COLREGs Steering and Sailing Rules: Rules 4 to 19

Background

Purpose and structure of the Steering and Sailing Rules

The Steering and Sailing Rules of the COLREGs are the operational rules that determine ship behaviour in encounter situations. Where the rest of the COLREGs (Part C lights and shapes, Part D sound and light signals) provide the visual and audible signalling system that supports collision avoidance, the Steering and Sailing Rules tell mariners what to do when an encounter develops.

The rules are structured to apply progressively as situations develop:

• Section I (Rules 4-10) applies in all conditions and provides general principles applicable whether or not vessels are in sight of one another.
• Section II (Rules 11-18) applies when vessels are in sight of one another and provides specific rules for the encounter types (overtaking, head-on, crossing).
• Section III (Rule 19) applies in restricted visibility when vessels are not in sight of one another.

The progressive structure means that Section I rules (lookout, safe speed, risk of collision, action to avoid collision) apply at all times, with Sections II and III providing additional specific rules as the encounter develops.

Application to all vessels

Unlike most maritime regulations that apply only to commercial vessels above a defined size, the COLREGs apply to all vessels in international waters: from the smallest sailing dinghy to the largest container ship, from naval warships to recreational craft, from fishing vessels to cruise ships. This breadth reflects the operational reality that collision avoidance requires consistent rules applied by all participants in the navigational environment.

The application breadth is reinforced through:

• National implementation: contracting states implement the COLREGs domestically, applying them to vessels in their territorial waters.
• Inland adaptations: many states adopt similar rules for inland waters with some local variations (the US Inland Rules, for example).
• Specific area rules: some areas have local rules supplementing the COLREGs (Strait of Bonifacio Special Rules, Singapore Strait STRAITREP, etc.).

Major amendment history

The COLREGs were adopted in 1972 (entered into force 15 July 1977) and have been amended several times:

• 1981 amendments: clarification of Rule 10 (traffic separation schemes).
• 1987 amendments: clarification of Rule 26 (fishing vessels lights) and other minor refinements.
• 1989 amendments: aligned with new ship signalling capabilities.
• 1993 amendments: Wing-In-Ground (WIG) craft additions.
• 2001 amendments: substantial update including additions for high-speed craft.
• 2007 amendments: WIG craft expansion and other updates.
• 2013 amendments: clarifications relevant to AIS use under Rule 7.

The amendment cycle has been relatively measured compared with other IMO instruments, reflecting the foundational nature of the COLREGs and the conservative approach to changes that affect mariner practice globally.

Section I: Conduct of vessels in any condition of visibility (Rules 4-10)

Rule 4: Application

Section I applies in any condition of visibility. The rules in Section I are the foundational requirements that apply at all times, regardless of whether vessels are in sight of each other or in restricted visibility.

Rule 5: Look-out

Rule 5 is among the most quoted COLREG rules: “Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.”

Rule 5 sets no exception for ship size, time of day, or weather. The phrase “at all times” means the lookout obligation never lapses while the vessel is underway, at anchor in a fairway, or stopped but not made fast. Courts have read the rule as a continuous duty: a single lapse long enough for an approaching vessel to close to collision range can establish fault even when every other rule was observed. The reference to “sight and hearing as well as by all available means” puts visual and aural watch first, then folds in everything else the ship carries.

The “all available means” formulation has expanded with technology. Today’s lookout includes:

• Visual observation by trained watchkeepers (Rule 5 explicit requirement).
• Hearing observation for sound signals from other vessels (Rule 5 explicit requirement).
• Radar surveillance with target tracking (ARPA where fitted).
• AIS monitoring of nearby ship positions, courses and intentions.
• VHF communication for situational awareness and intent clarification.
• Echo sounder for proximity to seabed (relevant for collision with submerged objects and grounding).
• Weather information affecting risk perception.
• GPS/ECDIS for position fixing and chart interpretation.

The Rule 5 obligation can’t be discharged by automation alone; the proper lookout requires human attention even when automated systems are operating. A common manning shortfall is the sole watchkeeper at night who also works the radar, the ECDIS, and the GMDSS console: when one of those tasks absorbs the officer, the visual watch goes dark for the same interval. Many investigated collisions trace to exactly that gap, where the officer of the watch was head-down at a screen while a target closed on a steady bearing outside the window.

Rule 6: Safe speed

Rule 6 requires safe speed: “Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions.” The rule doesn’t fix a number. It then lists the factors a master must weigh, splitting them into a set applicable to every vessel and a second set for vessels with operational radar.

