U.S. patent application number 10/550263 was filed with the patent office on 2007-04-26 for device and a method for stabilizing and controlling the lowering or raising of a structure between the surface and the bed of the sea.
This patent application is currently assigned to SAIPEM S.A.. Invention is credited to Michel Baylot.
Application Number | 20070089656 10/550263 |
Document ID | / |
Family ID | 33135524 |
Filed Date | 2007-04-26 |
United States Patent
Application |
20070089656 |
Kind Code |
A1 |
Baylot; Michel |
April 26, 2007 |
Device and a method for stabilizing and controlling the lowering or
raising of a structure between the surface and the bed of the
sea
Abstract
A device for stabilizing or controlling the lowering or raising
of a structure between the surface and the bed of the sea. The
device includes at least one connection element of the cable or
chain type. The connecting element has a first end that is
connected to and wound on a winch located on board a floating
support or ship on the surface, and a second end that is connected
to a fastener element on the structure. The length of the
connection element is such that the winch is capable of winding or
unwinding the first end of the connection element so that a bottom
portion of the connection element can hang beneath the fastener
element.
Inventors: |
Baylot; Michel; (Marseille,
FR) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE
551 FIFTH AVENUE
SUITE 1210
NEW YORK
NY
10176
US
|
Assignee: |
SAIPEM S.A.
1/7, avenue San Fernando,
Montigny le Bretonneux
FR
F-78180
|
Family ID: |
33135524 |
Appl. No.: |
10/550263 |
Filed: |
March 25, 2004 |
PCT Filed: |
March 25, 2004 |
PCT NO: |
PCT/FR04/00742 |
371 Date: |
September 22, 2005 |
Current U.S.
Class: |
114/53 ;
414/137.3 |
Current CPC
Class: |
E02B 2015/005 20130101;
E21B 43/0122 20130101; B63C 7/006 20130101; B63B 27/08 20130101;
E02B 15/08 20130101 |
Class at
Publication: |
114/053 ;
414/137.3 |
International
Class: |
B63C 7/00 20060101
B63C007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2003 |
FR |
03/03969 |
Nov 27, 2003 |
EP |
03/358019.2 |
Feb 26, 2004 |
EP |
04/358002.6 |
Claims
1-28. (canceled)
29. A device for stabilizing or controlling the lowering or raising
of a structure between the surface and the bed of the sea, said
device including at least one connection element of the cable or
chain type, having: a first end that is connected to a winch on
board a floating support or surface ship, and on which winch it is
wound; and a second end that is connected to a fastener element on
said structure, or on at least a first buoyancy element that is
connected to said structure; and the length of said connection
element is such that said winch is capable of winding or unwinding
said first end of said connection element, so that a bottom portion
of said connection element can hang beneath said fastener
element.
30. A device according to claim 29, including at least two of said
connection elements, said fastener elements preferably being
disposed symmetrically, respectively around and on the periphery of
said structure.
31. A device according to claim 29, wherein said connection element
is constituted by a cable having a bottom portion that comprises
weighting blocks disposed in a string on a said cable, said
weighting blocks preferably being metal blocks secured to said
cable by clamping.
32. A device according to claim 31, wherein said blocks present a
shape such that when said bottom portion hanging beneath said
fastener elements curves, two of said blocks disposed side by side
are capable of coming into abutment against each other, thereby
limiting the curvature of said cable.
33. A device according to claim 32, wherein the curvature of said
cable is limited so that the minimum radius of curvature (R.sub.0)
of said cables at said bottom portion enables a minimum distance
(2R.sub.0) to be maintained between said cable and said structure
that is sufficient to prevent any mechanical contact between them
while said structure is being lowered or raised.
34. A device according to claim 31, wherein each of said blocks
present a cylindrical central portion between two frustoconical
ends having axes that correspond to the direction of said cable
when said cable is disposed linearly, two adjacent blocks being in
contact at said frustoconical ends along a generator line of said
frustoconical ends in the curved parts of said bottom portion.
35. A device according to claim 29, wherein said connection element
comprises a chain having a bottom portion that comprises links that
are heavier than the links of the rest of the chain, and that are
preferably larger so as to limit any curvature of the chain.
36. A device according to claim 29, wherein said first buoyancy
elements are disposed above said structure.
37. A device according to claim 29, wherein said structure includes
second buoyancy elements, preferably integrated in the top of said
structure, and more preferably integrated above said fastener
element(s) so that the center of gravity of said structure together
with said first buoyancy elements is situated below the center of
thrust that is exerted both on said structure and on said first
buoyancy elements.
38. A method of lowering, raising, or stabilizing a structure
between the surface and the bed of the sea by means of a device
according to claim 29, said method comprising the following steps:
unwinding or winding each connection element at its first end by
means of a said winch; and controlling the speed at which each
connection element is lowered or raised by regulating the speed at
which each connection element is respectively wound off or on said
winch, so as to adjust the length of said bottom portion of said
connection element hanging beneath said fastener element, the
lowering, raising, or stabilizing of said structure being obtained
when the sum of the weight of the fraction of said bottom
portion(s) of the connection element(s) between firstly said
fastener point(s) for fastening to said fastener element(s) and
secondly the lowest point of said bottom portion(s), plus the
weight of said structure as a whole and of said first buoyancy
element(s), is respectively greater than, less than, or equal to
the buoyancy thrust that is exerted on said structure and on said
first buoyancy element(s).
39. A method according to claim 38, wherein said structure is a
rigid structure of steel, other metal, or composite synthetic
material containing at least one and preferably a plurality of
buoyancy compartments that are suitable for being filled with a
fluid that is lighter than water, and each being fitted with at
least one filling orifice and preferably with at least one emptying
orifice, said compartments preferably being distributed
symmetrically in said structure.
