Restricted visibility: read Rule 19 without importing slogans

Fog, mist, snow, heavy rain and similar causes can restrict visibility under Rule 3(l). Rule 19(a) concerns vessels not in sight while navigating in or near such an area.

It requires neither every target to be invisible in all directions nor merely nighttime. The framework includes visual condition between the vessels and visibility context.

MCA MGN 369 Amendment 1 distinguishes this scope from Section II without creating a universal speed or CPA figure. A radar target’s plotted geometry does not independently turn the encounter into Rule 15 crossing.

Rule 19(b) requires safe speed adapted to circumstances and conditions, with power-driven vessels’ engines ready for immediate manoeuvre. Paragraph (c) preserves due regard to those conditions when complying with Section I.

Lookout, available means, radar limitations and systematic appraisal continue under Rules 5–7. Application does not consist of replacing everything with “always turn starboard”.

Rule 19 does not assign Section II stand-on and give-way roles: both vessels have duties within its own framework. Readiness, speed and observation therefore belong to one continuing appraisal.

Paragraph (d) requires determining whether a close-quarters situation is developing and/or collision risk exists. If so, avoiding action is required in ample time.

Where that action is a course alteration, two cases are to be avoided so far as possible: port alteration for a vessel forward of the beam, except a vessel being overtaken; and alteration towards a vessel abeam or abaft. The overtaking exception belongs to the first case.

Neither so far as possible nor the two separate conditions should disappear into one universal arrow or automatic helm response.

Beam, forward and abaft reference our vessel in that wording. A target left of a north-up screen is not necessarily on our port side.

The figure identifies bow and relative references without alteration angles or tracks. Radar alone describes the means by which another vessel’s presence was detected; it does not establish all its characteristics.

Limitations, scanty information and other traffic remain in appraisal. The relationship between screen orientation and vessel-relative bearings is a technical learning topic, rather than an excuse to apply a diagram without confirming its reference.

Except where no collision risk has been determined, paragraph (e) concerns hearing another vessel’s fog signal apparently forward of the beam, or being unable to avoid close quarters with another forward of the beam. It requires reducing to the minimum speed at which course can be kept, taking all way off if necessary, and in any event navigating with extreme caution until danger is over.

This is not a recommended knot value. Neither does hearing any sound anywhere justify keeping speed unchanged because the vessel is invisible.

Rule 20 addresses lights in restricted visibility also by day, while Rule 35 concerns sound signals in or near the area, day or night. Lack of visual contact does not dispense with those signals.

Underway and making way through the water remain important distinctions between sound provisions. MCA references are identified as UK guidance; international text and national implementation remain linked to their sources.

Limited visibility changes the conditions that must be recognised; it does not turn partial information into an automatic priority. The account supplies no radar settings, CPA limits or real-location navigation advice.