GRAB DREDGES 169 



supporting an inclined swinging boom. The boom rests on a turn- 

 table and its upper end is able to revolve around the gauging pin 

 of the A frame, being kept in an inclined position by means of 

 iron rods furnished with turnbuckles. One or two sheaves located 

 at the top of the boom guide the chains controlling the bucket. The 

 bucket, made of steel, is divided into two or more sections provided 

 with lever arms and chains so arranged that the bucket can be 

 closed and open at will. The chains are wound around the drums 

 of hoisting engines placed on deck of the boat, and as the bucket 

 is operated by two chains there are two drums on the hoisting engine. 

 Steam power is supplied to the engines by boilers which are located 

 at the stern of the boat. The boat is built of rectangular form in 

 the shape of a float, with a structure above deck to house the boiler 

 and machines and in some cases even to provide accommodation for 

 the crew. While the machine is in operation the boat is fastened 

 to the bottom by three or four spuds which are constructed and 

 operated as with the dipper dredge. As the efficiency of the machine 

 is considered one bucket per minute, the manufacturers have increased 

 greatly the capacity of buckets and to-day we have grab dredges 

 with buckets of 8, 10 and 12 cu.yds. capacity. 



The English grab dredge consists of an ordinary locomotive 

 crane mounted on a boat. The locomotive crane is composed of 

 a large horizontal cog-wheel, whose axis is fitted into a socket of 

 an iron frame, with wooden platform, upon which are placed the 

 boiler and the engine. In front of the iron frame there is a jib or 

 boom braced by means of iron rods, connected to vertical iron 

 stands, and tied to the rear of the frame of the platform by rods 

 provided with turnbuckles. The boom or jib is made of various 

 designs and of different materials, but usually it is made of iron 

 except when very long, when it is made of trussed steel. The bucket 

 is attached to the hoisting chain, which after passing over a sheave 

 at the top of the boom is wound around the drum of the hoisting 

 engine. The engine is so arranged that by putting into gear another 

 small cogwheel whose cogs engage those of the large one supporting 

 the platform, the platform and boom and consequently the bucket 

 turn a complete circle. 



The English grab dredging machine is mounted on many kinds 

 of boats, depending upon the locality of the work. In dredging 

 along the quay walls or small harbors and also along canals and 

 rivers, the machine is mounted on any ordinary barge, being moved 



