Guidance

Offshore renewable energy installations: impact on shipping

How wind farms and wave and tidal energy devices can endanger navigation, emergency response operations, marine radar and GPS communications.

From:: Maritime and Coastguard Agency
Published: 21 September 2012
Last updated: 1619 ~~January~~May ~~2024~~2026 — See all updates

Introduction

In the UK, there is an increasing number of Offshore Renewable Energy Installations (OREIs) including wind farms, and wave and tidal energy devices. This forms part of the government’s commitment to reducing its carbon footprint and tackling climate change.

The location, size and irregular shape of OREIs present new challenges to the safe navigation and communication of shipping and emergency rescue. These difficulties could contribute to a marine casualty leading to injury, death or loss of property, either at sea or among the population ashore.

This guide provides details on the impact of OREIs on navigational safety and emergency response. The information is particularly useful for OREI developers. It also provides information on navigation and voyage planning to help you assess all risks and plan safe passage. Finally, this guide includes research on the impact of OREIs on marine radar, communications and positioning systems and search and rescue helicopter operations.

Offshore Renewable Energy Installation impact on navigational safety and emergency response

Existing or proposed OREIs in UK internal waters, territorial sea or in the Exclusive Economic Zone (EEZ) beyond the territorial sea have the potential to affect marine navigation and safety.

The impact must be assessed and mitigation measures put in place to ensure the safety of life at sea. Assessments need to be made of the consequences of ships deviating from normal routes and recreational or fishing vessels entering shipping routes in order to avoid proposed sites. As an OREI developer, you will need to ensure that you minimise the impact of your developments.

OREIs can include:

offshore wind farms
marine current turbines
wave generators
any other installation

Recommendations for OREI

If you are an OREI developer seeking formal consent for marine works, you will need to consider recommendations from the Maritime and Coastguard Agency (MCA). If you fail to consider these recommendations, there may be objections to your proposal on the grounds of navigational safety or emergency response preparedness. Download Marine Guidance Note (MGN) 645 (M+F) Navigational, safety and emergency response guidance for OREIs.

You can find information on development consents and licensing for OREIs over 100 megawatts in England and Wales on the Infrastructure Planning Commission website and for OREIs in Scotland on the Marine Scotland website.

You can also find information on development consents and licensing for OREIs between 1 and 100 megawatts on the Marine Management Organisation website and Natural.

The recommendations also include information to address the navigational impact and emergency response of proposed OREI sites. The development of an OREI requires a clear consent process to deal with potential detrimental effects and should take account of local factors, national standards and international aspects which could influence the establishment of an OREI.

The Energy Act 2004 also established a regulatory regime for OREIs beyond territorial waters, in the UK’s EEZ. This supplements the regime which already applies in UK internal and territorial waters and Section 99 deals specifically with navigation. Read the Energy Act 2004 on the Legislation.gov website.

How and when the OREI recommendations should be used

If you are an OREI developer, you and your contracted environmental and risk assessors should take the recommendations into account for all sites within the jurisdiction of port limits or in open sea areas for the preparation of:

Scoping Reports
Environmental Impact Assessments (EIA)
Environmental Statements (ES)

You may also be required to comply with specific criteria from port authorities. Also, where proposals within port limits could affect navigation or emergency planning or response, the port authorities will be under an obligation to review its safety management system, in accordance with the Port Marine Safety Code. You should undertake such reviews in parallel with your EIA, with the outcome addressed in the resulting ES.

You should comply with the recommendations during all phases of:

planning
construction
operation
decommissioning

During these phases, you should immediately send information concerning the navigational impact to all relevant mariners, organisations and authorities.

You should plan and practice contingency arrangements to deal with marine casualties in or adjacent to sites, including responses to environmental pollution, to test their efficiency.

These recommendations can be changed or modified by the MCA - on the basis of experience or in accordance with internationally recognised standards - in the interest of safety of life at sea and protection of the marine environment.

Navigational considerations

You should assess navigational and communication impacts or difficulties around the site area and surroundings to determine any potential obstruction of, or danger to, seafarers or emergency response services. This assessment will also help to establish the best options to be adopted, including those of operational site monitoring.

