Rule 1 – Application:

  • Applies to all vessels on high seas and connected waters.
  • No interference with special rules for specific areas.
  • Governments can set rules for lights and signals for warships, convoys, and fishing fleets.
  • Traffic separation schemes may be adopted.

Rule 2 – Responsibility:

  • Non-exoneration clause for vessels neglecting rules or precautions.
  • Compliance with rules considering all navigation dangers.

Rule 3 – General Definitions:

  • Defines terms like ‘vessel,’ ‘power-driven vessel,’ ‘sailing vessel,’ ‘vessel engaged in fishing,’ etc.
  • Clarifies terms related to vessels’ visibility, navigation, and specific operations.


Rule 4 – Application:

  • Rules apply in any visibility condition.

Rule 5 – Look-out:

  • Vessels must maintain a proper look-out using available means to assess situations and collision risks.

Rule 6 – Safe Speed:

  • Vessels must proceed at safe speeds considering visibility, traffic density, maneuverability, weather, and other factors.

Rule 7 – Risk of Collision:

  • Vessels must use all means to assess collision risk; radar should be used effectively.
  • No assumptions based on scanty information.

Rule 8 – Action to avoid Collision:

  • Positive and timely actions are required to avoid collisions.
  • Altered courses should be noticeable; safe passing distance must be maintained.

Rule 9 – Narrow Channels:

  • Rules for vessels in narrow channels, emphasizing safe navigation, overtaking, and right of way.

Rule 10 – Traffic Separation Schemes:

  • Guidelines for vessels using traffic separation schemes to follow lanes, avoid separation lines, and exercise caution.

Rule 11 – Application:

  • Rules in this section apply to vessels in sight of each other.

Rule 12 – Sailing Vessels:

  • Rules for sailing vessels approaching each other to avoid collisions based on wind direction.

Rule 13 – Overtaking:

  • Overtaking vessels must keep clear; criteria for overtaking defined.

Rule 14 – Head-on Situation:

  • Power-driven vessels meeting head-on must alter course to starboard.

Rule 15 – Crossing Situation:

  • Rules for power-driven vessels crossing paths.

Rule 16 – Action by Give-way Vessel:

  • Give-way vessels must take early action to keep clear.

Rule 17 – Action by Stand-on Vessel:

  • Stand-on vessels maintain course and speed; may take action if the give-way vessel doesn’t.

Rule 18 – Responsibilities between Vessels:

  • Right of way defined for power-driven and sailing vessels.

Rule 19 – Conduct of Vessels in Restricted Visibility:

  • Guidelines for vessels not in sight of each other in restricted visibility conditions.
  • This summary provides an overview of the key rules and principles outlined in the International Regulations for Preventing Collisions at Sea. The detailed rules cover various aspects of vessel navigation to ensure safe maritime practices.


Rule 20 – Application

  • (a) The rules in this part apply in all weathers.
  • (b) Lights must be used from sunset to sunrise, and no other lights shall be exhibited during this time, except if they can’t be mistaken for the specified lights, don’t impair visibility, or interfere with a proper lookout.
  • (c) Lights specified in these rules shall also be exhibited from sunrise to sunset in restricted visibility and may be used in other circumstances if deemed necessary.
  • (d) Shapes must be complied with during the day.
  • (e) Lights and shapes must comply with Annex I to these Regulations.

Rule 21 – Definitions

  • (a) ‘Masthead light’ is a white light over the fore and aft centerline showing over 225 degrees.
  • (b) ‘Sidelights’ are green on starboard and red on port, each showing over 112.5 degrees.
  • (c) ‘Sternlight’ is a white light at the stern over 135 degrees.
  • (d) ‘Towing light’ is a yellow light similar to the sternlight.
  • (e) ‘All-round light’ shows over 360 degrees.
  • (f) ‘Flashing light’ flashes at a frequency of 120 or more per minute.

Rule 22 – Visibility of Lights

  • Lights must have specified intensities for visibility at minimum ranges based on vessel length.

Rule 23 – Power-driven Vessels Underway

  • (a) Power-driven vessels must exhibit masthead, sidelights, and sternlight.
  • (b) Air-cushion vessels must display an all-round flashing yellow light.
  • (c) WIG craft, when taking off, landing, or in flight, must exhibit prescribed lights.
  • (d) Power-driven vessels under 12 meters may use alternative lights and sidelights.

Rule 24 – Towing and Pushing

  • (a) Towing vessels must exhibit masthead lights, sidelights, sternlight, towing light, and diamond shape for tows over 200 meters.
  • (b) Pushing vessels connected in a composite unit are considered power-driven and follow Rule 23.
  • (c) Power-driven vessels pushing or towing alongside must exhibit specific lights.
  • (d) Towed vessels display sidelights, sternlight, and diamond shape for tows over 200 meters.
  • (e) Inconspicuous towed vessels exhibit specific lights and shapes.
  • (f) Grouped towed vessels are lit as one vessel with specific requirements.
  • (g) Inconspicuous, partly submerged towed vessels exhibit specific lights and shapes.
  • (h) Measures should be taken if impractical to exhibit required lights.
  • (i) Vessels not normally towing may be exempt when assisting distressed vessels, following Rule 36.

