SEA-GOING HYDRAULIC DREDGES 117 



and as there could be no question of putting the dredges in 

 shelter when not in actual work, they had to be built seaworthy 

 throughout. They, in fact, traveled under their own steam from 

 Marseilles to Havre, having been built at Aries, in the south 

 of France, and behaved perfectly well in the crossing. The 

 central portion of the dredge in question is given in Fig. 33. 

 The hull is divided into compartments by eight watertight 

 bulkheads. The first compartment is the forepeak, used as a 

 hold; the second one is the crew space, with berths for eight 

 men. The next compartment contains the officers' cabins and 

 one cabin for the Fonts and Chaussees engineer, who has charge 

 of inspecting and supervising the work done. In the following 

 compartments are the sand and mud wells, the normal capacity 

 of which is 17,658 cu.ft., the maximum capacity being 20,483 cu.ft., 

 when extension tops are put round the openings of the hoppers, 

 which is possible in fine weather. The wells are seven in number, 

 fitted with two pairs of doors or sluices. The next compartment 

 forms the engine-room, and also contains the dredge pumps; the 

 one next to it is the stokehold, with coal bunkers, the last one being 

 the chain locker. 



There are in each dredge two vertical compound engines, capable 

 of developing together a total of 540 indicated horse-power at 150' 

 revolutions. This type of engine has been built in large numbers 

 by Messrs. Satre for various purposes. Their principal dimensions 

 are the following: 



Diameter of high-pressure cylinder 0.440 m. (17^ in.) 



Diameter of low-pressure cylinder 0.800 m. (31 in.) 



Stroke 0.450 m. (17ft in.) 



They are surface-condensing; the condenser is placed horizontally, 

 and forms part of the engine frame. The valves are easily accessible 

 for inspection and maintenance in good working order. The engines 

 are so arranged that they can readily be made to drive, together or 

 separately, both the propellers or the pumps. The boilers are 

 Belleville boilers, fitted with economizers of 2154 sq.ft. heating 

 surface, with two donkey pumps, and with an air compressor of 

 8830 cu.ft. A fresh-water tank can supply the boilers during a 

 continuous run of 75 hours; suitable apparatus are provided for 

 filtering the feed-water taken from the drain-pipes and condensers. 

 Each dredge is driven by two propellers worked from the engine 



