Interactive 3D Viewer
3DActive lights
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
(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.