apparently sound skin or may simply shrink, resulting in a wrinkled buoy with a considerable loss of buoyancy!
Repair
Urethane may be repaired with two component pouring or trowelling compounds. Correct working conditions are critical (temperature and humidity) and detailed health and safety precautions must be observed.
3. ALL FOAM (Fig 3)
Construction
These buoys are usually constructed by wrapping closed-cell foam around a central structural core, the layers of foam being heat sealed together during the wrapping process. The major US manufacturer uses ionomer foam which is produced in sheet form. The outer layer of the rolled foam shapes can be "densified" through the application of pressure and heat to make a hard, smooth surface. Pigments are usually incorporated into the foam during the extrusion process, so the colour is continuous throughout the entire hull and daymark. The buoys include a structural steel framework, steel lifting and mooring eyes, and stainless steel connecting hardware. Internal radar reflectors can be mounted in the daymarks. The concept is usually associated with small low cost buoys. The USCG uses a large number of closed cell foam buoys in size range up to l.6m.
The manufacturing technique particularly lends itself to the production of "one off" designs as a variety of body shapes can be made without the need for a mould. Buoys of this type are significantly lighter than steel buoys of the same size.
Use
The life and durability of the buoy is entirely dependant on the quality of the foam used. The flexibility of the foam can provide good impact resistance but resistance to aggressive abrasion is not good. This last factor is important for buoys which will dry out on a hard bottom at a tidal site or may be subject to moving ice conditions.
A foam buoy hull can sustain consider.able damage or loss of material without sinking and in some parts of the world the advantage of remaining afloat after being shot is of particular importance. A damaged buoy may be repaired or recycled by the manufacturer. Other advantages of foam buoys include their lighter weight which may result in good performance in fast water.
4. MOULDED THERMOPLASTIC (Figs 4 & 5)
General
This is a technique that has been widely used to manufacture small buoys, usually with integral
