Collision avoidance is a critical concern in marine navigation, where safe and efficient vessel operation is based on accurate and timely decision making. This paper presents a Decision Support System (DSS) for maritime collision avoidance that combines a waypoint-based trajectory planning algorithm with speed adjustment strategies. The proposed algorithm generates an optimized route by calculating waypoints that safely guide a vessel around other ships while adjusting speed to prevent imminent collisions. The DSS integrates input on vessel maneuvering capabilities, standard seamanship, and maritime traffic behavior to produce a flexible and responsive collision avoidance strategy that can maintain safe distances in complex navigational environments. A dynamic simulation model is used to evaluate the effectiveness of suggested routes, simulating real-world navigation scenarios, and the response of the vessel when actuating the calculated trajectory. Simulation experiments demonstrate the ability of the system to adapt to various collision scenarios, ensuring vessel safety while minimizing deviations from the intended course. The results indicate that the proposed DSS can significantly enhance navigational safety, reducing the risk of collision.