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DOT Home | Marine information | Commercial vessel safety | Collision regulations (lights / shapes) | Rule 21 - Definitions

Rule 21 - Definitions

Please note: The following information has been reproduced from Part C (Lights and Shapes) of the Prevention of Collision at Sea Regulations 1983 (external link). The purpose of the reproduction is to explain "graphically'' the requirements of navigation lights on a variety of vessels.

• Masthead light
• Sidelights
• Sternlight
• Towing light
• All round light
• Flashing light

Masthead light

"Masthead Light" means a white light placed over the fore and aft centreline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees.

Example of a masthead light

General masthead notes

Masthead lights

1. Shall be mounted in and above the keel line on a fixed mounting.
2. If shielded to avoid light emission on deck, the shielding shall not interfere with the prescribed arcs of vertical visibility.
3. On vessels of 20 metres or greater over all length the forward or only masthead light shall be mounted forward of the sidelights:
   • 6 metres above the deck or (lowest watertight deck); and
   • the beam of the vessel in metres above the deck, whichever is the greater. In no case is the light required to be more than 12 metres above the deck.
4. On vessels of 12 metres and over but less than 20 metres overall length the light shall be mounted not less than 2.5 metres above the gunwales.
5. On vessels less than 12 metres over all length the light may be mounted less than 2.5 metres above the gunwales but shall be not less than 1 metre above the sidelights.

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Sidelights

"Sidelights" mean a green light on the starboard side and a red light on the port side each showing an unbroken light over an arc of the horizon of 112.5 degrees. In vessels less than 20 metres in length the sidelights may be combined in one lantern carried on the fore and aft centreline of the vessel.

Example of a sidelight

General sidelight notes

1. Sidelights shall be mounted on the same athwartships line, at the same height above the deck and parallel and perpendicular to the construction water line.
2. Light shall be fitted into screens parallel to the fore and aft line of the vessel. On vessels 20 metres or greater overall length the screens are not to be less than 900 mm long, on vessels 12 to 20 metres overall length the screens are not to be less than 600 mm long, in vessels less than 12 m overall length the screens are not to be less than 450 mm. long. The height of the screen shall not be less than 1.2 times the overall depth of the Lantern. The inside of the screen is to be painted matt black.
3. Instead of screens, parts of the superstructure may be used provided that all the requirements of clauses 1 and 2 are met and there is no emission from the light into the deckhouse or other parts of the vessel.
4. On vessels of 20 metres or greater overall length the side lights shall be installed:
   1. close to the shipside as is practicable and in no case less than 0.5 of the beam of the vessel apart;
   2. abaft the forward or only masthead light; and
   3. at a height not greater than 0.75 of the height of the masthead light but not so low as to be interfered with by the deck lighting.
5. On vessels Of 12 metres and over but less than 20 metres overall length the side lights shall be installed not greater than 0.75 of the height of the masthead light. Where the masthead light is mounted less than 3 metres above the gunwales the sidelights should be installed not less than 1 metre below the masthead lights.
6. On vessels less than 12 metres over all length the side lights shall be installed not less than 1 metre below the masthead light.

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Sternlight

"Sternlight" means a white light placed as nearly as practicable at the stern showing an unbroken light over an arc of the horizon of 135 degrees.

Stern light notes

Towing

1. Stern lights shall be mounted in and above the Keel Line and preferably should be at or below the level of the sidelights.
2. Shall be mounted as close to the stern of the vessel as is practicable.
3. The requirements for (1) may be waived in the case of vessels less than 20 metres over all length where it is not practical to fit the light above the keel line.
4. The beam from the light shall not be obscured by any part of the vessels structure or equipment through a horizontal arc greater than 6 degrees.

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Towing light

"Towing Light" means a yellow light having the same characteristics as the "sternlight " defined in paragraph (c) of this rule.

Towing light notes

Towing

1. The additional masthead lights required shall be mounted directly above or below the light referred to in the Definition of a Masthead Light.
2. The yellow towing light shall be mounted directly above the stern light.
3. On vessels of 20 metres or greater over all length:
   1. the additional masthead light/s shall be mounted so that the distance apart of any lights is not less than 2 metres;
   2. the yellow towing light shall be not less than 2 metres above the stern light; and
   3. where lights are required to be carried indicating the vessel is restricted in its ability to manoeuvre. the lights may be fixed mounted or set in operation by hoisting. The lights shall be not less than 2 metres apart and may be positioned at a height below the top masthead light.
4. On vessels less than 20 metres over all length:
   1. the additional masthead lights shall be mounted not less than 1 metre from the masthead light referred to in the Definition of a Masthead light;
   2. the yellow towing light shall be mounted not less than 1 metre above the stern light; and
   3. where lights are required to be carried indicating the vessel is restricted in its ability to manoeuvre the lights may be fixed mounted or set in operation by hoisting, the lights shall not be less than 1 metre apart and may be positioned below the top mast head light.

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All round light

"All Round Light" means a light showing an unbroken light over an arc of the horizon of 360 degrees.

Example of an all round light

Trawlers and fishing

1. The lights may be fixed mounted or set in operation by hoisting. Green above white.
2. On vessels 20 metres or greater over all length the white light shall be not less than 4 metres above the sidelights and the distance apart of the coloured and the white light not less than 2 metres.
3. On vessels less than 20 metres over all length the white light shall be not less than 2 metres above the side lights and the distance apart of the coloured and the white light not less than 1 metre.

Not under command

1. The light may be fixed mounted or set in operation by hoisting. Red above Red.
2. On vessel 20 metres or greater over all length the lower of the two lights shall be not less than 4 metres above the Sidelights and the lights shall be not less than 2.0 metres apart.
3. On vessels less than 20 metres over all length the lower of the two lights shall be not less than 2 metres above the Sidelights and the lights shall be not less than 1.0 metres apart.

Flashing light

"Flashing Light" means a light flashing at regular intervals at a frequency of 120 flashes or more per minute.

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