COLREG / ARPA / AIS Bridge Rule 27(d) 🔒 Course / Premium

Rule 27(d) — Dredger / Underwater Ops

NIGHT. A vessel is engaged in dredging or underwater operations.

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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)

Rule 27(d) — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.

📸 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.

Dredger or underwater operations vessel viewed head-on (bow aspect) — COLREG Rule 27(d) night-recognition diagram — Bow

Dredger or underwater operations vessel viewed from her starboard bow — COLREG Rule 27(d) night-recognition diagram — STBD bow

Dredger or underwater operations vessel viewed from her starboard beam — COLREG Rule 27(d) night-recognition diagram — STBD beam

Dredger or underwater operations vessel viewed from her starboard quarter — COLREG Rule 27(d) night-recognition diagram — STBD qtr

Dredger or underwater operations vessel viewed dead astern (stern aspect) — COLREG Rule 27(d) night-recognition diagram — Stern

Dredger or underwater operations vessel viewed from her port quarter — COLREG Rule 27(d) night-recognition diagram — Port qtr

Dredger or underwater operations vessel viewed from her port beam — COLREG Rule 27(d) night-recognition diagram — Port beam

Dredger or underwater operations vessel viewed from her port bow — COLREG Rule 27(d) night-recognition diagram — Port bow

Why it matters

COLREG knowledge is the foundation of safe ship handling. Most maritime collisions happen because watchkeepers either misidentified the situation, applied the wrong rule, or acted too late. This scenario lets you train pattern recognition + correct response under time pressure — the exact skill the rules are designed to support. RYA, Yachtmaster, STCW and most national exams expect you to apply COLREGs reflexively, not just recite them.

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