Buoyage system 2

Other Buoys that are used to indicate isolated dangers, having navigable water around them, are known as Isolated Danger Buoys.
Buoys used to indicate the location of navigable water surrounding their position, e.g. middle channel, are known as Safe Water bouys
Other buoys can be used to indicate special features e.g. spoil grounds or prohibited anchorages.These are known as Special Buoys.
Do not rely entirely on any floating navigational aid. It could have been displaced or damaged by heavy weather, it could have been re-numbered or changed, or may have been removed for repairs and not replaced.
Always double check your position using Radar, GPS, and by taking bearings.