Buoys are floating devices that are anchored in order to maintain their position and 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 and met hydro data.

Lateral Marks are generally used for well defined channels. They indicate the port and starboard sides of the route to be followed. They are positioned in accordance with a Conventional Direction of Buoyage. Lateral Marks in region A use red to denote port and green to denote starboard. In region B the reverse applies.

A Cardinal mark is named after the quadrant in which it is placed. The name of a Cardinal mark indicates that it should be passed to the named side of the mark. The mariner will be safe if they pass north of a North mark, south of a South mark, east of an East mark and west of a West mark.

A Cardinal mark may be used, for example, to:

• Indicate that the deepest water in that area is on the named side of the mark
• Indicate the safe side on which to pass a danger
• Draw attention to a feature in a channel such as a bend, a junction, a bifurcation or the end of a shoal

Cardinal Marks are also used for permanent wreck marking whereby North, East, South and West Cardinal buoys are placed around the wreck. In the case of a new wreck, any one of the Cardinal buoys may be duplicated and fixed with a Radar Beacon (racon).

Special Marks are used to indicate a special area or feature whose nature may be apparent from reference to a chart or other nautical publication. Special marks are yellow. They may carry a yellow 'X' top-mark, and any light used is also yellow. Uses of Special Marks include:

• Ocean Data Acquisition Systems (ODAS) marks
• Traffic separation marks where use of conventional channel marking may cause confusion
• Spoil ground marks
• Military exercise zone marks
• Cable or pipeline marks
• Recreation zone marks
• Boundaries of anchorage areas
• Structures such as offshore renewable energy installations
• Aquaculture

MetOcean data systems

Met buoys are designed to improve weather forecasts and safety at sea. They provide vital data for weather forecasts, shipping bulletins, gale and swell warnings and data for general public information and research. Data Buoys are also classed as Special Marks and are coloured yellow.

Used to mark small, isolated dangers with navigable water around the buoy. Typically used to mark hazards such as an underwater shoal or rock. They are red and black in colour.

Safe Water marks serve to indicate that there is navigable water around the mark. These include centre line marks and mid-channel marks. They may also be used to indicate channel entrance, port or estuary approaches, or landfall.

These buoys mark new wrecks clearly and unambiguously. Used as a temporary response, they are coloured in an equal number of blue and yellow vertical stripes and fitted with an alternating blue and yellow flashing light.

A fixed manmade navigation mark that can be recognised by its shape, colour, pattern, topmark, or light character, or a combination of these.

• If carrying a signal light, termed a light or lighted beacon
• If not fitted with a light, called an unlighted or unlit beacon - and provides only a day mark
• As a leading line/range or conspicuous radar mark
• May also carry a topmark

Radar + beacon. In their basic form, signals from ships’ radars trigger the racon to emit a characteristic signal which is in turn received by the ship’s radar. Their signal is in the form of a series of response pulses which will show up on a ship’s radar as a Morse-coded trace and allow easy identification of the particular racon; e.g. Kish Bank Morse code T ( - ).

Racons can be placed on any navigational mark, such as a lighthouse, beacon or buoy. The return on the ship's radar will clearly identify the mark from surrounding targets and allow the mariner to accurately measure both range and bearing. We have made major improvements in the provision of racons on the Irish coast; 22 high-specification racons are in place. The racons provided respond on standard 3cm ships' radars (X-band 9300 – 9500 Mhz) and on 10cm radars (S-band 2900 – 3100 Mhz). They are strategically placed to serve through traffic, the approaches to major ports, and fishing and leisure interests.

Leading Lights:

A group of two or more marks or lights, in the same vertical plane such that the navigator can follow the leading line on the same bearing. Leading line structures can be any colour or shape that provides a distinctive mark that cannot be confused with adjacent structures.

Precision Sector Lights:

A sector light is a fixed aid to navigation that displays a light of different colours and/or rhythms over designated arcs. The colour of the light provides directional information to the mariner. A sector light may be used to:

• Provide directional information in a fairway
• To indicate a turning point, a junction with other channels, a hazard or other items of navigational importance
• Provide information on hazard areas that should be avoided

This is an autonomous broadcast system, operating in the VHF maritime mobile band. It exchanges information such as vessel identification, position, course, speed, etc. between mobile and fixed stations. It handles multiple reports, using Time Division Multiple Access (TDMA) technology ensuring reliable and robust operation.

AIS, as applied to aids to navigation, improves and enhances services provided to Mariners.

AIS AtoN Station

The primary purpose of an AIS AtoN station is to promote and enhance safety and efficiency of navigation by one or more of the following:

• Providing a positive and all-weather means of identification
• Complementing existing services (e.g. racons) from aids to navigation
• Transmitting accurate positions of floating aids to navigation
• Indicating if a floating aid to navigation is off position
• Promulgation of Application Specific Messages including marking or delineating tracks, routes, areas, and limits (e.g. areas to be avoided and Traffic Separation Schemes); marking offshore structures (for example, wind turbines, wave and tidal energy devices, oil and gas platforms); and providing weather, tidal, and sea state data.

Virtual Aids to Navigation

• A virtual AtoN does not physically exist it's a digital information object promulgated by an authorised service provider, which may be presented on navigational display systems.
• It can be used to inform the mariner about dangers to navigation as well as safe waterways, areas in which extra caution may be necessary and areas to be avoided.
• It may be used to represent a line, area, position or other form that may be displayed graphically.
• The information, including geographic position, carried by virtual AtoN may be fixed or may be changed over time (dynamic), depending on the intended purpose.
• A virtual AtoN is used primarily where there is a time critical consideration. They may also be used in places where permanent physical AtoN cannot be sited or maintained.

Authorities, AtoN providers and mariners have long been concerned that the growing background lighting in coastal, port approach and harbour areas is reaching critical levels and often overwhelming aids to navigation (AtoN).

It is often difficult to pick out and identify the aids or it is difficult for the mariner to use channel lights. Therefore, there is a need to emphasise the navigable channel, marked routes and specific areas.

The purpose of synchronising is to increase the conspicuity of the signal, and/or to indicate that the two or more lights are associated in some manner. For example, if two buoys form a ‘gate’ in a channel, the lights on them might be synchronised to make the gate pair more conspicuous.

• Sequencing of lights is when a series of lights are flashed in a time sequence to show the geographical relationship between them. Such a set of lights is sometimes likened to a “flare path”.
• It is also possible to combine the two effects, so that, for example, if a channel is marked by pairs of buoys, the lights on each pair are synchronised, and in addition the pairs lights are set to be in sequence