Digging Bigger In The Panama Canal
by John Thompson
from Equipment Echoes ... December, 1997  #47

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In describing the classic 15-cubic yard steam dipper dredges of the Panama Canal (Equipment Echoes 45, June 1997), justice could not be done the state-of-the-art cable-operated machine which replaced them in 1977, the Rialto M. Christensen.  Now that suitable data and illustrations are available, the "new look" to the canal's dipper dredges may be compared with rigs that served through most of the twentieth century.  Besides, the lone dipper machine that is to serve into the next century is now venerable enough to dipper dredge to carry on with hard digging in the canal was a far cry from the mode of placing an order with the Bucyrus Company in 1913.  This time two fruitless years of exploring the matter with dredge makers preceded solicitation of proposals, flowed by invitations (February 1976) for bids from finalists.  The international competition resulted in selecting the proposal by Hakodate Dock Company, Ltd., which began to construct the diesel-electric rig in October 1976.  The bid was over $5,506,000.

The all-steel dredge was erected in eight months at Hakodate, on northerly Hokkadio Island, Japan.  The craft was built in a dry-dock, where launching was accomplished by flooding the chamber in June 1977.  It was christened then, being named for a deceased employee of the Panama Canal whose ideas and energies were central to acquisition of the dredge.

Under direction of six of the builder's staff, the craft was fitted out at Gamboa by the Dredging Division's shop personnel and the prospective crew.  It took about a month to complete the task and to commence performance trials that led to acceptance on September 28, 1977.  Shortly thereafter, on the dredge's first job, serious problems developed in the swinging circle, its foundation, and elsewhere among moving parts that controlled the dipper and stick.  Warranty repairs and a redesign and strengthening of the swinging circle foundation were completed in a couple of months.

Besides being much larger than the original 15-yard dipper dredges, Christensen looks very different.  It appears more akin to dry-land excavators in that the hoisting machinery, sturdy A-frame and boom, long dipper stick, and operator's cabs ride on the swinging circle.  New, too, is the welded steel dipper stick, which lacks the flexibility of the steel-armored wooden dipper sticks of the past.  Necessarily, the working spuds are located aft of the machinery cab, about 30 percent of the length of the hull from the bow.  Gone is the gantry or gallows frame of old which helped raise spuds of 82'x4'.  Christensen's forward spuds are 97'x6'.  No longer is the upper deck used to house as many as three watches.  Today's single watch of 12 is accommodated on the main deck with day rooms, shower and dressing facilities, a kitchenette, and offices for the captain and chief engineer.  Below the main deck lie the engine room and spud winch room, a machine shop, and tanks for fuel, water and ballasting.   As on the old machines there are winches aft and on both sides of the housing to handle scows.

The Christensen's hull is about 164' x 71' x 16', with mean daft approaching 11 feet.  It is compartmentalized with a number of water-tight bulkheads.  Fully loaded and ready for work it displaced a little over 1,300 tons more.

The Christensen carries a true 15-cubic yard rock dipper, somewhat larger than on the earlier steam dredges.  With more than 87 feet of dipper handle, it can dig to 70 feet below the water's surface, 10 feet more than did its predecessors.  At that, it completes a cycle in a minute.  A pair of 203/8 inch cables hoist the bucket, as was the case with the earlier machines.  Lifting capacity is 250,000 pounds, 15,000 pounds greater than on the earlier rigs.

The Christensen's machinery is powered by a pair of Fuji 2,150 h.p. x 600 r.p.m. diesel-electric engines linked to A.C. and D.C. generators.  There is a smaller auxiliary engine, as well.

Whereas the steam machines were operated by a leverman standing on the main deck, and a craneman, today's dredge is provided with hand-operated controls in duplicate air-conditioned cabs that are perched on either side atop the machinery room.  the single operator works in whichever cab affords a better view of the scow loading operation, and he has a good view in all directions.  It is quite a change from the old rigs, where the leverman's view was restricted by the boom and housing, requiring hand-signal guidance from a man positioned on the bow to manage the dipper's positioning of scows and lading on the port side.

The single new 15-yard dredge should be able to handle maintenance, anticipated canal enlarging tasks, and such miscellaneous jobs as digging out around grounded ships.   Removal of slide material should be an infrequent and relatively small problem now that so much slide-prone materials has been removed by coordinated dry-land excavation and dredging.

Many thanks to the Bucyrus Company for providing us with this article.

Presented by CZBrats
January 24, 1999

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