Cold-ironing is the US Navy’s way of describing the practice of connecting a ship to a shore-side power supply in port with the ship’s machinery shut down, thereby causing the steam plant and hull to become ‘cold’. This term is now commonly used to describe a new generation of different high-voltage, high-power shore connections with fast plug connections and seamless load transfer without blackouts, which allow the full range of in-port activities to continue.

The increasing use of such arrangements has been driven by concerns for the environment and the health of residents in port communities. With existing installations in North America and the Baltic, implementation is being considered in other locations throughout the world.


In 2007, the state of California took a major step in cold iron use. This initiative includes the existing installations with planned expansion aimed at regularly calling ships to the US ports of Los Angeles and Long Beach. These facilities resulted from in-depth studies carried out by the state of California, which showed that measures such as cold ironing could contribute to improved air quality and health of local residents.

“With existing installations in North America and the Baltic, implementation is being considered in other locations throughout the world.”

These clean air initiatives now have a statutory footing following the approval by the California Air Resources Board of a new regulation to reduce emissions from auxiliary diesel engines operated on ocean-going vessels within state waters by the use of low sulphur content distillate fuels.

The Alternative Control of Emissions (ACE) provisions contained within these regulations permits equivalent measures that may give an equivalent reduction in emissions as would be achieved by using distillate fuel, including scrubbing systems.

Special provisions for the use of shore-side power are included in ACE. Proposed ACE plans are subject to approval before the vessel owner or operator can be considered as complying with the regulation. These special provisions are likely to favour cold-ironing.

The practical implications for ship operators complying with the regulation under the ACE use of shore-side power special provisions are as follows: vessels that connect to on-shore power supplies and shut down their electrical power generating machinery shall be considered to meet the emission reduction requirements of the regulation while travelling in regulated waters to the port where shore-side power is used and while travelling from that port to the next port of call.

In this way, they will not need to use the regulation set quality of distillate marine fuels or apply other strategies with their auxiliary engines while travelling to and from the port where on-shore power is used. However, this provision will only apply if the vessel can connect to the on-shore power supply and turn off all auxiliary engines within one hour of being secured at dockside and not revert to ship power until one hour before the vessel departs at the earliest.

In addition, the on-shore power supply must be supplied by a utility company or another source that satisfies emissions targets for the energy delivered. It is understood that another potential benefit of complying via the alternative on-shore power method is that any application would be simplified as it won’t be necessary to submit ship emissions calculations for consideration.

While this regulation is currently a local initiative it is worth noting that the Environmental Protection Agency is being encouraged to uniformly implement clean air standards in all ports in the US to ensure that ports not addressing these concerns are not at an unfair competitive advantage.


Already equipment manufacturers and on-shore power supply designers have a variety of commercially available different solutions. Major differences between these installations that could have an impact on ship safety, operability and compatibility of ship and shore arrangements include:

Operating frequency – mismatched ship and shore 50Hz and 60Hz systems are normally incompatible without relatively sophisticated frequency conversion.

System voltages – transformers are normally required to match the ship and shore voltage levels. Different ships have different operating levels (11kV, 6.6kV and 440V being common), thereby necessitating transformers.

Power rating – different ships have varying power-use profiles in port.

Electrical system design and compatibility – protection of ship and shore arrangements from electrical faults needs to be planned and ensured.

Electrical load transfer – for seamless load transfers without blackouts additional complex ship power management equipment is needed because of ‘stiff’ shore supplies.

Cable and connector types – there are no existing internationally accepted construction or test standards for shore connection flexible marine cables or high voltage plug and socket-outlets.

Cable management systems – for the in-port power levels required, cables and connectors will be too heavy for effective manual handling. Cable reels or cranes can be installed onboard or ashore to extend cables to the connection points.

Connection time – regulations may specify connection within a short timescale, generally necessitating the use of high voltage to minimise the number of connections, and plugs and socket-outlet to reduce connection time.

Control and safety arrangements – the available solutions have been diverse, ranging from simple to highly sophisticated, from manual operation to automatic connection and disconnection of submersible electrical equipment, fully integrated into the ship and shore-side emergency shutdown systems.

Ship safety should be given equal consideration as the environmental benefits of on-shore power supplies. The emergent technical difficulties, hazards and potential for serious injury and damage introduced are not to be understated and may include:

  • Live high voltage cables connected between moving ship and berth
  • Ship machinery not available due to shut-down state
  • Operating staff handling of high voltage Equipment
  • High voltage and power electrical faults due to cable or equipment damage or failure
  • Damage to ship or shore electrical Installations
  • Blackout of shore grid
  • Vessel black-outs also if ship slips moorings or leaves berth inadvertently
  • Risk to operating personnel safety


To assist in addressing these hazards, Lloyd’s Register has developed requirements for on-shore power supplies (OPS notation) in consultation with a wide variety of stakeholders to help ship owners and operators to adjust and adapt to the advent of on-shore power arrangements in port operations. The rules are based upon the general provisions of ship classification and were developed to ensure that port operations when connected to shore power can be as safe as conventional operation as far as is reasonably practicable.

The rules also help to address compatibility with a defined shore supply, the hazards described above and the support of safe working practices. These regulations also cover ship equipment and will be available as an optional classification notation.


To date, on-shore power supplies initiatives and legislation globally have tended to be localised and different in their approach, application, objectives and targets. This may be attributed to the reasons for adoption varying from location to location. The main driver may be the reduction of emissions to reduce their effect on the local environment or on public health as a result of airborne ship emissions or even noise in berths close to residential and public areas – or a combination of these factors.

Furthermore, the benefit against cost is a variable for each location dependant on factors requiring complex assessment.

“On-shore power supply must be supplied by a utility company or another source that satisfies emissions targets for the energy delivered.”

At an international level, the standardisation of on-shore power supplies has been subject to discussions within IMO’s Marine Environment Protection Committee, but IMO has not formally tasked any standards body to develop common standards for these arrangements. A submission to the IMO from the Institute of Marine Engineering, Science and Technology noted that it may not be feasible or desirable to provide a ‘one size fits all’ solution for all ship connections, and more than one solution is already commercially available.

However, both the International Organization for Standardization and the International Electrotechnical Commission hope to publish different Publicly Available Specifications in the near future.

These specifications have the advantage of being able to cover the ship, the connection and shore arrangements. Both documents are continuing to develop and improve but are different in their content and approach, particularly the extent of standardisation, and an agreed full international standard may be some years off.

It is hoped that the scope of the international standards and other industry documents may be produced to cover safe working practices on board and ashore.

In the absence of standardisation, the Lloyd’s Register Draft Rules have been written to be adaptable to the variety of commercially available solutions considered to be safe and effective. The aim is to harness best practice to mitigate the risks posed by the significant change to port operations that cold ironing represents. This could be simply the beginning and cold ironing may, in the medium term, become standard practice in ports around the world where the overall environmental benefit is considered worthwhile.