For all vessels, the six listed factors are the state of visibility; the traffic density, including concentrations of fishing vessels or any other vessels; the manoeuvrability of the vessel with special reference to stopping distance and turning ability in the prevailing conditions; at night, the presence of background light such as from shore lights or backscatter of her own lights; the state of wind, sea, and current, and the proximity of navigational hazards; and the draught in relation to the available depth of water. That last factor is why a loaded VLCC at 20 metres draught in a 22-metre channel must slow well below open-water speed: the underkeel margin removes most of her room to manoeuvre and lengthens her effective stopping distance.

For vessels with operational radar, Rule 6 adds a second list: the characteristics, efficiency, and limitations of the radar equipment; any constraints imposed by the radar range scale in use; the effect on radar detection of sea state, weather, and other sources of interference; the possibility that small vessels, ice, and other floating objects may not be detected by radar at an adequate range; the number, location, and movement of vessels detected by radar; and the more exact assessment of visibility that may be possible when radar is used to measure the range of vessels or other objects in the vicinity. The rule treats radar as an aid that can sharpen a speed decision, not as a licence to keep full speed in fog. A vessel that can’t be stopped within the range at which she first detects targets on her chosen scale is, by the rule’s own logic, going too fast.

The safe speed obligation is qualitative, not a posted limit, and it puts the judgement on the master and the officer of the watch. The penalty for getting it wrong shows up in the casualty record: in fog, a closing speed of 30 knots between two vessels each making 15 knots leaves under two minutes from first radar detection at one mile to closest approach, far too little to plot, decide, and turn a large ship.

Rule 7: Risk of collision

Rule 7 governs how to determine whether risk of collision exists:

“Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists; if there is any doubt such risk shall be deemed to exist.”

“Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects.”

“Assumptions shall not be made on the basis of scanty information, especially scanty radar information.”

Rule 7(d) then gives the test that decides most cases. It states that in determining if risk of collision exists, such risk shall be deemed to exist if the compass bearing of an approaching vessel doesn’t appreciably change, and that such risk may sometimes exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow, or when approaching a vessel at close range. The steady-bearing test is the operational heart of the convention: two vessels on courses that keep the relative bearing constant are, by definition, on collision courses, because constant bearing with decreasing range is the geometry of a meeting. The caveat about large vessels and tows matters in practice. A bearing can swing while the near end of a long tow still passes through your track, so a changing bearing on the tug doesn’t clear the barge half a mile astern of it.

The Rule 7 framework supports:

• Compass bearing observation: an unchanging compass bearing of an approaching vessel suggests risk of collision.
• CPA / TCPA monitoring: closest point of approach and time to CPA computed from radar tracking.
• AIS monitoring: position, course, speed of other vessels with computed CPA/TCPA in modern AIS receivers.
• Visual aspect change: changes in the visual aspect of an approaching vessel.
• Mast formation: alignment of own ship’s masts with the target indicates risk.

The CPA / TCPA calculator implements the Rule 7 quantitative analysis from observed bearing, range, course and speed data. The underlying geometry is simple relative motion: the closest point of approach is the perpendicular distance from own ship to the target’s relative-motion line, and the time to that point is $\text{TCPA} = R_0 \cos\theta / V_r$, where $R_0$ is the present range, $\theta$ the angle between the relative-velocity vector and the line of sight, and $V_r$ the relative speed. When the relative track passes through own ship’s position, the CPA is zero and the bearing holds steady, which is the radar-plot expression of the Rule 7(d) steady-bearing test. ARPA and the CPA logic in modern AIS receivers compute this continuously, but the rule still warns against trusting a single sweep: a target manoeuvring during the observation window invalidates a plot built on the assumption of constant target course and speed.

Rule 8: Action to avoid collision

Rule 8 sets the principles for action to avoid collision:

• Positive action: not gradual or tentative.
• Made in ample time: well before the encounter becomes critical.
• With due regard to good seamanship: not just minimum compliance.
• Large enough to be readily apparent to another vessel observing visually or by radar (a small course change may not be detected).
• Reduction of speed or going astern: where appropriate, especially in heavy weather or close-quarters situations.
• Avoiding turning to port for crossing situations from starboard (a common error that can convert a crossing into a head-on near miss).

Rule 8 adds further discipline that the bullet summary above compresses. Rule 8(b) states that any alteration of course or speed shall, if circumstances admit, be large enough to be readily apparent to another vessel observing visually or by radar, and that a succession of small alterations of course or speed should be avoided. The reasoning is that a radar observer plotting your relative motion can only see a course change once it builds up enough cross-track displacement to register; a 5-degree nudge held for a minute reads as noise, while a single 30-degree turn shows as an unambiguous new track within two or three sweeps. Rule 8(c) prefers an alteration of course alone, made in good time, where there is sea room, because a bold turn is the clearest signal of intent. Rule 8(d) sets the standard of success: the action taken to avoid collision shall result in passing at a safe distance, and its effectiveness shall be checked until the other vessel is finally past and clear. The duty doesn’t end when the wheel goes over; it ends when the target’s bearing has opened and the range is steadily increasing.

