sometimes inserted between the topping lift by which this is raised
and the end of the boom.

The margin of safety of steel wire rope is much larger than is that of
hempen rope, a fact of importance both in towing in a rough sea and in
hauling. Galvanized steel wire with a hempen core was first used by
Agassiz on the "Blake." He states that his wire weighed one pound per
fathom, against two pounds per fathom of hempen rope, and had a
breaking strain nearly twice that of hempen rope, which bore two tons.
Thus in hauling the wire rope has both greater capability and less
actual strain. It has also the advantages of occupying a mere fraction
(1/9) of the storage space needed for rope, of lasting much longer,
and its vibrations transmit much more rapid and minute indications of
the conduct of the dredge.

Wire rope is kept wound on reels supplied with efficient brakes to
check or stop its progress, and an engine is often fitted for winding
it in and veering it out. From the reel it passes to the drum of the
hauling engine, round which it takes some few turns; care is taken by
watching or by the use of an automatic regulator (Tanner) that it is
taken at a rate equal to that at which it is moving over the side.
From the hauling engine it passes over leading wheels (one of which
should preferably be a registering wheel and indicate the amount of
rope which has passed it), and so it reaches the end of the derrick
boom.

The dredge is lowered from the derrick boom, which has been previously
trained over to windward so that its end is well clear of the ship,
while the ship is slowly moving forward. The rope is checked until the
net is seen to be towing clear, and then lowered rapidly. Where a weight
is used in front of the trawl Captain Calver successfully adopted the
plan of backing after sufficient line had been paid out: the part of the
rope from weight to surface thus became more vertical, while the shorter
remainder, previously in line with it, sank to the bottom without change
of relative position of weight and dredge. The ship was then ready for
towing. When no front weight is used the manoeuvre is unnecessary.

There should be a relation maintained between speed of vessel onward and
of rope downward, or a foul haul may result owing to the gear capsizing
(in the case of a trawl), or getting the net over the mouth (in a
dredge). The most satisfactory method of ensuring this r