Clydebuilt helping build the Panama Canal

Clydebuilt helping build the Panama Canal 

More Science » Scientific American Volume 105, Issue 19 » Features Email Print

The British-Built Dredger for Panama

By Our English Correspondent, Hopper Capacity 1,200 Tons of Dredging, Bucket Ladder will Reach to Depth of 50 Feet

Nov 4, 1911

ONE of the vessels around which an acute political we can scarcely call it economic controversy has raged in America for some time is the “Corozal,” an extremely powerful bucket dredger which has been built in 1911  by Messrs. Wm. Simons&Company (Limited), of Renfrew, Scotland, to the order of the United States Government, for carrying out some of the most arduous underwater cutting to be done in connection with the Panama Canal. The vessel has a hopper capacity of 1,200 tons of dredging and the bucket-ladder is designed for dredging up to a depth of 50 feet. It is propelled at a speed of 10 knots per hour by two sets of triple-expansion, surface-condensing engines, supplied with steam from two cylindrical, multi-tubular boilers, constructed to Lloyd’s requirements for a working pressure of 180 -pounds per square inch. A complete outfit of the most modern auxiliary machinery is provided in the engine room, including independent air pumps, circulating pumps, feed pumps, feed heater and filter, etc. The dredging gear is of the most massive description and is arranged to give three speeds of buckets to suit the various kinds of material to be dealt with. The dredging gear can be driven by either of the main propelling engines. Two sets of buckets are provided, one of 54 cubic feet capacity for dredging soft material and one of 35 cubic feet capacity for dredging stiff clay. The bucket ladder is a steel girder of exceptional strength and an idea of the great strength of the bucket chain may be conveyed by the statement that the ladder with its chain of buckets, links and pins, weighs upward of 240 tons. The upper end of the bucket ladder is supported on an independent pivot shaft and the lower end is controlled by powerful steel wire-rope tackle and independent steam hoist gear, which is designed for raising the latter at a speed of 10 feet per minute. Steam manoeuvring winches are fitted at bow and stern, each driven by independent, two-cylinder engines, and each barrel is fitted with friction clutch and brake, to enable the mooring chains to work independently of each other, or simultaneously, as may be required. Shoots are provided for loading into the vessel’s own hopper, also overboard shoots controlled by independent steam winches, for loading into barges alongside. The hopper doors are controlled by independent hydraulic gear. This dredger, “Corozal/’ w”s launched on the Clyde in September and she is to undergo severe tests before being despatched on her voyage round South America to the western end of the canal. Before leaving British waters, she will be tested, first in lifting sand and mud from the bottom of the Gareloch, off Helensburgh, and, afterward, she will be taken back to Renfrew where the buckets will be changed, and subsequently she will be sent to Belfast and tested in the (hard clay of the Musgrave Channel. The dredger was constructed to Lloyd’s full requirements and Mr. T. M. Post and Mr. A. V. B. Candler have superintended the construction of the dredger on behalf of the United States Government for 

The Corozal has a centre well ladder so that it can make its own flotation, that is, it can dig into a bank ahead, when the ladder makes an angle of 45 degrees with the vertical, excavation can be carried on at a depth of 50 feet. It was required by the canal engineers that the dredger should be capable of digging 1,200 cubic yards of soft material an hour.

Coronal was classified as a ship rather than a Harbour Dredger due to her design. She also had complete living quarters for her crew, a laundry, and a fully equipped kitchen. This allowed her to sail under her own steam to any part of the world as required.

The trip from the Clyde to Balboa via the Straights of Magellan,  by the dredger was a memorable voyage. The log showed a total of 12064 miles covered known in the mechanical and scientific world as “The Liderwood System” was among the means chosen for this important journey, the actual sailing time consuming 96 days.

The system used by Corozal for dredging was on arriving on location, the propellers were disconnected, and one engine was reconnected to a huge line of scoops that looked like a very large-size ditch-digging machine. Each scoop could bring up 2 cubic yards of material, and there were 39 of them making up the complete bucket chain. To get an idea of the magnitude of this chain, each of these scoops , or buckets, was connected to the next one in line by three massive steel links. Each link weighed one ton. So never mind the huge scoops, just the connecting links for the complete bucket chain weighed 117 tons.

4 Anchors, two forward and two aft were put out.  She then moved from side to side as well as forward or back along the channel she was digging by adjusting the various anchor lines. From time to time as the work progressed, anchors had to be raised and reset which required the services of a good sized towboat to serve as the anchor setting vessel. The same tug towed away the barges that contained the material (in dredging terminology this is called “spoil”) the Corozal had dug out. 

When in operation this dredge scooped up material from the bottom with its chain of buckets. Then at the top of the bucket chain, the scoops emptied the dredge material into a chute that slid it down into the “spoil” barge that was tied up alongside. When the barge was full, a tow boat brought an empty barge alongside and towed the full one out to sea to dump it. Thus while working Corozal was accompanied by at least two barges and the tow boat, 4 vessels in all. 

The life expectancy of this type of ship was on average 20 years, the Corozal  in various parts of the world lasted 45 years being broken up in 1956 at Jacksonville.