Rule 8(e) is the rule that ties safe speed back to manoeuvre: if necessary to avoid collision or to allow more time to assess the situation, a vessel shall slacken her speed or take all way off by stopping or reversing her means of propulsion. Rule 8(f), added in the 1987 amendments, governs the not-to-impede vessels: a vessel required not to impede another’s passage shall take early action to allow sea room, remains fully bound by the steering and sailing rules when risk of collision develops, and the vessel whose passage is not to be impeded stays equally bound by those rules once the two come into risk of collision. The Rule 8 framework is complementary to the rules for specific encounter types in Section II.

Rule 9: Narrow channels

Rule 9 governs vessel conduct in narrow channels:

• Keep to starboard side of the channel as is safe and practicable.
• Vessels of less than 20 metres in length or sailing vessels shall not impede the passage of a vessel that can safely navigate only within a narrow channel.
• Fishing vessels shall not impede the passage of vessels in the channel.
• Crossing: a vessel shall not cross a narrow channel if such crossing would impede the passage of a vessel that can safely navigate only within the channel.
• Overtaking in a narrow channel requires sound signals (Rule 34) and confirmation between vessels.
• Sound signal for warning of approach to a bend or obstruction.

Narrow channels are common in port approaches, harbour entrances, and channelised waterways, and Rule 9 reorders the usual priorities inside them. A vessel less than 20 metres in length, a sailing vessel, and a vessel engaged in fishing must each not impede a vessel that can safely navigate only within a narrow channel or fairway, even though Rule 18 would otherwise hand the small craft or the fishing vessel the right of way. The overtaking provision in Rule 9(e) is specific: in a narrow channel where overtaking can take place only if the vessel to be overtaken takes action to permit safe passing, the overtaking vessel shall indicate her intention by the Rule 34(c) signals (two prolonged plus one short blast to pass on the other vessel’s starboard side, two prolonged plus two short to pass on her port side), and the vessel about to be overtaken shall, if in agreement, sound one prolonged, one short, one prolonged, one short, and take steps to permit safe passing. The bend signal in Rule 9(f) requires a vessel nearing a bend or an area where other vessels may be obscured to sound one prolonged blast, to be answered with the same signal by any approaching vessel within hearing. The rule is most important in pilotage waters, where the channel margins are tight and local knowledge governs how far a deep-draught ship can be pushed toward the bank.

Rule 10: Traffic separation schemes

Rule 10 governs vessel conduct in IMO-adopted Traffic Separation Schemes (TSS):

• Use of appropriate traffic lane: a vessel shall use the appropriate traffic lane in the general direction of traffic flow for that lane.
• Avoid crossing: a vessel shall, so far as practicable, avoid crossing traffic lanes.
• Crossing the lane: if crossing is necessary, it shall be done at right angles or as close to right angles as possible.
• Inshore traffic zone: vessels of less than 20 metres or sailing vessels may use inshore traffic zones; other vessels generally use the lane.
• Joining or leaving: vessel joining a lane shall do so at the end of the lane, with all reasonable means.

A point often missed is what Rule 10 doesn’t do. Rule 10(a) states the rule applies to traffic separation schemes adopted by the IMO and doesn’t relieve any vessel of her obligation under any other rule. Inside a scheme, the crossing, head-on, and overtaking rules of Section II still run; the lanes set the general flow but they don’t suspend Rule 15 when two ships meet at an angle within a lane. Rule 10(j) requires a vessel less than 20 metres, a sailing vessel, or a vessel engaged in fishing not to impede the safe passage of a power-driven vessel following a traffic lane, mirroring the narrow-channel reordering. Rule 10(i) protects vessels engaged in fishing within a separation zone or lane in the sense that they may operate there, but Rule 10(j) still bars them from impeding through traffic. The right-angle crossing requirement in Rule 10(c) exists for a radar reason: a vessel that crosses heading as nearly as practicable at right angles to the general direction of traffic flow presents the largest aspect change and the shortest exposure time to vessels running the lane, so following traffic can read her intention quickly and she clears the danger zone in minimum time.

Major TSS clusters sit around the Strait of Malacca, the Suez Canal approaches, the Panama Canal approaches, the Dover Strait in the English Channel, the Strait of Gibraltar, and many port approaches. The Dover Strait scheme, one of the busiest in the world, has been radar-monitored from shore since the 1970s after a series of collisions in the approaches, and TSS use is a leading contributor to collision avoidance in high-density waters.

