SEA-GOING HYDRAULIC DREDGES 119 



shafts through couplings. The propellers are independent one of 

 the other, and can turn inversely, this being rather a novel feature 

 for this kind of craft. 



The dredging device consists of two centrifugal pumps worked 

 from the main engine. The pump shells are cast in one piece, and 

 provided with manholes for removing all obstructions when necessary. 

 The suction turbines have four blades, and contain a special arrange- 

 ment which prevents the sand from penetrating between the blades 

 and the inside walls of the pump body. The door-pieces on the front 

 part of the pumps carry the suction necks, which are connected, 

 through an elbow that runs through the deck and a horizontal 

 conduit, to another neck; the latter is fitted to the suction pipe 

 through another elbow, a flexible length of tubing and a Hooke's 

 joint. The suction pipe can draw sand from a depth of 43 ft. below 

 water level, and can work even during a rolling swell of 91 in. The 

 joint with the suction pipe being level with the deck, all work of main- 

 tenance and repair is easily carried out. The discharge from the 

 pumps is effected through shoots, each with seven openings, provided 

 with sluice doors to regulate the delivery on the dredge. Hoppers 

 of perforated plates are provided in the sand wells. 



Double steam winches are placed on deck at both ends; these 

 are supplied with steam from an auxiliary boiler. Another steam 

 winch serves to work the sluice valves and the suction pipe. The 

 auxiliary boiler in question is multitubular, and supplies not only 

 the winches, but also gives steam for the electric lighting of the 

 boat and for heating the various berths. The electric-lighting 

 equipment serves to facilitate night work; three arc lamps of 1000 

 candle-power each are provided on deck for this purpose. 



These dredges give full satisfaction. They were to draw each 

 17,658 cu.ft. in 50 minutes; their traveling speed in a rolling swell 

 of 15 in. was specified to be 8 knots, with a coal consumption of 

 1.87 Ibs. per indicated horse-power per hour. During the tests 

 the wells were filled in 38 minutes; the speed reached was 8J knots, 

 with a coal consumption of 1.70 Ibs. only. 



