Restricted visibility Rule 19

Rule 19: Conduct of vessels in restricted visibility

a. This Rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility.

Meaning that this Rule applies to such vessels that may be close to each other but cannot visually see each other, electronic devices and sound signals may be the only possible means of detection and thus the action that would be taken would not be visible by the other vessel.
The areas are not only in areas of poor visibility but also areas near to that. Meaning that ships should be careful when approaching a fog bank, or an area of poor visibility caused
maybe by any weather or other condition.

b. 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.

c. Every vessel shall have due regard to the prevailing circumstances and conditions of restricted visibility when complying with the Rules of Section I of this Part.

d. 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 in course, so far as possible the following shall be avoided:

(i) An alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken;

Meaning: In restricted visibility when the vessels cannot see each other as required by the Rules, the above are to be complied with. Of course, alteration of course to Port has been advised against, and it should be followed as far as practicable if the situation deems that an alteration, of course, other than to Port is required then that may be done.- Rule 2, use your head. For overtaking situation after the Risk factor has been assessed the alteration may be done either way.

(ii) An alteration of course toward a vessel abeam or abaft the beam.

Meaning : Here too since the vessels are not in sight of one another and the observations are being carried out by electronic means, the proper assessment of the aspect of the vessel is not obtained, as such the above guidelines.

e. 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 be 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.

As stated in Rule 3 (l) 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.