Interactive 3D Viewer
3DDrag to rotate
Active lights
Red all-roundRed all-roundPort sidelightStarboard sidelightSternlight
Part CCritical
Rule 27: Not under command or restricted in ability to manoeuvre
NUC and RAM signals announce reduced manoeuvrability and require immediate recognition by others.
Detailed Explanation
NUC and RAM vessels display distinctive signals to warn others of their reduced manoeuvrability and claim priority in encounters.
A
NUC
- (i)two all-round red in vertical line
- (ii)two balls in vertical line
- (iii)if making way, add sidelights and sternlight.
B
RAM (except mineclearance)
- (i)red-white-red all-round
- (ii)ball-diamond-ball
- (iii)if making way add underway lights
- (iv)if at anchor add Rule 30 anchor light/shape.
C
Towing operation severely restricting deviation: show Rule 24(a) plus RAM signals from (b).
D
Dredging/underwater RAM with obstruction: show RAM signals plus
- (i)red-red/two balls on obstructed side
- (ii)green-green/two diamonds on safe-passing side
- (iii)when at anchor use these instead of Rule 30.
E
If vessel size in diving ops makes full (d) impracticable: show red-white-red and rigid Code Flag A (≥1 m) with all-round visibility.
F
Mineclearance: in addition to normal lights/anchor signals, show three all-round green lights or three balls indicating danger within 1000 m.
G
Vessels <12 m (except diving ops) are exempt from this Rule’s signals.
H
These are not distress signals (distress is Annex IV).
Key Points
- NUC: two red all-round lights vertical (by day: two balls)
- RAM: red-white-red all-round (by day: ball-diamond-ball)
- Mine clearance: 3 green all-round lights (do not approach <1000m)
- Making way: add masthead, sidelights, sternlight as applicable
Examples
- At night you see two all-round red lights in a vertical line with no other navigation lights. This is a vessel not under command (NUC) per Rule 27(a), not making way. By day she would show two black balls vertically.
- A cable-laying vessel shows red-white-red all-round lights vertically, plus sidelights and sternlight — she is RAM and making way under Rule 27(b). She also has a diamond and two balls by day.
- A dredger shows red-white-red all-round lights and additionally two red lights on her obstructed side and two green on her clear side per Rule 27(d)(ii). You pass on the side showing green.
Common Mistakes
- Displaying NUC lights (red over red) for a routine machinery breakdown that does not actually remove the ability to manoeuvre.
- Confusing the RAM day shape (ball-diamond-ball) with the aground shape (three balls in a vertical line).
- Forgetting that a dredger showing RAM signals must also indicate the obstruction side and the clear-passage side.