Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WREC~< CARGO RECO~ERY METHOD.
The present invention relates to a method of
recovering a cargo on board a wreck that has sunk in deep
water.
Numerous wrecks exist at the bottom of the oceans
containing cargoes of value which cannot be utilized at
present by conventional methods because of depth.
Present methods generally make use of divers and so they
are restricted to shallow waters.
Recovery of a cargo enclosed inside a wreck is a
very difficult task. Access needs to be made through the
wreck. This access may be provided through the hatches
if the configuration so allows (wreck lying horizontally
on the bottom). It may be made through the hull if the
wreck is on its side or upside-down on the bottom.
It is common practice for the wreck to be cut up by
means of explosives or oxygen cutting torches used by
divers. Once access has been provided, the cargo is
recovered by conventional hoisting means (e.g. buckets
operated from anchored barges).
Cargoes of value have thus been utilized from depths
of less than 500 meters (m).
For several years, in rescue applications, use has
been made of very strong dredging buckets to demolish
wrecks that constitute a danger to navigation. Such
buckets are actuated by cables under the control of
divers. Their closure force and their traction force can
reach 50 metric tons and thus allow large pieces of wreck
to be extracted by tearing off plates.
When cargoes are in deep water, utilization has been
possible only from wrecks that present few difficulties
of access, either because the cargo is lying on the
bottom due to the ship breaking up during the shipwreck,
or because the ship was made of wood that has
deteriorated greatly. Manned or remote controlled
submarines have been used for this purpose with success.
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Various attempts have been made with cargoes in deep
water enclosed on board modern wrecks made of steel, but
no method has been found to be technically and
economically satisfactory. Dismantling by means of
explosives has been tried in association with the use of
lightweight buckets handled by means of cables. The
effectiveness of explosives has been disappointing at
great depth.
The method of the invention enables both the problem
of dismantling the hull, and the problems of recovering
the cargo to be solved, even at great depth.
During the '70s, the first dynamically positioned
drilling vessel was developed for oil prospecting in deep
water (300 m to 3,000 m). In the world, there exist at
present about 15 vessels that are capable of drilling in
deep waters. They are fitted with heavy derricks capable
of exerting vertical forces of 500 metric tons. Pounding
compensators enable the motion of the vessel to be
compensated while the tool is in contact with the ground.
The size of the well beneath the derrick is such (5 m x
5 m) that it is possible to handle large packages.
The object of the invention consists in using a
large-capacity pincer from such a vessel by means of an
underwater module for moving the pincer and for actuating
it under the control of cameras.
The invention relates to a method of using a
dynamically positioned drilling vessel to recover a cargo
enclosed on board a wreck that has sunk in deep water.
The method is characterized by the fact that the wreck is
dismantled by means of a pincer and of a shock absorber
device located near the bottom of the drill string.
The invention also relates to a device for operation
from a dynamically positioned drilling vessel to
dismantle a wreck sunk in deep water. The device is
characterized in that it is constituted by a pincer and a
shock absorber device disposed near the bottom of the
drill string.
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The closure force of the jaws of the pincer as
actuated by means of hydraulic actuators is such (several
hundreds of metric tons) that it can manage to tear the
sides off the wreck so as to gain access to the cargo.
During the recovery stage, the pincer is fitted with
cheeks and it is used like a bucket having a capacity of
several cubic meters.
During the demolition stage, the pincer is clamped
powerfully onto the structure that is to be dismantled.
The pincer is then hoisted vertically so as to tear off
the piece held between the jaws. The sizes of the pieces
removed vary as a function of the tear lines obtained.
Some pieces resist more strongly than others, and it is
sometimes impossible to tear them off without running the
risk of breaking the drill string. The pincer is then
moved a little, and in general after a few attempts, the
piece is torn off. This work of destruction by clamping
onto pieces and tearing them off is quite different from
the work of taking samples by conventional grapplers.
The shock absorber device is essential in implementing
the method. At great depths, under maximum traction
force, the total elongation of the drill string is about
10 m. The accumulated energy in the "mass-spring" system
is such that without the shock absorber device, when
tearing takes place, the assembly comprising the module
and the pincers would rise with great acceleration, to a
height well above the equilibrium position. This would
give rise to uncontrolled buckling of the drill string
and would run the risk of breaking it.
