Rule 4 Conduct of vessels in any condition of visibility - the rules in this section applies in any conditions of visibility.

In other words, if there is zero visibility and the vessel does not have the instruments to proceed safely, the speed of the water craft should be reduced and course corrections made, until adequate vision is restored for safe operation of the vessel.

Autonomous robotic vessels may have the advantage here, where they would typically have superior instruments and access to geodata, AIS and other information that older ships with human operators may not be equipped with.

Rule 1 states that the rules apply to all vessels on the high seas and connected waters.
Rule 2 covers the responsibility of the master, owner and crew to comply with the rules.
Rule 3 includes definitions of applicable water craft (vessels).
Rule 4 says the section applies in any conditions of visibility.
Rule 5 every vessel shall at all times maintain a proper look-out by sight and hearing.
Rule 6 deals with safe speed.

Rule 7 risk assumptions shall not be made on scanty (radar) information.
Rule 8 covers action to be taken to avoid collision.
Rule 9 vessels proceeding along a narrow channel should keep to starboard.
Rule 10 deals with the behaviour of vessels in or near traffic separation schemes. 

Part C - LIGHTS & SHAPES (Rules 20-31)

Part D - SOUND AND LIGHT SIGNALS - DEFINITIONS (Rules 32-37)

Part E - EXEMPTIONS - Rule 38

Part F - Convention compliance verification provisions Rules 39 - 41

Annex I - Positioning and technical details of lights and shapes

Annex II - Additional signals for fishing vessels fishing in close proximity

Annex III - Technical details of sounds signal appliances

Annex IV - Distress signals indicating distress and need of assistance

International Maritime Organization (IMO)

4 Albert Embankment, London SE1 7SR

United Kingdom
+44 (0) 20 7735 7611

LINKS & REFERENCE

http://www.solarnavigator.net/boats/collision_at_sea_regulations_colregs.htm

https://www.bluebird-electric.net/COLREGS_International_Regulations_for_Preventing_Collisions_at_Sea_1972.htm

http://www.solarnavigator.net/boats/collision_at_sea_regulations_colregs.htm

https://www.bluebird-electric.net/COLREGS_International_Regulations_for_Preventing_Collisions_at_Sea_1972.htm