13.2 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 risk due to the limited use of VHF DF equipment and will not impact operational or SAR activities (MCA and QinetiQ, 2004).
Throughout the 2005 SAR trials carried out at North Hoyle, 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 array 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 Proposed Development is anticipated to have no significant risk upon VHF DF equipment.
13.3 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 risk is anticipated due to the presence of the Proposed Development.
13.5 Global Positioning System
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”.
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 risks associated with the use of GPS systems within or in proximity to the Proposed Development, noting that there have been no reported issues relating to GPS within or in proximity to any operational offshore wind farms to date.
13.6 Electromagnetic Interference
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 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 Electromagnetic Field (EMF) should be minimised 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 of cables associated with the Proposed Development will have a significant impact on vessel navigation. However some smaller craft (fishing or leisure) may rely on them as their sole means of navigation
The export and inter-array cables for the Proposed Development could be Alternating Current (AC), Direct Current (DC) or a combination of both. Studies indicate that AC 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).
The Moray Offshore Renewables Environmental Statement (Moray Offshore Renewables, 2012) notes that for both buried and protected DC cables the magnetic field will decrease exponentially with vertical distance from the seabed and with horizontal distance from the cables (within a few metres), irrespective of whether cables are buried or protected. It states that “in all cases, where cables are buried to 1 m depth, the predicted magnetic field is expected to be below the earth’s magnetic field (assumed to be 50 microtesla (µT)). Where DC cables cannot be buried and are instead protected, the magnetic field is expected to be below the earth’s magnetic field within 5 m from the seabed”.
The following are therefore considered to be important factors affecting the likelihood of EMF to affect compass deviation as a result of the presence of cables:
- water depth;
- burial depth (or protection);
- type of current (alternating or direct) running through the cables; and/or
- spacing or separation of the cables.
13.7 EMF from Cables Associated with the Proposed Development
Within their response (16 November 2021) to the Berwick Bank Wind Farm Scoping Report the MCA stated that a compass deviation of three degrees will be accepted for 95% of the cable route and a five degree deviation accepted for the remaining 5% (see 16 November 2021 entry in Table 4.1 Open ▸ ). Table 13.1 Open ▸ details assumed EMF mitigation for the Proposed Development.
Given that 95% of the offshore export cables will be buried and 99.1% (approximately) of it in water depths greater than 10 m there are not anticipated to be any effects on compass deviation for the majority of the Proposed Development export cable corridor. Within shallow waters effects of EMF will be mitigated by the offshore export cables being either Horizontally Direction Drilled (HDD) or direct piped (within up to 1,500 m of the LAT mark and also out to a minimum of -5 m LAT) and also buried or protected as required beyond the point of emergence. As noted in Moray Offshore Renewables Environmental Statement (Moray Offshore Renewables, 2012) “where DC cables cannot be buried and are instead protected, the magnetic field is expected to be below the earth’s magnetic field within 5 m from the seabed” and there are negligible effects on magnetic compasses. Therefore, in summary based on mitigations of water depth, burial and use of HDD/direct pipes within shallow water the Proposed Development is anticipated to be within the requirements defined by the MCA.
Inter-array cables have not been considered within this section but are considered within acceptable limits given water depths within the Proposed Development array area (33 to 69 m Chart Datum) and use of burial/protection methods as required.
13.7.1 Electromagnetic Fields and Structures
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 therefore 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).
13.7.2 Electromagnetic Fields to Date within Operational Offshore Wind Farms
No issues with respect to magnetic compasses have been reported to date in any of the trials (MCA and QinetiQ, 2004) carried out (inclusive of SAR helicopters) nor in any published reports from other operational offshore wind farms.
13.8 Marine Radar
This section summarises trials and studies undertaken in relation to radar effects from offshore wind farms in the UK. It is important to note that since the time of the trials and studies discussed, wind turbine technology has advanced significantly, most notably in terms of the size of wind turbines available to be installed and utilised. The use of these larger wind turbines allows for a greater spacing between wind turbines than was achievable at the time of the studies being undertaken, which is beneficial in terms of radar interference effects (and surface navigation in general) as detailed in sections 15.7.1 to 15.7.5.
13.8.1 Trials
During the early years of offshore renewables within the UK, maritime regulators undertook a number of trials (both shore-based and vessel-based) into the effects of wind turbines on the use and effectiveness of marine radar.
