Complete reference index
Read each signal’s meaning, context and limitations. Use the interactive cards above for visual or listening practice.
Diving: rigid Alfa replica
A diving vessel whose size makes the full underwater-work display impracticable shows a rigid replica of International Code flag A.
Rigid white-and-blue swallowtail Alfa replica, at least 1 metre high, with all-round visibility. A white-and-blue swallowtail board above a vessel. Keep well clear at slow speed. The size/impracticability condition matters; ordinary diving work may require the full Rule 27(d) display. The corresponding lights are red–white–red.
Source: Rule 27(e)
At anchor
A vessel at anchor shows one black ball where it can best be seen, in the fore part.
One black ball. One black ball above a vessel. A ball is not a “safe to pass close” signal. Vessels under 7 m have a limited exemption when away from channels, fairways, anchorages and normal navigation areas.
Source: Rule 30(a), (e)
Not under command
Exceptional circumstances prevent the vessel from manoeuvring as required by the Rules and therefore from keeping out of another vessel’s way.
Two black balls vertically. Two black balls in a vertical line. This is not merely a vessel choosing to stop or a yacht sailing without an engine. Do not confuse two balls with the three-ball aground signal.
Source: Rule 27(a)
Restricted in ability to manoeuvre
The nature of the vessel’s work restricts its ability to manoeuvre as required by the Rules.
Black ball, diamond, ball in a vertical line. Black ball above a diamond above another ball. The restriction comes from the work, not simply a mechanical failure or draught. Mineclearance and some diving operations have particular display provisions.
Source: Rule 27(b)
Aground
The vessel is aground rather than merely at anchor.
Three black balls vertically. Three black balls in a vertical line. Vessels under 12 m are exempt from these additional aground shapes. The day display is three balls—not an anchor ball added to three more balls.
Source: Rule 30(d), (f)
Constrained by draught
A power-driven vessel severely restricted by its draught in relation to the available depth and width of navigable water may show this shape.
One black cylinder. One upright black cylinder. This is an International COLREG signal, not a general claim that every large vessel is constrained. Its display is optional under Rule 28; assess the actual waterway and applicable duties.
Source: Rule 28 · International
Under sail and machinery
A vessel proceeding under sail while also propelled by machinery is a power-driven vessel for the navigation Rules.
One black cone, apex down, forward where it can best be seen. A black cone with its point down. Sails alone do not establish sailing-vessel status. Merely running an engine for charging, without using machinery for propulsion, is not the same condition.
Source: Rule 25(e)
Engaged in fishing
Fishing apparatus restricts manoeuvrability. The same day shape is used for trawling and other qualifying fishing.
Two black cones vertically with their apexes together. Two cones meeting at their tips, like an hourglass. This shape does not distinguish trawling from other fishing. A boat trolling with gear that does not restrict manoeuvrability does not qualify just because it is catching fish.
Source: Rule 26(b), (c)
Tow longer than 200 metres
The towing vessel and the vessel or object being towed show a diamond when the length of the tow exceeds 200 m.
One black diamond where best seen. One black diamond. Tow length is measured from the stern of the towing vessel to the after end of the tow—not just the towing line. There is no general diamond requirement for every short tow.
Source: Rule 24(a), (e)
Dredging or underwater work with an obstruction
The central display indicates restricted ability to manoeuvre. Two balls identify the obstructed side; two diamonds identify the side on which another vessel may pass.
Central ball–diamond–ball; two balls on one side and two diamonds on the other. A central ball–diamond–ball with two balls to one side and two diamonds to the other. The passing side is relative to the working vessel, not a fixed port/starboard rule for your yacht. “May pass” still requires safe clearance, depth and an assessment of the whole situation.
Source: Rule 27(d)
Mineclearance operations
It is dangerous for another vessel to approach within 1,000 m of this vessel.
Three black balls: one near the foremast head and one at each end of the fore yard. One black ball above two widely spaced black balls. This is not the vertical three-ball aground display. The vessel also carries the applicable power-driven or anchor signals; the danger distance is 1,000 metres.
Source: Rule 27(f)
Fishing gear extending more than 150 metres
A vessel engaged in fishing other than trawling shows an additional cone apex upwards in the direction of outlying gear extending more than 150 m horizontally.
Fishing cones apex-to-apex, plus an upright cone towards the gear. Two cones meeting at their tips, with an additional upright cone off to one side. The extra cone identifies the direction of the gear, not a safe passage side. Do not mistake it for the point-down motoring-sailboat cone.
Source: Rule 26(c)(ii)
Severely restricted towing with a long tow
A towing operation severely restricting the tug and tow’s ability to deviate displays restricted-manoeuvrability signals in addition to the relevant towing signals.
Ball–diamond–ball, plus the towing diamond when the tow exceeds 200 m. A vertical ball–diamond–ball and a separate diamond. Not every towing operation qualifies as restricted in ability to manoeuvre. The separate towing diamond depends on length; the central diamond belongs to the work-status display.
Source: Rules 27(c) and 24(a)