Day shapes: black balls, cones, diamonds and cylinders

One, two or three black balls

A single black ball is the general day signal for a vessel at anchor under Rule 30. Two black balls in a vertical line indicate not under command under Rule 27. Three black balls in a vertical line indicate aground under Rule 30. The full rule determines which display is required for a particular vessel and contains exceptions.

These meanings explain why speed alone is insufficient. A vessel can be stopped but underway, anchored, aground or unable to manoeuvre because of an exceptional circumstance. The distinction changes the information another mariner needs. Give an anchored vessel appropriate space for her hull and swing; a mark or shape does not prescribe one universal passing distance.

Ball–diamond–ball and the black cylinder

Ball–diamond–ball identifies a vessel restricted in her ability to manoeuvre because of the nature of her work. Examples include some surveying, cable work and underwater operations. It differs from not under command, which arises from an exceptional circumstance. The operation and the applicable encounter still need to be understood.

A power-driven vessel constrained by her draught may show a black cylinder under Rule 28. This status concerns draught in relation to the available depth and width, severely limiting deviation from her course. It is not a generic label for a large ship. Rule 18 sets out the relevant responsibilities, including action by other vessels to avoid impeding her safe passage when circumstances admit.

Some operations use additional shapes, such as dredging signals showing an obstruction side and a side where another vessel may pass. Ball–diamond–ball recognition is a starting point; the complete display and the full text of Rule 27 provide the detail.

Fishing cones and a motor-sailing cone

Two cones with their apexes together identify a vessel engaged in fishing under Rule 26. The definition refers to fishing apparatus that restricts manoeuvrability. A boat with fishing rods or trolling lines is not automatically a vessel engaged in fishing for these purposes. The same basic fishing day shape is used for trawling and other qualifying fishing.

A vessel under sail that is also propelled by machinery displays a cone with its apex down, forward where it can best be seen, under International Rule 25(e). She is power-driven for the steering and sailing rules. Look for the signal and the actual operation rather than assuming that raised sails alone establish a sailing vessel.

A diamond can warn of a long tow

Rule 24 prescribes a diamond for a tow exceeding 200 m, measured from the stern of the towing vessel to the after end of the tow. Where prescribed it is displayed by the towing vessel and by the vessel or object being towed. A towing relationship may be difficult to appreciate from one vessel alone, so keep looking for the rest of the operation.

A long tow is not automatically a vessel restricted in her ability to manoeuvre. The Rule 3 definition and the operation determine whether that status applies. This is a useful revision example because memorising “diamond equals towing” misses both the length condition and the distinct ball–diamond–ball signal.

Connect recognition to a safe encounter

Answer each recognition exercise in two stages: describe the observed pattern, then explain the operation it identifies. After feedback, compare the most easily confused signals: two balls with three balls, one downward cone with fishing cones, and a single diamond with ball–diamond–ball.

When preparing for a voyage or exam, revisit the matching night lights as a separate task. A daytime signal and a night display may describe the same status, but they are different observations. Neither removes the need to consider visibility, collision risk, channels, traffic schemes and the responsibilities of both vessels.