The Arcadia and two of her eight Mules

The Arcadia and two of her eight Mules

The Ships are guided though the lock chambers by electric locomotives, known as mulas or mules. They are used for side-to-side and braking control in the rather narrow locks. Forward motion into and through the locks is actually provided by the ship's engines and not the mules'. A ship approaching the locks first pulls up to the guide wall, where she is taken under control by the mules on the wall before proceeding into the lock. As she moves forward, additional lines are taken to mules on the other wall. With large ships, there are two mules on each side at the bow, and two each side at the stern — eight in total, allowing for precise control of the ship.
The mules themselves run on rack tracks, to which they are geared. Each mule has a powerful winch, operated by the driver; these are used to take the line in or pay it out, to keep the ship centred in the lock while moving it from chamber to chamber. With as little as 60 cm (2 ft) of space on each side of a ship, considerable skill is required on the part of the operators.

Right behind us the "Arcadia" , and we had an interesting view of how the lines from the mules were attached to her bow and stern.
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