HYDRAULIC DREDGES FOR CHANNELS 123 



resistances with full head of steam on the engines without risk of 

 breakage. The main gearing driving the cutter is of cast steel 

 5 in. pitch and 5 in. face. 



Steam is furnished by four boilers, having collectively 8500 

 sq.ft. of heating surface, and adapted for working pressures of 

 160 Ibs. There is coal bunker capacity of 200 tons. 



The main pump is of the centrifugal type, having cast-steel 

 runners of inclosed type and heavy cast-iron shell. The blades of 

 the runner and the heads of the pump are protected by renewable 

 steel wearing plates in the shell. This shell is exceedingly heavy, 

 so that it can stand a considerable amount of wear before it begins 

 to fail, and it is also so designed that the stream of material issuing 

 from the runner does not impinge to any extent upon it at any one 

 point. 



The entire operations of the dredge are controlled from the 

 pilot-house on the upper deck. Here are located the levers for 

 both the bow and stern anchorage winches and the lifting winch for 

 the suction pipes; also a system of bells and signals to the engine 

 room. The pilot-house is so placed that the operator has an unob- 

 structed view up and down the river; also of the entire discharge- 

 pipe (see Fig. 36). 



The dredge is fitted with complete quarters for a double crew 

 of 36 men, or 18 men on each shift. The dredge works continuously 

 from Sunday night till Saturday night, without stopping except 

 when necessary". The dredge is attended by a powerful light -draft 

 twin-screw tug. The principal duty of this tug is to fleet the anchors 

 as the dredge moves ahead. The side lines of the channel to be 

 made are marked at night by temporary range lights. 



The efficiency of the dredge " J. Israel Tarte " is estimated at 

 600,000 cu.yds. per month, although for short periods it has worked 

 at the rate of 2600 cu.yds. per hour. The average cost per cu.yd. 

 for the year is about 1} cents. This dredge was built by the Poison 

 Iron Works of Toronto, Can., at a cost of $163,800, excluding the 

 discharge pipe and the winches, which were not designed when the 

 contract was placed. 



Forward Feeding. The second group of the hydraulic dredges 

 employed in the improvements of channels and rivers are those 

 provided with a forward feeder and extensively used on the Mississ- 

 ippi River. The following description of the " Delta " taken from a 

 paper by Mr. Ockerson, will serve to illustrate this type of dredge. 



