Reference
COLREGs glossary
Every term and abbreviation used in the drills, explained in plain language. Look anything up before a quiz.
Status & right of way
- Constrained by her draughtCBDRule 3 →
- A power-driven vessel severely restricted in her ability to deviate from her course because of her draught in relation to the available depth and width of water. Shows three all-round reds in a vertical line.
- Give-way vesselRule 16 →
- The vessel required to keep out of the way of another. She must take early, substantial action — and, where possible, avoid crossing ahead of the other vessel.
- Making wayRule 35 →
- Moving through the water under her own propulsion. The distinction matters for fog signals: making way is one prolonged blast, underway but stopped is two.
- Not under commandNUCRule 3 →
- A vessel that, through some exceptional circumstance, is unable to manoeuvre as required by the Rules and so cannot keep out of the way. Shows two all-round reds in a vertical line.
- Pecking order (Rule 18)Rule 18 →
- The general order of responsibility between vessels: NUC and RAM come first, then fishing, then sailing, then power-driven. Overtaking and narrow-channel rules can override it.
- Power-driven vesselRule 3 →
- Any vessel propelled by machinery. A sailing vessel using her engine is a power-driven vessel, whatever sails are set.
- Restricted in her ability to manoeuvreRAMRule 3 →
- A vessel which, from the nature of her work (dredging, cable laying, towing, replenishment, launching aircraft), cannot keep out of the way. Shows red-white-red in a vertical line.
- Sailing vesselRule 3 →
- A vessel under sail with no propelling machinery in use.
- Stand-on vesselRule 17 →
- The vessel required to keep her course and speed. She may manoeuvre as soon as it is apparent the give-way vessel is not acting, and must act when collision cannot be avoided by the give-way vessel alone.
- UnderwayRule 3 →
- Not at anchor, not made fast to the shore, and not aground. A vessel can be underway while stopped in the water — drifting still counts as underway.
- Vessel engaged in fishingRule 3 →
- A vessel fishing with nets, lines or trawls that restrict manoeuvrability. Trolling lines do not count. Trawlers show green over white; other fishing vessels show red over white.
Geometry & bearings
- Abaft the beam
- Behind the widest point of the vessel — any relative bearing more than 90° from the bow, on either side.
- Compass bearingRule 7 →
- The direction of another vessel relative to true or magnetic north. A compass bearing that does not appreciably change while the range closes means risk of collision.
- Constant bearing, decreasing rangeCBDRRule 7 →
- The classic collision signature: the other vessel stays on the same compass bearing while getting closer. Treat it as risk of collision and act.
- Crossing situationRule 15 →
- Two power-driven vessels crossing with risk of collision. The vessel with the other on her own starboard side gives way and avoids crossing ahead.
- Head-on situationRule 14 →
- Two power-driven vessels meeting on reciprocal or nearly reciprocal courses. Each alters to starboard so they pass port to port. If in doubt, assume it is head-on.
- Narrow channelRule 9 →
- A channel or fairway where vessels must keep as near to the outer limit on their starboard side as is safe and practicable. Small craft and sailing vessels must not impede vessels that can only navigate within it.
- OvertakingRule 13 →
- Approaching another vessel from more than 22.5° abaft her beam — at night you would see only her sternlight. The overtaking vessel keeps clear until finally past and clear.
- Reciprocal course
- A course 180° opposite to your own — the two vessels are heading straight at each other.
- Relative bearing
- The direction of another vessel measured from your own bow: 000° dead ahead, 090° right on the starboard beam, 180° astern.
- Risk of collisionRule 7 →
- Determined by all available means. If there is any doubt whether risk exists, it shall be deemed to exist.
- Safe speedRule 6 →
- A speed at which you can take proper and effective avoiding action and stop within a distance appropriate to the conditions — visibility, traffic, manoeuvrability, sea state, draught and radar limits all feed into it.
- Traffic separation schemeTSSRule 10 →
- A routing system with one-way lanes. Join and leave at the ends where possible, keep clear of the separation zone, and cross on a heading as nearly as practicable at right angles to the traffic flow.
Lights & shapes
- All-round lightRule 21 →
- A light showing an unbroken 360° around the horizon — used for anchor, NUC, RAM and status lights.
