A contact on the radar
Restricted visibility. Developing level, about 3 min. COLREGs Rule 19.
The situation
Dense fog, visibility about 250 m, and you are already at a safe speed for it. Radar shows a vessel fine on your starboard bow, closing on a steady bearing. You cannot see her and have not yet heard her fog signal.
How do you avoid a close-quarters situation?
- Alter boldly to starboard: Open the distance and pass port to port.
- Alter to port, away from her: She is on your starboard bow, so turn the other way.
- Hold on until you can see her: Without sight of her, the steering rules do not apply.
Lookout: Vessels not in sight of one another have no stand-on or give-way vessel. Rule 19 governs, and an unseen ship ahead will most likely turn to starboard herself.
The sound answer
Alter boldly to starboard
Rule 19(d): a vessel detecting another by radar alone, with a close-quarters situation developing, takes avoiding action in ample time. For a vessel forward of the beam, she avoids altering to port. A bold starboard alteration is readily seen on the other ship’s radar and matches what she will most likely do herself.
Why the other options fall short
Alter to port, away from her
Rule 19(d)(i) says avoid an alteration to port for a vessel forward of the beam. She cannot see you either and will most likely turn to starboard, which brings your two turns together.
Hold on until you can see her
Rules 11 to 18 do not apply out of sight, but Rule 19 does: with close quarters developing you must take avoiding action in ample time, not wait for her to appear out of the fog.
Rule 19 · Conduct in restricted visibility
A vessel detecting another by radar alone determines whether a close-quarters situation is developing and, if so, takes avoiding action in ample time. She avoids altering to port for a vessel forward of the beam, other than one being overtaken, and avoids turning towards a vessel abeam or abaft the beam. On hearing a fog signal forward of the beam she reduces speed to the minimum needed to keep her course.