Know your Nautical terminology
CBDR
CBDR stands for Constant Bearing, Decreasing Range. These are the four letters every OOD hopes they don't hear on their watch. CBDR = collision course.
The actions taken by the OOD depend on the rules of the road which determine which ship is the 'burdened' ship and which is the 'stand-on' ship.
The burdened ship has the duty to maneuver to avoid an impending collision and the stand-on ship has the duty to maintain course and speed. The burdened ship has only to change their course and/or speed to avoid a collision. Generally course changes should be at least 30 degrees so that the aspect ratio change is obvious to the other ship. If everyone is on their toes means that nothing happens.
This doesn't mean that the stand-on ship should maintain their right of way all the way to a collision. If the other ship hasn't started maneuvering by about 3nm I would be on the bridge-to-bridge radio and have a call in to the captain. The captain will NEVER criticize you for calling him.
Just remember, a collision at sea can ruin your whole day.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)