MECHANICS AND USEFUL ARTS. 77 



FORBES' ROTARY DREDGER. 



This machine consists of a hull of suitable size to carry the machinery. 

 In the middle of the boat ath wart-ships, and near the bow, running fore 

 and aft, there is a well-hole, about three feet -wide, and twenty-six feet 

 long. In this hole works a wheel, carrying upon its periphery the buckets 

 or scoops, made in the usual manner, with a hinged bottom, secured by a 

 latch. The wheel has ten hubs, and ten sets of arms, stiffened with diago- 

 nal braces, to prevent lateral motion ; upon each side of the wheel is a seg- 

 ment spur-wheel, into which is geared the pinions driven by the engines. 



The journals of the scoop-wheel shaft work in boxes, that can be raised 

 or lowered by a chain and windlass, to suit the depth of the bottom to be 

 operated upon. In a frame at the bow of the boat there are two hinged 

 schutes, one of which, when the machine is in operation, is kept at one 

 inclination ; the other, situated above, and leading into the rirst, to which 

 it is hinged, is raised by each bucket as it passes upwards ; as the wheel 

 revolves, the bucket passes beyond the reach of the schute, where the end 

 next the wheel falls beneath the bucket, striking a trigger that opens its 

 bottom, leaving the contents free to fall into the schutes, and be conveyed 

 by them into the transporting scows alongside. 



This machine, for some kinds of work, must supersede all others. Where 

 a long stretch can be had, such as a bar of a river, the bottom of a canal, 

 &c., the performance must prove admirable. No time is lost except that 

 spent in replacing the loaded scows with empty ones, and that, by practice, 

 m.iy be reduced to almost nothing. As the material is cut away, the boat is 

 drawn forward by a rope anchored ahead, and passing round a barrel on 

 the wheel shaft ; the rate of progress for each kind of cutting being regu- 

 lated by the proper sized windlass barrel wheel, which can be quickly 

 taken off and replaced by another. 



It is said that a machine of the third class, having a wheel 24 feet in 

 diameter, with four buckets, has dug 1200 cubic yards of gravel bottom 

 in a day. Jour. Frank. Institute. 



HAMILTON'S IMPROVED DREDGING MACHINE. 



This machine consists substantially of a number of scoops, hung in 

 nearly a horizontal position, in a frame which is arranged to be raised or 

 lowered at pleasure, between two firmly- connected boats. As used in 

 lowering shoals and sand-bars, the whole apparatus is to be towed by a 

 steamboat backward and forward, discharging the dirt each time in the 

 deep water which is assumed to be adjacent. The forward end of the 

 frame is armed with joints projecting downward, the effect of which is to 

 harrow up the bottom. Each scoop is so connected to the frame that its 

 forward edge is capable of being raised and lowered to a considerable ex- 

 tent, forming, when raised to a horizontal position, a nearly water-tight 



