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COLREGs Convention

The Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs), is the international treaty laying down the navigational rules followed by all vessels at sea to prevent collisions. Adopted at an International Maritime Organization (IMO) conference in London on 20 October 1972 and entering into force on 15 July 1977, the 1972 COLREGs replaced the earlier 1960 collision regulations annexed to the SOLAS Convention. The 1972 text consolidates a body of practice dating back to the mid-19th century into a single convention containing 41 rules grouped into six parts and four technical annexes. It applies to all vessels on the high seas and on all waters connected to the high seas that are navigable by seagoing vessels; states are required to apply equivalent or more stringent rules to vessels operating exclusively in their inland waters. The treaty has been ratified by states representing close to 99% of world merchant tonnage by gross tonnage and has been adopted by reference by virtually all coastal jurisdictions. ShipCalculators.com hosts a suite of calculators implementing the practical computations associated with the rules: the IMO COLREGs compliance summary confirms applicability and basic compliance, the CPA / TCPA calculator supports Rule 7 risk-of-collision assessment, and the MASS time-to-collision calculator extends the framework to autonomous and remotely operated vessels. A full listing is available in the calculator catalogue.

Contents

Background and history

Nineteenth-century origins

The first formal collision rules in the English-speaking maritime world were issued by the Trinity House of Deptford Strond in the 1840s, prescribing a green light to starboard and a red light to port and a basic priority for steam vessels giving way to sail. These rules were given statutory force in the United Kingdom by the Steam Navigation Act 1846 and successive Merchant Shipping Acts. France and the United States adopted broadly equivalent provisions in the 1840s and 1850s. By 1863, the British and French rules had been harmonised in a joint instrument that was subsequently adopted by more than 30 maritime nations and became the de facto international rule of the road for the second half of the 19th century.

The 1863 rules established the basic principles that survive in the modern COLREGs: the use of red and green sidelights and a white masthead light, the priority of sail over steam, the duty of an overtaking vessel to keep clear, the head-on rule that two power-driven vessels meeting end-on must each turn to starboard, and the crossing rule that the vessel having the other on her starboard side must give way. These rules were drafted in plain English and short numbered articles, a stylistic tradition that the modern convention has retained.

The Washington and Brussels conferences

The first international conference convened specifically to harmonise the rules was the International Maritime Conference held in Washington in October 1889. The Washington Conference adopted a set of regulations that were enacted into national law by the major maritime states between 1890 and 1897 and that came into force internationally on 1 July 1897. The Washington rules introduced the requirement for a second masthead light on power-driven vessels exceeding 150 feet in length, a rule retained today for vessels of 50 metres and above.

A further revision was undertaken at the International Conference on Safety of Life at Sea held in London in 1929, with the collision regulations annexed to the 1929 SOLAS Convention. The 1948 SOLAS Conference and the 1960 SOLAS Conference each refreshed the collision rules in turn, with the 1960 rules entering into force on 1 September 1965. The 1960 rules introduced traffic separation references, expanded the catalogue of lights and shapes, and codified the response to vessels not under command and vessels restricted in their ability to manoeuvre.

The 1972 IMO conference and entry into force

The 1960 SOLAS rules were criticised throughout the 1960s on three grounds. First, the structure was opaque: rules dealing with risk of collision, action by the give-way vessel, and action by the stand-on vessel were dispersed through the text rather than grouped logically. Second, the rules did not address traffic separation schemes, which were being introduced unilaterally by coastal states from 1967 (notably in the Strait of Dover after the loss of MV Texaco Caribbean and MV Brandenburg in collisions in January and February 1971). Third, the rules predated the widespread fitting of marine radar and did not adequately address the conduct of vessels using radar in restricted visibility.

The Inter-Governmental Maritime Consultative Organization (IMCO, renamed the International Maritime Organization in 1982) convened an international conference in London on 4 October 1972. The conference adopted a new convention with regulations annexed, deliberately separating the convention text (which deals with treaty mechanics) from the regulations themselves (which contain the operative rules). The convention entered into force on 15 July 1977 after acceptance by 15 states representing not less than 65% of world merchant tonnage. The IMO Maritime Safety Committee (MSC) maintains the regulations and has amended them on six occasions: 1981, 1987, 1989, 1993, 2001 and 2007. Amendments enter into force under a tacit acceptance procedure analogous to that used for the SOLAS Convention and the MARPOL Convention.

The convention is short. The treaty text proper consists of nine articles dealing with general obligations, signature, ratification, entry into force, denunciation, languages, deposit and notification. The operative rules are in the 41-rule annex. By the standards of modern IMO instruments this is a remarkably compact treaty, a deliberate choice intended to keep the rule book accessible to bridge officers in any language and any condition.

Structure of the convention

The annex containing the rules is organised into six parts:

  • Part A: General (Rules 1 to 3). Application, responsibility and definitions.
  • Part B: Steering and Sailing Rules (Rules 4 to 19). The operative manoeuvring rules, divided into three sections by the visibility regime.
  • Part C: Lights and Shapes (Rules 20 to 31). The lighting and day-shape requirements that allow vessels to recognise each other’s category, heading and operational status.
  • Part D: Sound and Light Signals (Rules 32 to 37). Whistle, bell and gong signals; manoeuvring and warning signals; signals to attract attention; distress signals.
  • Part E: Exemptions (Rule 38). Transitional exemptions for vessels constructed before 15 July 1977.
  • Part F: Verification of compliance with the provisions of the Convention (Rules 39 to 41). Added by amendment in 2013 and entering into force on 1 January 2016, modelled on the equivalent SOLAS chapter.

Four annexes provide technical specifications:

  • Annex I: Positioning and technical details of lights and shapes (intensity, screening, vertical and horizontal arc, colour specification by chromaticity).
  • Annex II: Additional signals for fishing vessels fishing in close proximity.
  • Annex III: Technical details of sound-signal appliances (frequency, audible range, location).
  • Annex IV: Distress signals.

The standard pocket reference carried on the bridge of every commercial vessel is The International Regulations for Preventing Collisions at Sea, 1972, as Amended, published by the IMO with successive consolidated editions. National maritime administrations also issue annotated editions; the British annotated text known as the Mariner’s Handbook (NP 100, published by the United Kingdom Hydrographic Office) is widely used internationally.

Part A: General (Rules 1 to 3)

Rule 1: Application

Rule 1(a) extends the regulations to all vessels on the high seas and on all waters connected to the high seas that are navigable by seagoing vessels. Rule 1(b) preserves the right of any state to make special rules for roadsteads, harbours, rivers, lakes or inland waterways connected to the high seas, provided that those special rules conform as closely as possible with the international rules. Rule 1(c) preserves a similar right for special rules made by a government with respect to additional station or signal lights for ships of war or vessels proceeding under convoy, or for additional signal lights for fishing vessels engaged in fishing as a fleet. Rule 1(d) authorises the IMO to adopt traffic separation schemes for the purposes of Rule 10. Rule 1(e) provides that ships of special construction or purpose may be exempted from compliance with specific rules, provided that the exemption is documented in the ship’s certificates.

Rule 2: Responsibility

Rule 2 is the most-cited rule of the convention in admiralty case law. Rule 2(a), the “rule of good seamanship”, provides that nothing in the rules shall exonerate any vessel, or the owner, master or crew thereof, from the consequences of any neglect to comply with the rules or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case. Rule 2(b), the “general prudential rule”, provides that in construing and complying with the rules, due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from the rules necessary to avoid immediate danger.

The combined effect of Rule 2(a) and Rule 2(b) is that the rules establish a baseline of conduct from which departure is permitted only when strictly necessary to avoid immediate danger, and that compliance with the letter of a rule does not absolve a vessel from the consequences of bad seamanship. Both subparagraphs have been invoked in numerous collision cases to allocate liability between vessels each of which was technically compliant with the manoeuvring rules but which together produced a collision through inadequate seamanship.

Rule 3: General definitions

Rule 3 defines the operative terms used in the convention. The principal definitions include:

  • Vessel: every description of water craft, including non-displacement craft, WIG craft and seaplanes, used or capable of being used as a means of transportation on water.
  • Power-driven vessel: any vessel propelled by machinery.
  • Sailing vessel: any vessel under sail provided that propelling machinery, if fitted, is not being used.
  • Vessel engaged in fishing: any vessel fishing with nets, lines, trawls or other fishing apparatus that restricts manoeuvrability, but excluding vessels using trolling lines or other fishing apparatus that does not restrict manoeuvrability.
  • Seaplane: any aircraft designed to manoeuvre on the water.
  • Vessel not under command (NUC): a vessel that through some exceptional circumstance is unable to manoeuvre as required by the rules and is therefore unable to keep out of the way of another vessel.
  • Vessel restricted in her ability to manoeuvre (RAM): a vessel that from the nature of her work is restricted in her ability to manoeuvre as required by the rules and is therefore unable to keep out of the way of another vessel. The rule lists examples including cable layers, dredging vessels, vessels engaged in replenishment or transferring persons or cargo while underway, vessels engaged in launching or recovering aircraft, and vessels engaged in mineclearance operations.
  • Vessel constrained by her draught (CBD): a power-driven vessel that, because of her draught in relation to the available depth and width of navigable water, is severely restricted in her ability to deviate from the course she is following.
  • Underway: a vessel that is not at anchor, made fast to the shore or aground.
  • Restricted visibility: any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.

The 1987 amendments inserted the definition of WIG (wing-in-ground-effect) craft, recognising the emergence of these vessels and treating them as power-driven vessels for the purpose of the rules when not in flight, and as aircraft when in flight.

Part B: Steering and Sailing Rules

Part B is the operative core of the convention. It is divided into three sections according to the visibility regime: Section I applies in any condition of visibility (Rules 4 to 10); Section II applies only when vessels are in sight of one another (Rules 11 to 18); Section III applies in restricted visibility (Rule 19). The visibility regime determines which subset of rules applies and the conduct expected of each vessel.

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

Rule 4: Application

Rules 5 to 10 apply in any condition of visibility. The conduct required by these rules is independent of whether the vessels can see each other and is therefore not relieved by fog or darkness.

Rule 5: Look-out

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. The phrase “all available means” includes radar, AIS, sound signals received from other vessels and traffic information broadcast by Vessel Traffic Services (VTS) authorities. The Court of Appeal of England and Wales held in The Maloja II [1993] 1 Lloyd’s Rep 48 that a look-out by AIS or radar alone, without a visual look-out, is not a “proper look-out” within the meaning of Rule 5; the visual element cannot be substituted by electronic systems. The 1981 amendment to Rule 5 inserted the words “as well as by all available means appropriate in the prevailing circumstances and conditions” precisely to require the use of radar, ARPA and AIS in addition to, but not in substitution for, the visual and aural watch.

Rule 6: 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. Rule 6 enumerates non-exhaustive factors to be considered in determining a safe speed, including: visibility; traffic density; the manoeuvrability of the vessel with special reference to stopping distance and turning ability; the state of wind, sea and current; the proximity of navigational hazards; the draught in relation to available depth of water; and, for vessels with operational radar, the characteristics, efficiency and limitations of the radar equipment. Compliance with Rule 6 is closely linked to the radar horizon calculator, which establishes the geographical detection range under prevailing atmospheric conditions, and to the squat and shallow-water effects analysed in the squat calculator and the tuck-effect calculator.

The phrase “safe speed” is not synonymous with “slow speed”. A power-driven vessel proceeding at full sea speed in clear visibility on the open ocean with no other vessels in sight is at a safe speed; the same vessel proceeding at the same speed in fog is not. The judgment of safe speed is for the master and the officer of the watch and is reviewed retrospectively in court if a collision occurs.

Rule 7: Risk of collision

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. Rule 7(b) requires proper use of operational radar equipment, including long-range scanning to obtain early warning of risk of collision, and radar plotting or equivalent systematic observation of detected objects.

