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

Cost per cubic yard. Results. An Example of work done. (a) Depth of water at high and low tide. (b) Finished depth at high water required to be made. (s) A chart shewing the situation and formation of the rock, etc. The expense per cubic yard of average rock broken ready for convenient dredging may be estimated correctly for usual local conditions by the following rule, viz. :—■ A Single Cutter machine will break up per day of ten hours in average rock one hundred cubic yards for :— (t) One ton of coal for one cutter ; one and a half tons for two cutters, per day of ten working hours. (u) The wages of four men on a one-cutter plant ; six men on a two-cutter plant. Skilled labour is not required. (v) The cost of oil, stores, and repairs does not exceed the outlay for coal and wages. The Average Result from many works in hard rock is two cubic feet of rock broken ■per blow—i.e., broken to the most suitable size for dredging with a bucket-dredger, which is more efficient than the grab-dredger, because the jaws of the latter do not close readily owing to the frictional resistance of the stones. In most works 150 blows per hour are delivered on an average. This is equal to, say, ten cubic yards per working hour for a single-cutter machine. The output of a double-cutter plant is about one-half more than that of a single-cutter machine. Feed Water for the Boiler. The consumption of fresh water is about five times the weight of the coal used. Sea water may be used provided there is a fire- man on board the vessel who understands the working of a marine boiler with salt water. The following is an example of work accomplished by a single-cutter plant in connection with the deepening of the Manchester Ship Canal from 26ft. to 28ft. Average quantity (over a period of ten months) of rock broken up per month 6,403 cubic yards. Average cost of breaking ... ... ... 8.946. per cubic yard. Minimum quantity of rock broken per month ... ... ... ... ... 5,622 cubic yards. Maximum quantity of rock broken per month ... ... ... ... ... 10,180 cubic yards