Shipboard Energy Efficiency Measures
Optimized Ship Handling
Most ships are designed to carry a designated amount of cargo at a certain speed for certain fuel consumption. The same applies to ballast operations. Whether loaded and unloaded, for such conditions, normally there exists a ship trim that minimizes the propulsion power, thus main engines’ fuel consumption. In fact, for any given draft there is one optimum trim that gives minimum ship resistances. In some ships, it is possible to assess optimum trim conditions for fuel efficiency continuously throughout the voyage. Setting the ship trim is to a large extent in the hand of shipboard staff although loading, operational and navigational constraints may limit the full extent of proper use of this energy efficiency measure.
Ships normally carry ballast water to ensure ship’s stability and safety. Normally, ballast levels should be adjusted taking into account the requirements to meet ship stability, steering aspects of the ship and optimum trim. This does not necessarily mean carrying lots of ballast water all the time. This unnecessarily increases the ship displacement that directly increases fuel consumption and emissions. Thus, there is an optimum ballast condition that needs to be achieved through good cargo planning as well as voyage planning. Therefore, optimizing the ballast levels for energy efficiency within the framework of ship stability, safety, steer ability and optimum trim can be regarded as an energy efficiency measure.
Optimum use of rudder and autopilot:
There have been large improvements in automated heading and steering control systems technologies. Whilst originally developed to make the bridge team more effective, modern autopilots can achieve much more. An integrated navigation system can achieve significant fuel savings by simply reducing the distance sailed “off track”. The principle is simple; better course control through less frequent and smaller corrections will minimize losses due to rudder resistance. In some cases, retrofitting of a more efficient autopilot to existing ships could be considered. (MariEMS 2017)
Optimized Propulsion Condition
Hull fouling always happens in ships. The rate of hull fouling will depend on a number of factors such as quality of paint, ship service speed, periods of idle /waiting and ship geographical area of operation. Hull resistance can be optimized by new advanced coating systems, possibly in combination with hull cleaning at certain intervals. Regular in-water inspection of the condition of the hull is recommended. Consideration may be given to the possibility of timely full removal and replacement of underwater paint systems to avoid the increased hull roughness caused by repeated spot blasting and repairs over multiple dry dockings.
Propeller cleaning and polishing or even appropriate coating may significantly increase fuel efficiency. The need for ships to maintain efficiency through in-water hull and propeller cleaning should be recognized and facilitated by port States.
Main engine maintenance:
Marine diesel engines have a very high thermal efficiency (~50%). This is the best efficiently currently available on the market and is the main reason why diesel engines are unrivalled in shipping. The high efficiency is due to the systematic minimization of heat and mechanical loss of such engines and improved performance parameters that has taken place over many decades. In particular, the new breed of electronic controlled engines can provide efficiency gains with wider flexibility for example for slow steaming. To keep these engines in optimal condition and performance, they need to continuously undergo on-board condition and performance monitoring. Maintenance in accordance with manufacturers’ instructions in the company’s planned maintenance schedule will also maintain efficiency. The use of engine’s condition monitoring can be a useful tool to maintain high efficiency (MariEMS 2017).