Comparisons
NUC vs RAM — definitions, lights, shapes
NUC and RAM vessels both show red all-round lights, for different reasons: a NUC vessel because of some exceptional circumstance, a RAM vessel because of the nature of her work. The table shows what tells them apart, row by row.
Comparison study notes and reference passages. Read the linked complete rules, including qualifications, exceptions and any publication notes; translated study text is not an official instrument.
Side by side
| Aspect | NUC — Not Under Command | RAM — Restricted in Ability to Manoeuvre |
|---|---|---|
| Definition (3(f) / 3(g)) | NUC — Not Under Command(f) The term vessel not under command means a vessel which through some exceptional circumstance is unable to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel. | RAM — Restricted in Ability to Manoeuvre(g) The term vessel restricted in her ability to maneuver means a vessel which from the nature of her work is restricted in her ability to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel. The term vessels restricted in their ability to maneuver shall include but not be limited to: (i) a vessel engaged in laying, servicing or picking up a navigation mark, submarine cable or pipeline; (ii) a vessel engaged in dredging, surveying or underwater operations; (iii) a vessel engaged in replenishment or transferring persons, provisions or cargo while underway; (iv) a vessel engaged in the launching or recovery of aircraft; (v) a vessel engaged in mine clearance operations; (vi) a vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course. |
| Lights and day shapes (27(a) / 27(b)) | NUC — Not Under CommandNUC: two all-round red lights and two black balls vertically. When making way, add sidelights and sternlight, without masthead lights. Rule 27(g) provides the under-12 m exemption except diving vessels. | RAM — Restricted in Ability to ManoeuvreRAM other than mine clearance: red-white-red all-round lights and ball-diamond-ball. When making way, add masthead light(s), sidelights and sternlight. Rule 27(b)(iv) adds anchor signals; dredging/underwater operations have the distinct provisions of 27(d), and mine clearance uses 27(f). |
| Who keeps clear (18) | Same for bothRule 18 does not rank NUC above RAM. Its opening exceptions are Rules 9, 10 and 13; fishing vessels underway keep clear of NUC/RAM so far as possible. Equipment failure only creates NUC when Rule 3(f) is actually met; responsibility under Rule 2 remains. | |
| Sound signal in restricted visibility (35(c)) | Same for both(c) A vessel not under command, a vessel restricted in her ability to maneuver, a vessel constrained by her draft, a sailing vessel, a vessel engaged in fishing and a vessel engaged in towing or pushing another vessel shall, instead of the signals prescribed in paragraphs (a) or (b) of this Rule, sound at intervals of not more than 2 minutes three blasts in succession, namely one prolonged followed by two short blasts. | |
| At anchor in restricted visibility (35(g) / 35(d)) | NUC — Not Under Command(g) A vessel at anchor shall at intervals of not more than one minute ring the bell rapidly for about 5 seconds. In a vessel of 100 meters or more in length the bell shall be sounded in the forepart of the vessel and immediately after the ringing of the bell the gong shall be sounded rapidly for about 5 seconds in the after part of the vessel. A vessel at anchor may in addition sound three blasts in succession, namely one short, one prolonged and one short blast, to give warning of her position and of the possibility of collision to an approaching vessel. | RAM — Restricted in Ability to Manoeuvre(d) A vessel engaged in fishing, when at anchor, and a vessel restricted in her ability to maneuver when carrying out her work at anchor, shall instead of the signals prescribed in paragraph (g) of this Rule sound the signal prescribed in paragraph (c) of this Rule. |
Who keeps clear, and the special cases
Rule 18Power-driven and sailing vessels keep out of the way of both, and fishing vessels do so as far as possible; Rule 18 ranks neither one above the other.
- Rule 27(c)A tow that cannot deviate from her course adds the RAM lights or shapes to her towing lights.
Official text
(c) A power-driven vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course shall, in addition to the lights or shapes prescribed in Rule 24(a), exhibit the lights or shapes prescribed in subparagraphs (b)(i) and (ii) of this Rule. - Rule 27(d)Dredging or underwater work with an obstruction: two reds (or two balls) on the obstructed side, two greens (or two diamonds) on the side where you may pass.
Official text
(d) A vessel engaged in dredging or underwater operations, when restricted in her ability to maneuver, shall exhibit the lights and shapes prescribed in subparagraphs (b)(i), (ii) and (iii) of this Rule and shall in addition, when an obstruction exists, exhibit: (i) two all-round red lights or two balls in a vertical line to indicate the side on which the obstruction exists; (ii) two all-round green lights or two diamonds in a vertical line to indicate the side on which another vessel may pass; (iii) when at anchor, the lights or shapes prescribed in this paragraph instead of the lights or shape prescribed in Rule 30. - Rule 27(g)Under 12 metres, except when diving, a vessel need not show these lights and shapes.
