Details on Rules for Restricted Visibility

Rule 19: Conduct of Vessels in Restricted Visibility

For manoeuvring, there is just one rule that governs vessels not in sight of one another when navigating in or near an area of restricted visibility, namely Rule 19 in Section III. The purpose of this rule seems mainly to keep vessels and crews safe until they are eventually within sight of one another.

When operating under Rule 19, crews still need to apply Rule 5 (Lookout), Rule 6 (Safe Speed), and Rule 7 to Rule 10; these rules apply in all conditions of visibility. When operating under Rule 19 and no other vessels are in sight, Rule 11 to Rule 18 do not apply. 

If you are operating in or near an area of restricted visibility and a vessel should emerge from a nearby fog bank, then you may have to apply both the rules for vessels in sight of each other (Rule 11 to Rule 18) and for restricted visibility (Rule 19 and Rule 35). Life can get complicated, but fortunately such a situation is rare. 

Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. Although not mentioned in COLREGS, a guide is that a vessel should proceed at no more than a speed from which she can stop in half the visual range; if two converging vessels follow this guidance, they should both be able to stop before they make contact. 

A power-driven vessel shall have her engines ready for immediate manoeuvre. Even if a vessel is already stopped, it should be ready to respond immediately in case it has to move quickly. 

Every vessel shall have due regard to the prevailing circumstances and conditions of restricted visibility when complying with Rule 5 though Rule 10. These are the rules on "look out", "safe speed", "determining risk of collision", "responding if risk exists", "narrow channel", and "traffic separation scheme". When circumstances and conditions have changed with the presence of fog (or similar phenomena), these rules take on new significance: lookouts need to be even more diligent, best use should be made of radar, the safe speed should be reduced. Risk levels will have risen and the assessment of risk and appropriate responses will be different when other vessels are not within sight. 

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:

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. Since our SAR vessels can manoeuvre and maintain course (i.e., change the boat's heading) even when stopped, the minimum speed for us in these circumstances is ZERO.  

Extreme circumstances: Say your vessel is stopped to comply with Rule 19, because you believe there is clearly a risk of collision: Maybe you have a radar contact heading directly for you and not changing course. OK, you have been very cautious (complying fully with Rule 19) but it is not working due to the action (or inaction) of the other vessel. Now it may be time for Rule 2, that is: conditions now "make a departure from these Rules necessary to avoid immediate danger". But be aware that if you want to invoke this part of Rule 2 you should have your reasons ready for the accident investigation board (yikes!) if one needs to be convened. (But any such situation is exceedingly rare!)

Rule 35: Sound Signals in and near Restricted Visibility