Timing of stand-on ship actions for cooperative collision avoidance under calm water condition

Rule 17 of the COLREGS states that a stand-on ship should take cooperative action to avoid a collision when the action of the give-way ship will not be sufficient to avoid a collision. However, most studies on collision avoidance have focused on the action of the give-way ship and not on what the stand-on ship should do. In this study, a novel criterion was developed for assessing when a stand-on ship should take action for collision avoidance that is called the computed distance at collision (CDC). Simulations were performed of the maneuvering motions of two ships in various situations to assess whether or not a collision would occur. The results of the collision assessment were assessed by the CDC, which is calculated from the ship's parameters such as the ship's heading, length, and collision angle between the two ships. Meanwhile, the actual distance (AD) between the two ships can be calculated according to their coordinates. When the CDC is greater than the AD, this means that a collision is inevitable. In other words, the stand-on ship should take action to avoid a collision while the CDC is still less than the AD. Of course, this study may have the following limitations: The study was conducted on the same model ship under calm water conditions. The interactions of hull-propeller-rudder-engine of ship and interaction of hull-hull between the two ships was not considered, and uncertainty of MMG (Maneuvering Modeling Group) model may exist. However, this study should help determine the timing of actions by the stand-on ship for collision avoidance, whether manned or unmanned.