Section II: Conduct of vessels in sight of one another (Rules 11-18)

Rule 11: Application

Section II applies “to vessels in sight of one another.” Two vessels are in sight of one another only when one can be observed visually from the other. The Section II rules are more specific than Section I and provide the encounter-specific rules.

Rule 12: Sailing vessels

Rule 12 governs encounters between two sailing vessels. The give-way rules between sailing vessels are based on:

• Wind on different sides: the vessel with the wind on the port side gives way.
• Same wind side: the vessel to windward gives way to the vessel to leeward.
• Doubtful: when a sailing vessel cannot determine which side the other vessel has the wind on, it shall keep out of the way of the other.

For sailing vessels in encounters with power-driven vessels, Rule 18 applies (sailing vessels generally have right of way over power-driven vessels except in narrow channels and overtaking situations).

Rule 13: Overtaking

Rule 13 establishes that any vessel overtaking any other vessel shall keep out of the way of the vessel being overtaken.

The overtaking definition: “A vessel shall be deemed to be overtaking when coming up with another vessel from a direction more than 22.5 degrees abaft her beam, that is, in such a position with reference to the vessel she is overtaking, that at night she would be able to see only the sternlight of that vessel but neither of her sidelights.”

Key features of Rule 13:

• Override: Rule 13 takes precedence over the give-way / stand-on roles of Rules 14 and 15 once the encounter has been established as overtaking.
• Aspect dependence: the overtaking determination is from the perspective of the target vessel, the relative position of the overtaking vessel must be more than 22.5 degrees abaft the target’s beam.
• Permanent role: any subsequent change in bearing as the overtaking vessel approaches does not change her status as an overtaking vessel until she has finally passed and is clear.

The 22.5-degree threshold is the same angle that defines the rear edge of a sidelight arc, which is why the rule restates it in terms of lights: an overtaking vessel by night sees only the white sternlight of the vessel ahead, never a coloured sidelight. Rule 13(c) closes the obvious gap by stating that when a vessel is in any doubt as to whether she is overtaking another, she shall assume that she is and act accordingly. The doubt provision matters in a fine crossing-versus-overtaking situation near the 22.5-degree boundary, where misreading the geometry would otherwise let a faster vessel claim stand-on rights against the ship she is coming up behind. The encounter classification calculator implements the Rule 13 determination from the relative bearing of the overtaking vessel.

Rule 14: Head-on situation

Rule 14 governs head-on situations between two power-driven vessels:

“When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision each shall alter her course to starboard so that each shall pass on the port side of the other.”

The head-on situation is recognised by:

• Reciprocal or nearly reciprocal courses: typically within 6 to 10 degrees of opposite.
• Approach on the bow: each vessel sees the other on the bow (typically within 30 degrees of dead ahead).
• At night: each vessel sees both sidelights of the other (red on her port, green on her starboard).
• Aspect: each vessel sees the other roughly stern-to.

The Rule 14 action (both alter to starboard) produces a port-to-port passing situation. Both vessels are equally responsible for taking action; this is one of the few steering rules where there is no give-way and stand-on split, because by symmetry neither vessel can be the privileged one. Rule 14(c) supplies the same safety net as Rule 13: when a vessel is in any doubt as to whether a head-on situation exists, she shall assume that it does and act accordingly, that is, turn to starboard. The doubt clause forecloses the dangerous habit of treating a near-reciprocal meeting as a fine crossing and standing on. The classic failure mode is the mutual port turn, where one vessel reads the meeting as starboard-to-starboard and turns left while the other correctly turns right; the two alterations cancel and the vessels close on a converging track. Rule 14’s hard preference for a starboard alteration exists to remove that ambiguity.

Rule 15: Crossing situation

Rule 15 governs crossing situations between two power-driven vessels:

“When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel.”

The crossing situation:

• Vessel with target on starboard: gives way (Rule 15) and follows Rule 16.
• Vessel with target on port: stands on (Rule 17).
• The give-way vessel: takes early and substantial action to avoid the other.
• The stand-on vessel: keeps her course and speed unless an action by the give-way vessel becomes apparent or the situation becomes desperate.

The Rule 15 framework is fundamental to crossing waters such as port approaches, channels with intersecting traffic, and TSS crossings.

Rule 16: Give-way vessel

Rule 16 elaborates the give-way vessel’s responsibilities:

“Every vessel which is directed to keep out of the way of another vessel shall, so far as possible, take early and substantial action to keep well clear.”

Key elements:

• Early action: not delayed.
• Substantial action: not gradual or insufficient.
• Keep well clear: not just barely avoid.

A give-way vessel that takes inadequate action exposes herself to collision risk and to liability if collision occurs.

