Cross purpose
■ Re ‘Crossing a TSS with confidence’ (PBO July), this was a good article – but perhaps not from the viewpoint of a novice sailor. Here is the right way of crossing a TSS if you’re hampered by commercial shipping. From the cockpit, the horizon can be considered as being at a distance of 3NM. (This distance can also be approximately divided for 2NM, 1NM.) Also, for clarity let’s assume that our speed is 5 knots, and that of a large ship 15 knots. (Container ships and ferries can travel at 20 knots!) Einstein would say there is a relationship between distance, relative speed and time, so if we travel 1NM, the ship will have travelled 3NM. We need 12 minutes to do that, while the ship requires only 4 minutes.
Crossing a lane 5NM wide will take us 60 minutes. The ship will have travelled 15NM and already be out of sight: if we see his bow wave on the horizon, he will be 3NM and 12 minutes away. We will be 1NM inside the lane with a big ship close before our bow. If the ship is only 1NM away, it’s better if we wait outside the lane and let it pass. If it is below the horizon but his bridge and mast are visible (7 miles off), we could find ourselves, 30 minutes later, in the middle of the lane with a large ship close by. We have 30m to think it over. The absolute minimum distance to a big ship is his length (150-200m for a freighter, 300-400m for a tanker/ container ship). Keeping half a mile away at sea is much safer.
When the COLREGs mention that ‘all means’ should be used for safety reasons, that includes keeping the engine warm, running, or crossing under motor. Crossing under spi with reduced crew is not really advisable before a court. Supertankers (draught 21m) are very restricted and will NOT change course, while large container ships and ro-ro ferries will only do so very reluctantly.
Keep out of their path. It may surprise many people, but from high up on a ship’s bridge, small boats nearby are difficult to see not only by eye, but also on the radar. Many ships switch off their AIS ‘B’ reception.