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WIRE-DRAGGING THE
OCEAN'S BOTTOM
Bv STANLEY W. TODD
T
u
DISCOVERING UNCHARTED NEEDLE ROCKS
Pulled by two small vessels, and held up by intervening buoys, this wire drag catches all the sharp projections of the
ocean's floor.
N O sensible mariner would feel
safe in traversing the coasts
of the United States if he
were not well provided with
charts made by the government.
There are so many hidden rocks
and shoals, particularly along the Eastern
States and in Alaskan waters, that
if he did not know the "lay of the land",
his ship would eventually come to grief.
Surveys of all coast waters have been in
progress for many years, but ships have
grown so rapidly in size and displacement
that new surveys constantly have
been made necessary. So important is
this duty of the government that the
U. S. Coast and Geodetic Survey in the
Department of Commerce maintains several
surveying parties always making
new observations and charts.
This work has been greatly facilitated
in late years by what is known as the
"wire drag" process, which makes such
observations all the more sure. The old
way was to use a lead line from a moving
vessel. This was all right for sandy
portions of the coast, but it was not a
conclusive method along rocky coasts,
for often lines would escape many pin­
240
nacle rocks, sharp ledges and boulders
that must be located in order to make
shipping safe. The obstructions sometimes
cannot be seen and are very easy
to miss with a single line.
The "wire drag" consists chiefly of a
wire, called the "bottom wire", towed at
a certain distance below the surface of
the water, to find the location of any
hidden dangers to navigation. The other
parts of the* apparatus consist of additional
wires pulled down with weights
attached to the bottom wire and supported
by buoys, large and small, attached
to the surface wires dragged by
two motor launches.
The drag set is so constructed that it
keeps the bottom wire at a constant
known depth and allows changes to be
made to conform with the tides or pass
over shoals. If a part of the drag is
caught on a shoal, the rest of it is prevented
from sinking by stopping the towing
boats, and if there is a break, two
parts of the bottom wire at least will
hold in place. If there is any accident,
the broken portions of the drag can be
replaced.
One of the launches used in operating