Rule 27(d) — Dredger / Underwater Ops
NIGHT. A vessel is engaged in dredging or underwater operations.
Scenario briefing
NIGHT. A vessel is engaged in dredging or underwater operations. She shows: the three RAM lights vertically (RED-WHITE-RED); normal masthead/sidelights/sternlight while making way; AND on the side where an obstruction exists, TWO all-round RED lights in a vertical line; on the side on which another vessel may pass, TWO all-round GREEN lights in a vertical line. Which side may you pass?
Applicable COLREG rule(s)
📸 Night recognition — 8 aspects
The same vessel rendered every 45° of aspect — bow, starboard bow, beam, quarter, stern, port quarter, beam, bow. Use this strip to learn how the lights present from each approach angle. Click any image to view full size.
Key teaching points
- Rule 27(d): a vessel engaged in dredging or underwater operations, with an obstruction, shows the Rule 27(b) RAM lights PLUS:
- — two all-round RED lights vertically on the side of the obstruction,
- — two all-round GREEN lights vertically on the side where another vessel may pass.
- Day equivalent: ball/diamond/ball (Rule 27(b)) plus two balls (obstruction side) and two diamonds (safe side).
Common mistakes to avoid
- Passing the side with the red-red lights — that is the OBSTRUCTION side, never pass there.
- Treating a dredger as a simple RAM and missing the red/green pair — Rule 27(d) is mandatory when there is an obstruction.
Why it matters
Exam relevance
Rule 27(d) dredger lights are a probing detail question in STCW OOW orals and Yachtmaster Offshore.
Related scenarios
About SkipperCheck simulators
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