Sea Rules of the Road: Avoiding collisions when ships are in sight of one another, and in restricted visibility


We have been studying about the navigation rules of the road in our last two articles. In this article we will proceed to learn about the regulations that govern situations whenever two ships are in proximity and either are visible to each other or are invisible ships due to bad weather conditions. Learn about these interesting scenarios below.

Vessels in Sight of One another, Crossing


When two ships meet, and if risk of collision exists (see previous article in series), the Collision rules specify that unless one is overtaking the other, they are ‘crossing’. If they are crossing, the ship that has the other on her starboard side (right side, and this ship is the ‘give way’ vessel) will keep out of the way of the other vessel, which is the ‘stand on’ vessel, which must maintain its course and speed.

The give way vessel can alter speed or alter course, or indeed, a combination of the above. Usually in the open sea, an alteration of course is sufficient, as can be seen in the diagram.

If required, stipulated signals or sounds (foghorn) will be made by the vessels. For example, one short blast on the foghorn (or one flash of a light at night) will indicate “I am altering course to starboard” )

In any case, the give way vessel will avoid crossing ahead of the other vessel. At sea, a starboard alteration of course is invariably made in such situations.

If both vessels are head on (on reciprocal courses) each will alter course to starboard and keep out of the way of the other.

Vessels in sight of one another, overtaking.


An overtaking vessel must keep out of the way of a ship being overtaken. It can overtake on either side.

Sound and light signals are prudent to indicate to the vessel which side the intention is to overtake on. The vessel being overtaken will signal agreement with specified sound/light signals, foghorn and/or light.

Responsibilities between vessels. (see earlier articles for definitions)

  • A normal power driven vessel should keep clear of a vessel restricted in any way, whether in her ability to manoeuvre, not under command, fishing or sailing.
  • A sailing vessel must keep clear of all except a normal power driven vessel.
  • A fishing vessel (when actually fishing) should keep clear of a vessel restricted in her ability to manoeuvre or a vessel not under command.
  • Any vessel except a vessel not under command should keep clear of a vessel that is constrained by her draft. This ship should exercise extra caution.
  • A seaplane should keep clear of everything.

Conduct of vessels in restricted visibility

All ships of any kind should proceed at a safe speed in mist, fog or other such conditions that restrict visibility. They should be ready for immediate manoeuvre. They should stop engines and even go astern (reverse) if required.

If another vessel is detected on radar, and if there is risk of collision, all ships should take action well in advance. If required to alter course, they should avoid an alteration of course to port for a vessel that they are not overtaking. If they are overtaking, they should avoid an alteration of course towards a vessel that they are overtaking.

Fog signals are highly recommended in such situations. It is also imperative to navigate with extreme caution in fog, especially when other ships are close by and cannot be seen.


Diagrams from

This post is part of the series: Marine Navigation: The Rules of the Road

The first article will explain basic concepts and definitions. Subsequent ones will go in some detail in the nitty gritty and explanation of the Rules.
  1. The Basics of the Sea Rules of the Road in Navigation
  2. Basics of the Sea: Rules of the Road – In any Condition of Visibility.
  3. Basics of the Navigation Rules: When ships can see each other, and when they can’t
  4. Basics of Sea Collision Regulations: Lights, Shapes, and Sound Signals