During the last five weeks at Port Tewfik, the expense, including the repairs, was 8,850 francs ($1,770.00) for 1,600 cubic meters (2,093 cubic yards) extracted.  This would make the cost 5.52 francs per cubic meter, or $0.84 per cubic yard, not including the insurance, the interest and the depreciation of the plant.

After some improvements in details, suggested by practice, the machine was put in operation at Chalouf upon a hard rock, from 1.50 to 3 meters (4 ft. 11 in. to 9 ft. 10 in.) thick.  The battering rams were given a fall of 1.80 meters (5 ft. 11 in.).  To break the rock into fragments small enough not to be rejected by the buckets of the dredge, the operations of dredging and of disintegration were carried on separately, permitting the battering rams to work at a greater distance from the wall face.  The time consumed in thus pulverizing the rock by repeated blows was naturally found to be increased.  It was found more convenient to use only a single row of battering rams.  The production was from about seven to eleven cubic meters (9.2 to 14.4 cubic yards) per hour.  Toward the close of September, after it had been demonstrated that the “Derocheuse” was capable of accomplishing with celerity and economy the result for which it was designed, it was purchased by the Suez Canal Company.

During the month of September, an experiment, the details of which were carefully noted, extending over a period of sixteen days, gave the following results: 

Crew (33 men), 140 hours. 2,012.50 francs $402.50
Coal, @ 87.50 francs ($7.50) per ton 787.50 francs 157.50
Oil and supplies 220.00 francs 44.00
Fresh water, 16 days 210.00 francs 42.00
Sundries 42.50 francs 8.50
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Total expense for removing 764
cubic meters (999.2 cubic yards), 3,272.50 francs $654.50

Average, 4.28 francs per cubic meter ($0.65 per cubic yard).

This result cannot be taken as a universal basis, because after a year’s use there are numerous repairs to make to the plant, which would increase the average net cost.  This, besides, does not include the cost of removal of the dredged material, nor the depreciation, the interest and the insurance.

It should be added on the other hand, however, that the warm season was far from being favorable to the energy and perseverance necessary to carry on successfully experiments of this kind.  The temperature, even at midnight, was often 38 deg.  C. (100.4 deg.  F.).  Still further, the work was constantly interrupted by the passage of ships through the canal.  On an average not more than forty minutes’ work to the hour was obtained.  Notwithstanding this, there were extracted at Chalouf, on an average, 38.225 cubic meters (50 cubic yards) per day without interrupting navigation.  At Port Tewfik, where there was much less inconvenience from the passage of ships, the work was carried on from eight to eleven hours per day and the quantity extracted in this time was generally more than 76 cubic meters (99.4 cubic yards).