Rule 17: Stand-on vessel

Rule 17 elaborates the stand-on vessel’s responsibilities:

• Keep course and speed: the stand-on vessel maintains her course and speed (the predictability supports the give-way vessel’s action).
• Take action when the give-way vessel does not: if it becomes apparent that the give-way vessel is not taking appropriate action, the stand-on vessel shall take such action as will best aid to avoid collision.
• Last resort: the stand-on vessel may avoid collision by her own action if necessary, but shall not alter course to port for a vessel on her own port side (which would convert the situation into a head-on near miss).

Rule 17 protects the stand-on vessel from blame for a collision caused by the give-way vessel’s inaction, while still requiring the stand-on vessel to act when collision becomes imminent. The structure is graduated across three stages. In the first stage, the stand-on vessel must hold course and speed under Rule 17(a)(i), and a stand-on ship that alters early creates the same ambiguity that Rule 8(b) warns against. In the second stage, Rule 17(a)(ii) gives the stand-on vessel the option to take action when it becomes apparent that the give-way vessel is not taking appropriate action; this is permission, not yet a duty. In the third stage, Rule 17(b) makes action mandatory: when collision can’t be avoided by the give-way vessel’s action alone, the stand-on vessel shall take such action as will best aid to avoid collision. Rule 17(c) adds the constraint that a stand-on power-driven vessel taking action in a crossing situation shall, if circumstances admit, not alter course to port for a vessel on her own port side. Turning left toward a vessel that should be passing down your port side converts a controlled crossing into a head-on near miss, the same trap Rule 14 is built to prevent.

Rule 18: Responsibilities between vessels

Rule 18 establishes the priority hierarchy among different types of vessel:

• A power-driven vessel keeps out of the way of:
  • A vessel not under command.
  • A vessel restricted in her ability to manoeuvre.
  • A vessel engaged in fishing.
  • A sailing vessel.
• A sailing vessel keeps out of the way of:
  • A vessel not under command.
  • A vessel restricted in her ability to manoeuvre.
  • A vessel engaged in fishing.
• A vessel engaged in fishing keeps out of the way of:
  • A vessel not under command.
  • A vessel restricted in her ability to manoeuvre.
• Any vessel, except not-under-command and restricted-in-ability-to-manoeuvre: avoids impeding a vessel constrained by her draught.

The Rule 18 hierarchy tracks the relative ability of each vessel type to get out of the way, with the least manoeuvrable categories holding the highest priority. A vessel not under command, by the Rule 3 definition, is one that through some exceptional circumstance can’t manoeuvre as required and so can’t keep clear; a vessel restricted in her ability to manoeuvre is one whose work, such as dredging, cable-laying, or a replenishment-at-sea operation, restricts her ability to keep clear. Because those vessels can’t readily comply, the rule shifts the burden onto everyone who can. The order is not a free pass, though. Rule 18 itself is qualified by the not-to-impede provisions of Rules 9 and 10: a fishing vessel that outranks a power-driven vessel in open water must still stay out of the way of a deep-draught ship confined to a narrow channel. The vessel constrained by her draught sits at the bottom of the list as a vessel to be not impeded rather than given absolute right of way, and Rule 18(d) requires her to navigate with particular caution and to exhibit the Rule 28 signals, because her low manoeuvrability is a hazard she partly owns.

Section III: Conduct of vessels in restricted visibility (Rule 19)

Rule 19 framework

Rule 19 governs conduct in restricted visibility (fog, heavy rain, snow, mist):

• Apply Section I: Rules 4-10 continue to apply.
• Sound signals: vessels shall sound the prescribed sound signals (under Rule 35).
• Reduce speed: every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility.
• Engines ready: every vessel shall have her engines ready for immediate manoeuvre.
• Action when fog signal heard ahead: every vessel which hears apparently forward of her beam the fog signal of another vessel, or which cannot avoid a close-quarters situation with another vessel forward of her beam, shall reduce her speed to the minimum at which she can be kept on her course; and if necessary, take all way off.
• Action when target detected by radar alone: where vessels in or near restricted visibility have not in sight of one another but are detecting one another by radar alone:
  • Take action in ample time.
  • Avoid alteration of course to port for a vessel forward of the beam (other than for a vessel being overtaken).
  • Avoid alteration of course toward a vessel abeam or abaft the beam.