Operating times are relatively lengthy (one rising
and lowering cycle per day to a depth of 3,000 m),
however such operations can be economically profitable
given the value of certain cargoes of ore, for example.
The device enabling the method to be implemented is
described below with reference to the accompanying
drawings, in which:
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Figure 1 is a section through the apparatus of the
invention;
Figure 2 is a section through the underwater module;
and
Figure 3 is a section through the pincer.
Figure 1 shows the apparatus in section installed on
board a drilling vessel (1). The apparatus comprises a
pincer (2) installed at the end of the drill string (3)
and handled vertically by means of the derrick (4) and
the turntable (5). A control module (6) causes the
pincer to move horizontally by means of thrusters and
serves to operate it hydraulically. An umbilical cord
(7) paid out from a winch (8) transmits power and control
to the underwater module. It is attached along the drill
string by means of fast-acting fixing collars (9).
On the surface, the vessel (1) is held by dynamic
positioning to within a circle of radius 5 m. At the
bottom, the pincer (2) is displaced vertically by means
of the drill string (3) and horizontally by means of the
thrusters. In a preferred embodiment of the invention,
the thrusters are steered by rotating the drill string
(3) directly from the turntable (5).
A shock absorber device (10) made up of a series of
circular plates is disposed near the bottom of the drill
string so that the drill string cannot be put into
compression when contact is suddenly lost with the wreck
(11) during a tearing-off action. An uncontrolled
compression force would run the risk of damaging the
drill string by buckling its section. The energy that is
stored when the drill string is put under tension is very
large because the string lengthens by several meters when
subject to a force of several hundreds of metric tons.
Figure 2 is a section through the underwater module
(6). A hydraulic pump (12) driven by an electric motor
(13) powers the motors of the thrusters (14) and the
hydraulic actuators of the pincer via a set of
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electrically controlled valves (15) and a compensation
tank (16).
At the base of the module, a wide-angle camera (17)
and a floodlight (18) enable the situation of the pincer
(2) relative to the wreck (11) to be observed.
At its top, thrusters (14) are disposed
diametrically opposite each other about the drill string
(3).
The assembly is housed in a cylinder (19) made of
thick metal sheet, so as to protect the equipment while
working inside the wreck (11). The drill string (3)
passes through the module (6) and also through the shock
absorber device (10). The diameter of the cylinder and
the diameter of the plates constituting the shock
absorber device (10) are such as to allow them to pass
through the turntable (5) during on-board handling.
Figure (3) is a section through the pincer (2). The
jaws (20) are fitted with lips (21) and with teeth (22)
of large dimensions. In conventional manner, they are
actuated by actuators (23) and they are synchronized by
means of gearing (24). Removable cheeks (25) are bolted
onto the sides of the jaws (20) so as to transform them
into scoops while recovering the cargo.
The inside volume of the framework is trapezium-
shaped in section (26), being open at its bottom end.This volume is organized to protect a camera (27), two
floodlights (28), and a depth sounder (29). A device for
injecting clear water makes it possible to form a cone of
clear water in the field of the camera (27) and is
intended to increase visibility when the pincer is at the
bottom of a hole in a volume of water that is completely
cloudy because of the sediment in suspension and the lack
of current inside the wreck.
The apparatus makes it possible to identify the
target while the pincer is resting wide open on its
teeth.
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The clear water is pumped from the surface by means
of drilling pumps and it is conveyed to the pincer
through the drill string (3). It could equally well be
pumped from the underwater module by means of a pump
situated inside the module, for example.
The method and the apparatus of the invention are
described with respect to an embodiment that is preferred
but not limiting. Thus, the drilling vessel could be
replaced by a floating support fitted with a derrick and
a special drill string. The thrusters fitted to the
underwater module could be disposed in a different known
manner so as to displace the pincer without it being
necessary to steer it by means of the drill string.
The method and the apparatus of the invention apply
to recovering any kind of cargo, including radioactive
substances and nuclear reactors enclosed inside deep
wrecks.