In 2004, trials undertaken at the North Hoyle Offshore Wind Farm (MCA, 2004) identified areas of concern regarding the potential risks to marine- and shore-based radar systems due to the large vertical extents of the wind turbines (based on the technology at that time). This resulted in radar responses strong enough to produce interfering side lobes and reflected echoes (often referred to as false targets or ghosts).
Side lobe patterns are produced by small amounts of energy from the transmitted pulses that are radiated outside of the narrow main beam. The effects of side lobes are most noticeable within targets at short range (below 1.5 nm) and with large objects. Side lobe echoes form either an arc on the radar screen similar to range rings, or a series of echoes forming a broken arc, as illustrated in Figure 13.1 Open ▸ .
Figure 13.1 Illustration of Side Lobes on Radar Screen
Multiple reflected echoes are returned from a real target by reflection from some object in the radar beam. Indirect echoes or ‘ghost’ images have the appearance of true echoes but are usually intermittent or poorly defined; such echoes appear at a false bearing and false range, as illustrated in Figure 13.2 Open ▸ .
Figure 13.2 Illustration of Multiple Reflected Echoes on Radar Screen
Based on the results of the North Hoyle trials, the MCA produced a Shipping Route Template designed to give guidance to mariners on the distances which should be established between shipping routes and offshore wind farms. The latest version of the Shipping Route Template is included in MGN 654 (MCA, 2021).
A second set of trials conducted at Kentish Flats Offshore Wind Farm in 2006 on behalf of the British Wind Energy Association (BWEA) – now called RenewableUK (BWEA, 2007) – also found that radar antennas which are sited unfavourably with respect to components of the vessel’s structure can exacerbate effects such as side lobes and reflected echoes. Careful adjustment of radar controls suppressed these spurious radar returns, but mariners were warned that there is a consequent risk of losing targets with a small radar cross section, which may include buoys or small craft, particularly yachts or Glass Reinforced Plastic (GRP) constructed craft; therefore, due care should be taken in making such adjustments.
Theoretical modelling of the effects of the development of the proposed Atlantic Array Offshore Wind Farm, which was to be located off the south coast of Wales, on marine radar systems was undertaken by the Atlantic Array project (Atlantic Array, 2012) and considered a wider spacing of wind turbines than were considered within the early trials. The main outcomes of the modelling were the following:
- Multiple and indirect echoes were detected under all modelled parameters.
- The main effects noticed were stretching of targets in azimuth (horizontal) and appearance of ghost targets.
- There was a significant amount of clear space amongst the returns to ensure recognition of vessels moving amongst the wind turbines and safe navigation.
- Even in the worst case with radar operator settings artificially set to be poor, there is significant clear space around each wind turbine that does not contain any multipath or side lobe ambiguities to ensure safe navigation and allow differentiation between false and real (both static and moving) targets.
- Overall, it was concluded that the amount of shadowing observed was very little (noting that the model considered lattice-type foundations which are sufficiently sparse to allow radar energy to pass through).
- The lower the density of wind turbines the easier it is to interpret the radar returns and fewer multipath ambiguities are present.
- In dense, target rich environments, S-Band radar scanners suffer more severely from multipath effects in comparison to X-Band radar scanners.
- It is important for passing vessels to keep a reasonable separation distance between the wind turbines in order to minimise the effect of multipath and other ambiguities.
- The Atlantic Array study undertaken in 2012 noted that the potential for radar interference was mainly a problem during periods of reduced visibility when mariners may not be able to visually confirm the presence of other vessels in proximity (those without AIS installed which are usually fishing and recreational craft). It is noted that this situation would arise with or without wind turbines in place.
- There is potential for the performance of a vessel’s Automatic Radar Plotting Aid (ARPA) to be affected when tracking targets in or near the array. Although greater vigilance is required, during the Kentish Flats trials it was shown that false targets were quickly identified as such by the mariners and then by the equipment itself.
In summary, experience in UK waters has shown that mariners have become increasingly aware of any radar effects as more offshore wind farms become operational. Based on this experience, the mariner can interpret the effects correctly, noting that effects are the same as those experienced by mariners in other environments such as in close proximity to other vessels or structures. Effects can be effectively mitigated by “careful adjustment of radar controls”.
