Restricted Visibility

When the fog descends on your vessel, it is time for Rule 19 and Rule 35: Rule 19 for how to manoeuvre and Rule 35 on the sound signals that should be used. Following these rules should keep a vessel safe until it can see any vessel that may cause concern.

When other vessels cannot be seen due to restricted visibility, your vessel should not make those sound signals that require that “vessels are in sight of one another”; see Rule 34. This even applies to the “five short” signal where you indicate there may be some danger or that another vessel’s intentions are unclear. 

Around Comox it is rare to have severely restricted visibility, e.g., less than a hundred feet or so (but it can happen). In "normal" restricted visibility you are more likely to see a vessel emerge from fog (or a rain squall, or whatever) more than a cable or two away. So RCMSAR vessels moving at slow speed (due to the conditions) should be able to stop within one or two boat lengths and ensure that no collision takes place. For a safe speed mariners have traditionally used a guideline that you should not move so fast you cannot stop in half the prevailing visibility; if two approaching vessels use this guideline they should both be able to stop before they make contact. 

The likely sequence is, first, to become aware of another vessel while it is hidden in fog, perhaps still several cables or more away by hearing a fog signal or by seeing an appropriate target on radar. At this point your vessel should be aware that there is another vessel nearby and take suitable precautions (under Rule 19 and Rule 35). 

Should another vessel emerge from the fog, then the various sub-rules under Rule 34 can come into play — you are now in sight of one another. Up to that point Rule 19 (Conduct of Vessels in Restricted Visibility) and Rule 35 (Sound Signals in Restricted Visibility) should keep you safe, and the same for the folks on the other vessel.

Rules that specify technical characteristics of sound equipment (Annex III) require that sound signals from larger vessels be lower in tone: the horn of a small power boat must be higher in pitch than the whistle of a large commercial vessel (e.g., a BC ferry). Thus, if you hear a fog horn in restricted visibility that is at a very low frequency be aware it could be a very large vessel… yikes!