22 The Drainage of Fens and Low Lands, 



the shoal to be removed by the action of its own propeller, 

 and was then anchored and warped along the shoal. This 

 machine was afterwards converted into a suction dredger, 

 having a two-bladed propeller or fan 4 feet 6 inches in 

 diameter, which was brought halfway up the stern in a case, 

 and the sand pumped up, discharged into the river on the ebb 

 tide, and so carried away. 



The navigation of the Danube in Hungary, being frequently 

 impeded by shoals caused by the deposit driven out of the 

 tributaries in times of flood, the Danube Steam Navigation 

 Company employed a boat, fitted with a triangular rake 

 18 feet long, having thirty-four teeth 12 inches deep. This 

 rake was hung over the bow of a steamer and dragged across 

 the shallows, the steamer running astern, it being found that 

 if the rake was hung over the stern it interfered too much 

 with the steering. By the aid of this rake, the shoals, con- 

 sisting principally of shingle, were removed, and the depth of 

 water increased from 3 to 4 feet.* 



For breaking up the sand on Pluckington Bank in the 

 Mersey, to facilitate its removal by the scouring sluices, 

 various forms of rakes and dredgers were used, a description 

 and illustration of which will be found in the Trans. Inst. 

 C. E., vol, xc. 



A scouring dam, intended for the removal of shoals consist- 

 ing of sand, was brought out by Mr. John Kingston, and was 

 described and illustrated in ' Engineering' of August 4th, 1882. 

 This machine, which has been successfully used for clearing 

 the entrances to the tidal and coast canals at Balasore and 

 other places in India, consists of a barge, over the stern of 

 which is a framework, carrying a movable dam made of 

 wood, with appliances for raising or lowering the same. As 

 soon as this sheet dam is lowered into the water across the 

 stream, and within a few inches of the bottom, the water is 

 held up on the upper side of the dam and the current forced 



* Trans. Inst. C. E., vol. Ix. p. 387. 



