A potential close quarters situation in the approaches to the Cape Roca TSS

What a reporter told us

A ship approaching a TSS, still at a distance of 12 nautical miles, is concerned by the actions of another vessel – on the reporter’s port quarter, probably overtaking – who is closing on a steady bearing. ‘The other ship’ alters to port at just under a mile, giving a CPA of 3 cables. The reporter who is himself overtaking another vessel on his starboard side with a speed advantage of 0.4 knots, slows down, and alters to starboard to open the CPA on ‘the other ship’, presumably under the stern of the one he was very slowly overtaking.

The lessons to be learnt

Pressure of space in this edition of Maritime Feedback must limit the length of this article. The report highlights the kind of relatively close quarters situations which may arise as ships shape courses for the entrances to TSSs. This process requires action in plenty of time, and a well considered assessment of other ships’ intentions based on a good all-round lookout, so that – where other ships are present – an orderly separation of ships is already established before the scheme itself is entered.

The complication arises from what amounts to two simultaneous overtaking manoeuvres. The reporter is constrained to starboard, and will be for a long time as he gains less than half a mile per hour on the vessel on his starboard side. He could perhaps have minimised his constraints by instead ‘slotting in’ astern. ‘The other ship’ might have alleviated the reporter’s concern by allowing more sea room, and could also have decelerated; we do not know how or if he was constrained to port.

CHIRP Suggests

Plan well ahead and keep a complete all round lookout when taking up position in an approach to a TSS; take account of the manoeuvring options of other ships. If overtaking, do it as quickly as possible. If sea room is at a premium, slow down and don’t overtake. See ‘The Perils in TSSs’ (Maritime Feedback 42).