200
N. A . IiOLME
closing action in the Aberdcen grab (Smith and McIntyre, 1954) and
in Baird’s sampler (Baird, 1958). Greater mechanical advantage is
obtained by unwinding cable from a drum attached to the sampler.
This was achieved by Stetson (1938) who used a worm-drive to work
a small semi-circular corer, and by Holme (1949, 1963) who used large
and small drums attached side by side to obtain a considerable mechanical advantage and at the same time minimize the effects of sudden
jerks on the cable. The principle of a rotating drum is also employed
in Knudsen’s sampler (see p. 203).
Springs may also be used to assist penetration. Where these are
used to force the sampling parts down into the sediment there is,
naturally, an opposite reaction tending to lift the remainder of the
apparatus. This is, however, partially offset by the inertia and water
resistance of the frame. Springs have been used with some success
in the Aberdeen grab (Figs. 9, 11) (Smith and McIntyre, 1964), while
a horizontal closing movement actuated in part by springs is incorporated in Baird’s (1968) grab. In the latter the inclined surfaces of
two opposed blades exert shearing forces, tending to make them dig
deeper, so that a double wedge-shaped section is excavated (Fig. 19).
It is advisable to insert a safety locking pin when springs are used
to avoid the danger of premature release on board ship. The pin is
withdrawn after the sampler is hoisted over the ship’s side.
In the Otto Petterson (1928) sampler a heavy weight slides down
a rod to hammer a square corer into the bottom. Only a single blow
can, however, be struck. Undoubtedly a series of heavy blows would
be successful in making a coring tube penetrate and this has been
achieved on a small scale by Slack (1954), who describes a small
corer for use in fresh water. Yiggott (1936) used the force of an explosive charge to force a geological coring tube into the bottom, but this
method has been superseded by Kullenberg’s (1 947) piston-corer.
An interesting recent development is a 0.2 m2 Petersen grab closed
by compressed air from a small cylinder attached to the apparatus
(Flury, 1963). The release is actuated as the grab strikes bottom so
that closure is completed before the upward pull on the wire liftR the
grab off the bottom.
Several workers have attempted to use hydrostatic pressure &s a
source of power, one of the first such instruments being described by
Joly (1914). He devised an ingenious deep-sea coring tube with penetration aesisted by a semi-rotary movement imparted by a fourcylinder engine powered by water entering an evacuated chamber.
Although described in considerable detail, this instrument does not
seem to have been ever used.
N. A . IiOLME
closing action in the Aberdcen grab (Smith and McIntyre, 1954) and
in Baird’s sampler (Baird, 1958). Greater mechanical advantage is
obtained by unwinding cable from a drum attached to the sampler.
This was achieved by Stetson (1938) who used a worm-drive to work
a small semi-circular corer, and by Holme (1949, 1963) who used large
and small drums attached side by side to obtain a considerable mechanical advantage and at the same time minimize the effects of sudden
jerks on the cable. The principle of a rotating drum is also employed
in Knudsen’s sampler (see p. 203).
Springs may also be used to assist penetration. Where these are
used to force the sampling parts down into the sediment there is,
naturally, an opposite reaction tending to lift the remainder of the
apparatus. This is, however, partially offset by the inertia and water
resistance of the frame. Springs have been used with some success
in the Aberdeen grab (Figs. 9, 11) (Smith and McIntyre, 1964), while
a horizontal closing movement actuated in part by springs is incorporated in Baird’s (1968) grab. In the latter the inclined surfaces of
two opposed blades exert shearing forces, tending to make them dig
deeper, so that a double wedge-shaped section is excavated (Fig. 19).
It is advisable to insert a safety locking pin when springs are used
to avoid the danger of premature release on board ship. The pin is
withdrawn after the sampler is hoisted over the ship’s side.
In the Otto Petterson (1928) sampler a heavy weight slides down
a rod to hammer a square corer into the bottom. Only a single blow
can, however, be struck. Undoubtedly a series of heavy blows would
be successful in making a coring tube penetrate and this has been
achieved on a small scale by Slack (1954), who describes a small
corer for use in fresh water. Yiggott (1936) used the force of an explosive charge to force a geological coring tube into the bottom, but this
method has been superseded by Kullenberg’s (1 947) piston-corer.
An interesting recent development is a 0.2 m2 Petersen grab closed
by compressed air from a small cylinder attached to the apparatus
(Flury, 1963). The release is actuated as the grab strikes bottom so
that closure is completed before the upward pull on the wire liftR the
grab off the bottom.
Several workers have attempted to use hydrostatic pressure &s a
source of power, one of the first such instruments being described by
Joly (1914). He devised an ingenious deep-sea coring tube with penetration aesisted by a semi-rotary movement imparted by a fourcylinder engine powered by water entering an evacuated chamber.
Although described in considerable detail, this instrument does not
seem to have been ever used.