40. A method according to claim 38, wherein said structure is a
massive structure constituted by an open-based receptacle in the
form of a cap, the receptacle comprising a peripheral side wall
surmounted by a roof wall and being suitable for completely
covering a wreck of a ship on the sea bed in order to recover
polluting effluent escaping therefrom, said receptacle having at
least one emptying orifice for discharging said effluent contained
in the inside volume of said receptacle; said emptying orifice
preferably being situated in the roof of the receptacle.
41. A method according to claim 39, wherein said receptacle is
constituted as an upside-down double-walled ship hull comprising a
rigid structure of steel, other metal, or composite synthetic
material, said leaktight compartments being defined by spaces
between said double walls and by structural elements
interconnecting the double walls.
42. A method according to claim 40, wherein the rigid structure of
the walls constituting said receptacle is constituted by steel or
metal beams assembled to one another and having leaktight
compartments incorporated between them, said structure being
covered on at least one face, preferably the outer face, by
leakproof diaphragms or webs fixed to said rigid structure in
leaktight manner, said leaktight compartments being constituted by
a self-contained closed casing incorporated inside said structure
and secured thereto.
43. A method according to claim 39, wherein the rigid structure of
the walls of the receptacle is made of concrete, preferably
concrete lightened by clay beads, within which concrete hollow
volumes are provided for defining said leaktight compartments.
44. A method according to claim 39, wherein said receptacle
presents a vertical and longitudinal axial plane of symmetry XOZ,
and comprises: a roof wall comprising two longitudinally extending
side walls that are inclined relative to said vertical axial plane
of symmetry of said receptacle so as to form an upside-down V-shape
in cross-section YOZ; and a side wall comprising: two
longitudinally extending side walls that are vertical or inclined
relative to said vertical axial plane of symmetry, each being
contiguous with one of said longitudinally extending roof walls;
and two transverse end walls that are vertical or inclined,
preferably symmetrically about a vertical transverse plane of
symmetry.
45. A method according to claim 39, wherein said receptacle has
posts, at least some of which are preferably retractable, said
posts being suitable for supporting said receptacle in
quasi-isostatic manner when it is standing on the sea bed via said
posts, the posts being deployed where necessary, and with the open
base of said receptacle preferably being in a substantially
horizontal position.
46. A method according to claim 38, wherein said structure is
fitted on the outside: with fastener elements enabling cables or
chains to be secured thereto for lowering said structure from the
surface, and for putting it into place, and, where appropriate,
anchoring it to the sea bed; and preferably with thrusters, more
preferably steerable thrusters enabling said structure to be moved
in a horizontal direction in order to be positioned over said
wreck.
47. A method according to claim 38, comprising the following steps:
1) filling said leaktight compartments completely or partially with
a fluid, preferably a fluid that is lighter than sea water, with
the extent to which said leaktight compartments are filled being
adjusted so as to cause said structure to occupy an equilibrium
position when immersed close to the surface; 2) lowering said
structure to the desired position by means of a device according to
claim 1 for controlling lowering, so as to regulate the speed at
which the receptacle is lowered, and so as to provide equilibrium
to the open base of said substantially horizontal structure while
it is being lowered; and 3) once said structure is in place at the
desired depth, emptying said leaktight compartments filled with
fluid lighter than sea water, and simultaneously filling said
leaktight compartments with sea water.
48. A method according to claim 47, wherein, in step 1), additional
buoyancy is provided to said structure by means of said first
buoyancy elements consisting of additional floats connected to said
receptacle; and in step 3), once said structure is in the desired
position, said additional floats are detached.
49. A method according to claim 47, wherein, after step 1) and
before step 2), once said structure has reached the desired
position, the lengths of said heavy cables (or chains) hanging
beneath said fastening elements and supported by said structure are
reduced so as to stabilize said structure in suspension, and where
appropriate, said structure is anchored to the sea bed, and then
said heavy cables (or chains) are filly lowered so that their
entire weight contributes to stabilizing said structure.
50. A method according to claim 47, wherein said structure is a
said receptacle and includes posts, at least some of which are
preferably retractable, and said retractable posts, if any, are
deployed, in such a manner that said receptacle rests on the sea
bed on each of said posts in quasi-isostatic manner, and preferably
with the open base of said receptacle in a substantially horizontal
position.
51. A method according to claim 47, wherein the receptacle is
positioned on the axis above the wreck by actuating thrusters
mounted outside the receptacle and preferably distributed
symmetrically about its periphery.
52. A method according to claim 47, wherein the fluid lighter than
sea water filling said leaktight compartment is gas oil, oil, fresh
water, or a liquefied gas that is lighter than sea water such as
propane, butane, or ammonia.
53. A method according to claim 52, wherein, in step 1), said
leaktight compartments are filled with a first fluid that is
lighter than sea water; and in step 2), said structure is lowered
to a depth of 30 m to 60 m corresponding to a pressure of 3 bars to
6 bars, at which depth a liquefied gas that is lighter than sea
water is injected under pressure into said leaktight compartments
from a gas tanker ship on the surface.
54. A method according to claim 47, wherein said structure is a
said receptacle, and a fraction of the inside volume of said
receptacle defined on top by the roof of said receptacle and at the
bottom by a diaphragm or web tensioned between said side walls of
said receptacle is filled with a fluid that is lighter than sea
water, preferably with fresh water, so as to create additional
buoyancy while the receptacle is being towed at the surface and/or
while the receptacle is being lowered to the sea bed; and once said
receptacle is close to the sea bed, said diaphragm or web is
removed and said receptacle is placed on the sea bed over the
wreck, preferably via said posts, after they have been deployed,
where appropriate, and said fluid that is lighter than sea water is
removed from the inside of said receptacle via said top emptying
orifice while said receptacle is close to the sea bed.
55. A method of recovering polluting effluent that is lighter than
sea water, as contained in the tanks of a shipwreck lying on the
sea bed, in which method: 1) a said receptacle is put into place in
accordance with the method of claim 47; and 2) the effluent
recovered inside said receptacle is collected by being emptied out
through said top emptying orifice.
