Merely responding “Okay” isn’t the best way of ensuring that the other vessel actually understands your intentions. And, as Germany’s Bundesstelle für Seeunfalluntersuchung, BSU report into the collision between xontainerships CMV CCNI Rimac and CMV CSAV Petorca near the port of Yangshan, China, shows: Assume nothing.
Under conditions of reduced visibility at 1148, on 21 June 2011, VTS Yangshan, told the Petorca that she was outside the fairway and that a vessel in the fairway was approaching her. Petorca acknowledged the information and told the traffic centre that she intended to return to the northern part of the fairway immediately after the outbound ship passed. She did not mention the ship by name but was referring to the Rimac. VTS Yangshan repeated the information from the Petorca and acknowledged her intentions.
Rimac called VTS Yangshan about 15 seconds later and asked about the oncoming vessel now some 1.5 nm away. The Petorca heard this query and requested the Rimac to maintain her course at 1150. Petorca intended to alter her course a little further to port.