DEEP-SEA EXPLORATION. 
349 
The fiiiictioii of the boom is to lead the dredge rope clear of the shij)’s side. 
When rigged for service, elevated at aii angle of 50°, it gives a clearance of about 
10 feet. When not in use, it is lowered to a horizontal position with its forward end 
resting upon the topgallant forecastle. 
The register pulley t in the heel of the boom is of brass with a deep, narrow 
groove, and serves to lead the dredge rope from the accumulator g to the lower side of 
the dredging boom, besides ])erforming its function of registering pulley. The register 
is attached to the left .side of the sleeve at the heel of the dredging boom, is actuated 
by a worm wheel carried on the shaft of the register pulley, and records the number of 
fathoms of dredge rope out. 
The boom topping lift r is a twofold purchase of 3i-inch manila roi)e, its hauling 
part shackles to a link in the masthead band the loAver block is shackled to the 
upper end of an accumulator which, in turn, shackles to an eyebolt at the boom end. 
Shackles are used on the topping lift to prevent unhooking in case the dredge rope 
should part under heavy tension. An accumnlator is attached to the topping lift to 
supplement the action of the jnain accumnlator. 
The boom guys, one forward and one aft, ai'C twofold purchases of 2^-iuch manila 
rope, heavier than required for simply holding the boom, but they are used at times in 
hoisting an overloaded trawl over the rail. 
The boom purchase is a twofold tackle with 2Ainch manila roim used for hoisting 
the trawl on board; it hooks to one leg of a short pendant, the other leg carrying the 
after boom guy. 
The dredging blocks (plate xxx) two in number, used on the lower end of the 
accumulator and at the outer end of the dredging boom, are leads for the dredge rope; 
lig. 1 is a sectional elevation, and fig. 2 a side view. 
The frame a is composed of two pieces of bar iron 5i inches wide at one end, 
4i at the other, 3^ in the center, and inch thick; they are secured by riveted 
bolts to a block of Avrought iron 5^- inches in length, 2.J, in Avidth, and 2i in depth, 
having through its center a If-inch hole for the shackle bolt d. The sheave b is of com. 
Ijosition 21.t inches total diameter, 18 inches diameter at the bottom of the score, and 
24 inches in Avidth. It has three antifriction bushings i i i, the outer one of steel, 
fitted rigidly in idace, the middle one of phosphor bronze, and the inner one of iron. 
The two latter move freely, and they are furnished with oil grooves on both inner and 
outer surfaces. The pin c is of cast steel, inches in diameter. It has a shoulder at 
one end, Avhich acts as a spreader for the frame and is held in place by a scrcAV thread 
and nut. 
The shackle bolt d, the shackle e, and the pin / are of the best American iron. The 
former is held in place by a nut and Avasher, which allow it to turn freely and act as a 
swivel. The guard g is of Avrought iron and is intended to prevent the dredge rope 
from flying out of the sheave. The hood h acts as a guard and assists in turning the 
block in line with the rope so that it Avill lead fairly into the score of the sheave. It 
is a bronze ca.sting. The nuts on the block are secured with drift pins; the guard and 
hood are used only on the block at the boom end. 
The masthead collar and band (plate xxix) are placed 13 inches below the futtock 
band on the foremast, and the accumulator and topping lift are shackled to eyes in the 
band. The collar is fitted in the following manner: A strong Avrought-iron band, 
flanged on its lower edge, is secured to the mast by Avood scrcAvs; the band, also of 
