But one of the masters disobeyed the strict regulations set out in the International Maritime Organisation's rule book. The two vessels were in the area where they meet the boat containing the pilots who oversee large ships wishing to go into the estuary of the river Schelde, which is part of the busy complex of waterways that carry shipping to Antwerp, Rotterdam and Amsterdam. The Schelde is a busy waterway and all large vessels are required to carry a pilot unless they have an officer who is experienced in those waters and holds the required qualification.
Since they were travelling in fog, they should have followed rule 19 of the regulations which warns vessels to take extreme care. If a ship is in doubt about the manoeuvrings of another in such conditions, it should proceed slowly, or even come to a stop. All large ships are now fitted with a radar system which includes a back-up in case of failure.
Alec Bilney, marine adviser at the International Chamber of Shipping, said: 'A ship should be able to spot another one at around 48 miles on the radar, and then identify it as a large ship with certainty at 15-16 miles.'
The accident occurred just after the BP tanker British Trent, which was leaving the estuary to head for the Strait of Dover, and eventually Italy, had dropped off the pilot. To do so, it turned to create a lee for the pilot's boat to come alongside it and so was travelling very slowly.
The other vessel, the Western Winner, which was entering the Channel to drop cargo at Vlissingen and then Antwerp, would have needed to pick up a pilot from the same boat before entering the Schelde.
The Western Winner would have just left the channel which ships must follow through the Strait of Dover and which requires ships heading east to pass on the French/Belgian side, following maritime practice that dictates ships pass each other port to port. It would then have been piloted into the right-hand side of the Schelde.
The investigators will have to determine why the ships' paths crossed near the pilots' station and why the Western Winner appears to have been proceeding despite the thick fog and the presence of the British Trent which would have been heading for the British side of the Strait of Dover.
One problem for shipping in the area is that the pilot station is near a couple of sandbanks and shipping has to turn to reach it, a potentially dangerous manoeuvre.
Traffic in the Channel is monitored by three coastguard services but ships are not controlled in the same way as aeroplanes. Masters remains in control of their ships, although they should obey the IMO regulations. They can lose their certificates if they fail to do so.
The British Trent was equipped with an automatic collision avoidance system according to senior BP shipping officials. It is a computer system that alerts officers on the ship's bridge to the possibility of any impending crash. If officers are not monitoring surrounding shipping on the radar, visual and audible warnings will sound in the bridge.
It is generally accepted practice for ships' masters to have three people ensuring that collisions are avoided. One person would monitor the radar screen, another would look out from within the bridge and, in foggy conditions, a third would go outside to watch and listen.