[Gl] FISHEEIES OF THE UNITED STATES. 573 



Iron Dredge Block for the dredge-rope, as used on the steamer Blake. 

 Eepresented by a diagram (Plate 34 of Sigsbee's series). 



United States Coast and Geodetic Survey. 



On the steamer Blake the dredge-rope leads through one large snatch 

 block at the boom end, and through several similar ones placed upon 

 the deck. In the former the side plates are free to revolve, but in the 

 latter they are pinned to the strap, and connected by socket bolts, 

 which are intended to prevent the dredge-rope from getting between 

 the side plates and the strap. The pins or bolts are of steel, the 

 sheave of cast-iron, the side plates of thin plate-iron, the flap or hook 

 and strap of wrought iron. The pendant block has the sheave 1 inch 

 wider than the deck blocks. 



Iron Dredge Block, used on the steamer Fish Hawk. 

 United States Fish Commission. 



Two pendant dredge blocks are used on the Fish Hawk, one suspended 

 from the lower end of the accumulator, the other from the outer end of 

 the dredging boom, as shown in the photographs of that steamer. These 

 blocks are similiar to one another and to those of the Blake. The ex- 

 ample displayed is an exact copy of the one attached to the accumulator. 

 The side plates are 19J inches in diameter, five-sixteenths of an inch 

 thick, and have an intervening space of about 2 inches for the sheave. 

 The latter is 16 inches in diameter, about If inches thick, and grooved 

 to a depth of about 2 inches, the bottom of the groove being rounded 

 and just wide enough to accommodate with ease a single turn of the 

 dredge rope. The straps are in two pieces, fastened together in the 

 middle by the bolt or pin which passes through the sheave, and has a 

 nut at each end. The straps are one-half inch thick, 2 inches wide 

 above the middle, and 1J inches wide below. A strong swivel-hook at 

 the upper end furnishes the means of suspending the block. The mate- 

 rials used are the same as described for the Blake. In addition to these 

 blocks there is an iron sheave fastened in the heel of the boom. 



Brass Dredge Block, used on the steamer Albatross. 



United States Fish Commission. 



The same number of dredging blocks are used on the Albatross as on 

 the Fish Hawk, and they have the same positions, but their construction 

 is somewhat different, and the sheave revolves on a series of friction 

 rods, which do away with the necessity of oiling. There are no side 

 plates. The sheave is of brass, 21 J inches in diameter, and about one- 

 half an inch thick, excepting toward the center and rim. At the rim it 

 expands to a thickness of about 2\ inches, and is grooved to a depth 

 of 2 inches, as in the previously described block. The hole through the 

 center of the sheave is 3f inches across and 2J inches through, the 

 sheave being thickened around it to form a sort of hub. The strap 



