Depending on which organization we are talking about, there are varying technical and operational procedures required to reduce the emission of GHG. The International Council on Clean Transportation released a long list of recommendations that would reduce the GHG emission (Appendix I), while IMO through the Marine Environment Protection Committee (MEPC) identified different classifications for the same purpose.
On April 9, 2009, the MEPC released its second IMO GHG Study. In the study, MEPC identified four categories of options to reduce ships emissions, namely:
• Improving energy efficiency, that is, burning less fuel to attain the same output by optimizing the design and operation.
• Exploring renewable energy sources (sun and wind).
• Using emission-reduction technologies (chemical conversion, capture and storage)
• Using fuels that produce less emissions (natural gas and bio-fuels)
Improving energy efficiency through boiler design and operation
Optimizing ship design
The design technology is categorized as short to medium term; it has to be inputted during construction of new ships. However, some of these optimization steps can be applied to existing ships. Each new vessel’s design specifications, such as ship’s size and the targeted speed, are considered the main hurdle toward achieving the optimal energy efficiency for the ship. Furthermore, some ports and rivers may impose limitations on the ship’s draught which further reduces its efficiency.
Optimizing the hull and superstructure
Even if the ship’s hull and its superstructure may cause minimal resistance, there still exist areas for more optimization for attaining higher efficiency. Design optimization on the hull and superstructure minimizes air resistance and drifting, especially for large container ships which have huge superstructures. The latest technology to reduce the hull’s frictional surface resistance is through the use of the air-bubble system which involves blowing air bubbles underneath the ship’s hull, thus improving fuel-use efficiency.
This technology requires recycling the energy from the exhaust system through the use of power turbines. This energy can be utilized to drive a motor to generate electricity and also to support the main engine. The recovered energy can augment 10% to the total power. Likewise, Diesel-electric propulsion systems allow design flexibility that will result in energy saving.
Optimizing the propulsion systems
Increase in the propulsion power by using propeller vanes, contra-rotating propellers and ducts can significantly improve the energy efficiency. In like manner, using high-efficiency and asymmetric rudders can help optimize propulsion.
Operational improvements, such as enhanced weather routing, optimized trim and ballasting, better main and auxiliary engine maintenance and tuning, hull and propeller cleaning, speeding up ship unloading and slower steaming, can significantly affect the ship’s emissions. The IMO has estimated that a speed reduction of merely 10% across the global fleet by 2010 would result in more than 23% decrease in emissions.