Gravity Corer

• Head: consisting of a cylindrical galvanized iron mass with a variable weight of 200 to 800 Kg which provides the momentum necessary for the instrument to penetrate into the sedimentary layers.
• Barrel: in galvanized iron with a 105 mm external diameter and a variable length of 2 to 6 metres. A longer dimension is achievable by using a proper connecting sleeve. Inside the barrel a liner in PVC meets the right housing, with a 90 mm external diameter (84 internal), implemented to hold the sample.
• Nose, including cutter and catcher: the lowermost part of the barrel is reinforced by a core nose which ends with a stainless-steel cutter. A device with 4 spades of triangular shape locks the nose needed to keep the sample during the corer’s recovery. The closure of the spades is controlled by the liner at the start of the extraction of the seabed.

The most common techniques are two:

• Gravity: lowering the corer at the maximum speed permitted by the winch until it impacts with the seafloor.
• Free-fall: activated by a mechanical release system applied on the main wire and hooked to the eyebolt’s corer. It consists of a trigger, a counter-weight and a wire-releaser of a determined length depending on the height of the chosen fall.

 “Angel Descent” method can be used in deep and shallow water.

A loaded cell on the snatch block, an accessory instrument essential to the reconstruction of events during the coring, provides a digital output for on-line acquisition of the main wire’s strength data.

This data produces a tensiometric graph, which points out the significant events during the coring phase: the corer’s descent, the release, the seabed impact, the penetration, the extraction and the recovery.

A new instrument purchased by Carmacoring for a deep study of the coring dynamics is the accelerometer. Fixed at the corer head, records the acceleration every 2 milliseconds, up to a maximum depth of 3000 meters.

G. Busatti, A. Magagnoli, M. Mengoli: Carotiere a gravità 1.2 T. Rapporto Tecnico n. 13, C.N.R. – Istituto di Geologia Marina, Bologna, 1980.