Boat lighting regulations--the rules that govern the placement, color and use of navigation lights--make up Part C of the Navigation Rules, sometimes known as the "Rules of the Road." A boat's lights allow an observer to tell at a glance how large a vessel is, if it's moving and in which direction. Special lights tell you if it's one vessel or a tug and barge, a dredge to be dodged, a mine sweeper to be avoided or a boat anchored or aground. There are even ancient rhymes to help you remember those special lights.
Lights When Under Way
Lights while under way are covered in Rules 20 through 29 of the Navigation Rules.
Most vessels other than row boats are required to have a red light on their port (left) side, a green light on their starboard (right) side. The lights must be visible from the front and the sides, but not the rear, of the vessel. On smaller boats, those less than 12 meters (39.4 feet), the red and green sidelights may be combined in a single unit on the bow of the boat.
Most vessels other than rowboats must carry a masthead light that can be seen from ahead and the sides. Vessels less than 12 meters may carry an "all around" light in lieu of side lights and a stern light. Vessels more than 50 meters (164 feet) long must carry one masthead light on the forward mast and a second on the after-mast. The forward masthead light must be mounted lower than the aft masthead light.
All vessels except rowboats must have a stern light, visible only from astern. Under Rule 25, rowboats are required to carry a white light, such as a flashlight, to be shown as needed.
Fishing, Towing and Sailing
Commercial fishing boats carry special lighting under Rule 26. Trawlers--boats dragging a trawl net--display a green light above a white light, both visible for 360 degrees, called "all-around" lights. There's a mnemonic device to remember this: "Green Over White, Fishing At Night." If the trawler is less than 50 meters long, no masthead light needs to be shown. When the vessel is making way, it shows red and green side lights and a stern light.
A vessel towing astern displays two all-around white lights vertically on its mast, instead of a masthead light, red and green side lights and a white light above its stern light. If the object towed is more than 200 meters (656.2 feet) behind the towing vessel, three white all-around lights will be displayed on the mast of the towing vessel, plus side lights and a towing light above the stern light. There's a mnemonic for for this as well: "White Over White, Towing At Night." Tugs may train on a barge that's on a long tow line, warning of the tow line.
Barges pushed ahead of a tug display red and green side lights. A barge in a tow being pushed ahead will also have a flashing yellow bow light.
Under Rule 25, sailboats display side lights, a stern light and, on the mast, either a masthead light or an all-round red light above an all-around green light. Remember that "Red Over Green Is A Sailing Machine."
Pilot boats delivering a pilot to a ship at the mouth of a river show an all-around white light over an all-around red light instead of a masthead light. They also show side and stern lights. The mnemonic is, "White Over Red, Pilot Ahead."
Vessels Restricted in Maneuverability
Vessels restricted in their ability to maneuver, such as dredges, vessels with mechanical failures, diving support vessels or vessels engaged in mine-clearing operations, use the same lights as others, but all have additional lights specified by Rule 27.
Boats with a major mechanical problem, such as a steering failure or significant partial power loss are known as Vessels Not Under Command. They display side lights, a stern light and two all-around red lights vertically on their mast, instead of a masthead light. Give them wide berth since two all-around red lights is the same lighting as a vessel aground. The mnemonic is "Red Over Red, Trouble Ahead."
Other vessels restricted in their maneuverability, like dredges, diving support vessels or vessels engaged in mine-clearing operations will display side lights and a stern light, plus three all-around lights vertically on their masthead: the top light is red, the middle white and the bottom red. If an obstruction exists at the vessel, such as a dredge pipe, then the obstruction will be marked by two vertical all-around red lights and the safe passage side by two vertical all-around green lights. The mnemonic is "Red White Red, Rough Road Ahead."
Mine sweepers are marked by a point-up triangle of all-around green lights on their mast, in addition to the red-white-red combination. Stand off mine sweepers by at least 1,000 yards (1/2 mile).
Vessels less than 12 meters long will not show these lights.
Lights When Not Under Way
Vessels not under way are tied to a dock, anchored or aground. If anchored, they show an anchor light--a single all-around white light on the forward masthead, no side lights and no stern light. The decks of the vessel should be lighted. If aground, a vessel shows two all-around red lights vertically on the masthead, with no other lights. Once again, "Red Over Red, Trouble Ahead."
When Lights Must Be Displayed
The lights must be displayed at night. Rule 20(b) makes that clear: "The rules concerning lights shall be complied with from sunset to sunrise, and during such times, no other lights shall be exhibited, except such lights which cannot be mistaken for the lights specified in these rules or do not impair their visibility or distinctive character, or interfere with the keeping of a proper look-out." This means that at night, except for required lights, a dark ship is a happy ship.
The lights must also be displayed during the day, during conditions of reduced visibility, such as fog or haze. Rule 20(c) states, "The lights prescribed by these rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility and may be exhibited in all other circumstances when it is deemed necessary."
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