In a reminder of the balance needed for the safe use of the sea for international trade, energy, fishing, and leisure the Maritime and Coastguard Agency (MCA) is seeking views on amendments to its snappily titled "Marine Guidance Note 372 ("MGN 372") Safety of Navigation: Offshore Renewable Energy Installations ("OREIs") Guidance to Mariners operating in the vicinity of UK OREIs" following comments made in response to its 2020 consultation on the document. MGNs give guidance and recommendations about best practice to industry on the interpretation of the law and provide general safety advice.

The purpose of MGN 372 is to highlight issues to be considered by marine navigators when planning and undertaking voyages near offshore renewable energy installations off the UK coastline. With the last full review having taken place some sixteen years ago, the MCA's review is welcome given the rapid growth and expansion in the renewables industry in that period, which has resulted in a significant increase in the number of OREIs. OREIs include offshore wind farms, marine current turbines, wave generators and other offshore installations to produce energy. These new energy installations do mean that to ensure smooth sailing for mariners updated guidance for voyage planning is necessary for navigation in what is now differently charted waters.

Wind Farms

MGN 372 takes into consideration the risks that OREIs pose and provides information and guidance to navigators to ensure safe passage. For example, whilst wind farm structures are largely visible from a distance, they make look further away than they are. MGN 372 provides a table to show the theoretical visibility range of the structure from the perspective of different sea users in ideal conditions of visibility.

Wind farms (including when under construction) must be marked to be conspicuous by day and night. This includes, lining the boundary of the wind farm with a corner structure or other significant point, ensuring that it is visible from all directions.

MGN 372 also provides information on the minimum sound signals required; marking on individual turbines and the specific marking which must appear on all wind turbines.

From the mariner's perspective, MGN 372 states that navigators must carry out a risk assessment when travelling through wind farms, which must include an assessment of the spacing between turbines; the depth of the water; changes in the seabed, the effect of turbines on tidal streams; the likelihood of there being greater traffic around wind farms, especially during construction; the likelihood of shore markings being obstructed by the presence of wind farms; the presence of submarine cables from offshore electrical transformer stations; the possibility of turbines moving on their mooring according to weather conditions and rotor effects- turbines in UK are required to have a lowest sweep of at least 22 metres above mean high water springs.

Offshore Wave and Tidal Energy Installations

Whilst wind farm structures are largely visible, wave or tidal energy installations may not be and the MGN 372 provides information and guidance to enable mariners to make appropriate voyage planning decisions, both by describing them and their constituent parts, and by setting out how they are marked to ensure visibility, based on international standards for aids to navigation.

Safety Zones

MGN 372 reminds mariners that temporary safety zones may be established during the construction, major maintenance, and decommissioning period of OREIs, again, giving information and guidance on the appropriate action to be taken around such zones including that care should be taken and a wide berth ensured. The MGN advises mariners of how information about these zones is made known to them.

Although the purpose of the MGN is to ensure safe passage within OREIs, the MGN also reminds mariners that HM Coastguard must be informed immediately if an emergency takes place close to, or within, any OREIs.


At a time when there is a focus on energy transition with significant investment in infrastructure for that, and with safety of all who use the sea being paramount, this review which aims to bring the MGN 372 up to date and equip mariners to keep themselves and the infrastructure safe on this changing era is to be welcomed. It is a reminder of the ever-complex world in which we live. The obligation remains to ensure that relevant risks are adequately considered and mitigated; the updated MGN 372 will go some way towards easing the burden of doing this and should be carefully considered when carrying out voyage planning and associated risk assessments.