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The initial thoughts on locating the reef centred on finding a site with suitable depth, that could easily be identified by either meaningful GPS co-ordinates or through triangulation of on-shore feature:
For example – aligning a church spire with a wind turbine and a headland with a specific electricity pylon could mean that you were close to the reef.
Reef Depth: A suitable clearance will need to be maintained above the reef to allow the safe passage of shipping.
The Royal Yacht Association has requested a clearance of 3.5 metres below the Lowest Astronomic Tide.
To achieve this with a suitable safety margin, it has been suggested that 5 metres should be aimed for as the minimum clearance.
The depth of water required to achieve the desired clearance is dependent upon the amount of the ships top structure that is removed. Current thinking is that anything above the top of the funnel should be cut off, as this will leave the ship looking like a recognisable vessel for the scuba divers and will provide the various fast moving and water eddy areas needed to promote a good reef community of marine life.
On a Type 42 Destroyer the top of the funnel is 21 metres above the keel, therefore a minimum depth of 26 metres will be required between the seabed and the water level at the Lowest Astronomic Tide to achieve the desired clearance (figure 2).
Figure 2: Preferred Location Option A – 5 metre Clearance above Reef.
If the shipping traffic in the area is shown to have a greater draft than 5 metres there may be a requirement for a greater clearance depth. In response to this an alternate location, option B, was identified (figure 3).
Figure 3: Alternate Location Option B – 10 metre Clearance above Reef.
The deeper the artificial reef is placed the less accessible it will be to scuba divers. It needs to be remembered that the basic recreational scuba diving qualification limits divers to 18 metres of depth and that additional training is required to extend this to 30 metres – The majority of recreational scuba divers do not train for depths beyond this. However recreational 'deep dive' training will allow them to venture to 40 metres below the waves as the maximum 'no-stop' diving limit. Even with special breathing gas mixtures 'no-stop' dives to these sort of depths are very short.
Therefore the shallower the reef the better it will be for scuba diving.
Achieving either of the optional depths would place the reef five to six nautical miles off shore. This is because the seabed between Shoreham and Hastings has a very shallow slope. The distance involved prevents the identification of on-shore features, which does away with the possibility of being able to use on-shore features for triangulation.
The site would have to be buoyed as a warning to shipping and to provide moorings for visiting dive boats, so it will not be difficult for skippers to identify the exact location when dropping their divers at the site.
As a result, the focus fell on finding a meaningful GPS co-ordinate for the scuttling site. Maps and charts were consulted and it was noted that the Meridian line lay pretty much midway between Brighton and Newhaven; passing through the town of Peacehaven.
The charts revealed that there was a depression on the seabed on the Meridian line which bought the 30 metre depth contour approximately a mile closer to shore at N050o 041' 050" by W000o 000' 000".
It was decided that placing the reef at this location or a shallower site nearby, but still on the Meridian line would give the most meaningful GPS co-ordinates (figure 4).
Figure 4: Chart - Area of Interest (in red) for Reef Location.
Crown Estates were contacted and asked about this proposed site and a conflict check was produced which showed that the proposed site was well away from any dredging and cruising routes, pipelines or cables, other wrecks and obstacles, as well as the nearby proposed Rampion off shore wind farm (figure 5).
Figure 5: Conflict Check by Crown Estates.
Based on the chart, conflict check data plus the height details of the proposed vessel a formal chart and placement plan was drawn up for submission to the Marine Management Organisation (figure 6).
Figure 6: Formal Placement Plan