7.3 Special Category Vessels: NUC, RAM, CBD, Pilot & Anchored (Rules 27-31)

7.3 Special Category Vessels: NUC, RAM, CBD, Pilot & Anchored (Rules 27-31)

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Rule 27: Not Under Command (NUC) & Restricted Manoeuvrability (RAM)

Rule 27 distinguishes an exceptional inability to manoeuvre (NUC) from a restriction caused by work (RAM). Vessels under 12m, except those engaged in diving, are not required to display its lights and shapes.

1. Vessel Not Under Command (NUC) - Rule 27(a)

A vessel not under command (Rule 3(f)) is unable through exceptional circumstance (engine failure, rudder loss, steering gear breakdown) to manoeuvre as required by the Rules:

• Night Lights: Two all-round red lights in a vertical line (Mnemonic: "Red over red, captain is dead").
• Day Shape: Two black balls in a vertical line.
• Making Way: Displays sidelights and sternlight only when making way through the water; extinguished when stopped.
• Crucial Rule: An NUC vessel never exhibits masthead steaming lights.

2. Vessel Restricted in Ability to Manoeuvre (RAM) - Rule 27(b)

A vessel whose work restricts manoeuvrability (Rule 3(g)) (cable laying, dredging, surveying, replenishment, flight operations, heavy towing):

• Night Lights: Three all-round lights vertically: Red-White-Red (Mnemonic: "Red-white-red, working instead").
• Day Shape: Three shapes vertically: Ball-Diamond-Ball.
• Making Way: Exhibits masthead light(s), sidelights, and sternlight when making way through the water. Extinguishes them when stopped (retaining only Red-White-Red).
• At Anchor: General RAM vessels add the Rule 30 anchor signals. Dredging/underwater-operation vessels under Rule 27(d) instead display that paragraph's signals in place of Rule 30 signals.

3. Dredging and Underwater Operations - Rule 27(d)

Dredging vessels exhibit RAM lights/shapes plus directional passing signals:

• Obstructed Side (Do Not Pass):
  • Night: Two all-round red lights vertically.
  • Day: Two black balls vertically.
• Clear Side (Safe to Pass):
  • Night: Two all-round green lights vertically.
  • Day: Two black diamonds vertically.
• Mnemonic: Green diamonds are precious (pass here); red balls indicate danger (keep clear).

4. Small Diving Operations - Rule 27(e)

When vessel size makes the full Rule 27(d) signals impracticable, Rule 27(e) requires:

• Lights: Three all-round lights vertically, red-white-red.
• Day signal: A rigid replica of Code Flag A (Alpha) at least 1 metre high, with all-round visibility.
• Passing action: Keep well clear at slow speed. Check local restrictions and allow sea room for divers and equipment; Rule 27 specifies no universal 100m clearance.

5. Mine Clearance Vessels - Rule 27(f)

• Night Lights: Three all-round green lights in a cross configuration: one at the foremast head and one at each yardarm.
• Day Shape: Three black balls in the same cross configuration.
• Danger Zone: Dangerous to approach within 1,000 metres of the mineclearance vessel in any direction.

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Rule 28: Vessels Constrained by Their Draught (CBD)

A power-driven vessel severely restricted in her ability to deviate from course by available depth and width of navigable water:

• Night Lights: In addition to power-driven lights (mastheads, sidelights, sternlight), may exhibit three all-round red lights vertically (Mnemonic: "Three reds in a row, no place to go").
• Day Shape: A black cylinder displayed where best seen.
• Skipper's Responsibility: Under Rule 18(d), vessels other than NUC or RAM shall, if circumstances admit, avoid impeding the safe passage of a CBD vessel displaying Rule 28 signals. In deep-water channels, large laden tankers cannot alter course outside dredged tracks without grounding.

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Rule 29: Pilot Vessels

A vessel engaged on pilotage duty:

• Night Lights: Two all-round lights vertically at the masthead: White over Red (Mnemonic: "White over red, pilot ahead").
• Underway: Sidelights and sternlight. When anchored, anchor lights plus white-over-red.
• Prohibition: A pilot vessel on duty never displays a forward masthead steaming light.
• Day Signal: Rule 29 prescribes no special day shape. Code Flag H (Hotel) means 'I have a pilot on board'; local pilot-service identification flags are separate from this Rule.

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Rule 30: Anchored Vessels & Vessels Aground

Static collision hazards requiring prompt identification:

1. Anchored Vessels

• Vessels < 50 Metres: An all-round white light where best seen. Day shape: one black ball forward.
• Vessels ≥ 50 Metres: Two all-round white lights: one forward (higher) and one aft. Day shape: one black ball forward.
• Vessels ≥ 100 Metres: Must also use available working lights to illuminate decks.
• Exemption: Vessels < 7m are exempt only when not in or near a narrow channel, fairway or anchorage, or where other vessels normally navigate.

2. Vessels Aground

A vessel in contact with the seabed exhibits anchor lights according to length PLUS two all-round red lights vertically (NUC lights). Day shape: Three black balls in a vertical line ("Three balls = hard aground"). Vessels under 12m are exempt from the additional two red lights and three balls, but not automatically from anchor-light requirements.

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Seaplanes and WIG Craft: Rule 31

If a seaplane or WIG craft cannot practicably display the prescribed lights and shapes in their specified positions, it must display them as closely similar in character and position as possible. This does not remove its collision-avoidance duties.

Source: International Rule31.

Summary Reference: Special Categories