The standard quantitative tool for assessing risk of collision is the closest point of approach (CPA) and time to closest point of approach (TCPA) computation, performed automatically by Automatic Radar Plotting Aids (ARPA) and by AIS-integrated ECDIS. The CPA / TCPA calculator implements the geometric solution from the relative motion vector. Rule 7(c) cautions against assumptions made on the basis of scanty information, especially scanty radar information, and against making assumptions about the size of an echo or the speed of a target. Rule 7(d) provides two situations in which risk of collision shall be deemed to exist: when the compass bearing of an approaching vessel does not appreciably change, and 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.

Rule 8: Action to avoid collision

Any action taken to avoid collision shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship. Rule 8 requires that any alteration of course or speed to avoid collision shall, if circumstances permit, be large enough to be readily apparent to another vessel observing visually or by radar; a succession of small alterations of course or speed should be avoided. Rule 8(c) provides that an alteration of course alone may be the most effective action to avoid a close-quarters situation, provided that it is made in good time, is substantial and does not result in another close-quarters situation. Rule 8(e) provides that if necessary to avoid collision or 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.

The 1987 amendments added Rule 8(f), which establishes the general principle that a vessel required not to impede the passage or safe passage of another vessel shall, when required by the circumstances of the case, take early action to allow sufficient sea room for the safe passage of the other vessel. This subparagraph harmonised the language of “shall not impede” used in Rules 9, 10 and 18 with the conduct expected of a vessel under Part B in general.

Rule 9: Narrow channels

Rule 9 governs the conduct of vessels proceeding along the course of a narrow channel or fairway. The principal requirements are:

  • A vessel proceeding along the course of a narrow channel or fairway shall keep as near to the outer limit of the channel or fairway which lies on her starboard side as is safe and practicable.
  • A vessel of less than 20 metres in length, a sailing vessel, or a vessel engaged in fishing shall not impede the passage of a vessel that can safely navigate only within a narrow channel or fairway.
  • A vessel shall not cross a narrow channel or fairway if such crossing impedes the passage of a vessel which can safely navigate only within such channel or fairway.
  • A vessel shall not anchor in a narrow channel except in cases of necessity.

Rule 9 establishes the rule of the road for traffic in confined waters such as the entrances to ports, the Suez Canal, the Panama Canal and the Strait of Malacca. Local Vessel Traffic Service authorities frequently overlay additional traffic management on Rule 9 through routeing rules, mandatory pilotage and minimum-distance separation requirements.

Rule 10: Traffic separation schemes (TSS)

Rule 10 governs conduct in traffic separation schemes adopted by the IMO under SOLAS Regulation V/10. A TSS comprises a separation zone or line, traffic lanes, an inshore traffic zone, and roundabouts where lanes converge. The principal requirements are:

  • A vessel using a traffic separation scheme shall proceed in the appropriate traffic lane in the general direction of traffic flow for that lane.
  • So far as practicable a vessel shall keep clear of a traffic separation line or separation zone.
  • A vessel shall, so far as practicable, avoid crossing traffic lanes; if obliged to do so, she shall cross on a heading as nearly as practicable at right angles to the general direction of traffic flow.
  • Inshore traffic zones shall not normally be used by through traffic which can safely use the appropriate traffic lane within the adjacent TSS, but vessels of less than 20 metres in length, sailing vessels and vessels engaged in fishing may use the inshore traffic zone.

Rule 10(j) provides that a vessel of less than 20 metres in length, a sailing vessel or a vessel engaged in fishing shall not impede the safe passage of a power-driven vessel following a traffic lane. Rule 10(l) and Rule 10(m), added in 1987 and 2001 respectively, established that vessels engaged in fishing or operating in or near a TSS but not using the lane should keep clear of the lane and that vessels not crossing or joining or leaving a lane should so far as practicable avoid crossing the line.

The TSS in the Dover Strait was the first IMO-adopted scheme, taking effect on 1 June 1967, and was the principal motivation for the inclusion of Rule 10 in the 1972 text. Today over 200 traffic separation schemes are in force worldwide, including in the Strait of Malacca and Singapore Strait, the approaches to the major North European ports, both ends of the Suez Canal, and most of the Pacific coast of North America. Compliance is enforced by port state control and by criminal prosecution under the laws of the coastal state.

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

Rule 11: Application

Rules 12 to 18 apply only to vessels in sight of one another. “In sight” is interpreted strictly: vessels are in sight only when one can observe the other visually. Vessels detected only by radar are not “in sight” within the meaning of Rule 11; their conduct is governed by Rule 19 (restricted visibility). The distinction is important because the conduct expected differs significantly between the two regimes.

Rule 12: Sailing vessels

When two sailing vessels are approaching one another so as to involve risk of collision, one of them shall keep out of the way of the other as follows: when each has the wind on a different side, the vessel which has the wind on the port side shall keep out of the way of the other; when both have the wind on the same side, the vessel which is to windward shall keep out of the way of the vessel which is to leeward. If a vessel with the wind on the port side sees a vessel to windward and cannot determine with certainty whether the other vessel has the wind on the port or starboard side, she shall keep out of the way of the other.

Rule 12 reverses the earlier rule of the road that gave priority to the windward vessel; the modern rule favours the leeward vessel because it can normally manoeuvre more freely than the windward vessel. The 1972 text codifies a long-established practice in international yacht racing.

Rule 13: Overtaking

Rule 13(a) provides that any vessel overtaking any other shall keep out of the way of the vessel being overtaken, notwithstanding any other rule in Part B Section II. Rule 13 thus overrides Rules 14 to 18 in any overtaking situation.

Rule 13(b) defines overtaking as occurring when a vessel is coming up on another vessel from a direction more than 22.5 degrees abaft her beam, that is, in such a position with reference to the vessel being overtaken that at night she would be able to see only the sternlight of that vessel but neither of her sidelights. Rule 13(c) provides that when a vessel is in any doubt as to whether she is overtaking another, she shall assume that this is the case and act accordingly. Rule 13(d) provides that no subsequent alteration of the bearing between the two vessels shall make the overtaking vessel a crossing vessel within the meaning of these rules or relieve her of the duty to keep clear of the overtaken vessel until she is finally past and clear.

The practical consequence of Rule 13(d) is that an overtaking vessel cannot escape the duty to keep clear by altering course such that the geometric relationship becomes a crossing situation. The overtaking duty persists until the overtaking vessel is “finally past and clear”, a phrase interpreted in the cases as requiring that the vessels have separated to a distance at which there is no longer any risk of collision.

