COLREGS Rule 27 — Navigation Lights
Vessel Restricted in Ability to Maneuver — Navigation Lights (COLREGS Rule 27)
A vessel restricted in ability to maneuver (RAM) shows three all-around lights in a vertical line — red, white, red. When making way it adds masthead lights, sidelights, and a sternlight. The dayshape is a ball over a diamond over a ball. Dredges and vessels with underwater obstructions show additional colored signals indicating which side is clear.
Condition: Engaged in work that restricts its ability to maneuver as required by the Rules (dredging, cable laying, minesweeping, replenishment at sea, etc.)
Navigation lights required
| Light | Color | Arc | Position |
|---|---|---|---|
| All-around light (top) — red | Red | 360° | Top of three vertical all-around lights |
| All-around light (middle) — white | White | 360° | Middle of three vertical all-around lights |
| All-around light (bottom) — red | Red | 360° | Bottom of three vertical all-around lights |
| Masthead light(s) (when making way) | White | 225° | Forward, as required by vessel length (Rule 23) |
| Port sidelight (when making way) | Red | 112.5° | Port side |
| Starboard sidelight (when making way) | Green | 112.5° | Starboard side |
| Sternlight (when making way) | White | 135° | Stern |
| Obstruction side — all-around red lights (dredging/underwater ops) | Red | 360° | Two all-around red lights in a vertical line on the obstructed side |
| Clear side — all-around green lights (dredging/underwater ops) | Green | 360° | Two all-around green lights in a vertical line on the clear side |
Masthead light(s) (when making way): Added when the vessel is making way — unlike NUC, a RAM vessel making way DOES show masthead lights
Port sidelight (when making way): Added when making way
Starboard sidelight (when making way): Added when making way
Sternlight (when making way): Added when making way
Obstruction side — all-around red lights (dredging/underwater ops): Night signal only; indicates the side passage is NOT safe
Clear side — all-around green lights (dredging/underwater ops): Night signal only; indicates the side where passage IS safe
Dayshapes
| Shape | Position | When displayed |
|---|---|---|
| Ball over diamond over ball | Where they can best be seen | During daylight hours when restricted in ability to maneuver |
| Two balls in a vertical line (obstructed side) | On the side where passage is NOT safe | Dredging or underwater operations with an obstruction on one side — during daylight |
| Two diamonds in a vertical line (clear side) | On the side where passage IS safe | Dredging or underwater operations with a clear side — during daylight |
Exceptions and size rules
- →A RAM vessel under 12 m is not required to show RAM lights or shapes.
- →A vessel engaged in mineclearance operations is specifically excluded from showing RAM lights — it shows its own special signals instead.
- →A RAM vessel that is towing and unable to comply with Rule 27(b) signals may substitute the towing lights for the RAM lights.
Inland Rules differences
- !US Inland Rules are identical to COLREGS for RAM lights — no practical difference.
Common exam mistakes
- ✗Confusing RAM (red/white/red) with NUC (red/red) — RAM has a white light in the middle; NUC does not.
- ✗Forgetting that RAM vessels making way DO show masthead lights — unlike NUC vessels.
- ✗Reversing the dredging side signals: two RED lights on the OBSTRUCTED side; two GREEN lights on the CLEAR side.
- ✗Missing that a RAM vessel under 12 m is exempt from the RAM signals.
USCG exam questions — Vessel Restricted in Ability to Maneuver
These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.
1. A vessel not under command (NUC) shall show:
- A.One all-round red light and a flashing white light
- B.Two all-round white lights in a vertical line
- C.An all-round red light over an all-round white light
- D.Two all-round red lights in a vertical line and, when making way, sidelights and sternlight✓
Why: Rule 27(a) prescribes two all-round red lights in a vertical line for a NUC vessel. When making way, she adds sidelights and a sternlight. Red over red — not white — is the critical identifier distinguishing NUC from fishing (red over white) or RAM (red-white-red).
2. By day, what shapes does a vessel restricted in its ability to maneuver display?
- A.A black cylinder
- B.Two black balls in a vertical line
- C.Ball, diamond, ball — three shapes in a vertical line✓
- D.Two cones with apices together
Why: Rule 27(b)(ii) requires three shapes in a vertical line by day for a RAM vessel: ball on top, diamond in the middle, and ball at the bottom. This mirrors the night pattern of red-white-red lights.
