142 MANUAL OF THE MOTLUSCA. 
The dredges are put overboard on the weather-side, and the 
ropes made fast to a bulwark or thwart; each dredger holds 
the rope in his hand, after giving it a single turn round a thwart 
or ‘‘belaying pin,” to regulate the strain by means of the 
spare line. When a sufficient distance has been traversed, or 
the ropes strain with the weight of mud and stones, the vessel 
is brought to, and the dredges hauled up and emptied.* 
The length of line required is about double the depth of the 
water. If the line is too short, the dredge will only skim the 
bottom ; if too long, it will be in danger of getting fast. When 
the bottom is loose sand or soft mud, the line must be short- 
ened, or the vessel haye more way, or else the dredge will be 
apt to get buried. 
The strength of the line ought to be sufficient to anchor the 
vessel in smooth water,—though not, of course, when there is 
much way on her,—so that if the dredge gets foul it is necessary 
to let out the spare line and relieve the strain while the vessel 
is brought round. The dredge will then usually capsize, and 
may be hauled up. 
If the bottom is at all rocky, a small strong dredge is best. 
The line must be shortened, and some additional precautions 
may be taken, such as fastening the rope to one ring of the 
dredge, and tying the other with spun yarn, which will break . 
under a sudden and dangerous strain, and release one end of 
the dredge. 
In dredging on coral-ground, Mr. Cuming employed a 3-inch 
hawser, and had a patent buoy attached to the dredge by a 
14-inchrope. More than once the hawser parted, and the dredge 
was left down all night, but recovered the next day. 
Mr. McAndrew’s researches on the coast of Norway were 
conducted in the Naiad, a yacht of 70 tons, and extended from 
the shore to 250 fathom water. The dredge employed was at 
least twice as strong and heavy as the one we have represented, 
and all forged in one piece, instead of folding up. The bag was 
fastened on the frame with thongs cut from the hide. Before 
using, it requires to be towed astern for a couple of hours, to 
soften it. In three months’ work only two cow-hides were used, 
and one of those was torn by accident on sharp rocks. Several 
spare dredges were on board, in case of emergency, but not used. 
Dredging in deep water (50 to 300 fathoms) can only be done 
* The collector may go out with the fishermen and superintend his own dredge 
zimost any time of the year, although oyster catching is illegalinthe summer. The 
scallop-banks off Brighton are in 15 fms. water, and nearly out of sight of land. It is 
not always possible to werk over them and return the same night. 