Rule 14: Head-on situation

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. Rule 14 is the most-cited rule in collision cases between power-driven vessels. The rule applies when each vessel sees the other ahead or nearly ahead, and by night could see the masthead lights in a line or nearly in a line, or both sidelights, and by day observes the corresponding aspect of the other vessel.

The distinction between a head-on situation under Rule 14 and a crossing situation under Rule 15 turns on the geometry of approach. If the relative bearing between the two vessels is broadly along the meridian (within a few degrees of dead ahead), the situation is head-on. If the relative bearing is broadly across the meridian, the situation is crossing. In the marginal cases, Rule 14(c) provides that when a vessel is in any doubt as to whether such a situation exists, she shall assume that it does and act accordingly. The reason for this presumption in favour of Rule 14 is that the prescribed action (alter course to starboard) is unambiguous and symmetric, requiring no coordination between the vessels and producing a stable separation if both vessels comply.

Rule 15: Crossing situation

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. Rule 15 establishes the give-way / stand-on relationship for crossing situations. The vessel that has the other on her starboard side is the give-way vessel; the vessel on her own starboard side is the stand-on vessel.

The duty to “avoid crossing ahead” is fundamental and was added in the 1972 text precisely because crossings ahead of the stand-on vessel were a recurring source of collision. The give-way vessel is not entitled to assume that the stand-on vessel will hold her course at any specified speed; the stand-on duty under Rule 17 is to maintain course and speed only so long as it is safe to do so, and the stand-on vessel may take avoiding action if she perceives that the give-way vessel is not taking sufficient action to avoid collision.

Rule 16: Action by give-way vessel

Every vessel that 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. Rule 16 requires that the give-way vessel take action that is unmistakable in its character and that produces a wide separation. A series of small alterations is not “substantial action”; an alteration that leaves the closest point of approach close to the limit of safe passing is not “well clear”.

Rule 17: Action by stand-on vessel

Rule 17(a)(i) provides that where one of two vessels is to keep out of the way the other shall keep her course and speed. Rule 17(a)(ii) provides that the stand-on vessel may, however, take action to avoid collision by her manoeuvre alone, as soon as it becomes apparent to her that the vessel required to keep out of the way is not taking appropriate action in compliance with these rules. Rule 17(b) provides that when, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision. Rule 17(c) provides that a power-driven vessel which takes action in a crossing situation in accordance with subparagraph (a)(ii) to avoid collision with another power-driven vessel shall, if the circumstances of the case admit, not alter course to port for a vessel on her own port side. Rule 17(d) preserves the duty of the give-way vessel to keep out of the way.

The Rule 17 framework is a graduated response: in the first instance the stand-on vessel maintains course and speed; once it becomes apparent that the give-way vessel is not acting, the stand-on vessel may take action; once collision cannot be avoided by the give-way vessel alone, the stand-on vessel must take the best action available. The “must” stage is sometimes referred to in the literature as the “in extremis” stage. The transition between the three stages is judged on the facts and is a recurrent source of liability allocation in admiralty cases.

Rule 18: Responsibilities between vessels

Rule 18 establishes a hierarchy of duties between vessel categories. The hierarchy, from highest priority (vessel to be avoided) to lowest (vessel that must avoid), is:

  1. Vessel not under command (NUC).
  2. Vessel restricted in her ability to manoeuvre (RAM).
  3. Vessel constrained by her draught (CBD), as against power-driven vessels only.
  4. Vessel engaged in fishing.
  5. Sailing vessel.
  6. Power-driven vessel underway.

Each category in the hierarchy must keep out of the way of every category above it, except where Rules 9, 10 or 13 apply. A power-driven vessel underway must keep out of the way of any vessel above her in the hierarchy; a sailing vessel must keep out of the way of any vessel above sailing in the hierarchy; and so on. Rule 18(d) provides that a power-driven vessel proceeding in a constrained-by-draught situation shall navigate with particular caution and that other vessels shall, if the circumstances of the case admit, avoid impeding her safe passage. The 1989 amendment added Rule 18(f), establishing that WIG craft shall, when taking off, landing and in flight near the surface, keep well clear of all other vessels and avoid impeding their navigation; and that WIG craft operating on the water surface shall comply with the rules of this section as a power-driven vessel.

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

Rule 19 applies to vessels not in sight of one another when navigating in or near an area of restricted visibility. It is the conduct rule for fog, mist and similar conditions. The principal requirements are:

  • Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility.
  • A power-driven vessel shall have her engines ready for immediate manoeuvre.
  • Every vessel shall have due regard to the prevailing circumstances and conditions of restricted visibility when complying with Rules 4 to 10.
  • A vessel which detects by radar alone the presence of another vessel shall determine if a close-quarters situation is developing or risk of collision exists and, if so, take avoiding action in ample time.

When such avoiding action consists of an alteration of course, so far as possible the following shall be avoided: an alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken; and an alteration of course towards a vessel abeam or abaft the beam. The sense of these prohibitions is that an alteration to port for a vessel forward of the beam might bring two vessels closer together if the other vessel turns to starboard for the same reason. The Rule 19 framework therefore presumes that vessels in restricted visibility detect each other by radar, that neither vessel knows what the other will do, and that each must act conservatively to avoid making the situation worse.

The interaction between Rule 19 and Rule 17 is one of the most-litigated questions in collision law. Rule 17 applies only when vessels are in sight of one another; Rule 19 applies when they are not. A vessel that is detected only by radar in restricted visibility is not in sight, and so Rule 17 does not apply; both vessels must comply with Rule 19, and neither has the priority of a stand-on vessel. The 1972 text deliberately removed the older “starboard-bow rule” that had been read into the 1960 rules, replacing it with the more general restraint of Rule 19. The result is that the conduct of vessels in restricted visibility is governed by mutual avoidance rather than by give-way/stand-on roles.

The CPA / TCPA calculator is essential to Rule 19 compliance: in restricted visibility, the determination that “a close-quarters situation is developing” and that “risk of collision exists” is in practice made from radar/ARPA observation of CPA and TCPA values. The MASS time-to-collision calculator extends the same framework to autonomous and remotely operated vessels, where the determination is made by software rather than by a human officer of the watch.