You should consult with local and national search and rescue authorities, and consider the types of aircraft, vessels and equipment which might be used in emergencies. This should include the possible use of OREI structures as emergency refuges and any matters that might affect emergency response within or close to the OREI.

You should also assess the consequences of ships deviating from normal routes and recreational or fishing vessels entering shipping routes in order to avoid proposed sites. It is important to consider any situation which could lead to safety of navigation being compromised, eg:

an increase in end-on or crossing encounters
reduction in sea-room or water depth for manoeuvring - leading to choke points

When considering navigational priority, you should treat all seagoing water craft, operations and mariners as the same.

Navigation and voyage planning around Offshore Renewable Energy Installations

Around the UK, the number of Offshore Renewable Energy Installations (OREIs) is increasing and they may be close to shipping routes.

You should be aware that there is no right of access to any type of OREI. They are private property and appropriate warning signs are displayed. Access to an OREI requires skill and is limited by the state of the sea, and should only be undertaken in controlled circumstances by trained personnel.

The visibility of offshore wind, wave and tidal energy installations will depend on the device type as some installations are totally submerged while others may only protrude slightly above the sea surface. The marking of offshore wave and tidal energy installations will be based on recommendations of the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA). Download offshore structures marking guidance from the IALA website

Wind farms

When planning a voyage, mariners should assess all hazards and associated risks, including the proximity of wind farms and turbines, for example:

spacing - wind farm turbines are usually spaced 500 metres or more apart depending on the size of the turbine
depth of water - most wind turbines operate in relatively shallow water though new generations of wind farm will be constructed in deeper water, possibly restricting navigable channels
seabed changes - wind farm structures could, over time, affect the depth of water in their vicinity through scouring of the seabed making depth information unreliable
tidal streams - wind farm structures may obstruct tidal streams locally, creating eddies nearby
small craft - vessels involved in turbine maintenance and safety duties may be encountered or obscured within or around a wind farm - fishing vessels may also operate and be obscured in the area
shore marks - in coastal areas shore marks may also be obscured by wind farm structures
electrical transformer stations - can be found in or adjacent to larger wind farms
rotor effects - can change the flow of the wind and impact on a vessel

MGN 372 Amendment 1 (M+F) Guidance to mariners operating in vicinity of UK OREIs.

Offshore wave and tidal energy installations

Unlike wind farms, you may have difficulty seeing systems using wave or tidal energy as they are likely to be located at or near the surface, for example:

attenuators
point absorbers
oscillating wave surge converters
oscillating water columns
overtopping devices
submerged pressure differentials

There are also many other devices that may have unique and very different designs to the more well-established types of technology, for example:

tidal energy convertors (TECs)
horizontal axis turbines
horizontal axis turbines (enclosed blade tips)
vertical axis turbines
oscillating hydrofoils

The visibility of offshore wave and tidal energy installations will depend on the device type as some installations are totally submerged while others may only protrude slightly above the sea surface. The marking of offshore wave and tidal energy installations will be based on recommendations of the IALA. Download offshore structures marking guidance from the IALA website

Methods for fixing wave energy convertors (WECs) and TECs to the seabed

You will need to know the various methods by which WECs and TECs can be fixed to the seabed, as it will affect their visibility above the surface, for example:

seabed mounted/gravity base devices - physically sit on the seabed by virtue of the weight of the combined device/foundation - some may also have additional fixing to the seabed
pile mounted - attached to a pile penetrating the ocean floor
floating flexible mooring - tethered via a cable/chain to the seabed, allowing considerable freedom of movement
floating rigid mooring - secured into position using a fixed mooring system, allowing minimal movement
hydrofoil inducing down force - uses a number of hydrofoils mounted on a frame to induce a positioning down force from the tidal current flow
transformer station or hub - a special structure containing power conversion equipment either within or outside the wave/tidal energy group to which individual generators are connected via a power cable - a submarine cable transfers the power ashore from the hub, which may be a separate fixed or floating platform

Safety zones

There are a few safety zones in place around some UK offshore wind farms currently under construction, with more likely to be introduced in the near future, all of which will be monitored and policed.

A temporary safety zone may be established during the construction, major maintenance and decommissioning of OREIs and therefore should be avoided. Notices to mariners and radio navigation warning broadcasts may be used to inform people of such a zone, and chart and hydrographic publications will be used. These zones will be monitored by support craft which may include fishing vessels employed by developers as guard vessels.

