A ship needs a lot of energy to move through the water. At the same time it carries many tonnes of cargo. This is the reason why ships are the most efficient means of transport. However, both the global climate situation and rising costs for fossil fuels put a demand on shipping to become even more efficient.
The energy needed on board a ship is normally converted by diesel engines from chemical energy stored in the fuel oil into mechanical and electrical energy. But the combustion of fuel results in emissions of carbon dioxide (CO2). While CO2 as a natural component of the atmosphere is not a harmful substance in the stricter sense, it contributes to global warming and climate change.
The ship's propulsion motor which turns the propeller thus pushing the hull through the water demands most energy. The laws of physics rule that the propulsion power is disproportional to the ship's speed. This means that significantly more power is needed just to sail a bit faster. More power means more fuel consumption resulting in higher CO2 emissions.
The other way around, when the ship can sail slower, fuel consumption can be reduced quite a lot resulting in less CO2 emissions. Over recent years, TT-Line thoroughly analysed time schedules and port operations with the objective to reduce harbour times for the benefit of a longer journey. As a result, the annual fuel consumption could be reduced by abt. 15 % with accordingly fewer emissions.
Another room for improvement is onboard operations. Our well trained crews are highly aware of the fuel consumption of their ship. On basis of many years of experience and continuously taking into account nautical- and traffic conditions, ballasting and trim, the utilisation of the ship's power plant and many other operational aspects, the ships are operated as efficient as possible.
On the technical side, TT-Line has always tried to realize the most streamlined, thus efficient hull form design available when a new ship was built. A streamlined hull with low resistance means less propulsion power for the desired speed.
TT-Line's newest generation of ferries Nils Holgersson and Peter Pan are even driven by podded propulsors. The electric propulsion motors of these diesel-electric ships are located in two pods (gondolas) to which the propellers are attached. These steerable propulsion devices are located outside the hull, hanging underneath the stern. By omitting propeller shafts and separate rudders, quite significant power savings could be achieved compared to a conventional configuration.
Heat recovery is another technical means to reduce the energy demand on board. For instance on all diesel-electric ships of TT-Line, heat contained in the engine cooling water is used for heating purposes of the accommodation.
TT-Line is also modifying their existing ships whenever feasible in order to further reduce fuel consumption. Small modifications and reconditioning of the ship's hull is one aspect of this. As a good example, the underwater parts of hulls are sandblasted after a couple of years of operation in order to restore its initial smoothness.