Part C: Lights and shapes (Rules 20 to 31)

Part C prescribes the lights and day shapes that allow vessels to recognise each other’s category, heading and operational status. The lighting scheme has remained substantially unchanged since the 19th century, with refinements to specify the precise arc, colour and intensity of each light.

Rule 20: Application

Rule 20 provides that the lights shall be exhibited from sunset to sunrise, and during such times no other lights shall be exhibited except such lights as cannot be mistaken for the lights specified in the rules or do not impair their visibility or distinctive character or interfere with the keeping of a proper look-out. Rule 20 also requires that 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. Day shapes shall be exhibited by day. The 1981 amendment to Rule 20 made clear that lights and shapes have equal status; failure to exhibit a required shape by day is as serious as failure to exhibit a required light by night.

Rule 21: Definitions of lights

The principal lights defined are:

  • Masthead light: 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 and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on either side of the vessel.
  • Sidelights: a green light on the starboard side and a red light on the port side, each showing an unbroken light over an arc of 112.5 degrees from right ahead to 22.5 degrees abaft the beam.
  • Sternlight: a white light placed as nearly as practicable at the stern showing an unbroken light over an arc of 135 degrees from right aft to 67.5 degrees on each side of the vessel.
  • Towing light: a yellow light having the same characteristics as the sternlight.
  • All-round light: a light showing an unbroken light over an arc of the horizon of 360 degrees.
  • Flashing light: a light flashing at regular intervals at a frequency of 120 flashes or more per minute.

The arcs sum to 360 degrees: the masthead light covers the forward 225 degrees, the sternlight covers the aft 135 degrees. The sidelights together cover the same forward 225 degrees as the masthead light, with the green light visible to a vessel approaching from the starboard side and the red light visible to a vessel approaching from the port side.

Rules 22 to 24: Visibility ranges and the lights for power-driven vessels and vessels under tow

Rule 22 prescribes the minimum visibility range for each light: 6 nautical miles for the masthead light of a vessel of 50 metres or more in length, 5 nautical miles for the masthead light of a vessel of 12 metres or more but less than 50 metres in length, 3 nautical miles for the masthead light of a vessel of less than 12 metres in length, and lower ranges for the sidelights and sternlight. Rule 23 prescribes the lights for power-driven vessels underway: a masthead light forward; a second masthead light abaft of and higher than the forward one for a vessel of 50 metres or more in length; sidelights; and a sternlight. Rule 24 prescribes the lights for vessels towing or pushing, including the additional yellow towing light directly above the sternlight and the diamond shape exhibited by day when the length of the tow exceeds 200 metres.

Rules 25 to 27: Lights for sailing vessels, fishing vessels, and vessels not under command or restricted in their ability to manoeuvre

Rule 25 prescribes the lights for sailing vessels underway and vessels under oars: sidelights and a sternlight, with the option of two additional all-round lights at or near the top of the mast, the upper red and the lower green. Rule 26 prescribes the lights for fishing vessels, distinguishing trawlers (showing two all-round lights, the upper green and the lower white) from other fishing vessels (showing two all-round lights, the upper red and the lower white). Rule 27 prescribes the lights and shapes for vessels not under command or restricted in their ability to manoeuvre, including the well-known “red over red, the captain is dead” mnemonic for vessels not under command (two all-round red lights vertically) and the “red over white, fishing tonight” mnemonic for vessels engaged in fishing. Rule 27 also prescribes the special lighting for vessels engaged in dredging or underwater operations, with two all-round red lights and two all-round green lights arranged to indicate the side on which an obstruction exists and the side on which another vessel may pass.

Rules 28 to 31: Other vessels

Rule 28 prescribes the lights and shape for vessels constrained by their draught (three all-round red lights vertically, with a cylinder shape by day). Rule 29 prescribes the lights for pilot vessels (two all-round lights, the upper white and the lower red, in addition to the sidelights and sternlight when underway). Rule 30 prescribes the lights and shapes for vessels at anchor (an all-round white light at the bow and another at the stern, with a single black ball shape forward by day). Rule 31 provides that where it is impracticable for a seaplane or WIG craft to exhibit lights and shapes of the characteristics or in the positions prescribed by the rules, she shall exhibit lights and shapes as closely similar in characteristics and position as is possible.

Part D: Sound and light signals (Rules 32 to 37)

Rule 32: Definitions of sound signals

Rule 32 defines the terms used in the manoeuvring and warning signals: a “short blast” is a blast of about one second’s duration and a “prolonged blast” is a blast of from four to six seconds’ duration. Sound signals are produced by the whistle, bell or gong required by Annex III.

Rule 33: Equipment for sound signals

A vessel of 12 metres or more in length shall be provided with a whistle, a vessel of 20 metres or more in length shall be provided with a bell in addition to a whistle, and a vessel of 100 metres or more in length shall in addition be provided with a gong, the tone and sound of which cannot be confused with that of the bell. The whistle, bell and gong shall comply with the technical specifications of Annex III. A vessel of less than 12 metres in length is not obliged to carry the sound-signalling appliances prescribed but if she does not, she shall be provided with some other means of making an efficient sound signal.

Rule 34: Manoeuvring and warning signals

When power-driven vessels are in sight of one another and a vessel is taking action authorised or required by these rules, the vessel shall indicate that action by the following signals on her whistle:

  • One short blast: “I am altering my course to starboard.”
  • Two short blasts: “I am altering my course to port.”
  • Three short blasts: “I am operating astern propulsion.”

A vessel may supplement the whistle signals by light signals, repeated as appropriate, while the manoeuvre is being carried out. Rule 34(c) provides additional signals for vessels in narrow channels overtaking each other (two prolonged blasts followed by one short blast for overtaking on the starboard side, and two prolonged blasts followed by two short blasts for overtaking on the port side). Rule 34(d) provides the in-doubt signal: when vessels in sight of one another are approaching each other and from any cause either vessel fails to understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by giving at least five short and rapid blasts on the whistle. The “five short blasts” warning has become the universal sign of disapproval at sea.