Rule 19 is the primary rule for restricted-visibility operations and connects directly to the radar provisions of Rule 7 and the sound signals of Rule 35. The single most important thing about Rule 19 is what it abolishes. Once vessels are out of sight of one another in fog, the give-way and stand-on roles of Section II don’t exist: there is no privileged vessel in restricted visibility. Both ships are equally bound by Rule 19, and the early head-on or crossing instinct, hold course and let the other turn, is exactly wrong here. Rule 19(d) sets the avoidance geometry for a vessel detecting another by radar alone and determining that a close-quarters situation is developing or that risk of collision exists. She must take avoiding action in ample time, and if that action is an alteration of course she shall, so far as possible, avoid altering to port for a vessel forward of the beam other than for a vessel being overtaken, and avoid altering course toward a vessel abeam or abaft the beam. The forward-of-beam-to-starboard preference parallels the head-on rule and keeps two fog-bound ships turning the same way relative to each other. Rule 19(e) then handles the sound contact: a vessel that hears apparently forward of her beam the fog signal of another vessel, or that can’t avoid a close-quarters situation with another vessel forward of her beam, shall reduce her speed to the minimum at which she can be kept on course, unless she has determined that risk of collision doesn’t exist, and if necessary take all way off and in any event navigate with extreme caution until danger of collision is over. A fog signal heard ahead, with no radar contact to resolve it, is a near-mandatory order to slow down or stop.

Specific encounter scenarios

Power-driven vs power-driven: head-on

Two power-driven vessels approaching head-on each alter to starboard. Both are equally responsible. Specific considerations:

• Course alteration: typically 30 to 45 degrees to starboard, sufficient to ensure clear passing.
• Passing distance: aim for at least 1 nautical mile, more in heavy weather.
• Sound signals: optional but recommended (one short blast indicating “I am altering my course to starboard”).
• VHF communication: not required but commonly used to confirm intentions.

Power-driven vs power-driven: crossing

In a crossing, the vessel with the target on her starboard side gives way. The give-way vessel takes early and substantial action; the stand-on vessel keeps course and speed.

Common errors in crossing situations:

• Late action by the give-way vessel: not “early and substantial”.
• Crossing ahead by the give-way vessel (forbidden by Rule 15 except in unusual circumstances).
• Premature action by the stand-on vessel: maneuvering before the give-way vessel’s action is needed (creates ambiguity).
• Both vessels acting: if both alter course, the action paths may converge.

Power-driven overtaking

Overtaking under Rule 13: the overtaking vessel keeps clear of the vessel being overtaken. Specific considerations:

• Sound signals: required when overtaking in narrow channels (Rule 34); optional in open waters.
• Passing distance: typically at least 0.5 nautical miles for moderate-sized vessels in open water.
• Confirmation: in narrow channels, overtaking requires confirmation between vessels.

Encounters with sailing vessels

Power-driven vessel encountering sailing vessel: Rule 18, power-driven vessel gives way (with exceptions for narrow channels and overtaking). The power-driven vessel must:

• Take early action to keep well clear.
• Avoid making conflicting maneuvers that might confuse the sailing vessel.
• Recognise sailing vessel’s manoeuvring constraints: sailing vessels cannot easily reverse, may need to tack, etc.

Sailing vessel-to-sailing vessel encounters use Rule 12 wind-side rules.

Encounters with fishing vessels

Vessels engaged in fishing have priority over power-driven vessels (Rule 18). Specifically:

• Trawling: fishing vessels with gear deployed have very limited manoeuvrability.
• Long-lining and gill-netting: similar limitations.
• Recognition: fishing vessel lights and shapes (Rule 26) help identification.

Power-driven vessels must keep clear of fishing vessels engaged in fishing.

Encounters in restricted visibility

In restricted visibility, the rules of Section III (Rule 19) apply. The key actions are reducing speed to safe, sounding fog signals, having engines ready for immediate manoeuvre, and taking action in ample time when target is detected by radar.

Common errors in restricted visibility:

• Continuing at full speed: in violation of Rule 6 and Rule 19.
• Failure to sound fog signals: in violation of Rule 35.
• Course alteration to port for forward target: in violation of Rule 19.
• Late action: continuing on plan when radar shows risk.

The Costa Concordia (2012) and many other casualties involved restricted-visibility failures.

Bridge Resource Management and COLREGs

BRM under COLREGs

Bridge Resource Management (BRM) is the operational framework for applying COLREGs in practice. BRM principles include:

• Team operation: master, officers, helmsman, lookout work as a team.
• Communication: clear communication of observed data, planned actions, and decisions.
• Cross-checking: between bridge team members.
• Situation awareness: continuous appreciation of own ship’s situation in relation to other vessels and hazards.
• Decision making: by the master, with input from the team.
• Challenge and response: protocol for crew members to challenge a decision they believe is unsafe.

BRM training is mandatory under STCW Section A-VIII/2 and is verified at PSC inspection.

