430
N. A . IIOLME
I). Pingrrs
When \\orking ill deep water, when the weight of wire paid out is
considerablc, it may be ciificnlt to tell when all but the heaviest of
gear has touched bottom. Alternatively, it may be necessary to suspend
gear (such as an underwater camera) only a few feet above the bottom.
The piiiger is an instrument which is attached et a point on the wire,
or to the gear itself, which enables this to be carried out. The pinger
radiates very brief pulses of sound a t a precisely controlled rate;
and the unit is self-contained, with no electric cable to the surface.
On a hydrophone hung below the ship two sound signals are recordedone direct from the pinger, the other an echo off the bottom. These
will tend to merge and eventually coincide when the pinger is on the
bottom, so enabling a precise measurement at any time of the position
of thepinger relative to the bottom (Edgerton and Cousteau, 1959;
Horsey, 1060). Nalwalk et al. (1061) describe the use of such a pinger in
deep-sea dredging. The pinger is attached to the wire 90 m above the
dredge, and then lowered until signals from the pinger show that it is
some 30 m above the bottom. I t is then certain that the dredge is on
the bottom, and by this means considerable economy in the length of
wire paid out is possible. This is a much more precise method than
Kulleiiberg’s calculations of wire angle (pp. 181-2).
-
X. TREATMENT OF SAMPLES ON BOARD SHIP
A dredge fitted with a fairly wide-meshed net will sievc any sediment which enters, retaining only stones and larger animals. Thomw
(1960) has t1escril)ed a special anchor-dredge with sdf-nicving net
designed to sieve out members of the hirrowing fauna, hut for many
purposes it will be necessary to UHP a fine-meshcd nr:t which will
bring up a sample of the deposit with its contained animals, SO avoiding
loss of smaller specimens. Sometimes the sample of sediment is very
large, and if only a rough sorting to collect the larger animals is required,
there are various simple ways in which this may be achieved without
too milch effort.
If the dredge bag is not lined with canvas or stramin much of the
sediment will wash out during hauling, and the remainder may be
disposed of either by use of the hose directed into the dredge bag, or
by hauling up the dredge until the mouth is clear of the water, and then
steaming ahead, SO washing the contents in the sea. A refinement of
this method was used by Gustafson (1934) when working the heavy ring
dredge. The dredge bag had a fairly wide mesh (20 mm between knots)
and after hauling up the bag to the surface an outer bag of smaller-
N. A . IIOLME
I). Pingrrs
When \\orking ill deep water, when the weight of wire paid out is
considerablc, it may be ciificnlt to tell when all but the heaviest of
gear has touched bottom. Alternatively, it may be necessary to suspend
gear (such as an underwater camera) only a few feet above the bottom.
The piiiger is an instrument which is attached et a point on the wire,
or to the gear itself, which enables this to be carried out. The pinger
radiates very brief pulses of sound a t a precisely controlled rate;
and the unit is self-contained, with no electric cable to the surface.
On a hydrophone hung below the ship two sound signals are recordedone direct from the pinger, the other an echo off the bottom. These
will tend to merge and eventually coincide when the pinger is on the
bottom, so enabling a precise measurement at any time of the position
of thepinger relative to the bottom (Edgerton and Cousteau, 1959;
Horsey, 1060). Nalwalk et al. (1061) describe the use of such a pinger in
deep-sea dredging. The pinger is attached to the wire 90 m above the
dredge, and then lowered until signals from the pinger show that it is
some 30 m above the bottom. I t is then certain that the dredge is on
the bottom, and by this means considerable economy in the length of
wire paid out is possible. This is a much more precise method than
Kulleiiberg’s calculations of wire angle (pp. 181-2).
-
X. TREATMENT OF SAMPLES ON BOARD SHIP
A dredge fitted with a fairly wide-meshed net will sievc any sediment which enters, retaining only stones and larger animals. Thomw
(1960) has t1escril)ed a special anchor-dredge with sdf-nicving net
designed to sieve out members of the hirrowing fauna, hut for many
purposes it will be necessary to UHP a fine-meshcd nr:t which will
bring up a sample of the deposit with its contained animals, SO avoiding
loss of smaller specimens. Sometimes the sample of sediment is very
large, and if only a rough sorting to collect the larger animals is required,
there are various simple ways in which this may be achieved without
too milch effort.
If the dredge bag is not lined with canvas or stramin much of the
sediment will wash out during hauling, and the remainder may be
disposed of either by use of the hose directed into the dredge bag, or
by hauling up the dredge until the mouth is clear of the water, and then
steaming ahead, SO washing the contents in the sea. A refinement of
this method was used by Gustafson (1934) when working the heavy ring
dredge. The dredge bag had a fairly wide mesh (20 mm between knots)
and after hauling up the bag to the surface an outer bag of smaller-