Rule 35: Sound signals in restricted visibility

In or near an area of restricted visibility, whether by day or night, the signals prescribed by Rule 35 shall be used. A power-driven vessel making way through the water shall sound at intervals of not more than two minutes one prolonged blast. A power-driven vessel underway but stopped and making no way through the water shall sound at intervals of not more than two minutes two prolonged blasts in succession with an interval of about two seconds between them. A vessel not under command, a vessel restricted in her ability to manoeuvre, a vessel constrained by her draught, a sailing vessel, a vessel engaged in fishing, and a vessel engaged in towing or pushing another vessel shall sound at intervals of not more than two minutes three blasts in succession, namely one prolonged followed by two short blasts. A vessel at anchor shall ring the bell rapidly for about five seconds at intervals of not more than one minute. A vessel of 100 metres or more in length shall, in addition, sound the gong rapidly for about five seconds aft of the bell. A vessel aground shall give the bell signal and, if required, the gong signal as for a vessel at anchor and shall in addition give three separate and distinct strokes on the bell immediately before and after the rapid ringing of the bell.

Rule 36: Signals to attract attention

Any vessel may make light or sound signals to attract attention, provided such signals cannot be mistaken for any signal authorised elsewhere in these rules.

Rule 37: Distress signals

When a vessel is in distress and requires assistance, she shall use or exhibit the signals described in Annex IV to these rules.

Part E: Exemptions (Rule 38)

Rule 38 contains transitional exemptions for vessels constructed before 15 July 1977 (the date of entry into force) from specific lighting and equipment requirements introduced by the 1972 rules. The exemptions cover the visibility ranges of lights, the colour specifications, and the positioning of lights. The exemptions are now of historical interest only as the affected vessels have largely been scrapped.

Part F: Verification of compliance (Rules 39 to 41)

Part F was added to the rules by Resolution A.1085(28) of 4 December 2013, entering into force on 1 January 2016. The new part applies the IMO Member State Audit Scheme (IMSAS) to the COLREGs framework, requiring contracting parties to comply with the implementation provisions of the IMO Instruments Implementation Code (III Code) and to be subject to mandatory audit by the IMO. Rule 39 sets out the application; Rule 40 the verification of compliance; Rule 41 the certificates of compliance, harmonised with the analogous provisions of SOLAS Chapter XIII and MARPOL.

Annexes

Annex I: Positioning and technical details of lights and shapes

Annex I prescribes the precise vertical and horizontal position of each light, the screening required to limit the arc of visibility to the prescribed sectors, the chromaticity of the light (red, green, white, yellow) by reference to the International Commission on Illumination (CIE) chromaticity diagram, and the photometric intensity required to achieve the visibility ranges of Rule 22. The intensity I (in candelas) required for a given range D (in nautical miles) is given by:

I = 3.43 × 10⁶ × T × D² × K⁻ᴰ

where T is the threshold of illumination (2 × 10⁻⁷ lux) and K is the atmospheric transmissivity (0.8 for the prescribed visibility conditions). Annex I also specifies the day shapes (balls, cones, cylinders, diamonds), each at least 0.6 metres in greatest dimension on a vessel of 20 metres or more in length, with proportionally smaller shapes permitted on smaller vessels.

Annex II: Additional signals for fishing vessels in close proximity

Annex II prescribes the additional white-and-red flashing lights to be exhibited by fishing vessels engaged in fishing in close proximity, allowing them to communicate the direction of their gear to each other.

Annex III: Technical details of sound-signal appliances

Annex III prescribes the fundamental frequency of the whistle (in the range 70 Hz to 700 Hz, with the precise frequency dependent on vessel length), the audible range (2 nautical miles for vessels of 200 metres or more in length, 1.5 nautical miles for vessels of 75 to 200 metres, 1 nautical mile for vessels of 20 to 75 metres, and 0.5 nautical mile for vessels of less than 20 metres), the directional properties (the sound pressure level forward of the beam shall not exceed the level dead ahead by more than 4 dB), and the location (mounted as high as practicable, with the orientation calibrated to project sound forward).

Annex IV: Distress signals

Annex IV lists the recognised distress signals, which include: a gun or other explosive signal fired at intervals of about a minute; a continuous sounding with any fog-signalling apparatus; rockets or shells throwing red stars fired one at a time at short intervals; a signal made by radiotelegraphy or by any other signalling method consisting of the group SOS in the Morse code; a signal sent by radiotelephony consisting of the spoken word “Mayday”; the International Code Signal of distress indicated by N C; a signal consisting of a square flag having above or below it a ball or anything resembling a ball; flames on the vessel (as from a burning tar barrel, oil barrel, etc.); a rocket parachute flare or a hand flare showing a red light; a smoke signal giving off orange-coloured smoke; slowly and repeatedly raising and lowering arms outstretched to each side; a distress alert by means of digital selective calling (DSC) on a designated VHF, MF or HF frequency; a ship-to-shore distress alert transmitted by the ship’s INMARSAT or other mobile satellite service provider; signals transmitted by emergency position-indicating radio beacons (EPIRBs); approved signals transmitted by radiocommunication systems, including survival craft radar transponders. Annex IV is closely linked to the GMDSS framework, which provides the modern radio infrastructure for distress alerting under SOLAS Chapter IV.

Implementation in national law and special local rules

Rule 1(b) authorises states to make special rules for harbours, rivers, lakes and inland waterways connected to the high seas, provided that those rules conform as closely as possible with the international rules. The principal divergent national systems are:

  • United States Inland Navigation Rules (33 CFR Subchapter E), enforced by the United States Coast Guard, applicable to vessels operating shoreward of the COLREGS Demarcation Lines (33 CFR Part 80). The Inland Rules largely parallel the international rules, with significant differences in the conduct of vessels in narrow channels, the use of sound signals (one short blast for “I intend to leave you on my port side”, under a “cross-signal” tradition unique to North American inland waters), and the carriage of certain lights.
  • United Kingdom Distress Signals and Prevention of Collisions Regulations 1996 (SI 1996/75), as amended, enacting COLREGs into UK domestic law and extending it to UK-flag vessels worldwide.
  • Canadian Collision Regulations (CRC c. 1416), enacting COLREGs and supplementing them with rules for the Great Lakes and St Lawrence Seaway under a separate part.
  • Panama Canal Authority Notices to Shipping, supplementing COLREGs in the Panama Canal with detailed pilotage rules, lock-transit procedures and tug-assist requirements.
  • Suez Canal Rules of Navigation, supplementing COLREGs in the Suez Canal with traffic-direction rules, mandatory pilotage, and the convoy system used for the southbound and northbound passages.
  • Singapore Strait Vessel Traffic Information System rules, supplementing COLREGs in the Strait of Malacca with mandatory reporting, deep-draught vessel routeing and one-way traffic in the eastbound deep-water lane.

