long term adhesion between polyester resin and metals. A better option is to use through-bolted fixings with generous backing plates and resilient washers or coatings between the metal and the GRP.
Non corrosive fasteners of marine grade stainless steel or bronze must be used in all cases.
Similar problems may exist with the fastening of lifting eyes and tower type superstructures. It is important that any high loads are distributed throughout the structure of the buoy and not concentrated in small areas of the skin. One solution to this problem is to incorporate a central (usually steel) spine to connect the mooring eyes, lifting eyes and superstructure.
Repair Procedures
Repair of GRP is usually straightforward but does require standards of cleanliness and high working temperatures which may be difficult to achieve. Effective drying of damaged laminates or foam cores may also be difficult in cold climates. It may be necessary to use infrared heaters to warm and dry damage areas and to ensure effective curing of the repair.
The use of laminating resins and solvents is subject to increasing control by health and safety regulations.
2. URETHANE COATED FOAM (Fig 2)
General
These buoys typically consist of a thick (up to 10mm) flexible urethane elastomer skin on a flexible closed cell foam core. They have the advantage of overall flexibility and resilience.
The use of such buoys has been mandatory in some areas of the North Sea where the hazards presented to small flshing boats by drifting steel buoys were considered to be unacceptable.
The flexibility will also be an advantage when the buoy has to be lifted or serviced in rough weather when a steel buoy may damage a small servicing craft.
Construction
The buoys are usually manufactured by spraying the urethane skin material onto a shaped foam core and can thus be made to almost any required shape without the need for an expensive mould.
The points noted regarding mooring eyes on CRP buoys apply equally to these buoys.
The concept of a central structure steel spine between the mooring and lifting eyes is commonly employed.
The attachment or the interface between the flexible skin and steel mooring eyes requires particularly careful design to prevent water penetration into the foam or tearing of the skin.
The quality of the skin and foam materials is of the utmost importance. The consequences of failure of the skin are self evident but poor quality foam may absorb water through an
ENG8/5.2/1-Page 4/8-21 Oct. 1997