Specific BRM applications to COLREGs

BRM applies to COLREG situations through:

• Risk of collision determination (Rule 7): radar/AIS data analysed by team, with multiple sources cross-checked.
• Action to avoid collision (Rule 8): proposed action discussed before execution.
• Encounter classification (Rules 13, 14, 15): determination by team observation.
• Stand-on action (Rule 17): the bridge team monitors give-way vessel response and prepares for own action if needed.
• Fog procedures (Rule 19): pre-fog briefing for all bridge team members.

COLREGs and modern technology

AIS and COLREGs

AIS (Automatic Identification System) under SOLAS Chapter V Regulation 19 transmits identity, position, course, speed and other data. AIS use under COLREGs:

• Information for risk of collision (Rule 7): AIS supplements visual and radar.
• Identification of other vessels: by name and type.
• Voyage data: destination and ETA.
• Communication channel: VHF can be used for voice communication based on AIS-identified targets.

AIS is not a substitute for proper lookout under Rule 5 or for visual/radar observation, but is a powerful supplementary tool.

ECDIS and COLREGs

ECDIS supports COLREG application through:

• Position fixing with high accuracy.
• Route monitoring with cross-track error detection.
• AIS overlay showing nearby vessels.
• Radar overlay in some configurations.
• Watchkeeper alarms for proximity to hazards.

ECDIS supports but does not replace COLREG situation awareness and decision-making.

Autonomous ships and COLREGs

Maritime Autonomous Surface Ships (MASS) raise specific COLREG questions:

• Lookout (Rule 5): how is “proper lookout” interpreted for unmanned ships?
• Risk of collision (Rule 7): who or what makes the determination?
• Action (Rules 8, 13, 14, 15): who is responsible?
• Master responsibility: with no master on board, who has the responsibility?

The IMO MASS regulatory framework under development addresses these questions, with the COLREGs likely amended to accommodate autonomous operations through the late 2020s and 2030s.

Notable casualties

Andrea Doria - Stockholm collision, 1956

The Italian liner Andrea Doria collided with the Swedish-American liner Stockholm on 25 July 1956 off Nantucket. The collision involved a head-on encounter in restricted visibility. Specific COLREG violations identified in the investigation:

• Rule 5 (lookout): arguably inadequate.
• Rule 6 (safe speed): both vessels at near-full speed in fog.
• Rule 7 (risk of collision): incomplete determination based on radar information.
• Rule 8 (action): late action by both vessels.

The casualty drove subsequent COLREG refinements and contributed to the requirement for radar carriage and use.

MV Hyundai Independence collision, 2019

The container ship MV Hyundai Independence collided with another vessel in 2019. The investigation identified BRM and COLREG application failures.

MV Costa Concordia, 2012

The Costa Concordia struck a rock off Isola del Giglio after a deviation from the planned voyage track. While the immediate cause was deviation rather than COLREG failure per se, the casualty illustrated the importance of voyage planning under SOLAS Chapter V Regulation 34 in conjunction with COLREG observance.

Numerous AIS-related encounters

Multiple recent casualties have involved AIS misuse or excessive reliance on AIS:

• Vessels running into AIS-tracked targets: assuming AIS confirms the absence of risk.
• AIS false targets: due to spoofing or transmitter malfunction.
• AIS in heavy weather: where reliability degrades.

Specific operational scenarios

Pilot waters and COLREGs

In pilot waters (port approaches, channels, anchorages), COLREGs apply with additional considerations:

• Pilot’s recommendations: the pilot provides expert local knowledge but the master retains command authority and COLREG responsibility.
• VTS coordination: Vessel Traffic Services may direct vessel movements but the master is still responsible for collision avoidance.
• Local rules: some pilot areas have specific local rules supplementing COLREGs.
• Communication discipline: VHF channels prescribed for the pilot waters.

Anchored vessel encounters

Encounters with anchored vessels:

• Anchored vessel is not “engaged in navigation” and has anchor light/shape rather than navigation lights.
• Approaching vessel must keep clear of anchored vessels.
• Special signals: anchor signals (Rule 35) in restricted visibility.
• Dragging anchor: vessel that drags anchor presents specific risk to other vessels.

Multiple-vessel scenarios

Multiple-vessel scenarios are common in busy waters:

• Three-vessel encounters: Rules 13-15 apply pairwise.
• TSS with multiple vessels: Rule 10 plus Rules 13-15 as applicable.
• Anchorage areas: navigation among many anchored vessels.
• Fishing fleet areas: navigation among many fishing vessels.

The bridge resource management approach is essential in multi-vessel scenarios.

Limited manoeuvrability scenarios

Limited manoeuvrability scenarios:

• Loss of propulsion: vessel becomes “not under command” with corresponding lights/shapes.
• Steering gear failure: vessel cannot manoeuvre normally.
• Heavy weather: reduced manoeuvrability in stand-on situations.
• Cargo operations: tankers in cargo operations may have reduced manoeuvrability.

