Smit of Kinderdijk, near Rotterdam. In the same discussion Mr A. A. Langley, then engineer to the Great Eastern railway, gave particulars of a sand pump upon the Bazin system, which had been used successfully at Lowestoft. The boat was 60 ft. long by 20 ft. wide, and the pump was 2 ft. in diameter, with a two-bladed disk. The discharge pipe was 12 in. in diameter. The pump raised 400 tons of sand, gravel and stones per hour as a maximum quantity, the average quantity being about 200 tons per hour. The depth dredged was from 7 ft. to 25 ft. The pump was driven by a double-cylinder engine, having cylinders of 9 in. diameter by 10 in. stroke, and making 120 revolutions per minute. An important improvement was made by fitting the working faces of the pump with india-rubber, which was very successful and largely reduced the wear and tear. The cost of the dredging at Lowestoft was given by Mr Langley at 2d. per ton, including delivery 2 m. out at sea. The quantity dredged was about 200,000 tons per annum.
One of the earliest pumps to be applied to dredging purposes was the Woodford, which consisted of a horizontal disk with two or more arms working in a case somewhat similar to the ordinary centrifugal pump. The disk was keyed to a vertical shaft which was driven from above by means of belts or other gear coupled to an ordinary portable engine. The pump within rested on the ground; the suction pipe was so arranged that water was drawn in with the sand or mud, the proportions being regulated to suit the quality of the material. The discharge pipe was rectangular and carried a vertical shaft, the whole apparatus being adjustable to suit different depths of water. This arrangement was very effective, and has been used on many works. Burt & Freeman’s sand pump, a modification of the Woodford pump, was used in the construction of the Amsterdam Ship Canal, for which it was designed. The excavations from the canal had to be deposited on the banks some distance away from the dredgers, and after being raised by the ordinary bucket dredger, instead of being discharged into the barges, they were led into a vertical chamber on the top side of the pump, suitable arrangements being made for regulating the delivery. The pump was 3½ ft. in diameter, and made about 230 revolutions per minute. The water was drawn up on the bottom side and mixed with the descending mud on the top side, and the two were discharged into a pipe 15 in. in diameter. The discharge pipe was a special feature, and consisted of a series of wooden pipes jointed together with leather hinges and floated on buoys from the dredger to the bank. In some cases this pipe was 300 yds. long, and discharged the material 8 ft. above the water level. Each dredger and pump was capable of discharging an average of 1500 cub. yds. per day of 12 hours. Schmidt’s sand pump is claimed to be an improvement on the Burt & Freeman pump. It consists of a revolving wheel 6 ft. in diameter, with cutters revolving under a hood which just allows the water to pass underneath. To the top side of the hood a 20 in. suction pipe from an ordinary centrifugal pump is attached. The pump is driven by two 16 in. by 20 in. cylinders, at 134 revolutions per minute, the boiler pressure being 95 ℔ per sq. in. This apparatus is capable of excavating sticky blue clayey mud, and will deliver the material at 500 to 650 yds. distance. The best results are obtained when the mixture of mud and water is as 1 to 6.5. The average quantity excavated per diem by the apparatus is 1300 cub. yds., the maximum quantity being 2500 cub. yds.
Kennard’s sand pump is entirely different from the pumps already described, and is a direct application of the ordinary lift pump. A wrought iron box has a suction pipe fitted at the bottom, rising about half way up the inside of the box; on the top of the box is fitted the actual pump and the flap valves. The apparatus is lowered by chains, and the pump lowered from above. As soon as the box is filled with sand it is raised, the catches holding up the bottom released, and the contents discharged into a punt.
Sand-pump dredgers, designed and arranged by Mr Darnton Hutton, were extensively used on the Amsterdam Ship Canal. A centrifugal pump with a fan 4 ft. in diameter was employed, the suction and delivery pipes, each 18 in. in diameter, being attached to an open wrought-iron framework. The machine was suspended between guides fixed to the end of the vessel, which was fitted with tackle for raising, lowering and adjusting the machine. The vessel was fitted with a steam engine and boiler for working and manipulating the pumps and the heavy side chains for the guidance of the dredger. The engine was 70 h.p., and the total cost of one dredger was £8000. The number of hands required for working this sand-pump dredger was one captain, one engineer, one stoker and four sailors. Each machine was capable of raising about 1300 tons of material per day, the engines working at 60 and the pump at 180 revolutions per minute. The sand was delivered into barges alongside the dredger. The cost of raising the material and depositing it in barges was about 1d. per ton when the sand pumps were working, but upon the year’s work the cost was 2.4d. per cub. yd. for working expenses and repairs, and 1.24d. per cub. yd. for interest and depreciation at 10% upon the cost of the plant, making a total cost for dredging of 3.64d. per cub. yd. The cost for transport was 3.588d. per cub. yd., making a total cost for dredging and transport of 7.234d. per cub. yd. Dredging and transport on the same works by an ordinary bucket dredger and barges cost 8.328d. per cub. yd.
