PPT Slide
A big ship, with the superstructure on his stern, will have turned up to 30 -40 degrees before the antenna (or the part of the ship which the arpa radar is tracking), on the super-structure has deviated from the original track. The arpa radar needs another minute to detect the change in course, which means that a tanker could have changed the course up to 60 degrees before it is detected in the radar on a ship or in a VTS.