Chrissie
Well-Known Member
I was very impressed with the detail given in the reply from Navitus Bay Wind Farm, and Its certainly put my mind at rest with regard to the impact to myself and other leisure sailors. I have posted the replies here to share with you all.
Dear Chrissie Davis,
Thank you for your correspondence, this has been recorded and will be included within the consultation report which will accompany the planning application.
Please see below answers to your questions raised:
1, I am seeking clarification on noise levels from the turbines, will it be sufficient to mask the sounds of ferries, ships, support vessels and other leisure boats approaching?
During operation the maximum noise level at the centre of the blades is up to 110dBA. However, the background noise from wind and the sea largely masks this noise even when within the wind park. If you are considering the noise levels from onshore then the turbines will not be heard over any background noise due to their distance from shore. The wind park will not mask the sound of any of the vessels you mention.
2, The turbines will be lit, but my experience of lights on shore is that it can lead to reduced clarity, visibility being confused with so many extra lights, trying to identify the lights that could be due to a vessel approaching me, will be harder.
The turbines will be lit with flashing yellow lights, yellow lights have been specially chosen by international authorities for offshore structures so as not to be confused with lights on vessels - white, red and green fixed lights. Also, to prevent light pollution and / or confusion, not all turbines will be marked. Current marking schemes used by regulators include the marking of significant peripheral structures (SPS), which are on the corner or other significant point on the periphery of the wind park.
For reference more information about the lighting of offshore structures is available in ‘IALA Recommendation O-139 - The Marking of Man-Made Offshore Structures’.
3, As I pass the turbine lights, my lights will blend in and make me less visible to other vessels.
You comment has been noted.
4, What impact will the turbine blades have on wind distubance? Are there studies that show the wind disturbace from a bank of turbines? As a sailing vessel, would I find my progress disturbed as the wind is disturbed? Would my wind vane steering system be affected?
The impact of the turbine blades on the wind is known as a wake effect and a large amount of monitoring and review of this effect has been completed. The air flow behind a turbine (relative to wind directions) becomes turbulent but the impact is focussed in the area behind the blades. There is a much lower impact on wind turbulence at or near sea leavel (up to 20m above sea level as the blades do not reach lower than 22m above LAT). There will inevitably be a minimal impact on wind distribution but this will not be significant for sailing activities and your steering system should not be impacted. There have been no reported incidents in operational wind farms of this occurring to our knowledge.
5, How many support vessels would be crossing between shore and the development sight, on a daily/hourly basis?
During the operational period we would expect each turbine to be visited 2-3 times per year with a higher concentration of visits in the summer period due to better weather conditions. This access will be required to carry out planned maintenance work. However, in a single trip one vessel could carry out work on 2 or more turbines. If we assume that maximum number of turbines (218) then on average you could expect 2 vessels per day in the summer and 1 vessel or less per day in the winter. However, there will be some periods of higher movements where weather has restricted access or if more significant work is being completed that could see 6 or more vessels visiting the site in a single day.
During construction it is difficult to estimate vessel movements as they will be travelling from both local and remote ports but there will be more than 10 vessels in the site on most good weather days. Not all will travel to shore every day.
6, What size would they be?
Our support vessels would typically be in the range of 18-24m length with 8m beam and 1.5m draft but there could be some variation in exact dimensions dependent upon a detailed review of requirements and design details.
7, What speed will they travel at?
A cruising speed of 20 knots would be typical for our vessels.
8, Would they be operating in the dark?
We will prefer to carry out the majority of our work in daylight but will undertake night transfers if required and subject to any restrictions that might be placed on us for the work we are completing.
9, Naturally they will be fitted with AIS units?, but the majority of small leisure vessels will have recieve only units, indeed, the majority of small vessels will not have AIS at all.
The support vessels we will use would typically have transmit and receive AIS systems
10, During construction, what restrictions on passage making are planned?
If the project receives planning consent, we will be implementing a rolling 500m safety zone around the areas where we are working during the construction of the wind park, where only construction vessels will be able to enter.
11, When the weather is bad or the seas are high due to bad weather in the proceding days, many yachts divert South of the IOW to enter the Solent at the Nab tower /Portsmouth end, in order to avoid the major overfalls off the Needles. Indeed navigation/pilot books advise against a Needles entry in many sea or wind conditions, but to avoid the Needles would entail passing through the turbines, in lumpy seas, with the associated wind disturbance, so possibly having to motor for hours to keep a safe course. This has to make the passage more dangerous, has it been considered?
Consultation with maritime bodies including the Maritime Coastguard Agency, Trinity House, RYA and local clubs commenced in 2010 and is on-going. Discussions with these bodies covers a wide range of areas, including any possible impact on passage.
12, What sound levels are anticipated at 1/2 mile, 1 mile, 2 miles, 3 miles 4 and 5 miles off?
We are still awaiting our final results of the in air noise assessment, which will give project specific noise levels at these distances. Using data from other projects onshore and offshore typical values for these distances would be:
½ miles 57dBA
1 mile 50dBA
2 miles 43dBA
3 miles 38dBA
4 miles 36dBA
5 miles 34dBA
6 miles 30dBA
These levels are typical and INDICATIVE only.
13, The majority of boats will be passing at about 2.5 miles, particularly if they are heading straight to Dartmouth or similar, so need to stay offshore to avoid the adverse tidal influence at the headlands, what do the coridors shown on your charts actually mean in terms of disturbance?
We can confirm that we have discussed the impacts of our development on shipping lanes and that expected shipping traffic will be able to safely navigate around our zone. Smaller vessels including recreational craft will be permitted to travel through our zone with a 50m exclusion zone around each turbine the only restriction. A minimum separation of 750m will exist between each turbine.
