more energy-efficient. Whereas 90% of intercontinental freight transport is handled by seagoing vessels, these only account for around 2.7% of global emissions. However, as with all modes of transport, substantial energy savings can also be attained in maritime shipping, thereby reducing costs. Numerous technologies have been and are being developed in Germany which help to make shipping more economic. The new rules of the International Maritime Organisation (IMO) on the transition from heavy fuel oil to much more expensive marine diesel are also resulting in ongoing efforts to conserve energy.

Propulsion technologies

In recent years, a number of efficient propulsion technologies have been developed which have yet to be deployed in many types of vessels. The diesel engine has become accepted as the dominant propulsion technology for ships. Electronic direct injection (the common rail system) in particular has achieved clear efficiency gains. German technology is also used in efficient automatic engine control systems, which can save 1% of fuel. If this is optimised to provide a maximum steady output, the "Dual/Multi Maximum Continuous Rating" (MCR), the savings can be as high as 3%.

Substantially higher fuel savings, of around 12%, can be produced by waste heat recovery (WHR). The pod drive, which has proved its worth as a propulsion system for certain types of vessel, such as ferries, is also particularly energy efficient. Unlike conventional ship drives, pod drives are not installed in the hull, but beneath it in a nacelle. Since the nacelle/propeller unit can be turned full circle, the combination of the two serves as a rudder. Conventional (shaft) drives, in contrast, also require a rudder for steering. The advantage derives from the diesel-electrical drive concept which can be adapted to suit the prevailing conditions for different loads and speeds and which can thus conserve up to 15% of fuel.

Electrically powered vessels using fuel cells are regarded as particularly forward-looking. These utilise a key technology for a sustainable energy supply, and are therefore at the focus of research and development, demonstration and marketing of efficient energy technologies. Their principle is as simple as it is ingenious: electricity and heat are generated in a single step when hydrogen and oxygen react. One innovation by Germany's shipbuilding and component supply industry is the development of fuel cell technology for the onboard power supply of vessels, particularly at sea, but also for the energy supply in port.

Alternative propulsion systems and energy sources

In Germany, research is currently taking place not only into hydrogen, but also natural gas and biofuels as alternative fuels for use in maritime transport. Here, liquefied natural gas (LNG) offers great potential: it is already in use in dual-fuel engines on gas tankers. As the compressed raw material is transported from the gas fields, the LNG carriers use part of their load for fuel. On the empty return journey, in contrast, the engines use diesel fuel. If the necessary fuel-supply infrastructure were in place, purely gasdriven engines could be used in scheduled coastal and ferry services. This could cut CO2 emissions by around 20%, and emissions of other pollutants would also drop significantly. During waiting times in ports, the provision of a gas connection to the on-board electricity generator could offer an efficient and low-emission alternative to powerlines from the land. Wind also appears to be a highly promising source of propulsion. Some German shipping firms have installed German-developed skysail systems on their vessels. These systems can cut fuel consumption by up to 35%, depending on the wind. A German firm is currently developing Flettner rotors for ships which save between 30 and 50% of fuel and thus make a decisive improvement to energy efficiency. The Flettner rotor is an aerodynamic drive in the form of a rotating cylinder exposed to a moving airstream, and thanks to the Magnus effect it generates a force perpendicular to the direction of the airstream. Germany has developed a high level of skills in this field and has correspondingly capable manufacturers.

Technical innovations

The skysails systems
The skysails systems
German shipping firms are increasingly banking on technical innovations to save energy or fuel. An optimised hull design slides more efficiently through the waves. Optimisation of the design and shape of the rudder and propeller can save additional energy. By reducing the water resistance of the ship, anti-fouling paint reduces fuel consumption by between 1 and 6%. The innovative "air cavity system" (ACS) produces fuel savings of up to 15%: it uses compressors to force compressed air into channels under the flat hull. The air cushion reduces the contact area between the hull and the water, thereby minimising friction which slows down the ship's movement. Also, the use of a dynamic trimming assistant (DTA), which calculates the optimal trimming of a vessel, can reduce resistance and save up to 5% fuel.

In addition to payload optimisation, many shipping companies are now also looking to "slow steaming" to cut fuel consumption. Even an 8% cut in speed can - calculated over the lifetime of the vessels - save around a quarter of the propulsion energy required. This more than covers the longer transport periods and additional operating costs.