Rule 25 – Sailing Vessels underway and Vessels under Oars

  • (a) Sailing vessels exhibit sidelights and sternlight.
  • (b) Lights for sailing vessels under 20 meters may be combined in one lantern.
  • (c) Additional lights for sailing vessels under specific conditions.
  • (d) Vessels under 7 meters may use alternative lights.
  • (e) Sailing vessels with machinery exhibit a conical shape when under sail.

Rule 26 – Fishing Vessels

  • (a) Fishing vessels exhibit specific lights and shapes.
  • (b) Trawling vessels have additional lights when making way.
  • (c) Fishing vessels, excluding trawlers, have specific lights and shapes.
  • (d) Additional signals apply to fishing vessels near each other.
  • (e) Fishing vessels not engaged in fishing follow regular lighting rules.

Rule 27 – Vessels not under Command or Restricted in their Ability to Manoeuvre

  • (a) Vessels not under command exhibit specific lights and shapes.
  • (b) Restricted vessels display lights, shapes, and additional lights when at anchor.
  • (c) Power-driven vessels towing in a way that limits maneuverability follow specific rules.
  • (d) Dredging vessels exhibit lights and shapes indicating obstruction and when at anchor.
  • (e) Diving vessels exhibit specific lights and shapes.
  • (f) Mineclearance vessels exhibit specific lights and shapes indicating danger.
  • (g) Vessels under 12 meters are exempt.
  • (h) Signals here are not distress signals; distress signals are in Annex IV.

Rule 28 – Vessel constrained by their draught

  • Vessels constrained by draught may exhibit additional lights.

Rule 29 – Pilot Vessels

  • (a) Pilot vessels engaged in duty exhibit specific lights.
  • (b) Pilot vessels not on duty follow regular lighting rules for their size.

Rule 30 – Anchored Vessels and Vessels Aground

  • (a) Anchored vessels exhibit specific lights or shapes.
  • (b) Vessels under 50 meters may use an all-round white light instead.
  • (c) Additional lights can be used to illuminate decks.
  • (d) Aground vessels exhibit specific lights and shapes.
  • (e) Vessels under 7 meters at anchor may be exempt.
  • (f) Vessels under 12 meters aground may be exempt.

Rule 31 – Seaplanes

  • Seaplanes exhibit lights and shapes as closely similar as possible to the rules when impracticable to follow exactly.


Rule 32 – Definitions:

  • Whistle, short blast, prolonged blast.
  • Specifications in Annex III.

Rule 33 – Equipment for Sound Signals:

  • Vessels >12m: Whistle.
  • Vessels >20m: Whistle + bell.
  • Vessels >100m: Whistle + bell + gong.
  • All comply with Annex III.
  • Vessels <12m to have an alternative sound signal.

Rule 34 – Manoeuvring and Warning Signals:

  • Whistle signals for manoeuvring.
  • Light signals supplement manoeuvring.
  • Overtaking signals.
  • Doubt signals.
  • Bend or obstruction signals.
  • Single whistle if distance >100m.

Rule 35 – Sound Signals in restricted Visibility:

  • Power-driven underway: 1 prolonged blast.
  • Power-driven stopped: 2 prolonged blasts.
  • Various signals for vessels based on type and activity.
  • Anchored vessels, aground vessels, and pilot vessels have specific signals.
  • Vessels <12m have simplified signals.

Rule 36 – Signals to attract Attention:

  • Signals not conflicting with navigation aids.
  • High-intensity intermittent lights avoided.

Rule 37 – Distress Signals:

  • Annex IV signals used when in distress.

Part E – Exemptions (Rule 38):

  • Vessels under construction exempt from some rules for a specified period.
  • Exemptions for light installations, repositioning, and sound signals duration.
  • Permanent exemptions for specific cases.


Rule 39 – Definitions:

  • Audit: A systematic, independent, and documented process to evaluate the fulfillment of audit criteria.
  • Audit Scheme: Established by IMO, guided by IMO’s resolutions, including the Framework and Procedures for the IMO Member State Audit Scheme.
  • Code for Implementation: The IMO Instruments Implementation Code, also referred to as the III Code.
  • Audit Standard: Refers to the Code for Implementation.

Rule 40 – Application:

  • Contracting Parties: Must use the provisions of the Code for Implementation to fulfill obligations under the Convention.

Rule 41 – Verification of Compliance:

  • Audit by IMO: Contracting Parties undergo periodic audits by IMO to verify Convention compliance.
  • Responsibilities: IMO Secretary-General administers the Audit Scheme; Contracting Parties facilitate audits and implement action plans.
  • Audit Schedule: Developed by IMO Secretary-General, considering guidelines set by IMO, conducted periodically.

These rules establish a systematic auditing process, ensuring Contracting Parties adhere to Convention regulations, promoting effective implementation and compliance. The IMO Secretary-General oversees the Audit Scheme, and periodic audits are conducted based on established schedules and guidelines.



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