154 A TREATISE ON DREDGES AND DREDGING 



engines. The rope for lowering the spuds passes over a grooved 

 sheave fixed at the top of the spud, and its free end is fastened to 

 the forward side of the spud casting. The rope for raising the spud 

 is also attached to the forward castings and passes around the sheave 

 in a slot close to the foot of the spud. The other ends of the rope 

 are attached to opposite ends of the drum of the spud engine. The 

 spud at the stern is operated by a rope fastened to the bottom of the 

 spud and passing over a sheave on deck and thence to the drum of 

 another engine. 



The dredging apparatus consists of a steam shovel proper of 

 large dimensions and made up as usual of an A frame supporting 

 a swinging boom with its dipper handle and bucket. 



The A frame is composed of two slanting beams firmly fixed to the 

 keelson of the hull and resting on top, one against the other, thus 

 forming a truss in the shape of the letter A. This frame is a little in- 

 clined toward the front and it is held in position by iron rods or back- 

 stays provided with turnbuckles fixed to the stem. In dredges of small 

 capacity the A frame is generally composed of two simple wooden 

 beams, but in dredges of larger capacity the frame is made of two 

 built-up iron beams so as to form a very stiff and solid structure. 

 The top of the A frame is always furnished with a gudgeon pin around 

 which swings the iron rod supporting the top of the boom. According 

 to the capacity of the dredge the A frame is made of different heights, 

 varying from 16 or 20 ft. in the smallest up to 75 ft. in dredges of 

 large capacity. 



The boom or jib is a heavy trussed steel beam with a long slot 

 in the middle kept in an inclined position by iron rods, holding its 

 upper end to the top of the A frame, while its lower end rests on a 

 revolving table. The trussed beam forming the boom is usually 

 made with the lower chord straight and the upper one curved or 

 vice versa, but in very large dredges to make the boom more solid 

 and stiff and in better condition to support the weight of the loaded 

 bucket, the boom is built up with curved top and bottom chords. 

 The length of the boom varies with the capacity of the dredge and 

 it is made of different lengths, varying from 20 to 50 ft. It is the 

 swinging of the boom that causes the bucket to revolve in a large 

 radius, thus covering a large field from a single station. The swing- 

 ing of the boom is done by means of a turntable in whose center 

 is fixed the lower end of the boom. The turntable is built up of 

 steel plates and angles and is supported by steel wheels moving 



