On January 3rd, the Island Princess made a dawn entry into the Gatun Locks for its trip from the Caribbean Sea to the Pacific Ocean.
There are three sets of locks in the canal. A two-step flight at Miraflores
, and a single flight at Pedro Miguel, lift ships from the Pacific up to Lake Gatun; then a triple flight at Gatun lowers them to the Atlantic side. (The Island Princess entered from the Atlantic side on this cruise.)
All three sets of locks are paired; that is, there are two parallel flights of locks at each of the three lock sites. This, in principle, allows ships to pass in opposite directions simultaneously; however, large ships cannot cross safely at speed in the Gaillard Cut
, so in practice ships pass in one direction for a time, then in the other, using both "lanes" of the locks in one direction at a time.
The lock chambers are 33.53 meters (110 ft) wide by 320.0 meters (1050 ft) long, with a usable length of 304.8 metres (1000 ft). These dimensions determine the maximum size of ships which can use the canal; this size is known as Panamax
. The total lift (the amount by which a ship is raised or lowered) in the three steps of the Gatun locks is 25.9 m (85 ft); the lift of the two-step Miraflores locks is 16.5 m (54 ft). The single-step Pedro Miguel lock has a lift of 9.5 m (31 ft). The lift at Miraflores actually varies due to the extreme tides on the Pacific side, between 13.1 m (43 ft) at extreme high tide and 19.7 m (64.5 ft) at extreme low tide; the tides on the Atlantic side, however, are very small.
The lock chambers are massive concrete structures. The side walls are from 13.7 to 15.2 metres (45 to 55 feet) thick at the bases; towards the top, where less strength is required, they taper down in steps to 2.4 m (8 ft). The centre wall between the chambers is 18.3 m (60 ft) thick, and houses three long galleries which run the full length of the centre wall. The lowest of these is a drainage tunnel; above this is a gallery for electrical cabling; and towards the top is a passageway which allows operators to gain access to the lock machinery.
© Sam Markman Photography