The Reflector Sheet
The reflector is made from thin metallized polymer sheet, not dissimilar from the material used in food packaging to enclose greasy food such as potato crisps or food which would deteriorate if not encapsulated. This material is surprisingly strong and is expected to prove adequate for this application with thickness in the range 50 to 100 microns.
The material is made up into strips having a width of 7.5 metres and a total length of 8.4 Km however one strip would then weigh about 6 tonnes and would be difficult to transport when not installed. It is therefore broken down into lengths of about 500 metres with one side of a zip fastener at each end, thus a complete strip is made up of 17 panels zipped end to end. This structure also makes it easy to replace a damaged panel. The strips also have zips along their span-wise edges which enables them to be zipped together in groups of four as they deploy from their on-board storage. Each group of four then deploys between the stern floats.
On board, the individual strips are each stowed in a large compartment about 3m fore and aft and 7.2m wide where they hang from rails along each side of the compartment in a Z-fold. The hangers are temporarily clamped by the folding mechanism to the strips at 7m intervals thus the Z-fold is 3.5m deep. The hangers are no more than 4 mm thick, however this is far thicker than the double thickness of the strip material (including buoyancy and spreader tubes), so they are the deciding factor in the length of the storage compartment. Advantage is taken of this by hanging alternate folds on a second rail below the first thus significantly reducing the length of stowage compartment required.
Fig.2 shows the on board arrangements for the handling and stowage of the individual strips of the reflector sheet.
Details of the reflector sheet and its deployment/recovery
We start with the whole reflector system stowed in a craft which has just flown in to a PHDA and made a turn in the buoyancy mode on to the heading in which the sheet is to be deployed. At the outboard end of each strip there is a smallish float which carries a radio set for communication with “mother” and a controllable drogue. These floats are first lowered into the water and the drogues are set to ‘open’. The craft then goes gently ahead and the drag from the open drogues, plus the powered rollers within the craft, draw the individual strips of reflective material out of their stowage tanks. The strips first pass through the washing area (used only when they are being recovered) and then out on to the deployment platform. This is a section of the under surface of the wing, hinged at its leading edge, which is lowered to form a sloping platform down which the strips slide. The undersides of each strip incorporate two buoyancy tubes (about 450mm diameter) which are vented and rolled flat during recovery but are inflated during deployment so that the strip itself is kept clear of the water surface and only the buoyancy tubes are floating. The tubes are slotted length wise where they join the strip as also is the strip. The slots are held closed with an airtight zip. Interposed in each of these zips there are two zippers fixed to the platform which open and then close the slot so that it passes round the charge/discharge vent. There are also lateral spreader tubes (about 150mm diameter) at intervals along the strip which are vented to the buoyancy tubes; these maintain the lateral width of the groups of strips. During deployment air is pumped in through the vent to inflate the tubes and during recovery is vented to atmosphere to allow the tubes to be rolled flat for stowage.
Fig.4 shows the general arrangement of the the sheet and strips, the drogue float and the buoyancy tubes and stiffener tubes.
In order to accommodate the aircraft wing structure (a rib every 7.5m) the reflector strip stowage tanks are less than 7.5m wide. For this reason there is a zip guidance track to set/remove folds of the edges of the strip immediately inboard of the zipper which joins/separates the individual strips to/from their neighbours. The zipper and guidance tracks are situated on the deployment platform.
Fig.3 shows the zipper and guide rails on the recovery platform which create the folds in each strip necessary for the strip to fit into its stowage tank.
As soon as the whole sheet has been deployed the drogues are closed and the craft is now free to tow the sheet as necessary to maintain station with the nascent hurricane. It is estimated that it may be possible to tow at up to 10 knots.
During recovery of the strips, the washing areas, which are immediately astern of the stowage tanks, are brought into play. They consist of an inclined plane which is the width (7m) of the now laterally folded strips and up which the strips slide. They first pass under a fluffy car-wash type roller using a salt water spray and then under a soft rubber squeegee to remove the residual water. The aim is to maximise reflectivity for the next deployment. During recovery the craft will go slowly astern to ease the load on the rollers.
It is an interesting point that once the sheet has been deployed the sea state under it will change markedly; as far as sea state (i.e. the shorter wavelengths)is concerned there will be a virtual calm but the longer wavelengths will be more enduring with the longest hardly affected. In order to explain fully the laying and recovery arrangements for the reflective sheet it is first necessary to review the operating plan put into action as soon as the order is received to attend at a PHDA. There is likely to have been a preliminary warning and Albedo will be ready for take-off heading into wind and having terminated or completed any re-supply operations that may have have been in progress and disconnected from the re-supply vessels.