The known navigational systems in use and methods of navigational decision support perform information functions and as such are helpful in the process of safe conduct of a vessel. However, none of these known systems provides a navigator with ready solutions of collision situations taking account of all the vessels in the proximity of own ship, where the Collision Regulations apply. This paper presents testing results of NAVDEC — new Navigational Decision Supporting System created by research team from Szczecin Maritime University both for ocean going ships and pleasure crafts Tests were carried out in real condition on board container vessel. Testing results were presented on example encounter situation between Hammonia Berolina (own ship) and FR8 Fortitude (target ship). Encounter parameters were compared with data received from Full mission simulator.