One important point that needs to be noted is that fuel efficiency and pollution levels are different across the operating range of ships i.e. the speed at which a ship may run. Ships classified in the optimum range of working have a better fuel efficiency and lower pollution levels compared to those that work in the low operating range. The solution is to maintain an optimum operating range for engines at all times.
Mechanical transmission, a traditional technique for operating engines, is not very effective since the speed of an engine is very closely associated to the speed of the propellers. Electric transmission techniques are comparatively better than mechanical transmission techniques, as they incorporate cables to connect generators and motors. The cables provide flexibility over mechanical shafts and the freedom to choose the ideal location for the engines.
A technique called counter rotating propeller (CRP) propulsion technology also helps in fuel efficiency by improving the ship’s hydrodynamic ability. This refers to the ability to minimize air resistance to its motion in water. As part of the technique, two propellers run in opposite directions thus balancing out the effect of torque. The propulsion systems are arranged in a co-axial manner without being directly connected.
A lot of research is being carried out to develop marine engines that can use alternative fuels like solar or tidal energy to lower their emissions.
A technique using a powerful kite controlled by electronics onboard a ship has been tried to propel a ship. The kites are launched from the bow of the ship and can provide around 20 % of the required power thus reducing the fuel consumption for propulsion. Use of such kites is a novel technique which can enable the ships particularly cargo ships to cut fuel costs and emissions. However the technique needs to be worked upon to enable its use on fast moving ships.
Research is on into the use of air bubbles for propulsion of the ship. As part of the research, air bubbles are blown along the hull creating less drag on the hull and this leads to saving on energy.
Researchers have even tried innovative design of ballast tanks to let the sea water flow through them instead of storing the water. These new designs are expected to solve environmental concerns involved in the use of conventional ballast tanks.
All these techniques, however, require extensive study before being used in the operation of a ship.
