Ships International Collision Regulations Day Signals

Ships International Collision Regulations Day Signals are mast head signals visually indicating the status of a vessel to other vessels on navigable waters during daylight hours whether making-way, anchored, or aground. These signals consist of a set of simple geometric shapes: ball, cylinder, cone, and diamond that are displayed, hung from a mast, in a prescribed manner to indicate a vessel’s operational status; some of these signals maybe somewhat involved.

The meanings of the shapes are defined by the International Regulations for Preventing Collisions at Sea (ColRegs).


Day shapes from COLREG

Day shapes are black in color and their sizes are determined by the ColRegs, for instance the size of the ball is not less than 0.6 meter diameter. The vertical distance between shapes is at least 1.5 meters. Vessels of less than 20 meters length may use shapes of smaller size commensurate with the size of the vessel.

Day shapes of standard and reduced sizes are both commercially available. Day shapes are commonly constructed from a light weight frame covered with fabric and are designed to be collapsible for ease of storage.


A US Navy Seaman lowers day shapes: “ball, diamond, ball” signaling the end of restricted maneuvering

Ships International Collision Regulations Day Signals

Day shapes are designed to correspond to the various navigation lights required to be shown at night, and are required to be complied with by day from sunrise to sunset. The appropriate lights may also be displayed during the day at times of restricted visibility or other necessary circumstances.[3] Vessels under 7 meters are generally not required to display day shapes even if they are required to display lights at night.

A square black flag displayed over the ball may be used as a distress signal.

Some of the most common signals are as follows:

Navigation status Day shape Restriction
Vessel under sail & power Cone > 12m
Anchored Ball > 7m (not in channel) > 20m (in anchorage)
Constrained by draft Cylinder
Aground 3 balls (vert. line) > 12m
Not under command 2 balls (vert. line) > 12m
Restricted in ability to maneuver 1 ball+1 diamond+1 ball > 12m (except dive boats)
Fishing (commercial) 2 cones (vert. line) > 20m (but must display (nets or trawling) basket shape
Vessel towing Diamond Tow > 200m
Vessel being towed Diamond Tow > 200m