What is meaning of Tactical Diameter of ships?

Tactical Diameter is the transfer for a turn of 180°, which is almost equal to the max transfer and about the maximum advance. The diameter will vary, based on the speed, the amount of rudder used and the trim.

• When the vessel is trimmed by the stern, the tactical diameter of  turn is increased
• When the vessel is trimmed by the head, the tactical diameter of turn is decreased
• The vessel with a list will take longer to execute the turn, and, when turned into the list, will develop a larger circle
• The vessel with a right-hand turn propeller, if making a turn to port, will end up with a smaller diameter than starboard due tothe effect of transverse thrust.