56. A method according to claim 55, comprising, in step 2), the
following steps: lowering an empty said shuttle tank; positioning
said shuttle tank over said receptacle in such a manner that its
open bottom orifice is just above said emptying orifice of said
receptacle; preferably securing said shuttle tank to said
receptacle; emptying the effluent contained in said shuttle tank;
and once full, detaching said tank from said receptacle, and
raising said tank full of effluent to the surface.
Description
[0001] The present invention relates to a device and a method for
stabilizing and controlling the lowering or raising of a structure
between the surface and the bed of the sea, and more particularly a
structure constituting a receptacle having a leaktight compartment
useful for recovering polluting effluent from a wreck.
[0002] The term "structure" refers to any equipment, tool, machine,
and in particular underwater well-head elements on oilfields, oil
processing units, or even segments of underwater pipe that are
towed on the open sea from their site of manufacture for
installation on the sea bed.
[0003] The present invention also relates to a method and an
installation for confining and recovering effluent at sea, and more
particularly polluting effluent contained in a sunken and damaged
ship lying on the sea bed, and it also relates to a method of
putting the installation into place on the sea bed.
[0004] When an oil tanker is wrecked, the ship sinks, generally
after it has been severely damaged and has already lost part of its
cargo. When the depth of water is considerable, for example 100
meters (m) or 200 m, it is generally not practical to recover or
refloat the wreck, however the hull must be completely emptied and
rinsed, or covered in an external "big top" type structure so as to
ensure that corrosion of the shipwreck over time leading to local
or generalized holes will not allow the content of the ship to be
released and dispersed by currents, thereby leading to pollution
that might extend over years or even tens of years.
[0005] Numerous methods and devices have been studied and used in
the past in an attempt to recover highly polluting cargoes, but
they are very difficult to implement, and the operations involved
take a great deal of time, generally leading to secondary
pollution, since recovery rates are far from satisfactory,
particularly when a method needs to be implemented at great
depth.
[0006] In particular, French patent No. FR 2 804 935 in the name of
the Applicant describes a method of recovering polluting effluent
that is lighter than water and that mixes poorly or not at all with
water, the effluent being contained in a tank in a sunken and/or
damaged ship lying on the sea bed, that method comprising the
following steps:
[0007] 1) a receptacle having a bottom orifice is lowered with the
help of positioning means to directly in the vicinity of and
vertically above at least one opening in the hull and/or the tank
of the ship that is putting the inside of the tank of the ship into
communication with the outside, so as to recover said polluting
effluent directly as it flows out through said hole directly facing
the receptacle, by virtue of the effluent rising into said bottom
orifice of said receptacle;
[0008] 2) when said receptacle is full of polluting effluent, it is
raised using said positioning means until means for emptying said
receptacle are accessible from the surface, said emptying means
comprising a closable top orifice in said receptacle and/or an
emptying pipe connected to said top orifice at the top of said
receptacle;
[0009] 3) said receptacle is emptied into an installation or a ship
on the surface via said emptying means accessible from the surface;
and
[0010] 4) steps 1) to 3) are repeated until the desired quantity of
effluent has been recovered.
[0011] In a first variant described in FR 2 804 935:
[0012] a) said receptacle consists in a funnel-shaped bell whose
open large base constitutes said bottom orifice and covers solely
the zone through which said effluent is leaking out, said zone
being a localized zone of small area including one or more of said
openings in the hull and/or the tank of said ship, and the top
small base of said funnel gives access to said top orifice;
[0013] b) said positioning means comprise: [0014] means for
anchoring said receptacle to the ship, said means comprising cables
connecting attachment points fixed to the circumference of said
large base of the funnel to attachment points on the ship or in the
vicinity thereof; and [0015] tensioning means comprising: [0016]
floats connected to the circumference of said open large base of
said receptacle and around the tubular section in the top portion
of the small base of said funnel; and [0017] winches corresponding
to said attachment points on the ship or in the vicinity thereof;
and
[0018] c) said emptying means comprise a said emptying pipe
connected at one end to said top orifice of said tubular section at
the top of said funnel, said pipe being put under substantially
vertical tension by means of a float connected to the free end of
said pipe.
[0019] In that first variant, operating said positioning means
during successive operations of lowering and raising said
receptacle takes a very long time and is quite difficult to perform
at great depth. In addition, pumping through a said emptying pipe
is not possible at said depth, in particular when the effluent is
highly viscous and tends to freeze in the form of a paraffin. Even
if a heating system were to be installed in the collection zone or
in the top of the bell while rising, the viscous effluent tends to
freeze, thus making pumping very difficult.
[0020] In a second variant described in FR 2 804 935, said
receptacle consists in: [0021] a rigid container of substantially
tubular shape which is held in a vertical position by means of
floats installed at least at the top end or at both the top and
bottom ends of said container; and [0022] said top and bottom
orifices of said container are closable such that said receptacle
can be raised to the surface and installed floating in a horizontal
position when said orifices are closed, said receptacle then being
suitable for towing to an installation or a ship for storing said
effluent.
[0023] Such rigid containers of a so-called "cigar" shape are large
in size and difficult to lower to the sea bed, and in order to
avoid successive operations, a preferred implementation is
described in which said container occupies the full depth of the
water between the wreck and the surface. However it is clear that
that second variant cannot be envisaged for depths in excess of
1000 m since that would require a receptacle that is much too
large, impossible to install or lower frequently.
[0024] In practice, the various implementations described in FR 2
804 935 are not suitable for acting in depths greater than 1000 m
since because of the very great depth of water, the accumulated
length of time for go-and-return trips to depth becomes completely
unacceptable given the very high cost of the intervention ships
used to perform those operations.