The general principle is that COLREGs apply on the high seas, and special local rules apply within the demarcated waters where they are in force. Vessels crossing demarcation lines transition between the two regimes; a master is expected to know the rules applicable to the waters being entered. Compliance is enforced by port state control and by criminal prosecution under the laws of the coastal state.

Recent amendments

The IMO MSC has amended the regulations on six occasions since their entry into force.

  • 1981 amendments (entered into force 1 June 1983). Insertion of “all available means” in Rule 5; clarification of safe speed in Rule 6; minor adjustments to Rule 8 and Rule 24.
  • 1987 amendments (entered into force 19 November 1989). Insertion of definitions for WIG craft and “vessel constrained by her draught”; addition of Rule 8(f) on vessels required not to impede another; clarification of Rule 10 on traffic separation schemes.
  • 1989 amendments (entered into force 19 April 1991). Addition of Rule 18(f) on WIG craft.
  • 1993 amendments (entered into force 4 November 1995). Updates to the technical annexes including light positioning and sound-signal characteristics.
  • 2001 amendments (entered into force 29 November 2003). Insertion of definition for high-speed craft and provisions for unmanned vessels; updates to Rule 26 on fishing vessels.
  • 2007 amendments (entered into force 1 December 2009). Recognition of WIG craft as a distinct category; updates to lighting requirements.
  • 2013 amendments (entered into force 1 January 2016). Insertion of Part F (verification of compliance) implementing the IMO Member State Audit Scheme.

A series of further amendments is under negotiation at the IMO Sub-Committee on Navigation, Communications and Search and Rescue (NCSR) to address Maritime Autonomous Surface Ships (MASS), the use of AIS-derived data in compliance with Rule 7, and the carriage of e-Navigation systems integrating ECDIS, AIS and ARPA. The MASS regulatory scoping exercise completed at MSC 103 in 2021 identified COLREGs as one of the instruments requiring modification or interpretation to accommodate autonomous and remotely operated ships; a draft MASS Code was approved at MSC 109 in 2025 with an expected entry into force in the late 2020s.

Common collision scenarios and case law

Head-on collisions and Rule 14

The leading modern head-on case is The Sanwa [1998] 1 Lloyd’s Rep 283, in which two vessels meeting in the Strait of Malacca at night each interpreted the other’s masthead lights as a crossing situation and altered to port, with a head-on collision following at a closing speed of about 28 knots. The Court held that the geometry was clearly a head-on situation, that Rule 14(c) required each vessel to assume so when in doubt, and that liability was apportioned 50:50 because each vessel had altered to port in clear breach of Rule 14. The case is widely cited as authority for the principle that Rule 14 requires unambiguous and symmetric action and that any departure from “alter to starboard” creates an immediate risk of mutual confusion.

Crossing collisions and the give-way / stand-on framework

The standard expression of the crossing-rule framework is in The Maloja II [1993] 1 Lloyd’s Rep 48 (the case also cited above in connection with Rule 5). The Court of Appeal held that the give-way vessel had failed to take early and substantial action to keep clear, that the stand-on vessel had been entitled to maintain course and speed in the first instance and to take action under Rule 17(a)(ii) only when it became clear that the give-way vessel was not acting, and that the in-extremis action under Rule 17(b) had been required only at the last moment. Liability was apportioned 70% against the give-way vessel and 30% against the stand-on vessel, the latter for an excessive delay in taking action under Rule 17(a)(ii).

Restricted-visibility collisions and Rule 19

The leading restricted-visibility case in the modern era is The Genimar [1977] 2 Lloyd’s Rep 17, in which two vessels in dense fog in the Channel each took avoiding action on radar plot, with one altering to starboard and the other altering to port (in the latter case for a vessel forward of the beam, in breach of Rule 19(d)(i)). The collision was held to be entirely the fault of the vessel that altered to port, with no contribution from the vessel that altered to starboard. The case established the firm interpretation of Rule 19(d)(i) as a near-absolute prohibition on alteration to port for a vessel forward of the beam in restricted visibility, departing from the looser standard that had prevailed under the 1960 rules.

USS Fitzgerald and ACX Crystal (2017)

The collision between the United States Navy destroyer USS Fitzgerald and the Philippine-flag containership ACX Crystal off Yokosuka, Japan, on 17 June 2017 killed seven Fitzgerald sailors and was the subject of investigations by both the US Navy and the Japan Transport Safety Board (JTSB). Both investigations concluded that Fitzgerald had failed to maintain a proper look-out under Rule 5, had failed to determine the risk of collision under Rule 7, and had failed to take action as the give-way vessel under Rule 15. The case is a textbook illustration of the cumulative failure mode in which the give-way vessel does not even recognise that she is in a crossing situation requiring her to act. The US Navy subsequently implemented major changes to bridge watchkeeping training and the Surface Warfare Officer course curriculum in direct response to the Fitzgerald and the closely connected USS John S. McCain / Alnic MC collision two months later.

USS John S. McCain and Alnic MC (2017)

The collision between the United States Navy destroyer USS John S. McCain and the Liberia-flag tanker Alnic MC near Singapore on 21 August 2017 killed ten McCain sailors. The US Navy investigation found that McCain had crossed in front of Alnic MC after a loss of steering control attributed to a confused transfer of helm and throttle control between bridge stations, and that the bridge team had failed to declare an emergency or to use the manoeuvring signal under Rule 34(d) (five short blasts) to indicate doubt to the approaching tanker. The case emphasised the integration of human-machine interface design with COLREGs compliance: a poorly designed steering console can produce a steering failure that is then masked by inadequate signalling to nearby vessels.

