Navigation Buoys

Trinity House maintains nearly 500 buoys and inspects those maintained by port and harbour authorities, utility companies and by oil/gas rig and wind farm operators (totaling more than 10,000 Aids to Navigation). 

Trinity House buoys are moored to the sea bed using a sinker constructed from cast iron with weights varying between 1 and 8 tonnes. The sinker is placed on the Assigned Position (AP). The weight of the sinker and the length of chain used to moor the buoy depend on the type of buoy, depth of water, strength of tide and the exposure of the buoy. 

Moorings

Most Trinity House buoys have two mooring eyes to which shackles are attached to two pieces of chain forming a bridle. The bridle runs down to a swivel allowing the buoy to rotate and prevents the bridle from twisting and dragging the buoy under the water. From the swivel, a length of chain (known as a riser) runs to a sinker on the sea bed. 

Buoys are essential in providing the mariner with visual orientation and spatial awareness. They also provide hazard, channel and waypoint marking. Equipment can be added to buoys to provide additional services such as the transmission of AIS, meteorological and hydrological data. 

Classes of Buoy

Buoys are grouped into various classes (or sizes) with Class One Buoys being the largest. Class One Buoys are typically used to mark major waypoints or hazards in deeper water and are made up of three parts – a top mark, a buoy body and a tail tube to counter-balance the top mark. The diameter of a Class One buoy body is approximately 5 metres and a fully configured buoy weighs in at approximately 10 tonnes (excluding moorings).

Maintaining the Fleet

Looking after nearly 500 buoys (as well as buoys for our commercial customers) requires the services of our vessels and Buoy Yards (located in Harwich and Swansea). Buoys are lifted out of the sea (usually on an annual basis) and inspected. The entire buoy and mooring arrangement is lifted from the sea bed and examined onboard the vessel. Areas such as the solar panels, lantern and mooring eyes are all inspected. The buoy is jet-washed and returned to the sea.

When a buoy is required to be replaced, a new buoy of equivalent character is prepared for the station and the existing buoy is removed to be landed at Harwich or Swansea. There it progresses through the refurbishment process whereby is is repaired and made good for sea at a future time. A buoy may have been placed on various different stations throughout its lifetime (and been painted various different colours). Some Trinity House buoys are 50-70 years old.

Why not visit our depot in Harwich on one of our tours to find out more about what we do? Click here to see how.

What do the different colours mean?

You can use the links on the right of this page to find out more about the different types of buoys and what they are used to indicate.

The Buoy Maintenance Process

Click here to download a pdf document detailing the Buoy Maintenance process (opens in new window).