[0025] The various devices and installations described above need
to be implemented over each leakage zone from the wreck, and that
represents a serious difficulty in terms of operation and duration
of operations since as a general rule wrecks contain numerous
leakage zones and in addition, as the wreck is emptied, because
that leads to deformation of the hull, new cracks generally arise
thus requiring substantially continuous monitoring of the wreck and
correcting actions to be taken at once.
[0026] Open-based rigid receptacles have been proposed that are
bell- or cap-shaped for the purpose of covering not a localized
leakage zone but an entire shipwreck on the sea bed in order to
recover the polluting effluent escaping therefrom via a plurality
of leakage zones in said wreck. Such receptacles are of large
dimensions since they are designed to cover ships of large
dimensions of the oil tanker type. Putting such a structure of
large dimensions into place on the sea bed raises problems of
manufacture and of positioning on the sea bed under conditions that
are technically reliable. Such structures present a considerable
amount of weight and require the use of numerous and bulky floats
in order to place them on the sea bed using procedures that are
complex and costly to implement since the effects of currents, even
if they are smaller at great depth, nevertheless remain
considerable because of the immense areas of such structures.
[0027] A recovery method is also known in which said effluent is
recovered using a shuttle tank including at least one bottom
orifice fitted with a valve that is suitable for co-operating with
an emptying device secured to a tank wall, and the method comprises
the following steps:
[0028] 1) lowering said shuttle tank from the surface to the bed of
the sea, causing said bottom orifice of the shuttle tank to
co-operate with an emptying device on the wall, and closing the
valve of the bottom orifice;
[0029] 2) filling said shuttle tank until it is full of
effluent;
[0030] 3) allowing the shuttle tank to rise to the surface, said
shuttle tank including buoyancy elements which enable it to rise to
the surface more easily;
[0031] 4) preferably storing the shuttle tank full of effluent in a
surface ship, and emptying said shuttle tank into said ship, or
transporting it to a site where it is emptied; and
[0032] 5) where appropriate, lowering said shuttle tank again or
lowering another shuttle tank, and repeating steps 1 to 4 until the
desired quantity of effluent is recovered.
[0033] The lowering and raising of the shuttle tanks, as with any
massive structure that is to be lowered to the sea bed or raised
from the sea bed to the surface, is difficult because of the mass
of said structures or of said shuttle tanks. It is known to lower
loads having an apparent weight in water of several hundred
(metric) tonnes to the sea bed using hoist means situated on a
floating support, e.g. a crane; but when the depth becomes
considerable, the use of conventional steel cables is problematic
since, in addition to the load of said structure, it must also
support its own weight, and that can represent up to 50% of said
load capacity for a depth of 3000 m. Synthetic cables can also be
used that do not present that drawback, but their cost is very high
and their use with winches or capstans presents extreme
difficulties for heavy loads and depths of 1000 m to 4000 m, or
even greater.
[0034] Thus, it is generally sought to reduce the apparent weight
in water of such loads by creating buoyancy. But, the mass of said
loads is thus increased by the mass of said buoyancy elements, and
by the "added mass" of water, i.e. the mass of water adjacent to
the load that is entrained upwards or downwards during vertical
movements, and this can represent an overall inertial mass of 400
tonnes or 500 tonnes for a load mass of 100 tonnes.
[0035] The cable connecting the load to the floating support is
tensioned in a vertical straight line, and since said floating
support is subjected to swell, said cable is subjected to rolling
and pitching which requires the use of winches having controlled
tension, or the use of hydraulic devices known as pounding
compensators, which prevent said cable from rupturing by limiting
the tension in said cable to an acceptable value. Such equipment is
technically complicated and very costly, especially for heavy loads
or for depths of 2000 m to 3000 m, or even 4000 m or greater.
[0036] The object of the present invention is to provide a device
and a method for controlling and facilitating the lowering and
raising of a structure that is heavy, and possibly bulky, such as
the above-mentioned receptacles or shuttle tanks for recovering
effluent. However, the invention is also applicable to any other
type of structure, and it is even applicable to stabilizing such a
structure between the surface and the bed of the sea, particularly
at great depth.
[0037] Another object of the present invention is to provide a
method and an installation making it possible to confine and
recover the content of the hold and/or tanks of a ship, e.g. an oil
tanker, resting on the sea bed in great depths, e.g. greater than
3000 m or even 4000 m to 5000 m, while avoiding the drawbacks of
prior art methods and devices, and in particular being easy and
simple to implement in spite of being of very large dimensions.
[0038] Another object of the present invention is to provide a
method and an installation making it possible to confine and
recover polluting effluent from a vessel that has sunk,
particularly in great depth, by means of an open-based rigid
receptacle in the form of a cap that completely covers the
shipwreck so as to channel all of the effluent escaping therefrom
into a single volume, and so as to organize raising the polluting
effluent to the surface from said receptacle at the sea bed under
the best possible conditions.
[0039] A more particular object of the present invention is thus to
provide an open-based receptacle of cap-shape suitable for
completely covering a wreck on the sea bed and for recovering
polluting effluent escaping therefrom, and which is technically
reliable and capable of being implemented on the sea bed using a
method that is simple and technically reliable.
[0040] To do this, the present invention provides a device for
stabilizing or controlling the lowering or raising of a structure
between the surface and the bed of the sea, said device being
characterized in that it includes at least one connection element
of the cable or chain type, having: [0041] a first end that is
connected to a winch on board a floating support or surface ship,
and on which winch it is wound; and [0042] a second end that is
connected to a fastener element on said structure, or on at least a
first buoyancy element connected to said structure; and [0043] the
length of said connection element is such that said winch is
suitable for winding or unwinding said first end of said connection
element, so that a bottom portion of said connection element can
hang beneath said fastener element, i.e. beneath the fastener point
for fastening said second end to said fastener element.
[0044] Where appropriate, said structure is therefore suspended
from one or a plurality of said first buoyancy elements disposed
thereabove. Said structure can also include second buoyancy
elements integrated or incorporated inside said structure, i.e.
said second buoyancy elements do not displace a volume of water
that is additional to the volume of water displaced by said
structure.
