The daytime signal for divers is an international Code Flag ‘A’, at least 750 mm long and 600 mm wide, in the case of a vessel that is less than 10 m. For vessels longer than 10 m, the dive flag must be at least 1 m. It should be placed to ensure all-round visibility. 

During night diving, the vessel must show the international signal for a vessel restricted in its ability to manoeuvre. These must be at least three lights in a vertical line, with the top and bottom being red and the middle one white, only where the size of the vessel makes it impracticable to exhibit the lights and shapes otherwise required. 

For Masters

Be aware that divers in the water may not be near a vessel. A diver who is not operating from a vessel that is displaying a dive flag will be attached to a buoy that has a dive flag attached to a rigid replica of the flag. A master of the vessel must not operate at a speed exceeding 5 knots within 100 m of a vessel or a buoy on which a dive flag is displayed. Divers may ascend at any time.