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12.2 Very High Frequency Direction Finding

During the North Hoyle Offshore Wind Farm trials in 2004, the VHF Direction Finding (DF) equipment carried in the trial boats did not function correctly when very close to wind turbines (within approximately 50 m). This is deemed to be a relatively small-scale impact due to the limited use of VHF direction finding equipment and will not impact operational or SAR activities (MCA and QinetiQ, 2004).
Throughout the 2005 SAR trials carried out at the North Hoyle Offshore Wind Farm, the Sea King radio homer system was tested. The Sea King radio homer system utilises the lateral displacement of a vertical bar on an instrument to indicate the sense of a target relative to the aircraft heading. With the aircraft and the target vessel within the North Hoyle array area, at a range of approximately 1 nm, the homer system operated as expected with no apparent degradation.
Since the trials detailed above, no significant issues with regards to VHF DF have been observed or reported, and therefore the presence of the Array is anticipated to have no significant impact upon VHF DF equipment.

12.3 Automatic Identification System

No significant issues with interference to AIS transmission from operational offshore wind farms have been observed or reported to date. Such interference was also absent in the trials carried out at the North Hoyle Offshore Wind Farm (MCA and QinetiQ, 2004).
In theory there could be interference when there is a structure located between the transmitting and receiving antennas (i.e. blocking line of sight) of the AIS. However, given no issues have been reported to date at operational developments or during trials, no significant impact is anticipated due to the presence of the Array.

The Navigational Telex (NAVTEX) system is used for the automatic broadcast of localised Maritime Safety Information (MSI) and either prints it out in hard copy or displays it on a screen, depending upon the model.
There are two NAVTEX frequencies. All transmissions on NAVTEX 518 kilohertz (kHz), the international channel, are in English. NAVTEX 518 kHz provides the mariner (both recreational and commercial) with weather forecasts, severe weather warnings and navigation warnings such as obstructions or buoys off station. Depending on the user’s location, other information options may be available such as ice warnings for high latitude sailing.
The 490 kHz national NAVTEX service may be transmitted in the local language. In the UK, full use is made of this secondary frequency including useful information for smaller craft, such as the inshore waters forecast and actual weather observations from weather stations around the coast.
Although no specific trials have been undertaken, no significant effect on NAVTEX has been reported to date at operational developments, and therefore no significant impact is anticipated due to the presence of the Array.

Global Positioning System (GPS) is a satellite based navigational system. GPS trials were also undertaken throughout the 2004 trials at North Hoyle Offshore Wind Farm and it was stated that “no problems with basic GPS reception or positional accuracy were reported during the trials” (MCA and QinetiQ, 2004).
The additional tests showed that “even with a very close proximity of a wind turbine to the GPS antenna, there were always enough satellites elsewhere in the sky to cover for any that might be shadowed by the wind turbine tower” (MCA and QinetiQ, 2004).
Therefore, there are not expected to be any significant impacts associated with the use of GPS systems within or in proximity to the Array, noting that there have been no reported issues relating to GPS within or in proximity to any operational offshore wind farms to date.

A compass, magnetic compass or mariner's compass is a navigational instrument for determining direction relative to the Earth's magnetic poles. It consists of a magnetised pointer (usually marked on the north end) free to align itself with the Earth's magnetic field. A compass can be used to calculate heading, used with a sextant to calculate latitude, and with a marine chronometer to calculate longitude.
Like any magnetic device, compasses are affected by nearby ferrous materials as well as by strong local electromagnetic forces, such as magnetic fields emitted from power cables. As the compass still serves as an essential means of navigation in the event of power loss or as a secondary source, it is important that potential impacts from EMF are reduced to ensure continued safe navigation.
The vast majority of commercial traffic uses non-magnetic gyrocompasses as the primary means of navigation, which are unaffected by EMF. Therefore, it is considered highly unlikely that any interference from EMF as a result of the presence the Array will have a significant impact on vessel navigation. However, some smaller craft (fishing or leisure) may rely on it as their sole means of navigation (this is considered further in section 12.6.1).

As per section 6.3, there will be inter-array cables and interconnector cables within the Array. The inter-array cables will be High Voltage (HV) Alternating Current (AC), while the interconnector cables will be HVAC and /or HV Direct Current (DC). Studies indicate that HVAC does not emit an EMF significant enough to impact marine magnetic compasses (Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR), 2008).
With regards to potential use of HVDC interconnector cables, the following key points are noted:

Minimum water depths within the site boundary are in excess of 60 m, with vertical distance decreasing any EMF impacts.
It is considered unlikely that vessels this far offshore would be relying purely on a magnetic compass.
Input from the MCA during consultation confirmed that there is likely to be less concern with the HVDC interconnectors within the Array (see section 4) given water depths.

On this basis, electromagnetic interference associated with shipping and navigation due to cables associated with the Array are not considered any further. Any associated effects from the Proposed offshore export cable(s) will be considered within a separate NRA.

MGN 654 (MCA, 2021) notes that small vessels with simple magnetic steering and hand bearing compasses should be wary of using these close to wind turbines, as with any structure in which there is a large amount of ferrous material (MCA and QinetiQ, 2004). Potential effects are deemed to be within acceptable levels when considered alongside other mitigation such as the mariner being able to make visual observations (not wholly reliant on the magnetic compass), lighting, sound signals and identification marking in line with MGN 654 (MCA, 2021), noting lighting and marking will be agreed with NLB. As per section 12.6.1, it is considered very unlikely that vessels this far offshore would be relying purely on a magnetic compass.

No issues with respect to magnetic compasses have been reported to date in any of the North Hoyle Offshore Wind Farm trials (MCA and QinetiQ, 2004) undertaken (inclusive of SAR helicopters) nor in any published reports from operational offshore wind farms in the UK.