244 THE DEPTHS OF THE SEA. [CHAP. VI. 
far the most common error in amateur dredging, 
from the low angle at which the line is lying in the 
water the dredge has its best chance of getting an 
occasional scrape. It is bad economy to use too 
light a rope. For a dredge such as that described, 
and for work round the coasts of Europe at depths 
attainable from a row-boat or yawl, I would recom- 
mend bolt-rope of the best Russian hemp, not less 
than one and a half inch in circumference, which 
should contain from eighteen to twenty yarns 
in three strands. Each yarn should bear nearly a 
hundredweight, so that the breaking strain of such a 
rope ought to be upwards of a ton. Of course it is 
_never voluntarily exposed to such a strain, but in 
shallow water the dredge is often caught among 
rocks or coral, and the rope ought to be strong 
enough in such a case to bring up the boat, even if 
there were some little way on. 
Dredging in sand or mud, the dredge-rope may 
simply be passed through the double eye formed by 
the extremities of the two arms of the dredge ; but in 
rocky or unknown ground it is better to fasten the 
rope to the eye of one of the arms only, and to tie the 
two eyes together with about three or four turns of 
rope yarn. This breaks much more readily than the 
dredge rope, so that if the dredge get caught it is 
the first thing to give way under a strain, and in 
doing so it very often so alters the position and form 
of the dredge as to allow of its extrication. 
The dredge is slipped gently over the side, either 
from the bow or from the stern—in a small boat 
more usually the latter—while there is a little way 
on, and the direction which the rope takes indi- 