The MCA has also produced guidance to mariners operating in proximity to OREIs in the UK which highlights radar issues amongst others to be taken into account when planning and undertaking voyages in proximity to OREIs (MCA, 2008). The interference buffers presented in Table 13.2 Open ▸ are primarily based on MGN 654 (MCA, 2021) but also consider the content of MGN 371 (MCA, 2008), MGN 543 (MCA, 2016) and MGN 372 (MCA, 2008).
Table 13.2 Distances at which Risks for Marine Radar Occur
As noted in Table 13.2 Open ▸ , the onset range from the wind turbines of false returns is approximately 1.5 nm, with progressive deterioration in the radar display as the range closes. If interfering echoes develop, the requirements of the Convention on International Regulations for Preventing Collisions at Sea (COLREGs) Rule 6 Safe Speed are particularly applicable and must be observed with due regard to the prevailing circumstances (IMO, 1972/77). In restricted visibility, Rule 19 Conduct of Vessels in Restricted Visibility applies and compliance with Rule 6 becomes especially relevant. In such conditions mariners are required, under Rule 5 Look-out to take into account information from other sources which may include sound signals and VHF information, for example from a VTS or AIS (MCA, 2016).
13.8.2 Experience from Operational Developments
The evidence from mariners operating in proximity to existing offshore wind farms is that they quickly learn to adapt to any effects. The example of the Galloper and Greater Gabbard Offshore Wind Farms, which are located in proximity to IMO routeing measures is presented in Figure 13.3 Open ▸ . Despite this proximity to heavily trafficked Traffic Separation Scheme lanes, there have been no reported incidents or issues raised by mariners who operate within the vicinity. The interference buffers presented in Figure 13.3 Open ▸ are as per Table 13.2 Open ▸ .
Figure 13.3 Illustration of Potential Radar Interference at Greater Gabbard and Galloper Offshore Wind Farms
As indicated by Figure 13.3 Open ▸ , vessels utilising these Traffic Separation Scheme lanes experience some radar interference based on the available guidance. Both developments are operational, and each of the lanes is used by a minimum of five vessels per day on average. However, to date, there have been no incidents recorded (including any related to radar use), or concerns raised by the users.
AIS information can also be used to verify the targets of larger vessels (generally vessels over 15 m LOA – the minimum threshold for fishing vessel AIS carriage requirements). Approximately 15% of the vessel traffic recorded within the Proposed Development array area study area was under 15 m LOA, although throughout the vessel traffic surveys over 99% of vessels were recorded via AIS, indicating a high level of AIS take-up among vessels for which AIS carriage is not mandatory.
For any smaller vessels, particularly fishing vessels and recreational vessels, AIS Class B devices are becoming increasingly popular and allow the position of these small craft to be verified when in proximity to an offshore wind farm.
13.8.3 Increased Radar Returns
Beam width is the angular width, horizontal or vertical, of the path taken by the radar pulse. Horizontal beam width ranges from 0.75° to 5°, and vertical beam width ranges from 20° to 25°. How well an object reflects energy back towards the radar depends upon its size, shape, and aspect angle.
Larger wind turbines (either in height or width) will return greater target sizes and/or stronger false targets. However, there is a limit to which the vertical beam width would be affected (20° to 25°) dependent upon the distance from the target. Therefore, increased wind turbine height in the array will not create any effects in addition to those already identified from existing operational wind farms (interfering side lobes, multiple and reflected echoes).
Again, when taking into consideration the potential options available to marine users (such as reducing gain to remove false returns) and feedback from operational experience, this shows that the effects of increased returns can be managed effectively.
13.8.4 Fixed Radar Antenna Use in Proximity to an Operational Wind Farm
It is noted that there are multiple operational wind farms including Galloper that successfully operate fixed radar antenna from locations on the periphery of the array. These antennas are able to provide accurate and useful information to onshore coordination centres.
13.8.5 Application to the Proposed Development
Upon commissioning of the Proposed Development, some commercial vessels may pass within 1.5 nm of the wind farm structures and therefore may be subject to a minor level of radar interference. Trials, modelling, and experience from existing developments note that any risk can be mitigated by adjustment of radar controls.