3. A vessel engaged in dredging or underwater operations, when underway and making way, shows in addition to the RAM lights:
- A.Two all-round red lights on the obstruction side and two all-round green lights on the clear side✓
- B.A flashing red light on the obstruction side
- C.An all-round white light on the side where vessels may pass
- D.A yellow diamond shape
Why: Rule 27(d) requires a dredging or underwater operations vessel to show two all-round red lights vertically on the side where the obstruction exists and two all-round green lights vertically on the side where passing is safe. Red means restricted passage; green means go.
4. A vessel constrained by her draft may in addition to the lights prescribed for a power-driven vessel underway show:
- A.Three all-round red lights in a vertical line OR a cylinder shape by day✓
- B.Two all-round red lights in a vertical line OR two black balls by day
- C.An all-round red light over an all-round white light
- D.A flashing red light and a cylinder
Why: Rule 28 permits (not requires) a vessel constrained by her draft to show three all-round red lights in a vertical line OR a cylinder shape by day. This is the only light/shape combination in the COLREGS that uses three vertical red lights; NUC uses only two.
5. A vessel engaged in underwater operations that is unable to deviate from its course shall show the RAM lights PLUS, on the side with the obstruction, which additional lights?
- A.Two all-round red lights vertically and on the clear side two all-round green lights vertically✓
- B.A flashing red light on the obstruction side only
- C.An all-round white light on each side
- D.A yellow all-round light above the RAM lights
Why: Rule 27(d) prescribes that a vessel conducting underwater operations that is at anchor or underway but impeded shall show two all-round red lights (vertically) on the obstruction side and two all-round green lights (vertically) on the safe passing side, in addition to the RAM lights.
6. Under COLREGS Rule 3(g), which vessel qualifies as restricted in her ability to maneuver?
- A.A vessel engaged in dredging, surveying, or underwater operations✓
- B.A vessel with a temporary engine malfunction causing reduced speed
- C.A vessel waiting at anchor for a berth to become available
- D.A vessel towing astern with a tow less than 25 meters in length
Why: Rule 3(g) explicitly includes vessels engaged in dredging, surveying, or underwater operations among RAM vessels, because these activities physically restrict the vessel's ability to deviate from her course.
7. A vessel restricted in her ability to maneuver (RAM) underway and making way shall exhibit which lights in addition to the RAM identity lights?
- A.Masthead lights, sidelights, and a stern light✓
- B.Sidelights and a stern light only
- C.Masthead lights and sidelights only
- D.All-round white lights and sidelights
Why: Under COLREGS Rule 27(b)(iii), a vessel restricted in her ability to maneuver when making way through the water shall exhibit masthead light(s), sidelights, and a sternlight in addition to the RAM identity lights (the red-white-red all-round lights of Rule 27(b)(i), with the ball-diamond-ball dayshapes by day under 27(b)(ii)).
8. A vessel restricted in her ability to maneuver during daylight hours must display which dayshapes?
- A.Ball, diamond, ball in a vertical line✓
- B.Cone, ball, cone in a vertical line
- C.Three balls in a vertical line
- D.Diamond, ball, diamond in a vertical line
Why: Rule 27(b)(ii) requires a RAM vessel to exhibit three shapes in a vertical line — a ball, a diamond, and a ball from top to bottom — which corresponds visually to the red-white-red all-round light pattern shown at night.
Frequently asked questions
- What lights does a RAM vessel show when making way?
- A RAM vessel making way shows: three all-around lights in a vertical line (red top, white middle, red bottom); masthead light(s) appropriate for its length; port and starboard sidelights; and a white sternlight. The full complement distinguishes it from a NUC vessel, which never shows masthead lights.
- How do you tell which side of a dredge is safe to pass at night?
- Two all-around red lights in a vertical line mark the obstructed side — do not pass on that side. Two all-around green lights in a vertical line mark the clear side — passage is safe there. By day, two balls indicate the obstructed side and two diamonds indicate the clear side.
- What is the RAM dayshape?
- The RAM dayshape is three shapes in a vertical line: a ball on top, a diamond in the middle, and a ball on the bottom. This is often compared to the NUC dayshape (two balls) and the aground dayshape (three balls) — the diamond in the middle is the key differentiator for RAM.
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