A three ton hand crane is placed upon the bridge for use in making repairs to the chain which carries the buckets.  A six ton steam crane is placed upon the top of the cage which supports the hydraulic apparatus for raising the battering rams, thus permitting them to be easily lifted and replaced.

The dredging machine is also furnished with two screws driven by an engine of 300 indicated horse power, as well as with two independent boilers.  Two independent series of pumps, with separate connections, feed the hydraulic lifting apparatus, thus permitting repairs to be made when necessary, without interrupting the work.  A special machine with three cylinders drives the pumps of the condenser.  An accumulator regulates the hydraulic pressure and serves to raise or lower the spuds.

At the end of the Suez Canal next to the Red Sea, the bottom consists of various conglomerates containing gypsum, sandstone and sometimes shells.  It was upon a bed of this nature that the machine was first put to work.  The mean depth of water, originally 8.25 meters (26 ft. 3 in.), was for a long time sufficient for the traffic of the canal; but as the variations in level of the Red Sea are from 1.8 to 3 meters (5 ft. 11 in. to 9 ft. 10 in.), the depth at the moment of low water is scarcely adequate for the constantly increasing draught of water of the steamers.  Attempts were made to attack the rocky surface of the bottom with powerful dredges, but this method was expensive because it necessitated constant repairs to the dredges.

[Illustration:  Fig. 3.—­Dredge movement.]

These last, although of good construction, seldom raised more than 153 cubic meters (200 cubic yards) in from eight to fifteen days.  Their daily advance was often only from sixty to ninety centimeters (about 2 to 3 ft.), while with the “Derocheuse” it was possible to advance ten times as rapidly in dredging to the same depth.  The bottom upon which the machine commenced its work was clean and of a true rocky nature.  It was soon perceived that this conglomerate, rich in gypsum, possessed too great elasticity for the pointed battering rams to have their proper effect upon it.  Each blow made a hole of from fifteen to sixty centimeters (6 in. to 2. ft.) in depth.  A second blow, given even very near to the first, formed a similar hole, leaving the bed of the rock to all appearances intact between the two holes.  This result, due entirely to the special nature of the rock, led to the fear that the action of the battering rams would be without effect.  After some experimentation it was found that the best results were obtained by arranging the battering rams very near to the chain of buckets and by working the dredge and battering rams simultaneously.  The advance at each oscillation was about 90 centimeters (about 3 ft.)

The results obtained were as follows:  At first the quantity extracted varied much from day to day; but at the end of some weeks, on account of the greater experience of the crew, more regularity was obtained.  The nature of the conglomerate was essentially variable, sometimes hard and tenacious, like malleable iron, then suddenly changing into friable masses surrounded by portions more elastic and richer in gypsum.