- Day shapesRule 27 →
- Black shapes shown by day in place of the night light signals: a ball for anchored, two balls for NUC, ball-diamond-ball for RAM, a cone point-down for sail under power, a cylinder for constrained by draught.
- Flashing lightRule 21 →
- A light flashing at regular intervals of 120 flashes or more per minute.
- Green over whiteRule 26 →
- Trawler at work. The old memory line is "green over white, trawling at night".
- Masthead lightRule 21 →
- A white light over the fore-and-aft centreline showing 225° — from dead ahead to 22.5° abaft the beam on each side.
- Red over redRule 27 →
- Two all-round reds in a line: not under command — "red over red, the captain is dead".
- Red over whiteRule 26 →
- Fishing vessel other than a trawler — "red over white, fishing at night".
- SidelightsRule 21 →
- Green to starboard, red to port, each showing 112.5° from dead ahead to 22.5° abaft the beam on its own side.
- SternlightRule 21 →
- A white light at the stern showing 135°, centred dead astern — 67.5° each side.
- Towing lightRule 21 →
- A yellow light with the same characteristics as a sternlight, shown above it when towing astern.
- White over redRule 29 →
- Pilot vessel on duty — "white over red, pilot ahead".
Sound & signals
- Bend signalRule 34 →
- One prolonged blast when approaching a blind bend or an obstruction in a channel. A vessel on the other side answers with one prolonged blast.
- Distress signalsRule 37 →
- Signals in Annex IV indicating distress and need of assistance — including continuous fog-horn sounding, SOS, a red parachute flare, orange smoke, and slowly raising and lowering outstretched arms.
- Doubt signalRule 34 →
- Five or more short and rapid blasts, meaning "I doubt you are taking sufficient action to avoid collision". May be backed up by the same in light flashes.
- Fog signalsRule 35 →
- In or near restricted visibility: power-driven making way sounds one prolonged blast every 2 minutes; underway but stopped sounds two prolonged; NUC, RAM, CBD, fishing, sailing and towing vessels sound one prolonged plus two short.
- Manoeuvring signalsRule 34 →
- In sight of one another: one short blast = altering to starboard, two short = altering to port, three short = operating astern propulsion.
- Prolonged blastRule 32 →
- A blast of four to six seconds.
- Short blastRule 32 →
- A blast of about one second.
Radar & navigation
- Automatic Identification SystemAIS
- A system broadcasting a vessel's identity, position, course and speed. It supports a proper look-out but never replaces sight, hearing and radar.
- Automatic Radar Plotting AidARPA
- Radar that automatically tracks targets and computes their course, speed, CPA and TCPA. Rule 7 warns against making assumptions from scanty radar information.
- Closest point of approachCPA
- The smallest distance by which the other vessel will pass if both hold course and speed. A small CPA means you need to act.
- In sight of one anotherRule 3 →
- Vessels are only "in sight" when one can be observed visually from the other. Radar contact alone does not count — that is why the fog rules exist.
- Restricted visibilityRule 19 →
- Fog, mist, falling snow, heavy rain, sandstorms or similar. Vessels not in sight of one another follow Rule 19: safe speed, engines ready, and avoid altering to port for a vessel forward of the beam.
- Time to closest point of approachTCPA
- The time remaining until the CPA occurs — how long you have left to act.
General
- COLREGs
- The International Regulations for Preventing Collisions at Sea, 1972 — the rules of the road for all vessels on the high seas and connected navigable waters.
- General prudential ruleRule 2 →
- Rule 2 — nothing exonerates a vessel from the consequences of neglecting the Rules or of any precaution required by ordinary good seamanship. A departure from the Rules is allowed where necessary to avoid immediate danger.
- Ordinary practice of seamenRule 2 →
- The standard of care expected of a competent mariner — the benchmark Rule 2 applies when judging conduct.
- Proper look-outRule 5 →
- A continuous watch by sight and hearing and by all available means, sufficient to make a full appraisal of the situation and the risk of collision. The most cited failure in collision cases.
- SeaplaneRule 3 →
- Any aircraft designed to manoeuvre on the water — treated as a vessel under the Rules.
- VesselRule 3 →
- Every description of water craft used or capable of being used as a means of transport on water, including non-displacement craft, WIG craft and seaplanes.
- Wing-in-ground craftWIG
- A multimodal craft that operates close above the surface using ground effect. On take-off, landing and near the surface it must keep well clear of all other vessels.