From the outset, it was considered an important safety feature that ships be guided through the Panama Canal lock chambers by electric locomotives, known as mulas (mules, named after the animals traditionally used to cross the isthmus of Panama), running on the lock walls. These mules are used for side-to-side and braking control in the locks, which are narrow relative to modern-day ships. 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, which is an extension of the center wall of the locks, where it is taken under control by the mules on the wall before proceeding into the lock. As it 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 with broad gauge, 5 ft, to which they are geared. Traction is by electric power, supplied through a third rail laid below surface level on the land side. Each mule has a powerful winch, operated by the driver; these are used to take two cables in or pay them out in order to keep the ship centered in the lock while moving it from chamber to chamber.
The old canal locks can barely fit the huge container ships – they often come too close to the edge with hardly room to spare. With as little as 2 ft (60 cm) of clearance on each side of a ship, considerable skill is required on the part of the mule operators.
Little Room to Spare
A 3,500 car-container ship enters the Miraflores Locks on the Panama Canal
Entering the Locks
Stops just a few yards from our small boat – a little too close for comfort! The “mules” make sure it doesn’t escape.
Once the ship is completely in the lock and gate is closed, the water level is reduced to match the other side. The other gate is then opened and the tugboats guide the ship from the Panama Canal onto open waters of the Atlantic Ocean.
The lock gates for the third set of locks (expansion) on Panama Canal basically consist of two orthotropic steel plates (skins) held apart by truss structures and plates forming the compartmented buoyancy chamber that, when submerged, reduce the operational weight carried by two rolling wagons. These steel structures, as large as 187 by 105 by 33 feet, are supported by an upper wagon, running on rails situated in the gate recess, and a lower wagon, running on rails situated in the lock chamber. The gates are opened and closed by drive systems consisting of cables, winches, and sheaves.
Closing the Gate
Under the old lock system at Panama Canal, tugboats’ engagement with ships has been limited to guiding them in open waterways and to the entrance of the locks, where powerful locomotives known as “mules” take over, latching on and keeping the vessels in place as the water level is raised or lowered.
There are no mules in the new locks setup. Instead tugs approach a ship, latch on at both the bow and stern and accompany it inside the 1,400-foot locks. With the lock doors closed on a 1,200-foot New Panamax, there’s little room to operate for the roughly 90-foot tugs positioned both fore and aft.
The shipping vessels run on their own propulsion throughout, and are under the control of a canal pilot who goes on board to steer. Communication between the tugs and the pilot are key.
A tugboat gently guides a large ship through the Aqua Clara Lock, Panama Canal
Entering the Lock