Permanent safety zones are not expected to be established around entire wind farm groups, though single installations may be considered.

The effect on navigation and communication systems of OREIs

OREIs can be large and there could be several of them within a particular area. As a result, OREIs that cover large areas of open water can present potential hazards to navigation. This is particularly dangerous if there are a number of OREIs close to or encroaching into waters where there is a high density of shipping movements, fishing vessels and recreational craft usage.

Because of their nature, OREI positions are exposed to weather conditions and are often in shallow water, which could affect the navigation of vessels, particularly small craft and inshore shipping, gaining access to ports or to waters that provide a more sheltered passage required in bad weather and sea conditions. Also, tidal streams of varying sets and rates pass through all wind farm sites and some sites are within port limits or lie within Vessel Traffic Services (VTS) operational limits.

Maritime communication

Mariners and organisations require consistent and effective radio communications systems.

If you are within close range of an OREI, you should be able to rely on marine navigation systems as much as if you were in open sea. However, those requiring line of sight promulgation may be affected by wind turbines. You will also need to be able to detect other craft in the area and to take appropriate avoiding action.

Port authorities and VTS operators require effective detection, identification and tracking of vessels navigating in their areas to:

organise traffic
provide traffic information
provide navigational assistance services to vessels operating within port approaches
prescribe routing schemes to meet their statutory responsibilities in respect of the safety of navigation

Emergency services such as Royal National Lifeboat Institution vessels and HM Coastguard require the ability to rapidly detect and react to maritime casualties.

If there is a failure of any radar, navigation or communication system it could:

reduce safety levels
lead to marine casualties
reduce the effectiveness of emergency service operations

If an incident involves a passenger vessel, or a vessel carrying dangerous and polluting cargo, it could have serious consequences for the public and the environment, both at sea and ashore.

Theoretical studies into the impact of OREIs on radio systems

Experiments were carried out to test the theoretical results from an earlier study that predicted the impact on marine radio systems by the North Hoyle wind farm, off the North Wales coast.

In the theoretical study, results showed that wind turbines have very large radar cross-sections, which scatter a large proportion of any incident electromagnetic energy. The turbines also cast shadows behind themselves, looking from the direction of the transmitter.

The study suggested that small vessels within the North Hoyle wind farm would be detectable with marine radar - both 3 gigahertz and 9 gigahertz - if they were not in the shadow of a turbine. However, detection of the vessel could be compromised if it was very close and directly behind a turbine. The effect of the shadow at 3 gigahertz was found to be much less severe than at 9 gigahertz.

The impact on Global Positioning Systems (GPS) was found to be minimal, with any interference very rarely causing any corruption to the GPS data. Unless a GPS receiver was within 70 metres (based on a signal-to-noise ratio of 15 decibels) of a wind turbine then any interference would be insignificant.

The study looked at very high frequency (VHF) communications and concluded that due to the wavelength of the VHF systems, any interference caused by wind turbines would be negligible.

Scientific and practical research

The North Hoyle wind farm research tried to obtain scientific and practical operational data on the performance of various navigation and communications systems within and in the vicinity of offshore wind farms. The research focused on how the performance of systems would be adversely affected, with cost effective solutions recommended.

Four different trials were designed to test the validity of the results from the theoretical study and indicated that there is minimal impact on:

VHF radio
GPS receivers
cellular telephones
automated identification system

Ultra high frequency and other microwave systems suffered from the normal masking effect when turbines were in the line of the transmissions.

The turbines produced strong radar echoes giving early warning of their presence.

At close range, turbines may produce multiple reflected and side lobe echoes that can mask real targets. These develop at about 1.5 nautical miles, with radar displays becoming worse as the range closes.

Where a shipping lane passes within this range, considerable interference may be expected along a line of turbines.

The target size of the turbine echo increases close to the turbine, with target definition and bearing discrimination becoming worse on both 3 and 10 centimetre radars.

Following on from these trials, a critical assessment of search and rescue (SAR) activities within and close to offshore wind farms was carried out. This outcome may be used to inform the consents process of offshore wind farm applications.