An illustration of potential radar interference due to the Proposed Development and cumulative offshore wind farm developments is presented in Figure 13.4 Open ▸ . NnG is represented by the final array layout plotted on Admiralty Charts and Seagreen is represented by the final array layout published in the Safety Zone application (Seagreen Wind Energy Ltd, 2021), whereas Inch Cape is represented by the array area boundary published by Crown Estate Scotland, noting that a final array layout has not been published at the time of writing.
Figure 13.4 Illustration of Potential Radar Interference at the Proposed Development and Cumulative Offshore Wind Farm Developments
Vessels navigating internally within the Proposed Development array area will be subject to a greater level of radar interference, with risks becoming more substantial in close proximity to the wind turbines. This will require additional mitigation by vessels, including consideration of the navigational conditions (visibility) when passage planning and compliance with the COLREGs (IMO, 1972/77) will be essential.
For vessels transiting through the navigational corridor between the Proposed Development array area and Inch Cape, there may be a potential for increased exposure to radar interference depending upon the nature of the passage through the corridor. However, the distance and duration of the transit for which the distance from wind turbines will be less than 1.5 nm will be low and it is very unlikely that vessels will navigate within 0.5 nm of a wind turbine. Mitigations are available to vessels as listed throughout this section (e.g. adjustment of radar controls) and the risk is within parameters already safely managed at existing offshore wind farm developments.
Overall, the risk of marine radar interference is expected to be low and no further risk to navigational safety is anticipated outside the parameters which can be mitigated by operational controls. From existing experience within UK offshore wind farms, vessels do navigate safely internally within arrays including with spacing significantly less than at the Proposed Development array area.
13.10 Noise
No evidence has been found to date with regard to existing offshore wind farms to suggest that prescribed sound signals are in any way impacted by acoustic noise produced by the wind farm.
13.11 Summary of Risk
Based on the detailed technical assessment of the effects due to the presence of the Proposed Development on navigation, communication, and position fixing equipment in the previous subsections, the assessment of frequency and consequence and the resulting significance of risk for each topic is summarised in Table 13.3 Open ▸ .
Table 13.3 Summary of Risk on Navigation, Communication, and Position-fixing Equipment
On the basis of the NRA findings, associated risks are screened out of volume 2, chapter 13.
14 Cumulative and Transboundary Overview
Cumulative risks have been considered for activities in combination and cumulatively with the Proposed Development. This section provides an overview of the baseline used to inform the cumulative risk assessment, including the developments and projects screened into the cumulative risk assessment based on the criteria outlined in section 3.3.
The outputs of the cumulative risk assessment are then provided in section 19.2.
14.1 Screened In Developments
14.1.1 Other Offshore Wind Farms
In addition to the Proposed Development, there are a number of other offshore wind farm developments in the outer Firth of Forth and Firth of Tay region and the UK east coast as a whole. Table 14.1 Open ▸ includes details of these offshore wind farm developments and includes the cumulative risk assessment scenario applied as well as whether each development is screened in or out of the cumulative risk assessment based on the methodology outlined in section 3.3. The project statuses are as of August 2022 when the most up-to-date vessel traffic data used to inform the baseline was collected. Additionally, although Forthwind was consented in 2016, an EIA Report for a new project design was submitted in May 2022 (Marine Scotland, 2022) following a scoping report in August 2021 and so this development is defined as scoped.
As per the methodology, any development greater than 50 nm from the Proposed Development array area is not considered.
Figure 14.1 Open ▸ presents the locations of the offshore wind farm developments screened into the cumulative risk assessment.
Figure 14.1 Offshore Wind Farms Developments Screened into Cumulative Risk Assessment
14.1.2 Oil and Gas Infrastructure
The only oil and gas infrastructure within 50 nm of the array site are seven wellheads, all of which are decommissioned, and therefore have no future influence of vessel movements. The closest surface oil and gas infrastructure is the BW Catcher FPSO at the Catcher Area Development, located approximately 73 nm to the east.
Therefore, no oil and gas infrastructure has been screened into the cumulative risk assessment.
14.1.3 Other Developments and Infrastructure
The Cambois connection is a potential secondary offshore export cable option for the Proposed Development which will connect at the southern extent of the Proposed Development array area and make landfall at Blyth on the UK east coast[9]. Given that this development will not include any surface infrastructure there is a limited pathway through which a hazard can be transmitted between the development and shipping and navigation users. Therefore, the Cambois connection is screened out of the cumulative risk assessment.
