What should the shipping industry do to rapidly reduce its emissions in the near term? There are many technical measures and operational improvements already being investigated in industry and academia. Apart from renewable energy and energy storage through the use of batteries and cold ironing there are so far only two technologies, namely slow steaming and the bulbous bow.
Slow steaming refers to the practice whereby the (operational) speed of the ship is reduced. It basically means that the ship’s engine is not used at full power, thus saving fuel, reducing CO2 and air pollutant emissions2. Slow steaming has been adopted by the majority of shipping companies and ship owners in order to survive in these tough times of rising fuel prices and financial recession. Originally started for container shipping by Maersk Lines and justified by the cost sheets and economics, the concept has been borrowed by other kinds of ships including the dry bulk ships, whose operating speeds are traditionally low. Concerns with regard to slow steaming:
- Frequent and thorough scavenge and under piston inspections must be carried out.
- Slow steaming causes fouling of the turbochargers and loss of efficiency.
- Turbochargers operating outside their designed range produce less air flow leading to more deposits.
- Causes increased carbon deposits on the injectors compromising their performance.
- Causes fouling of the exhaust gas economizer resulting in reduction of capacity as well as increased danger of soot fire.
- Causes a reduction in scavenge air pressure resulting in improper combustion.
- Leads to improper atomization of the fuel as well as impingement.
- Causes increased carbon deposits and maintenance intervals have to be modified likewise.
- Causes low exhaust gas temperatures. Running the engine with exhaust gas temperatures below 250 deg C can cause low temperature corrosion.
- Causes reduced peak compression pressure.
- Damage occurs and becomes imminent when engine is run at full load after long period of slow steaming.
- Compromises the piston ring pack efficiency, leading to increased under piston and scavenge deposits.
- Increases the risk of scavenge fires and needs extra scavenge and under piston area draining.
- Cause loss of heat transfer due to carbon deposits and failure of components due to thermal stresses.
- Causes reduction in the efficiency of the economizer causing the need of oil fired boiler to operate and adding to extra cost and maintenance.
the bulbous bow
To date, the only invention that has addressed fuel efficiency is the bulbous bow. The bulbous bow is a protruding bulb at the bow of a ship just below the waterline. The bulb modifies the way the water flows around the hull, reducing drag. The bulbous bow has been adopted by many large vessels and under optimum conditions, fuel savings of up 12% have been achieved. However, the design is 'speed specific' and 'load specific' At slower speed and with reduced load, the benifits are minimal. Crew members are also worried that the large and heavy bulbous bow will reduce the vessel's ability to ride the waves in heavy weather and the risk of foundering is ever present, especially when the ship is fully loaded.
1. Source: Big Ship Slow Steaming: How Prevalent is It?