Navigation planning system and navigation planning method

A navigation planning system, comprising:

• processing circuitry configured to:
• acquire planned route information indicating a movable body on the water;
• acquire movable body information including a position, a moving direction, and a speed of the movable body;
• acquire obstacle information including each of a position, a moving direction, and a speed of a plurality of obstacles located in a surrounding area of the movable body;
• calculate a collision risk indicating a risk level of collision between the movable body and an obstacle of the plurality of obstacles based on the movable body information and the obstacle information;
• calculate congestion risk indicating a degree of approaching the plurality of obstacles simultaneously based on the collision risk between the movable body and each of the plurality of obstacles;
• select a maximum collision risk obstacle corresponding to a maximum collision risk among the plurality of obstacles;
• compare the maximum collision risk with a maximum collision risk threshold;
• determine necessity of evasion by comparing the congestion risk with the maximum collision risk threshold;
• and
• set and implement an evasion route different from the navigation planning route for a part of or entire unnavigated route of the navigation planning route when the processing circuitry determines the necessity of the evasion route.