Other developments within 50 nm of the Proposed Development array area include the Inch Cape Met Mast (located approximately 8.3 nm to the west) and Energy Park Fife (located within the Firth of Forth). Both are existing developments and are therefore considered as part of the baseline.
There are no other known future developments (other than offshore wind farm developments) within 50 nm of the Proposed Development array area.
Therefore, no other developments or infrastructure has been screened into the cumulative risk assessment.
Table 14.1 Cumulative Screening
14.2 Cumulative Pre-Wind Farm Routeing
Figure 14.2 Open ▸ presents a plot of the main commercial routes within the Proposed Development array area shipping and navigation study area (full extent) alongside the screened in cumulative developments. Descriptions of the vessel traffic on each of the main commercial routes are provided in Table 11.1 Open ▸ .
Figure 14.2 Offshore Wind Farms Developments Screened into Cumulative Risk Assessment with Main Commercial Routes (Pre Wind Farm)
Table 14.2 Open ▸ summarises which main commercial routes interact with which cumulative developments (i.e. are defined as requiring a deviation due to the future presence of a cumulative development). As per the methodology for re-routeing due to the Proposed Development in isolation (see section 15.5.1), it has been assumed that any main commercial route within 1 nm of an offshore installation will require a deviation.
Table 14.2 Anticipated Cumulative Routeing Interaction with Cumulative Developments
In summary, three routes are anticipated to require a deviation due to the additional presence of Inch Cape (Scenario 1). There are no Scenario 2 developments and therefore no further deviations are considered noting that, as per the cumulative risk assessment methodology, Scenario 3 developments are considered only qualitatively and at a high level due to the limited information available.
15 Future Case Vessel Traffic
This section presents the future case level of activity within and in proximity to the Proposed Development and the anticipated shift in the mean positions of the main commercial routes post wind farm.
The future case activity and routeing has been fed into the collision and allision risk modelling. The future case is considered throughout the risk assessment undertaken in volume 12, chapter 13 where future case refers to the assessment of risk based upon the predicted growth in future shipping densities and traffic types. The future case also refers to foreseeable changes in the marine environment, as discussed in the following subsections.
15.1 Increases in Commercial Vessel Activity
Forth Ports are the port operator for the major ports within the Forth including Grangemouth, Dundee, Leith and Rosyth. Given the influence of ports within the Firth of Forth and Firth of Tay in relation to vessel traffic movements within and in proximity to the Proposed Development, Forth Ports were consulted regarding future case traffic levels.
Forth Ports indicated that no terminal or berth changes are planned that may affect vessel traffic in the future with vessel numbers expected to remain reasonably consistent. Additionally, there are no commercial ferry routes planned. If anything, over the next five years any volume changes out of the Firth of Forth are likely to be decreases and beyond five years is difficult to forecast. At the Port of Dundee there is a lease for development relating to an offshore wind base.
The Scottish Whitefish Producers Association indicated that once Aberdeen South Harbour is operational there could be an increase in cruise traffic through the region.
In the longer-term, there may be increases in wind farm related traffic associated with the ScotWind developments north and east of the Proposed Development. This was raised during consultation, with the potential for terminals within the Forth to be used. However, given the low data confidence associated with these developments it is not possible to make any quantitative assumptions.
Given the uncertainty associated with long-term predictions of vessel traffic growth, as indicated by Forth Ports, two conservative and independent scenarios of potential growth in commercial vessel movements of 10% and 20% have been estimated throughout the lifetime of the Proposed Development. In reality, future case traffic growth is likely to fluctuate depending on seasonality and cargo and industry trends.
15.2 Increases in Commercial Fishing Vessel Activity
There is similar uncertainty associated with long-term predictions for commercial fishing vessel transits given the limited reliable information on future trends upon which any firm assumption can be made. Therefore, again to ensure a conservative approach, 10% and 20% growths in commercial fishing vessel movements have been estimated throughout the lifetime of the Proposed Development. Changes in commercial fishing activity are considered further in volume 2, chapter 12.
15.3 Increases in Recreational Vessel Activity
There are no known major developments which will increase the activity of recreational vessels in the region. As with commercial fishing vessels, given the limited reliable information on future trends, conservative 10% and 20% growths in recreational vessel movements have been estimated throughout the lifetime of the Proposed Development.