Each scenario requires specific COLREG consideration. Other vessels must recognise the limitations through proper observation of lights and shapes (under Rules 20-31) and modify their behaviour accordingly.

COLREG application in fairways and rivers

Inland and confined waters often have local rules supplementing or modifying COLREGs:

• Inland waters of the United States: governed by the Inland Navigation Rules (33 CFR Part 83) which closely parallel but are not identical to COLREGs.
• European inland waterways: governed by CEVNI (European Code for Inland Waterways) which has its own set of rules.
• Specific port bylaws: many ports have additional rules for vessel traffic within port limits.
• Channel-specific rules: rivers, canals, and dredged channels often have specific traffic rules.

Mariners operating in such waters must be familiar with both COLREGs and the applicable local rules; the local rules typically take precedence within their geographical scope while COLREGs continue to apply outside.

Limitations

This article describes the steering and sailing rules as a regulatory framework, not as a substitute for the certificated judgement of a watchkeeper. Several caveats apply when working from a summary like this one.

The COLREGs are read as a whole. Rules 4 to 19 don’t stand alone: a crossing decision under Rule 15 depends on correctly identifying the other vessel from her lights and shapes under Rules 20 to 31, and the action under Rule 8 is announced through the manoeuvring and warning signals of Rule 34. Reading one rule in isolation is how mariners arrive at confidently wrong answers in court.

The rules set principles, not numbers, in most places. Rule 6 lists the factors for safe speed but fixes no speed; Rule 16 demands early and substantial action but defines neither word in metres or minutes; Rule 14 says alter to starboard but doesn’t say how far. A practitioner must convert each qualitative duty into a quantity for the specific ship, loading, and conditions, and two competent officers can reach different but defensible numbers.

The text quoted here follows the IMO consolidated convention and the US Coast Guard amalgamated rules. Vessels in inland or coastal waters of many states operate under national rules that parallel but don’t exactly match the international text: the US Inland Navigation Rules (33 CFR Part 83) differ in several signal and lighting provisions, and the European inland code (CEVNI) is a separate regime. Where a vessel crosses the demarcation line between international and inland waters, the applicable rule set changes, and the master must know which one governs at each point.

Case-law interpretation evolves and is jurisdiction-specific. The steady-bearing test of Rule 7(d) and the doubt provisions of Rules 13(c) and 14(c) are stated in the text, but how a fault is apportioned after a collision depends on the admiralty court hearing the case and on the facts recorded by each vessel’s voyage data recorder. Nothing here predicts an outcome in litigation.

Finally, autonomous and remotely operated vessels sit at the edge of the current text. The IMO is developing a regulatory framework for Maritime Autonomous Surface Ships, and the steering and sailing rules were drafted on the assumption of a human keeping a lookout and taking action. Until that work concludes, the application of Rules 5, 7, and 8 to an unmanned bridge remains an open regulatory question rather than settled practice.

Documentation

Every vessel covered by COLREGs maintains:

• COLREG copy on board: required as a navigational publication.
• Bridge resource management procedures: in the safety management system.
• Training records: for officers under STCW.
• Voyage planning records: under SOLAS V/34.
• Voyage data recorder records: with bridge audio supporting any post-incident investigation.

Related Calculators

• COLREG - CPA / TCPA Calculator
• COLREG - Encounter classification (head-on / crossing / overtaking) Calculator
• Rule of Sixty, Track Error Calculator

See also

• COLREGs Convention parent article
• SOLAS Chapter V: Safety of Navigation
• AIS and ECDIS
• STCW Convention
• Strait of Malacca
• Suez Canal
• Panama Canal
• GMDSS Overview
• Weather Routing

Additional calculators:

• CPA / TCPA
• MASS Time-to-Collision

Additional related wiki articles:

• COLREGs Lights and Shapes: Rules 20 to 31
• COLREGs Sound and Light Signals: Rules 32 to 37

References

• IMO, Convention on the International Regulations for Preventing Collisions at Sea (COLREG), 1972, as amended.
• IMO Resolution A.464(XII) (1981), Adoption of amendments.
• IMO Resolution A.626(15) (1987), Adoption of amendments.
• IMO Resolution A.736(18) (1993), Adoption of amendments (WIG craft).
• IMO Resolution A.910(22) (2001), Adoption of amendments.
• IMO MSC/Circ.1503, Operational guidance for the use of radar in the application of the COLREGs.
• ICS Bridge Procedures Guide, current edition.
• IAMSAR Manual.

Related formulas

• Mercator Sailing - Rhumb Course & Distance
• Mercator Sailing
• Sailing Yacht Fuel & CO₂