Lateral mark
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A lateral buoy, lateral post or lateral mark, as defined by the International Association of Lighthouse Authorities, is a sea mark used in maritime pilotage to indicate the edge of a channel.
Each mark indicates the edge of the safe water channel in terms of port (left-hand) or starboard (right-hand). These directions are relative to the direction of buoyage; this is usually a nominally upstream direction. In a river, the direction of buoyage is towards the river's source; in a harbour, the direction of buoyage is into the harbour from the sea. Where there may be doubt, it will be labelled on the appropriate chart.
A vessel heading in the direction of buoyage (eg into a harbour) and wishing to keep in the main channel should:
Marks are distinguished by their colour, being red or green, and shape. For historical reasons, two different schemes are in use worldwide, differing in their use of colour. The IALA defines them as System A and System B:
- System A is used by nations in Europe, Australia, New Zealand, parts of Africa and most of Asia other than the Philippines, Japan and Korea.
- System B is used by nations in North America, Central America and South America, the Philippines, Japan and Korea.
In System A:
- port marks are red and may have a red flashing light.
- starboard marks are green and may have a green flashing light.
(Port) (left) (Red) _____________________________________ (Starboard) (right) (Green)
In System B:
- port marks are green, and may have a green flashing light.
- starboard marks are red and may have a red flashing light.
(Port) (left) (Green) _____________________________________ (Starboard) (right) (Red)
In both systems:
- port marks are square or have a flat top
- starboard marks are conical (or present a triangular shape) or have a pointed top.
The shape is an important feature, as colours cannot be distinguished in some light conditions, or by persons with red-green colour blindness. Marks may also carry unique markings of letters and numbers; these may be used to identify the mark as one indicated on a nautical chart. Likewise, a mark's light may flash in a distinctive sequence for the same purpose.
Also defined in the lateral mark systems is a bifurcation mark, which has both red and green horizontal bands, one over the other. This mark indicates that a "preferred" channel (often, a deep channel suitable for heavy commercial traffic) lies to one side, and a secondary channel on the other. Vessels wishing to use the preferred channel observe the top colour of the mark, and vessels wishing to use the secondary channel observe the bottom colour.
In System B only, the phrase "red right returning" may be used as a mnemonic, indicating that a red mark must be kept on the right when returning to (i.e., entering) a harbour or river.
The alternative system of cardinal marks is used where there is no clear upstream reference direction.
[edit] External links
- A web site of Transport Canada, showing lateral marks in System B.
