Restricted Visibility

Definition

The term “restricted visibility” means any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.

—Rule 3.l

Vessel Conduct

Applicability

Applies when navigating in or near an area of restricted visibility. Section I rules apply, Section II rules do not.

Safe Speed and Ready to Manoeuvre

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.

—Rule 19.b

Decision Making

Decisions for avoiding actions are far more simplified in restricted visibility, because in such situations you can’t verify the situation through sight like you would normally.

Detection by Radar Alone

A vessel which detects by radar alone the presence of another vessel shall determine if a close-quarters situation is developing and/or risk of collision exists. If so, she shall take avoiding action in ample time, provided that when such action consists of an alteration of course, so far as possible the following shall be avoided:

1. an alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken;

2. an alteration of course towards a vessel abeam or abaft the beam.

—Rule 19.d

Detection by Sound Signal

Except where it has been determined that a risk of collision does not exist, 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. She shall if necessary take all her way off and in any event navigate with extreme caution until danger of collision is over.

—Rule 19.e

Sound signal detection is more fallible than radar due to echoes, and as such the rules require you to simply reduce speed and allow the situation develop, rather than take an incorrect action that hastens the collision situation.

Sound Signalling in Restricted Visibility

In or near an area of restricted visibility, whether by day or night…

—Rule 35

Underway

Vessels are obliged to make sound signals to identify and locate themselves, at intervals of no more than 2 minutes between signals.

Power Driven Vessel: \(\text{—}\)

Power Driven Vessel underway but making no way: \(\text{— —}\)

NUC, RAM, Constrained by draught, sailing, fishing, towing/pushing: \(\text{— • •}\)

Last vessel of a tow, if manned, ideally immediately after the towing vessel’s signal: \(\text{— • • •}\)

At Anchor

Vessels are obliged to make sound signals to identify and locate themselves, at intervals of no more than 1 minute between signals. Vessels engaged in fishing or restricted in ability to manoeuvre shall use underway signals.

All vessels sound: \(\text{🕭 5 seconds}\)

All vessels over 100 metres, in addition to bell in fore part of vessel, in after part of vessel sound: \(\text{Gong - 5 seconds}\)

May in addition use a sound signal: \(\text{• — •}\)

Aground

Use at anchor signalling, starting and ending each 5 second ringing with 3 separate and distinct strokes on the bell and gong.

Pilot Vessels

May identify themselves with an additional signal: \(\text{• • • •}\)