Official text
(g) Vessels of less than 12 meters in length, except those engaged in diving operations, shall not be required to exhibit the lights and shapes prescribed in this Rule.
Read the underlying rules
Frequently asked questions
What does NUC mean on a vessel?
(f) The term vessel not under command means a vessel which through some exceptional circumstance is unable to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel.
What does RAM mean on a vessel?
(g) The term vessel restricted in her ability to maneuver means a vessel which from the nature of her work is restricted in her ability to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel. The term vessels restricted in their ability to maneuver shall include but not be limited to:
(i) a vessel engaged in laying, servicing or picking up a navigation mark, submarine cable or pipeline;
(ii) a vessel engaged in dredging, surveying or underwater operations;
(iii) a vessel engaged in replenishment or transferring persons, provisions or cargo while underway;
(iv) a vessel engaged in the launching or recovery of aircraft;
(v) a vessel engaged in mine clearance operations;
(vi) a vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course. RAM other than mine clearance: red-white-red all-round lights and ball-diamond-ball. When making way, add masthead light(s), sidelights and sternlight. Rule 27(b)(iv) adds anchor signals; dredging/underwater operations have the distinct provisions of 27(d), and mine clearance uses 27(f).
What lights does a NUC vessel show?
NUC: two all-round red lights and two black balls vertically. When making way, add sidelights and sternlight, without masthead lights. Rule 27(g) provides the under-12 m exemption except diving vessels.
What lights does a RAM vessel show?
RAM other than mine clearance: red-white-red all-round lights and ball-diamond-ball. When making way, add masthead light(s), sidelights and sternlight. Rule 27(b)(iv) adds anchor signals; dredging/underwater operations have the distinct provisions of 27(d), and mine clearance uses 27(f). (d) A vessel engaged in dredging or underwater operations, when restricted in her ability to maneuver, shall exhibit the lights and shapes prescribed in subparagraphs (b)(i), (ii) and (iii) of this Rule and shall in addition, when an obstruction exists, exhibit:
(i) two all-round red lights or two balls in a vertical line to indicate the side on which the obstruction exists;
(ii) two all-round green lights or two diamonds in a vertical line to indicate the side on which another vessel may pass;
(iii) when at anchor, the lights or shapes prescribed in this paragraph instead of the lights or shape prescribed in Rule 30.
What is the difference between NUC and RAM lights?
NUC: two all-round red lights and two black balls vertically. When making way, add sidelights and sternlight, without masthead lights. Rule 27(g) provides the under-12 m exemption except diving vessels. RAM other than mine clearance: red-white-red all-round lights and ball-diamond-ball. When making way, add masthead light(s), sidelights and sternlight. Rule 27(b)(iv) adds anchor signals; dredging/underwater operations have the distinct provisions of 27(d), and mine clearance uses 27(f).
What are the NUC and RAM day shapes?
(a) A vessel not under command shall exhibit:
(i) two all-round red lights in a vertical line where they can best be seen;
(ii) two balls or similar shapes in a vertical line where they can best be seen;
(iii) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight. (b) A vessel restricted in her ability to maneuver, except a vessel engaged in mine clearance operations, shall exhibit:
(i) three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white;
(ii) three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond;
(iii) when making way through the water, a masthead light or lights, sidelights and a sternlight, in addition to the lights prescribed in subparagraph (i);
(iv) when at anchor, in addition to the lights or shapes prescribed in subparagraphs (i) and (ii), the light, lights or shape prescribed in Rule 30.
Which has priority — NUC or RAM?
Rule 18 does not rank NUC above RAM. Its opening exceptions are Rules 9, 10 and 13; fishing vessels underway keep clear of NUC/RAM so far as possible. Equipment failure only creates NUC when Rule 3(f) is actually met; responsibility under Rule 2 remains.
Is a fishing vessel NUC or RAM?
(d) The term vessel engaged in fishing means any vessel fishing with nets, lines, trawls or other fishing apparatus which restrict maneuverability, but does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict maneuverability. Rule 18 does not rank NUC above RAM. Its opening exceptions are Rules 9, 10 and 13; fishing vessels underway keep clear of NUC/RAM so far as possible. Equipment failure only creates NUC when Rule 3(f) is actually met; responsibility under Rule 2 remains.
Reviewed by Ramon Curto, Nautical teacher at IECNPC · Last reviewed: