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will again enter a part of the old river channel and find its way to the sea close to the mouth of the canal.
THE CANAL LOCKS The passage of a vessel through locks wherein it remains continually water-borne is simple, as compared with the usual process of placing vessels in dry dock, involving the removal of water from the dock and support of the ship on blocking.
The percentage of accidents in both cases is found to be exceedingly small. About 90 per cent of the accidents in locking vessels are due to failure of signals from the bridge to the engine room, and these will be eliminated at Panama through the adoption of a part of the process in common use in docking; namely, the vessel will not move into the lock under its own steam, but will come to a full stop at the approach wall, and the movement of the ship will then be controlled by the lock operatives. Two lines to the bow and two to the stern will be used, the strains being obtained from four electric locomotives with winches on board, running on rack railroads on the edge of the lock walls, two on each side of the lock. For large ships more lines and more locomotives may be found necessary. The process is not dissimilar to towing canal boats, but with amplifications. With experience there will no doubt be developed the proper order of seamanship to handle all vessels expeditiously under these novel conditions. (See plan No. 6.)
The canal has in all twelve lock chambers, two flights of three each at Gatun, two flights of one each
Fig. 14. — One of the Gatun Locks used as a dry dock for docking ladder dredge “Corozal” and class “C” U. S. submarines. Note height of lock walls. Vessel beyond steel lock gates is tied up at approach wall in Gatun Lake.
at Pedro Miguel, and two flights of two each at Miraflores. The twelve locks are alike in their principal features, but variations occur from differences in arrangements of gates and protective devices. The lock chamber must have at least one gate at each end, to separate it from the adjoining chamber or from the adjoining body of water. The minimum number of gates that would fulfil this condition for the arrangement of locks adopted is 18. The actual number used is, for various reasons to be explained later, increased to 46.
Each lock has a chamber 110 feet wide and 1000 feet long, but as about 95 per cent of all ocean-going vessels are under 600 feet long, the locks are divided by a second set of gates into two parts, one 400 feet long and the other 600 feet long. There is no saving of time in filling a small chamber rather than the full 1000-foot lock, since all filling is done at the rate of 2 feet per minute; but advantage in the use of divided locks arises from the great saving in water, which is an element of importance, as we have seen in considering Gatun Lake. This feature adds ten pairs of lock gates to the installation. One duplicate lock, namely, the lower one at Miraflores, is not provided with the dividing gates. This is because the designing engineers found that the cost of the gates and additional length of concrete structure in this particular lock, due to tidal conditions, outweighed the saving in water.
Should a vessel approaching the first lock of any flight not come to a stop through some misunderstanding, a collision with the lock gate will be prevented by a chain of 3-inch iron stretched from one side of the lock to the other. The impact will be taken up by hydraulic cylinders in the lock walls to which the ends of the chain will be attached. The resistance is sufficient to stop a 10,000-ton vessel moving at 4 knots per hour in a length of 73 feet. When not in use the chain will rest in a groove in the floor and side walls. If the chain should give way, or not be in position, the impact would be received by a pair of guard or safety gates, which it is expected would check the vessel and prevent it from injuring the next set of gates. Should the inconceivable accident happen of a vessel passing both the guard chain and safety gate and wrecking the next one while all the other gates in the lock were open, due to a vessel having just passed through, then Gatun Lake would begin to flow out to the full capacity of the channel now formed by the lock, and similarly for Lake Miraflores. Four guard gates are required to protect the entrances to the four lock chambers adjoining Gatun Lake at Gatun and Pedro Miguel, and four more to protect the exits from the same locks, as an accident at the exits would have the same consequences as at the entrances. Similarly, two gates each are required at the entrances and exits of the upper Miraflores lock chambers, or a total of twelve guard gates.