Two of the largest and most successful instances of sand-pump dredgers are the “Brancker” and the “G. B. Crow,” belonging to the Mersey Docks and Harbour Board. Mr A. G. Lyster gave particulars of the work done by these dredgers in a paper read before the Engineering Congress in 1899. They are each 320 ft. long, 47 ft. wide and 20.5 ft. deep, the draught loaded being 16 ft. They are fitted with two centrifugal pumps, each 6 ft. in diameter, with 36 in. suction and delivery pipes, united into a 45 in. diameter pipe, hung by a ball and socket joint in a trunnion, so as to work safely in a seaway when the waves are 10 ft. high. The suction pipe is 76 ft. long and will dredge in 53 ft. of water. The eight hoppers hold 3000 tons, equivalent when solid to 2000 cub. yds.; they can be filled in three-quarters of an hour and discharged in five minutes. Mr Lyster stated that up to May 1899, the quantity removed from bar and main-channel shoals amounted to 41,240,360 tons, giving a width of channel of 1500 ft. through the bar, with a minimum depth of 27 ft. The cost of dredging on the bar by the “G. B. Crow” during 1898, when 4,309,350 tons of material were removed, was 0.61d. per ton for wages, supplies and repairs. These figures include all direct working costs and a proportion of the charge for actual superintendence, but no allowance for interest on capital cost or depreciation. On an average, 20% of the sand and mud that are raised escapes over the side of the vessel. Mr Lyster has, however, to a considerable extent overcome this difficulty by a special arrangement added to the hoppers (see Proc. Inst. C.E. vol. 188).
At the Engineering Conference, 1907, Mr Lyster read a note in which he stated that the total quantity of material removed from the bar of the Mersey, from the Crosby channel, and from other points of the main channel by the “G. B. Crow” and “Brancker” suction dredgers amounted to 108,675,570 tons up to the 1st of May 1907. “In the note of 1899 (he added) it was pointed out that the Mersey was a striking instance of the improvement of a river by dredging rather than by permanent works, and the economy of the system as well as the advantage which its elasticity and adaptability to varying circumstances permit, was pointed out.... The most recent experience, which has resulted in the adoption of the proposal to revet the Taylor’s bank, indicates that the dredging method has its limitations and cannot provide for every contingency which is likely to arise; at the same time, the utility and economy of the dredging system is in no way diminished.... Having regard to the ever-increasing size of vessels, a scheme for new docks and entrances on a very large scale received the authority of parliament during the session of 1905-1906 In this scheme it was considered necessary to make provision for vessels of 1000 ft. in length and 40 ft. in draught, and having regard to this prospective growth of vessels it has been determined still further to deepen and improve the outer channel of the Mersey. No fixed measure of improvement has been decided on, but after careful survey of existing conditions and a comparison with probable requirements, it has been determined to construct a dredger of 10,000 tons capacity, provided with pumping power equivalent to about three times that of any existing dredgers. By the use of this vessel it is anticipated that it will be possible to deal with very much larger quantities of sand at a cheaper rate, and to 10 ft. greater depth than the existing plant permits.”
The vessel in question was launched on the Mersey from the yard of Messrs Cammell, Laird & Co. in October 1908, and was named the “Leviathan.” Her length is 487 ft., beam 69 ft., and depth 30 ft. 7 in. Her dredging machinery consists of four centrifugal pumps driven by four sets of inverted triple expansion engines, and connected to four suction tubes 90 ft. long and 42 in. in internal diameter. Her propelling machinery, consisting of two sets of triple expansion engines, is capable of driving her at a speed of 10 knots.
Another powerful and successful sand-pump dredger, “Kate” (Plate I. fig. 7), was built in 1897 by Messrs Wm. Simons & Co. Ltd. for the East London Harbour Board, South Africa. Its dimensions are: length 200 ft., breadth 39 ft., depth 14 ft. 6 in., hopper capacity 1000 tons. The pumping arrangements for filling the hopper with sand or discharging overboard consist of two centrifugal pumps, each driven from one of the propelling engines. The suction pipes are each 27 in. in diameter, and are so arranged that they may be used for pumping either forward or aft, as the state of the weather may require. Four steam cranes are provided for manipulating the suction pipes. Owing to the exceptional weather with which the vessel had to contend, special precautions were taken in designing the attachments of the suction pipes to the vessel. The attachment is above deck and consists of a series of joints, which give a perfectly free and universal movement to the upper ends of the pipes. The joints, on each side of the vessel, are attached to a carriage, which is traversed laterally by hydraulic gear. By this means the pipes are pushed out well clear of the vessel’s sides when pumping, and brought inboard when not in work. Hydraulic cushioning cylinders are provided to give any required resistance to the fore and aft movements of the pipes. When the vessel arrived at East London on the 18th of July 1897, there was a depth of 14 ft. on the bar at high tide. On the 10th of October, scarcely three months afterwards, there was a depth of 20 ft. on the bar at low water. Working 22 days in rough weather during the month of November 1898, the “Kate” raised and deposited 2½ m. at sea 60,000 tons of dredgings. Her best day’s work (12 hours) was on the 7th of November, when she dredged and deposited 6440 tons.
A large quantity of sand-pump dredging has been carried out at Boulogne and Calais by steam hopper pump dredgers, workable when
