Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

The cutter has worked on double shift regularly, and the average cost of working in this manner has been £240 per month, made up as follows Wa?es .................................................... lf8 Coals and stores ______________........ 27 Repairs and renewals, including new ropes and repairs to needle .............................................. 105 Z'240 advance per . 1 he rate °f ad^nce of the rock-cutter averages 36ft. per diem, the bottom day- width ol the canal being- 120ft. Nature of rock : Sandstone of varying degrees of hardness. “ LS f0Und mOre efficient tO have a hcaV-V cutter faIling a short dlStanCe than a hSht cutter dropped from a greater height. For instance a 5-ton cutter, given a 20-feet drop, would give a striking energy of 100 foot-tons. A 10 ton cutter dropped from a height of 10 feet, although not increasing the energy would prove much more effective in rock-cutting. In the former case the action would be the making of fissures and the breaking of the material into large cubes, whereas in the latter the effect would be tn , r wvruiu ue to pulverise the material ready for dredging. The weight of the cutter varies with the hardness of the materials The 15-ton cutter with a 10-feet drop has been found satisfactory in breaking up „ - . On moderately hard rock in shallow water, a 6-ton cutter gives fair granite. On moderately hard rock in shallow results. Pitch Of holes The pitch of the holes for the blows is usually to a fppt r for the blows. 1 v 3 4 reet in the case of sandstone, but in extremely hard rock it is as close as 2 feet 6 inches. Cost Of Plant. The approximate cost of a single rock-cutter plant, with barge complete, for a depth of 5o feet, would be from £5,000 to £6,000, the actual price depending on the conditions, which vary with the locality. Double and treble cutter plants are more expensive in proportion, and arc not so often used as the single-cutter machine.