With a canal lock that has only one chamber, it's probably faster for southbound
and northbound ships to alternate through the lock. But where there is a
staircase of locks (three at Gatun, two at Miraflores) you can get more ships
through in a given time by using
the convoy system: a convoy one way followed by a convoy the other way. So the
Panama canal now has ships moving from the sea to Gatun Lake in the
mornings, and from the lake to the sea later in the day. But this means that in
the mornings, all the mules would accumulate at the Lake end of each lock, and
in the afternoons, at the sea-level ends of the locks, so there has to be
provision for returning the mules to their starting points.
To do this, each
flight of locks has a return track set back from the towing-track which is at
the water's edge. The return track
does not need the cog-wheel and rack, as the mule does not have to provide any
towing force. But there's another complication:
in the centre island, between the two parallel flights of locks at each
location, there is only one return track for both towing tracks. And since the
mule picks up its electrical power from a conduit, and since the conduit is at
one side of the track, each mules must
be turned to the correct orientation before it goes onto the return track and
before it is positioned on the towing track.
These pictures, taken at Gatun, show mules being positioned after they have
returned to the start point.
||Only one mule is parked on the track adjacent
to the Statendam, so others are being sent down the return track to
assist. They will be turned on the turntable and put on the adjacent
track. The first one is approaching the first control panel, set on
a post so that the operator does not even have to leave his
air-conditioned cab. He will make the table rotate until its track
is in line with the return track.
||The mule parked on the "adjacent" track has
moved forward to service the Statendam. The first return mule is
moving onto the turntable, and the second return mule is approaching
the turntable control
||The first return mule is on the turntable,
and the operator is about to lean out and punch instructions into
the second control station, mounted on a pole actually on the
||The operator pushes the buttons . . .
||and the table begins to turn.
||Table is now halfway around. More ships
approaching in the distance.
||Table almost completely around: when the turn
is complete, the mule can move off the table and allow it to be used
by the next mule.
||The operator of the next mule (158) directs
the turntable to rotate so that the tracks are aligned to allow his
machine to run forward onto the table.
||Table has turned, and mule 158 can roll onto
||The table, with mule 158 on it, is rotating.
When the tracks line up, mule 158 can move forward onto the track
adjacent to the water.
||The central return-track (with no rack-rail)
for mules cannot be used at Pedro Miguel as there is a crane parked
there, so mules have to return to the start point in convoy, between
||Aerial view of a turntable, at Gatun.
This page last updated on 16/05/2009 10:17:43.