[0045] The term "buoyancy element" refers to an element that
presents a dead weight that is lighter than sea water, and that
thus makes it possible to increase the overall buoyancy that it
forms together with the structure to which it is connected or in
which it is integrated.
[0046] The term "to increase the buoyancy" of an element when it is
immersed refers to increasing the ratio .omega. between the
buoyancy thrust exerted on said element and its dead weight out of
water. Thus, if said ratio is .omega.<1, the element has
negative buoyancy, so it tends to sink, if .omega.=1, said element
is in equilibrium, and if .omega.>1 said element floats and its
buoyancy increases as .omega. increases.
[0047] The buoyancy of the structure can be made positive so as to
make it easier for said structure to rise. For "positive buoyancy",
said buoyancy elements compensate the weight of said structure, so
that the buoyancy thrust that is applied both to said structure and
to said buoyancy elements is not less than the dead weight of said
structure and said buoyancy elements taken together, also
including, in particular, one or more connection-element bottom
portions, with the resultant of the forces being directed upwards
for positive buoyancy.
[0048] It should be understood that the device of the invention
makes it possible to vary the length and therefore the weight of
said bottom portion of the connection element hanging beneath said
fastener element on said structure and supported by said
structure.
[0049] For a massive structure, the stabilizing and control device
of the invention includes at least two of said connection elements
and said structure includes a plurality of said fastener elements,
and said connection elements and said fastener elements are
preferably disposed symmetrically, respectively around and on the
periphery of said structure.
[0050] More precisely, the present invention also provides a method
of lowering, raising, or stabilizing a structure between the
surface and the bed of the sea by means of a device, said method
comprising the following steps: unwinding or winding each
connection element at its first end by means of a said winch; and
controlling the lowering and raising of each connection element by
regulating the speed at which each connection element is
respectively wound off or on said winch, so as to adjust the length
of said bottom portion of said connection element hanging beneath
said fastener element on said structure or said first buoyancy
element and supported by said fastener element, the lowering,
raising, or stabilizing of said structure being obtained when the
sum of the weight of the fraction of said bottom portion(s) of the
connection element(s) between firstly said fastener point(s) for
fastening to said fastener element(s) or said first buoyancy
element on said structure, and secondly the lowest point of said
bottom portion(s), plus the weight of said structure as a whole and
of said first buoyancy element(s), is respectively greater than,
less than, or equal to the buoyancy thrust that is exerted on said
structure and on said first buoyancy element(s) (i.e. the weight of
the total volume of water displaced).
[0051] In an embodiment, the stabilizing and control device of the
present invention includes a said connection element constituted by
a cable having a bottom portion that comprises weighting blocks
disposed in a string on a said cable, said weighting blocks
preferably being metal blocks secured to said cable by
clamping.
[0052] In a preferred embodiment, said blocks present a shape such
that when said bottom portion hanging beneath said fastener
elements curves, two of said blocks disposed side by side are
capable of coming into abutment against each other, thereby
limiting the curvature of said cable.
[0053] More particularly, the curvature of said cable is limited so
that the minimum radius of curvature of said cables at said bottom
portion enables a minimum distance to be maintained between said
cable and said structure that is sufficient to prevent any
mechanical contact between them while said structure is being
lowered or raised.
[0054] Still more particularly and advantageously, each of said
blocks presents a cylindrical central portion between two
frustoconical ends having axes (i.e. the axes of said cylinder and
of the two frustoconical ends covering its end faces) that
correspond to the direction of said cable when said cable is
disposed linearly, two adjacent blocks being in contact at said
frustoconical ends along a generator line of said frustoconical
ends in the curved parts of said bottom portion.
[0055] In another embodiment, said connection element comprises a
chain having a bottom portion that comprises links that are heavier
than the links of the rest of the chain, and that are preferably
larger so as to limit any curvature of the chain.
[0056] Where appropriate, said first buoyancy elements are
advantageously disposed above said structure, with said structure
being suspended therefrom, and where appropriate, said second
buoyancy elements are integrated in the top of said structure,
preferably integrated above said fastener elements so that the
center of gravity of said structure together with said first
buoyancy elements is situated below the center of thrust that is
exerted both on said structure and on said first buoyancy elements,
so as to provide overall stability during the entire installation
stage.
[0057] The term "center of thrust" refers to the point at which the
resultant of the buoyancy thrust is exerted. (The center of thrust
is the center of gravity of the volume of water displaced by said
structure).
[0058] As mentioned above, said heavy structure can be constituted
by any load, in particular a heavy load, module, tool, or base as
described in unpublished European patent application No. 0435802.6
in the name of the Applicant, that is to be immobilized in the
vicinity of the sea bed or anchored on a wall or an element lying
on the sea bed.
[0059] Preferably, said structure is a rigid structure of steel,
other metal, or composite synthetic material containing at least
one and preferably a plurality of buoyancy compartments that are
preferably leaktight and that are suitable for receiving a fluid
that is lighter than sea water so as to form a said buoyancy
element, said compartments each being fitted with at least one
filling orifice and preferably with at least one emptying orifice,
said preferably leaktight compartments preferably being distributed
symmetrically in said walls.
[0060] In a particularly advantageous embodiment, said structure is
a massive structure constituted by an open-based receptacle in the
form of a cap, the receptacle comprising a peripheral side wall
surmounted by a roof wall and being suitable for completely
covering a wreck of a ship on the sea bed in order to recover
polluting effluent escaping therefrom, said receptacle having at
least one emptying orifice for discharging said effluent contained
in the inside volume of said receptacle; said emptying orifice
preferably being situated in the roof of the receptacle.
[0061] The preferably leaktight compartments are designed to be
filled completely or in part with a fluid that is lighter than sea
water, and they thus constitute compartments that provide buoyancy
to the structure constituting the receptacle, thereby enabling it
to be towed at the surface and then to be lowered to the sea bed
while it is being put into place, under conditions that are
technically reliable and simple to implement, as explained
below.