I trust the above is satisfactory. If you have any further questions then please do not hesitate to contact us.
Dear Chrissie Davis,
Thank you for your correspondence, this has been recorded and will be included within the consultation report which will accompany the planning application.
Please see below answers to your questions raised:
1, I am seeking clarification on noise levels from the turbines, will it be sufficient to mask the sounds of ferries, ships, support vessels and other leisure boats approaching?
During operation the maximum noise level at the centre of the blades is up to 110dBA. However, the background noise from wind and the sea largely masks this noise even when within the wind park. If you are considering the noise levels from onshore then the turbines will not be heard over any background noise due to their distance from shore. The wind park will not mask the sound of any of the vessels you mention.
2, The turbines will be lit, but my experience of lights on shore is that it can lead to reduced clarity, visibility being confused with so many extra lights, trying to identify the lights that could be due to a vessel approaching me, will be harder.
The turbines will be lit with flashing yellow lights, yellow lights have been specially chosen by international authorities for offshore structures so as not to be confused with lights on vessels - white, red and green fixed lights. Also, to prevent light pollution and / or confusion, not all turbines will be marked. Current marking schemes used by regulators include the marking of significant peripheral structures (SPS), which are on the corner or other significant point on the periphery of the wind park.
For reference more information about the lighting of offshore structures is available in ‘IALA Recommendation O-139 - The Marking of Man-Made Offshore Structures’.
3, As I pass the turbine lights, my lights will blend in and make me less visible to other vessels.
You comment has been noted.
4, What impact will the turbine blades have on wind distubance? Are there studies that show the wind disturbace from a bank of turbines? As a sailing vessel, would I find my progress disturbed as the wind is disturbed? Would my wind vane steering system be affected?
The impact of the turbine blades on the wind is known as a wake effect and a large amount of monitoring and review of this effect has been completed. The air flow behind a turbine (relative to wind directions) becomes turbulent but the impact is focussed in the area behind the blades. There is a much lower impact on wind turbulence at or near sea leavel (up to 20m above sea level as the blades do not reach lower than 22m above LAT). There will inevitably be a minimal impact on wind distribution but this will not be significant for sailing activities and your steering system should not be impacted. There have been no reported incidents in operational wind farms of this occurring to our knowledge.
5, How many support vessels would be crossing between shore and the development sight, on a daily/hourly basis?
During the operational period we would expect each turbine to be visited 2-3 times per year with a higher concentration of visits in the summer period due to better weather conditions. This access will be required to carry out planned maintenance work. However, in a single trip one vessel could carry out work on 2 or more turbines. If we assume that maximum number of turbines (218) then on average you could expect 2 vessels per day in the summer and 1 vessel or less per day in the winter. However, there will be some periods of higher movements where weather has restricted access or if more significant work is being completed that could see 6 or more vessels visiting the site in a single day.
During construction it is difficult to estimate vessel movements as they will be travelling from both local and remote ports but there will be more than 10 vessels in the site on most good weather days. Not all will travel to shore every day.
6, What size would they be?
Our support vessels would typically be in the range of 18-24m length with 8m beam and 1.5m draft but there could be some variation in exact dimensions dependent upon a detailed review of requirements and design details.
7, What speed will they travel at?
A cruising speed of 20 knots would be typical for our vessels.
8, Would they be operating in the dark?
We will prefer to carry out the majority of our work in daylight but will undertake night transfers if required and subject to any restrictions that might be placed on us for the work we are completing.
9, Naturally they will be fitted with AIS units?, but the majority of small leisure vessels will have recieve only units, indeed, the majority of small vessels will not have AIS at all.
The support vessels we will use would typically have transmit and receive AIS systems
10, During construction, what restrictions on passage making are planned?
If the project receives planning consent, we will be implementing a rolling 500m safety zone around the areas where we are working during the construction of the wind park, where only construction vessels will be able to enter.
11, When the weather is bad or the seas are high due to bad weather in the proceding days, many yachts divert South of the IOW to enter the Solent at the Nab tower /Portsmouth end, in order to avoid the major overfalls off the Needles. Indeed navigation/pilot books advise against a Needles entry in many sea or wind conditions, but to avoid the Needles would entail passing through the turbines, in lumpy seas, with the associated wind disturbance, so possibly having to motor for hours to keep a safe course. This has to make the passage more dangerous, has it been considered?
Consultation with maritime bodies including the Maritime Coastguard Agency, Trinity House, RYA and local clubs commenced in 2010 and is on-going. Discussions with these bodies covers a wide range of areas, including any possible impact on passage.
12, What sound levels are anticipated at 1/2 mile, 1 mile, 2 miles, 3 miles 4 and 5 miles off?
We are still awaiting our final results of the in air noise assessment, which will give project specific noise levels at these distances. Using data from other projects onshore and offshore typical values for these distances would be:
½ miles 57dBA
1 mile 50dBA
2 miles 43dBA
3 miles 38dBA
4 miles 36dBA
5 miles 34dBA
6 miles 30dBA
These levels are typical and INDICATIVE only.
13, The majority of boats will be passing at about 2.5 miles, particularly if they are heading straight to Dartmouth or similar, so need to stay offshore to avoid the adverse tidal influence at the headlands, what do the coridors shown on your charts actually mean in terms of disturbance?
We can confirm that we have discussed the impacts of our development on shipping lanes and that expected shipping traffic will be able to safely navigate around our zone. Smaller vessels including recreational craft will be permitted to travel through our zone with a 50m exclusion zone around each turbine the only restriction. A minimum separation of 750m will exist between each turbine.
I trust the above is satisfactory. If you have any further questions then please do not hesitate to contact us.