15.4 Increases in Traffic Associated with Project Operations
The anticipated number of vessels associated with the Proposed Development during the construction and operation and maintenance phases are presented in section 6.5.
15.5 Commercial Traffic Routeing (Project in Isolation)
15.5.1 Methodology
It is not possible to consider all potential alternative routeing options for commercial traffic and therefore alternatives have been considered where possible in consultation with operators. Assumptions for re-routeing include:
- All alternative routes maintain a minimum mean distance of 1 nm from offshore installations and existing offshore wind farm boundaries in line with industry experience. This distance is considered for shipping and navigation from a safety perspective as explained below; and
- All mean routes take into count sandbanks, aids to navigation and known routeing preferences.
Additionally, some routes which pass at a mean distance greater than 1 nm are sufficiently wide that there may be some interaction with the offshore wind farm boundaries (within the 90th percentile range). In such instances the width of the route has been reduced within reason and if required the mean position of the route has been shifted to a distance further from the offshore wind farm boundary to ensure there is no direct interaction.
Annex 1 of MGN 654 defines as methodology for assessing passing distance from offshore wind farm boundaries but states that it is “not a prescriptive tool but needs intelligent application”.
To date, internal and external studies undertaken by Anatec on behalf of the UK Government and individual clients show that vessels do pass consistently and safely within 1 nm of established offshore wind farms (including between distinct developments) and these distances vary depending upon the sea room available as well as the prevailing conditions. This evidence also demonstrates that the Mariner defines their own safe passing distance based upon the conditions and nature of the traffic at the time, but they are shown to frequently pass 1 nm off established developments.
Evidence also demonstrates that commercial vessels do not transit through arrays and this has been supported by feedback from Regular Operators during consultation (see 24 September 2021, 27 September 2021 and 1 October 2021 entries in Table 4.1 Open ▸ ).
The NRA also aims to establish the maximum design scenario based on navigational safety parameters, and when considering this the most conservative realistic scenario for vessel routeing is considered to be when main commercial routes pass 1 nm off developments. Evidence collected during numerous assessments at an industry level confirms that it is a safe and reasonable distance for vessels to pass; however, it is likely that a large number of vessels would instead choose to pass at a greater distance depending upon their own passage plan and the current conditions. One such example is Evergas, who have indicated during consultation (via charted passage plans) that they will pass further than 1 nm off the Proposed Development Array Area. This has been accounted for when establishing the main commercial route deviations (specifically for Route 14).
15.5.2 Main Commercial Route Deviations
An illustration of the anticipated worst case shift in the mean positions of the main commercial routes within the Proposed Development array area study area following the development of the Project is presented in Figure 15.1 Open ▸ . These deviations are based on Anatec’s assessment of the maximum design scenario including the outputs of consultation.
Figure 15.1 Anticipated Main Commercial Routes within Proposed Development Array Area Study Area (Post Wind Farm)
Deviations from the pre wind farm scenario would be required for seven out of the 14 main commercial routes identified, with the level of deviation varying between a 0.1 nm decrease for Route 4 and a 26.0 nm increase for Route 14. For the displaced routes, the increase in distance from the pre wind farm scenario is presented in Table 15.1 Open ▸ .
Table 15.1 Summary of Post Wind Farm Main Commercial Route Deviations within Study Area
In the case of Route 14, although the increase in route length is very high, since this is a transatlantic route the percentage change in the total route length is relatively low. Moreover, there will be large periods where vessels on this route are in open seas and should be able to make up any time losses incurred due to the deviations.
In the case of Route 11, although the deviation is negligible, the route does pass through the gap between the Proposed Development array area and Seagreen. This gap has variable width; at the western extent the minimum width is approximately 6.0 nm and at the eastern extent is approximately 2.8 nm. Usage of Route 11 is very low (an average of less than one vessel per day) and so the likelihood of an encounter between vessels is very low. Additionally, given the width of the gap there is sufficient sea room to allow a vessel navigating within to maintain a minimum distance of 1 nm from wind farm structures, minimising allision risk. Additionally, with the additional presence of Inch Cape immediately west of the gap, mariners are expected to choose a routeing option passing north of Inch Cape and Seagreen rather than utilise the gap (see section 15.6.6).