My vessel was in an Easbound Gulf of Aden Group Transit, escorted by a warship, and coming to the final waypoint where convoy would split up and vessels go their separate ways.
There were two columns of ships. My ship was the lead vessel in the port column.
At around 0330 Local Time the vessel two behind me, a fully laden tanker bound for Singapore (per AIS), began to increase her speed. At 0430 LT, my duty officer called me to the bridge, concerned about the actions of this tanker. When I came to the bridge, I found the tanker five cables on my port side, in line with me and doing the same speed, 12 knots.
She showed no sign of altering away and made no attempt to contact me. Other vessels were still in the basic convoy formation.
I kept in the convoy as I could not go to starboard where the lower column lead vessel was on my starboard beam, distance six cables, and same speed. Speed could not be reduced as ship astern also in convoy formation and distance under 1mile.
Shortly before the final way point when the convoy escort warship was calling all vessels that the convoy could now disband, the tanker, still the overtaking vessel and still at only five cables distance on my port beam, called me up and asked me to reduce speed and go around her stern, i.e. a hard over to port once enough room, as she would increase to her max speed of 14 knots and continue on her east-bound course towards Singapore. She said she knew I was bound Northeast (from our AIS) and she was bound for the East.
I asked her why she had not overtaken me on my starboard side and when free to do so, i.e. at the final way point, and advised her that she should reduce her own speed, and keep well clear of me. She made no response but continued her course and speed with no increase in the latter.
The situation being impossible and dangerous, I reduced speed and let her continue ahead, then swung around her stern and continued back once clear to our intended course heading towards the Persian Gulf.
Before making our large alteration I asked her why she had not overtaken me on my starboard side? There was plenty of sea-room to pass to starboard of both my vessel and the vessel in the lower column and abeam to starboard. With a nice big ocean, why take the most awkward and dangerous course?
We followed up this report with the manager of the tanker who, in turn, followed it up with the Master and provided us with a comprehensive report In summary, at 0300, with two hours remaining to the convoy dispersal point, the tanker had requested permission from the warship to leave the convoy in order to increase speed and clear the piracy prone area at full speed. Permission was granted and the tanker altered course to port and commenced increasing speed as the entire convoy formation was on her starboard side. Thereafter there were various communications between the tanker, the warship and other ships in the convoy.
Following from the review of this report, the manager of the tanker has advised all vessels in its fleet that vessels should stay in the convoy until it is dismissed by the warship.
We make the general point that operating in convoys requires “lane discipline”. Particular care is required as the convoy disperses. By breaking away early from the convoy a few miles from the final waypoint and gradually increasing speed, it is not apparent that her security was enhanced and the saving in overall voyage time for the tanker was minimal. However it caused anxiety for at least one other vessel that was properly maintaining convoy discipline.