Buoy Construction-Materials
Plastic buoys may be grouped into 4 basic types which are listed with comments on their design and construction.
1. GRP OR FIBREGLASS (Fig 1)
GRP is the usual abbreviation for glass reinforced plastic which in its most common form consists of glass matt bonded by polyester resin. As many commonly available types of glass fibre and polyester resin have limited resistance to extended immersion in water these manufacturing materials must be carefully specified and certification obtained from the manufacturer to ensure that correct quality materials have been used. Confirmation must also be obtained that laminating and curing have taken place in the correct environmental conditions.
Construction
Complex shapes can be easily produced by laying-up resin and glass reinforcement into a mould by hand (or spray machine). The cylindrical buoy body is usually formed by joining two half body shapes.
The strength of GRP is basically dependent on the ratio of glass fibre to resin and thus this is another area which requires def1nition and quality control. Light weight and high strength can be achieved by the use of carbon or kevlar fibres but their cost is usually prohibitive.
The outer layer of resin, the gell coat, prevents water absorption into the glass reinforcement and must be protected from mechanical damage. This is usually provided by some form of fendering which must be carefully designed to ensure that it does not "hang up" on the fenders or gunwale of the servicing craft.
Foam Core
In the event of a collision a GRP buoy may well crack from an impact which would only dent a steel buoy. To prevent the buoy sinking the buoy should be divided into separate watertight compartments or filled with floatation foam. If foam is used it must be of the highest quality closed-cell specification. If the foam is porous it may absorb water over a long period of time and increase the weight of the buoy to such an extent that it cannot be lifted by the servicing craft or the buoy may sink.
Mooring Attachment
The mooring eye (or eyes) will usually be metal and must thus be fastened to the buoy by some means. If the buoy is expected to last longer than the wear life of the mooring eye then it must be possible to replace the eye.
Fasteners
Fasteners bonded into GRP are seldom satisfactory due to the considerable difference in expansion rates between metals and plastics, the inherent flexibility of the plastic and the poor
ENG8/5.2/1-Page 3/8-21 Oct. 1997
