COLREGS Rule 30 — Anchored Vessels and Vessels Aground

Rule Text

What it means on the water

• →Vessels at anchor ≥ 50m: all-around white forward (higher) + all-around white aft (lower).
• →Vessels at anchor < 50m: may show just one all-around white light where best seen.
• →Dayshape for anchor: black ball (1 ball).
• →Vessel aground: anchor lights PLUS two all-around red lights in a vertical line.
• →Vessel aground dayshape: anchor ball(s) PLUS three black balls in a vertical line.
• →A vessel aground may also use working lights to illuminate the deck.

Common exam mistakes

• ✗Giving a vessel under 50m two anchor lights — under 50m only one all-around white is required.
• ✗Forgetting that an aground vessel shows BOTH anchor lights AND two red lights.
• ✗Confusing the aground lights (2 red) with NUC lights (also 2 red) — the aground vessel also shows anchor lights, NUC does not.

USCG exam questions — Rule 30

These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.

1. 1. A vessel at anchor shall show by night:

   • A.An all-round white light where it can best be seen
   • B.An all-round white light forward and an all-round white light aft, the after light being lower✓
   • C.Sidelights and an all-round white light
   • D.A flashing white light

   Why: Rule 30(a) requires an anchored vessel to show an all-round white light in the fore part of the vessel and a second all-round white light at or near the stern, lower than the forward light. This two-light combination helps observers judge the vessel's length and orientation.

2. 2. A vessel less than 50 meters in length at anchor may, instead of the two prescribed anchor lights, show:

   • A.A flashing white light
   • B.A red over white all-round light
   • C.A single all-round white light where it can best be seen✓
   • D.Sidelights only

   Why: Rule 30(b) allows vessels less than 50 meters at anchor to show just one all-round white light where it can best be seen, instead of the two-light forward/aft arrangement required for larger vessels.

3. 3. A vessel aground at night shall show the anchor lights PLUS:

   • A.Two all-round red lights in a vertical line✓
   • B.A red flashing light
   • C.Three all-round red lights in a vertical line
   • D.A ball-diamond-ball sequence

   Why: Rule 30(d)(i) requires a vessel aground to show the appropriate anchor lights (one or two all-round white lights) PLUS two all-round red lights in a vertical line. These red lights warn other mariners that the vessel is not merely at anchor but is stranded and completely immovable.

4. 4. By day, a vessel aground shall display:

   • A.Three black balls in a vertical line✓
   • B.Two black balls in a vertical line
   • C.A cylinder shape
   • D.A black ball and a cylinder

   Why: Rule 30(d)(ii) requires a vessel aground to display three black balls in a vertical line by day. This contrasts with the anchor shape (one black ball) or NUC (two balls), making three balls the unambiguous 'stuck on the bottom' signal.

5. 5. A vessel of 50 meters or more in length at anchor shall exhibit which lights?

   • A.A forward all-round white light and an aft all-round white light lower than the forward one✓
   • B.A single all-round white light visible all around the horizon
   • C.Two all-round white lights of equal height
   • D.A forward all-round white light and an all-round red light aft

   Why: Rule 30(a) requires a vessel of 50 meters or more at anchor to exhibit a white all-round light forward and a second all-round white light at or near the stern at a lower height than the forward light, creating a distinctive anchor light profile.

6. 6. A vessel aground shall exhibit which lights in addition to the anchor lights prescribed by Rule 30?

   • A.Two all-round red lights in a vertical line✓
   • B.Two all-round red lights and sidelights
   • C.Three all-round red lights in a vertical line
   • D.One all-round red light

   Why: Under COLREGS Rule 30(d)(i), a vessel aground exhibits the anchor lights required by Rule 30(a) or (b) plus two all-round red lights in a vertical line (and, by day, three balls in a vertical line per 30(d)(ii)). These are a status signal identifying the vessel as aground — not a distress signal (distress signals are separately listed in Annex IV) — and do not denote not-under-command or restricted ability to maneuver under Rule 27.

7. 7. A vessel of less than 50 meters in length at anchor shall exhibit which light?

   • A.A single all-round white light where it can best be seen✓
   • B.Two all-round white lights — one forward, one aft
   • C.A white masthead light only
   • D.A flashing all-round white light

   Why: Rule 30(b) requires a vessel under 50 meters at anchor to exhibit a single all-round white light in the forward part of the vessel or where it can best be seen, simpler than the two-light requirement for larger vessels under Rule 30(a).

8. 8. A vessel aground during daylight hours must display which dayshapes?

   • A.Three balls in a vertical line✓
   • B.Two balls in a vertical line
   • C.A single ball
   • D.A ball above a diamond

   Why: Under COLREGS Rule 30(d)(ii), a vessel aground exhibits three balls in a vertical line as her dayshape (in addition to her anchor lights/shape), distinct from the single ball shown by a vessel at anchor under Rule 30(a)(i). The three-ball signal marks the vessel as aground and unable to maneuver. (Vessels under 12 m aground are exempted by Rule 30(f).)

Frequently asked questions

What lights does a vessel show when anchored at night?

A vessel 50 meters or more in length shows two all-around white lights: one forward at the highest point and one aft at a lower level. A vessel under 50 meters may show a single all-around white light positioned where it can best be seen. The daytime equivalent is a single black ball displayed forward.

What additional lights does a vessel show when aground?

In addition to the anchor lights appropriate for her length, a vessel aground shows two all-around red lights in a vertical line. During the day, she shows anchor ball(s) plus three black balls in a vertical line. The two red lights are what distinguish a vessel aground from one merely anchored.

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