[0062] Concerning the distribution of the compartments in the
walls, the term "symmetrically" means that the compartments are
disposed symmetrically about one or more midplanes of symmetry of
said receptacle, thus making it possible as explained below to
facilitate balancing and positioning the open base of said
receptacle in a manner that is substantially horizontal.
[0063] In general, said receptacle presents a longitudinal axis of
symmetry like that of the ships it is designed to cover, and said
receptacle presents a vertical longitudinal axial plane of symmetry
when the open base of the receptacle is in the horizontal position,
and more particularly, said receptacle also presents a second
vertical plane of symmetry that extends transversely.
[0064] In known manner, the walls constituting said roof flare so
as to define a narrow top space. Similarly, the side wall which
forms a peripheral skirt of the cap is also preferably inclined so
as to form a flared funnel defining at its bottom the open base of
said receptacle and encouraging effluent escaping from the wreck to
rise and accumulate under the roof of the receptacle.
[0065] In an advantageous embodiment, the receptacle is in the form
of an upside-down hull with a longitudinal axial plane and with
lateral roof walls constituted by contiguous plane walls of
different inclinations, thus defining flat sloping surfaces of the
hull.
[0066] In a more particular embodiment, the receptacle presents a
vertical and longitudinal axial plane of symmetry XOZ, and it
comprises: [0067] a roof wall comprising two longitudinally
extending side walls that are inclined relative to said vertical
axial plane of symmetry of said receptacle so as to form an
upside-down V-shape in cross-section YOZ; and [0068] a side wall
comprising: [0069] two longitudinally extending side walls that are
vertical or inclined relative to said vertical axial plane of
symmetry XOZ, each being contiguous with one of said longitudinally
extending roof walls; and [0070] two transverse end walls that are
vertical or inclined, preferably symmetrically about a vertical
transverse plane of symmetry YOZ.
[0071] In an advantageous embodiment, said receptacle is
constituted as an upside-down double-walled ship hull comprising a
rigid structure of steel, other metal, preferably a light metal
such as aluminum or titanium, or composite synthetic material, said
leaktight compartments being defined by spaces between said double
walls and by structural elements interconnecting the double
walls.
[0072] The term "double-walled" is used herein to mean a wall
constituted by an inner wall and an outer wall spaced apart by
structural elements of the beam type forming framing that unites
said inner and outer walls, themselves being made of rigid or
semirigid material, specifically steel, some other metal,
preferably a light metal such as aluminum or titanium, or a
composite synthetic material, for example glass fibers embedded in
a matrix of epoxy or polyester resin type.
[0073] In this embodiment, the compartments are thus formed by the
inner and outer walls of said double walls together with transverse
or longitudinal structural elements interposed between the double
walls and uniting them.
[0074] In another variant embodiment of the invention, the rigid
structure of the walls constituting said receptacle is constituted
by steel or metal beams assembled to one another and having
leaktight compartments incorporated between them, said structure
being covered on at least one face, preferably the outer face, by
leakproof diaphragms or webs, for example made of reinforced cloth
covered in a thermoplastic material, and fixed to said rigid
structure in leaktight manner. In this embodiment, said leaktight
compartments are constituted by a self-contained closed casing
incorporated inside said structure and secured thereto.
[0075] Also advantageously, the rigid structure of the walls of the
receptacle is made of concrete, preferably lightened concrete,
preferably lightened by hollow expanded clay beads, within which
concrete hollow volumes are provided for defining said leaktight
compartments.
[0076] In a preferred embodiment, the receptacle has posts,
preferably regularly distributed around its periphery, with at
least some of them preferably being retractable, said posts being
suitable for supporting said receptacle in quasi-isostatic manner
when it is standing on the sea bed via said posts, the posts being
deployed where necessary, and with the open base of said receptacle
preferably being in a substantially horizontal position. The
lengths of said posts, as deployed, where appropriate, possibly
differing from one another so as to enable said open base of the
receptacle to be maintained in a substantially horizontal
position.
[0077] In order to make it easier to put the receptacle of the
invention into place on the sea bed, the walls of said receptacle
are fitted on the outside: [0078] with second fastener elements
enabling cables or chains to be secured thereto for lowering said
receptacle from the surface, and for putting it into place and
anchoring it to the sea bed; and [0079] preferably with thrusters,
more preferably steerable thrusters enabling the receptacle to be
moved in a horizontal direction in order to be positioned over said
wreck.
[0080] Said second fastening elements may also be used for
fastening additional floats to the receptacle.
[0081] The present invention also provides a method of putting a
structure, and in particular a receptacle of the invention, into
place in order to cover a shipwreck on the sea bed and recover
polluting effluent escaping therefrom, the method being
characterized in that it comprises the following steps:
[0082] 1) filling said leaktight compartments completely or
partially with a fluid, preferably a fluid that is lighter than sea
water, with the extent to which said leaktight compartments are
filled being adjusted so as to cause said structure, and in
particular said receptacle, to occupy an equilibrium position when
immersed close to the surface, in particular several meters
therefrom, e.g. 10 meters therefrom; and
[0083] 2) lowering said structure, and in particular said
receptacle, to its desired immersed position close to the sea bed
over the wreck by controlling lowering by means of a device for
stabilizing or controlling the lowering or raising of a structure
of the invention, in particular by means of a plurality of cables
preferably unwound from winches on board surface ships, said cables
being connected to lengths of heavy chain, the chains themselves
being connected at their opposite ends to said fastener elements
secured to said structure, and preferably being distributed
symmetrically around the periphery of said structure, the weights
of the lengths of chain hanging beneath the fastening points on
said fastening elements enabling said structure to be lowered, and
the lengths of said chains hanging beneath said fastening points of
the fastening elements being adapted by winding said cables out or
in, preferably around said winches so as to regulate the rate of
descent of the receptacle and so as to ensure that the base of said
structure, and in particular the open base of the receptacle, is
maintained in substantially horizontal equilibrium throughout the
descent;
[0084] 3) once said structure is in place in its desired position,
in particular when said receptacle is in position on the sea bed so
as to cover said wreck, emptying said leaktight compartments filled
with fluid lighter than sea water, and simultaneously filling said
leaktight compartments with sea water.
