1. Atlantic Larch meets the inbound Tsing Ma Bridge. The outbound Zim Beijing uses the centre of the channel, and Tsing Ma Bridge favours the east to allow room for passing. Middle Ground Shoal is to the west (right.)
2. Once made up on the starboard quarter, Atlantic Larch provides some drag to slow the ship, and assists her in moviong back out into the main channel to give her room to turn.
3. Once the ship reaches the right position, Larch pushes up on the ship to turn her 180 degrees.
4. The ship is turning, with the assistance of her thruster, and has some sternway on. Atlantic Larch lets go to move round to the port quarter.
5. It is a quick move, allowing for the sternway on the ship, the tug has to turn 180 degrees too.
6. Larch "gives it the gas" to get into position around the stern of the slow moving ship.
7. Rounding up on the port quarter.
8. Getting in position.
9. Ready to push, at an angle, to give the ship more sternway and to complete the turn.
Tugs working at Halterm usually turn container ships when they arrive, so that the ships berth starboard side to, facing out to sea. This is done because it requires fewer tug movements when the ship is under way in bound and can use its own momentum in the turn. Outbound ships, with little way on would be much harder to turn, and they would be going astern.
To turn the inbound ships the tug must make up on the ship's starboard quarter as it approaches. Once the ship has made most of its turn and is ready to back in, the tug them moves around astern of the ship and makes up again on the port side to push her in alongside the pier.
It is usually a one tug job, since most container ships are fitted with a bow thruster, which also assists in the turn.
Today's arrival of Tsing Ma Bridge (see also Shipfax on this one) was a textbook example of how it is done. Atlantic Larch is a 4000 bhp ASD tug, built in 2000.