Some combinations of wave length and wave height under certain operational condi-tions may lead to dangerous unstable motions for ships in accordance with the IS Code. The susceptibility of a ship to dangerous phenomenon will depend on the stabil-ity parameters, ship speed, hull shape and ship size. This signifies that the vulnerabil-ity to dangerous responses, including capsizing, and its probability of occurrence in a singular sea state may differ for each ship. During navigation periods these unstable motions are able to be encountered, which may lead to a cargo or equipment damage and the unsafety of the persons on board. The main reason for these causes is rarely known and currently there are just few work such as the International Maritime Organ-ization guidelines which tries to ensure adequate dynamic stability (IMO, MSC.1/Circ.1228, 2007). Ship routing systems are gaining importance in the maritime sector as the use of these systems can lead to the reduction of fuel usage and reduce costs. Therefore, a mitiga-tion of carbon emis¬sions and improvement of maritime safety happens due to the avoidance of bad weather conditions. The implementation of pathfinding algorithms to determine the optimal ship routing has been widely used for transoceanic distances. However, the evaluation of short distance routes with ship-weather routing algorithms is still scarce, due to the low spatial resolution of wave fields. Mixing both concepts, that is to say, implementing the ship routing system with com-mon unstable motions makes the algorithm more complete and useful than it was. Thus, equipping ships with these systems will be profitable for the officers because they will be able to modify the stablished route or, at least, alter the course depending on the danger faced. Results derived from such calculations should only be regarded as a supporting tool during the decision-making process.