[0085] Before and/or after step 1), but before above step 2), it is
possible to use ships to tow said structure, and in particular said
receptacle, while it is floating at the surface, said leaktight
compartments being filled with air and the receptacle floating with
neutral buoyancy level with the surface or with said leaktight
compartments being completely filled with a fluid that is lighter
than sea water.
[0086] At above step 1), it will be understood that the filling of
said leaktight compartments with a fluid that is lighter than sea
water is performed in the various compartments as a function of how
they are distributed in the walls of the receptacle, so that the
open base of the receptacle remains substantially horizontal and so
that the center of buoyancy of the receptacle remains substantially
above the center of gravity of the receptacle. This applies to
selecting which compartments to fill and also the rates at which
they are filled.
[0087] Advantageously, in step 1), additional buoyancy is applied
to said receptacle using additional floats by means of said first
buoyancy elements connected to said structure, and in particular to
said receptacle, and in step 3), once said structure is in the
desired position, said additional floats are released.
[0088] Also advantageously, after step 1) and before step 2), once
said structure, and in particular said receptacle, has reached the
desired position in the vicinity of the wreck, overlying it, the
lengths of said heavy chains hanging beneath said fastening
elements and supported by the structure are reduced so as to
stabilize said structure in suspension, and said receptacle is
anchored to the sea bed, and then said heavy chains are fully
lowered so that their entire weight contributes to stabilizing said
structure, and in particular said receptacle, on the sea bed.
[0089] The heavy chains may be recovered by being disconnected from
the receptacle, but as explained below, in order to increase the
stability of said structure, and in particular of said receptacle,
said heavy chains may have both ends connected to said fastening
elements on said structure, or more simply the free ends of said
heavy chains may be laid over the roof of said structure, and in
particular of said receptacle, while still connected to the cables
themselves connected to the surface ships, and then the cables
connected to the surface ships are separated from said chains.
[0090] Preferably, said receptacle includes posts, at least some of
which are preferably retractable, and said retractable posts, if
any, are deployed, in such a manner that said receptacle rests on
the sea bed on each of said posts in quasi-isostatic manner, and
preferably with the open base of said receptacle in a substantially
horizontal position.
[0091] Advantageously, in the method of the invention, the
receptacle is positioned on the axis above the wreck by actuating
thrusters mounted outside the receptacle and preferably distributed
symmetrically about its periphery.
[0092] The fluid lighter than sea water filling said leaktight
compartment may be gas oil, oil, fresh water, or a liquefied gas
that is lighter than sea water such as propane, butane, or ammonia,
said gas remaining in the liquid state at the temperature of sea
water (2.degree. C. to 20.degree. C.) providing the pressure
exceeds a few bars.
[0093] Still more particularly, in a method of the invention, in
step 1), said leaktight compartments are filled with a first fluid
that is lighter than sea water; and in step 2), said structure is
lowered to a depth of 30 m to 60 m corresponding to a pressure of 3
bars to 6 bars, at which depth a liquefied gas that is lighter than
sea water is injected under pressure into said leaktight
compartments from a gas tanker ship on the surface.
[0094] Using liquefied gas as the fluid lighter than sea water
makes it possible to obtain fluids presenting relative density in
the liquid state lying in the range 0.55 to 0.7, thus giving two to
three times more buoyancy than gas oil (d=0.85), and thus making it
possible to use leaktight compartments of considerably smaller
volume. In addition, in the event of an accident occurring such
substances are much less polluting than gas oil or other oil, since
they disperse naturally on reaching the surface.
[0095] Still in order to make it easier to lower the receptacle and
avoid having to use leaktight compartments of excessive volume, it
is advantageous in the method of the invention for installing the
receptacle to fill a portion of the inside volume of said
receptacle as defined on top by the roof of said receptacle and at
the bottom by a diaphragm or web tensioned between said side walls
of said receptacle, using a fluid that is lighter than sea water,
preferably fresh water, thereby providing additional buoyancy while
the receptacle is being towed at the surface, and once said
receptacle is close to the sea bed, said diaphragm or web is
removed and the receptacle is placed over the wreck on the sea bed,
preferably by means of said posts, as deployed, where appropriate,
and then said fluid that is lighter than sea water is emptied from
the inside of said receptacle via said top emptying orifice.
[0096] Finally, the present invention also provides a method of
recovering polluting effluent that is lighter than sea water, as
contained in the tanks of a shipwreck lying on the sea bed, in
which method:
[0097] 1) a receptacle is put into place in accordance with a
method of the invention for stabilizing and controlling descent;
and
[0098] 2) the effluent recovered inside said receptacle is
collected by being emptied out through said top emptying
orifice.
[0099] In order to recover effluent escaping through said top
emptying orifice, it is possible to use a pipe connected to a
surface ship or recovery devices of the kind described in French
patent No. FR 2 804 935 in the name of the Applicant, or indeed to
use shuttle tanks as described in as yet unpublished European
patent application No. 03/358003.6 in the name of the
Applicant.
[0100] More particularly, step 2) of the above-mentioned method of
recovering effluent comprises the following steps: [0101] lowering
an empty said shuttle tank; [0102] positioning said shuttle tank
over said receptacle in such a manner that its open bottom orifice
is just above said emptying orifice of said receptacle; [0103]
preferably securing said shuttle tank to said receptacle; [0104]
emptying the effluent contained in said shuttle tank; and [0105]
once full, detaching said tank from said receptacle, and raising
said tank full of effluent to the surface.
