Observe and identify
Advanced level, about 3 min. International COLREGs / IRPCS.
The situation
You are heading north at four knots toward a vessel working slowly southward in a fairway. The supplied passage plan confirms sufficient depth and room on either outer route for your draught, but submerged working equipment obstructs one side of the vessel. Inspect the central and side light groups before selecting a passage. No other traffic is closing either route.
Which configuration is shown, and which passage should you plan?
- Dredging operations: use the green-marked western side
- Dredging operations: keep to the eastern side by habit
- A pilot vessel: continue down the centre
Answers and explanations
Lookout: Separate the central operating-status lights from the two side signals. Translate the vessel’s passing side into your own view, then keep checking depth, room and traffic.
The sound answer
Dredging operations: use the green-marked western side
Central red-white-red marks restricted manoeuvrability. Two all-round reds indicate the obstructed side; two greens indicate the side another vessel may pass. Facing this southbound vessel, her green-marked starboard side is on your left, west of her. The supplied plan provides the depth and room needed for this authored passage; keep checking conditions.
Why the other options fall short
Dredging operations: keep to the eastern side by habit
These green lights belong to the working vessel and mark her available passing side. They are not lateral channel marks. On the eastern side you enter the red-marked obstruction and the authored submerged equipment.
A pilot vessel: continue down the centre
A pilot vessel shows white over red, not the central red-white-red stack with additional red and green side pairs. This vessel is restricted by underwater work; your power-driven vessel must keep clear of her.
Rules 18 & 27(d) · Dredging or underwater operations
A vessel restricted in her ability to manoeuvre while dredging or undertaking underwater operations shows the restricted-manoeuvrability signals and, when an obstruction exists, two all-round reds on the obstructed side and two all-round greens on the side another vessel may pass. Interpret the signals with the actual geometry and other navigation constraints.