COLREGs and Maritime Autonomous Surface Ships

The COLREGs were drafted with an implicit assumption of human officers of the watch, human look-outs and human decision-makers. The advent of Maritime Autonomous Surface Ships (MASS) raises questions across the entire convention. Rule 5 requires “a proper look-out by sight and hearing”; an autonomous ship operating under remote control or fully autonomously cannot perform a visual look-out in the traditional sense, and must demonstrate that the algorithmic equivalent is a sufficient substitute. Rule 7 requires the use of “all available means” to determine if risk of collision exists; for an autonomous ship, the algorithmic CPA/TCPA computation is the primary mechanism, supported by the MASS time-to-collision calculator and analogous on-board systems. Rule 8 requires action that is “readily apparent to another vessel observing visually or by radar”; an autonomous ship must produce manoeuvres that are recognisable to a human bridge officer on a conventional vessel. Rules 14 to 17 require judgments about give-way / stand-on roles and about in-extremis action that are conceptually difficult to encode into deterministic software.

The IMO MASS regulatory scoping exercise at MSC 103 in 2021 identified COLREGs as one of the instruments requiring substantive amendment for the MASS framework. The Sub-Committee on Navigation, Communications and Search and Rescue (NCSR) has been working since 2022 on draft amendments and interpretive guidelines covering the four MASS degrees (Degree 1: ship with automated processes and decision support, with seafarers on board to operate and control shipboard systems and functions; Degree 2: remotely controlled ship with seafarers on board; Degree 3: remotely controlled ship without seafarers on board; Degree 4: fully autonomous ship). A goal-based MASS Code was approved at MSC 109 in 2025 and is expected to enter into force in the late 2020s. The Code does not replace COLREGs; rather, it sits alongside the convention and sets out the additional requirements that apply to MASS operations, including the responsibilities of the remote operator, the documentation of the ship’s autonomy capabilities in its statutory certificates, and the cyber security and software integrity requirements for the autonomous decision systems.

Bridge officer training

COLREGs is one of the core competencies of the STCW Convention for officers in charge of a navigational watch. The STCW competence “Plan and conduct a passage and determine position” requires that officers demonstrate the ability to apply the rules of the road in the simulator and at sea. The STCW competence “Maintain a safe navigational watch” requires demonstrated proficiency in collision avoidance under Rules 5 to 8 and the take-over of the watch under standard procedures. The STCW competence “Use of radar and ARPA to maintain safety of navigation” requires demonstrated proficiency in Rule 7 risk-of-collision assessment using ARPA and in Rule 19 conduct in restricted visibility.

The model courses that operationalise these competencies are IMO Model Course 1.07 (Radar Navigation and Plotting at the Operational Level), Model Course 1.08 (Radar, ARPA, Bridge Teamwork and Search and Rescue), and Model Course 1.34 (Operational Use of ECDIS). The model courses are revised periodically to incorporate amendments to COLREGs and developments in technology; the most recent revisions of Model Courses 1.07 and 1.08 in 2022 added modules on AIS-aided collision avoidance and on the integration of e-Navigation systems with the bridge watch.

The interaction between bridge resource management and COLREGs is increasingly emphasised in modern training. The 2010 Manila amendments to the STCW Convention introduced mandatory training in bridge resource management (BRM) and engine resource management (ERM); the BRM curriculum specifically addresses the cognitive and team-coordination factors that contributed to the USS Fitzgerald and USS John S. McCain collisions. The lesson from those casualties, and from the long line of collision cases dating back to the 19th century, is that COLREGs compliance is a matter of seamanship, not of mechanical rule-following: the rules establish a baseline of conduct, but the actual avoidance of collision requires judgment, situational awareness and the willingness to act under uncertainty.

See also

Additional calculators:

Additional related wiki articles:

References

  1. IMO. Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs), Consolidated Edition 2018. IMO, London, 2018. Sales No. IB904E.
  2. Cockcroft, A.N. and Lameijer, J.N.F. A Guide to the Collision Avoidance Rules, 7th edition. Butterworth-Heinemann, Oxford, 2012.
  3. Allen, C.H. Farwell’s Rules of the Nautical Road, 8th edition. Naval Institute Press, Annapolis, 2005.
  4. United Kingdom Hydrographic Office. The Mariner’s Handbook (NP 100), 11th edition. UKHO, Taunton, 2020.
  5. United States Coast Guard. Navigation Rules and Regulations Handbook. USCG, Washington, 2014.
  6. IMO MSC. Resolution A.1085(28) - Amendments to the International Regulations for Preventing Collisions at Sea, 1972 (Verification of compliance with the provisions of the Convention). IMO, 4 December 2013.
  7. IMO MSC. Maritime Autonomous Surface Ships (MASS) Regulatory Scoping Exercise: Final Report. MSC 103/5/1, 2021.
  8. United States Navy. Memorandum for Distribution: Report on the Collision between USS Fitzgerald (DDG 62) and Motor Vessel ACX Crystal. Department of the Navy, Washington, 2017.
  9. United States Navy. Memorandum for Distribution: Report on the Collision between USS John S. McCain (DDG 56) and Motor Vessel Alnic MC. Department of the Navy, Washington, 2017.
  10. Japan Transport Safety Board. Marine Accident Investigation Report: Collision between Container Ship ACX Crystal and Destroyer USS Fitzgerald (Public Vessel). JTSB, Tokyo, 2018.

Further reading

  • Mankabady, S. The International Maritime Organization, 2nd edition. Routledge, London, 1986.
  • Healy, N.J. and Sweeney, J.C. The Law of Marine Collision. Cornell Maritime Press, Centreville MD, 1998.
  • Marsden, R.G. British Shipping Laws Vol 4: Marsden and Gault on Collisions at Sea, 14th edition. Sweet and Maxwell, London, 2016.
  • IMO. International Regulations for Preventing Collisions at Sea, 1972: Background and Negotiating History. IMO, London, 1973.