Unlike navies, whose ships can berth for extended periods at their bases,
merchant ships have shorter port stays, during which they sustain electrical loads through on-board fossil fuel powered electrical generators (auxiliary engines). Oceangoing ships have generally not been subject to emissions controls, so merchant vessels throughout the world have been using
bunker fuel or HFO – which is residual petroleum – as the optimal choice of fuel. This fuel has high
particulate matter. Studies show that a single ship can produce particulate emissions equal to the same amount as 50 million cars annually. Further research indicates cardio-pulmonary conditions caused by particulate matter from ship emissions are responsible for 60,000 deaths annually. These deaths have been detected far inland due to prevailing wind conditions. The total world trading fleet stands at 50,000+
merchant ships (Lloyds data as of January 2008), and each ship spends some 100 days in port in a year.
For every of electricity, about 200 g of bunker fuel is consumed. Each 1 kg of bunker oil generates 3.1 kg of carbon dioxide. It is assessed that globally ships use 411,223,484 tonnes of fuel annually. Keeping these reports in mind, new regulatory norms have been mandated by the
International Maritime Organization (IMO). The level of sulphur is one of the benchmarks in measuring quality of fuel and
Marpol Annex VI requires use of <4.5% sulphur fuel, effective 2010. The target is to reduce world maritime sulphur output to <0.5% by 2020. Some regions (e.g., California) already require ships switch to cleaner fuel when in their local waters. Cold ironing does away with the need to burn
fossil fuel on board the ships while they are docked. Under this concept as it is legally implemented, ships visiting ports are hooked on to local
grid power or other power sources, which are already regulated by local pollution norms. This externally sourced power serves the ship's internal cargo handling machinery and hotelling requirements. Effectively, all the power generating sources are shut down and the ship is hence cold-ironed. This brings immediate relief from
pollution by shipboard emissions and allows a more holistic maintenance schedule to be followed by ship operators, which are typically hard pressed to maintain planned maintenance schedules due to commercial operating pressures. The immediate result is lowered heat outputs from ships, lowered air emissions, lowered risk of accidents from fuel based machinery, lowered disturbance to the
ecosystem, and various others. ==Concerns and problems==