Overtaking or Crossing?

This is a summary of a report from the Master of a vessel that had sailed from a port on the East coast of the UK in daylight and good visibility.

Report Text:

We had just left port and were steering 045 degrees and doing 12 knots. A Roll-on/Roll-off vessel heading to the North according to the AIS was coming up behind us and was going to overtake on our starboard side at a distance of 8 cables.  That was the situation when I came up to relieve the Mate for his dinner.

I went to the aft end of the bridge to have a look at a nearby fishing vessel as it had gone into the radar blind spot.  When I was satisfied that it was going to pass clear I returned forward and noticed the collision alarm on the radar.  The Ro-Ro had altered course to port and had closed the Closest Point of Approach to 0.5 cables with a Time to CPA of 5 minutes.  I put the wheel over to port and steadied up on a northerly course and opened the CPA up to 0.8 cables again.  I kept my eye on the ferry and within minutes it was altering course to port again.  I called the ferry up on VHF channel 16 to ascertain that she had seen me and the officer on watch asked me to go to channel 06 and said to me that he had an alter course position to get to and he would pass ahead off me.  I said that was OK but could he please wait until he was past and clear off me before he altered course again.  I slowed down to approx 9 knots and the ferry was doing approx 17 knots.  I was restricted in slowing down any further due to the fishing vessel astern of me.  The mate came back up to the bridge at this point and the ferry altered course again and crossed our bow at half a mile.  The mate called up the ferry and asked if he thought half a mile is an acceptable distance to cross ahead of another vessel and he said since he was going much faster than us then there was no problem.  We then watched him cross the stern of the other supply boat at approx half a mile again.

CHIRP Comment:

We do not have data recordings from either vessel, but, from the report and also from information received from the manager of the Ro-Ro, we surmise that the reporting vessel had initially been proceeding on an Easterly course out of port before picking up her North Easterly track, whilst the Ro-Ro was Northbound.  If the vessels were in sight of each other at the time, this would imply that this was a crossing situation, with the reporting vessel being the give-way vessel.  Even though the reporting  vessel may subsequently have altered course to port onto her planned North Easterly track, this would not have changed the crossing situation into an overtaking situation, or relieved her of the  obligation to keep clear of the Ro-Ro. As the stand-on vessel, the Ro-Ro would have been obliged to keep her course and speed.

If this interpretation of the situation is correct, it highlights the importance of

• Early identification of the traffic situation on leaving harbour.
• Recognition that a crossing situation may exist with another vessel broad on or abaft the starboard beam.
• Comprehensive description of the traffic situation when the watch is being handed-over.
• Not giving precedence to keeping to the planned track over compliance with the ColRegs.