[0106] Other characteristics and advantages of the present
invention appear better on reading the following description given
in illustrative and non-limiting manner with reference to the
accompanying drawings, in which:
[0107] FIG. 1 is a side view in section of a receptacle referred to
herein as a "sarcophagus" while it is being lowered towards a
wreck;
[0108] FIG. 2 is a side view in section of a rigid receptacle
resting on the sea bed and completely covering the wreck;
[0109] FIG. 3 is a cutaway perspective view showing the structure
of the sarcophagus;
[0110] FIG. 4 is a side view in section of the sarcophagus as it is
being lowered, showing how lowering is controlled with the help of
heavy chains;
[0111] FIGS. 4a and 4b show details of how said heavy chains can be
implemented in varying manner;
[0112] FIG. 5 is a side view in section of the sarcophagus while it
is being lowered, with its buoyancy being produced by gas oil in
leaktight compartments integrated in its walls, in combination with
fresh water inside the internal volume of the
sarcophagus-receptacle;
[0113] FIG. 6 is a side view in section of the sarcophagus, showing
details of orifices for filling and discharging buoyancy fluids to
and from the insides of the leaktight compartments, and for
removing effluent contained inside the receptacle;
[0114] FIG. 7 is a side view in section of a sarcophagus made up of
a rigid load-carrying structure made of metal beams associated with
buoyancy tanks filled with a low-density fluid integrated between
the beams and closed by leakproof diaphragm webs on the outside
face of the structure;
[0115] FIG. 8 is a side view in section of a sarcophagus made out
of lightweight concrete, having internal volumes forming leaktight
compartments filled with a low-density fluid for providing
buoyancy;
[0116] FIGS. 9a and 9b are side views in section of a sarcophagus
respectively while it is being towed, its buoyancy compartments
being filled with sea water (FIG. 9a), and vertically above the
wreck during the stage in which said buoyancy compartments are
filled with a low-density liquefied gas (FIG. 9b);
[0117] FIG. 10 shows a said receptacle fitted with posts on which
it stands on the sea bed;
[0118] FIG. 11a is a side view of a shuttle tank that is
stabilized, while rising, by a connection cable that is weighted by
blocks secured to said cable and also serving to limit
curvature;
[0119] FIGS. 11b and 11c show states similar to those in FIG. 11a,
with the shuttle tank being in the rising stage in FIG. 11b and in
the lowering stage in FIG. 11c;
[0120] FIG. 11d shows a detail of two blocks 31 in contact with
each other, when said connection cable is curved;
[0121] FIG. 12 shows a shuttle tank co-operating with the top wall
of a structure of the sarcophagus type, for recovering therefrom,
the oil flowing from a ship that has sunk and that is confined
beneath the sarcophagus; and
[0122] FIG. 13 shows an anchoring and drilling device controlled by
a stabilizing chain of the invention and by buoyancy elements.
[0123] FIG. 1 shows the hull of a wreck or a wall of a tank 6 lying
on the sea bed 7 and filled with hydrocarbon 8 of density lower
than that of sea water. Said hydrocarbon is confined in the top
portion of the tank or the wreck 6, its bottom portion being filled
with sea water. The ship 6 generally possesses multiple openings
that are hermetically closed at deck level, and leakage might occur
whenever the sealing becomes damaged because of the hull becoming
deformed or breaking while the ship was being wrecked.
[0124] A rigid receptacle 1 referred to herein as a "sarcophagus"
constituted by a rigid structure is lowered from the surface under
the control of cables 12 connected to dynamically-positioned ships
20 on the surface, as shown in FIGS. 1 and 2.
[0125] The receptacle 1 shown in FIGS. 1 to 3 has a vertical and
longitudinal axial plane of symmetry XOZ and comprises: [0126] a
roof wall (3, 3a, 3b) comprising two longitudinally extending side
walls (3a, 3b) that are inclined relative to said vertical axial
plane of symmetry of said receptacle so as to form an upside-down
V-shape in cross-section YOZ; and [0127] a side wall 2 comprising:
[0128] two longitudinally extending side walls (2a, 2b) that are
vertical or inclined relative to said vertical axial plane of
symmetry XOZ, each being contiguous with one of said longitudinally
extending roof walls (3a, 3b); and [0129] two transverse end walls
(2.sub.1) that are vertical or inclined, preferably symmetrically
about a vertical transverse plane of symmetry YOZ.
[0130] As shown in detail in FIG. 3, the sarcophagus 1 is
constituted by an upside-down hull shape, said hull being leaktight
and double-walled, thus constituting leaktight compartments 4,
preferably a multitude of leaktight compartments in continuity one
with another. The structure is constituted by transverse framing
members 4.sub.3 that may be perforated or solid within a given
leaktight compartment, and associated with perforated or solid
framing members extending longitudinally 4.sub.6. In FIG. 3, there
can be seen in an exploded cross-section corresponding to the plane
YOZ, a right-hand half of the double wall 3b of the roof which is
plane and inclined relative to the horizontal, e.g. at 10.degree.
to 20.degree., but which could be horizontal, and when it is
inclined, it co-operates with the other double-walled half of the
roof 3b to form a roof with an upside-down V-shape. Each
longitudinal roof wall 3a, 3b is connected via its bottom edge to a
plane double-walled side wall 2a, 2b which is vertical or inclined
relative to the vertical, in particular at an angle of 5.degree. to
20.degree., and preferably at an angle that is smaller than the
angle of said inclined longitudinally extending roof walls. The two
ends of the sarcophagus 1 in the longitudinal direction XX' are
closed by end double walls 2, 2a, 2.sub.1 that provide a connection
between the end edges of the side double walls 2a, 2b and the
ceiling double walls 3, 3a, 3b, with said end side walls 2.sub.1
being perpendicular to the longitudinal axis XX'. The bottom is
entirely free so as to enable the sarcophagus to act like a bell to
cover the wreck 6 that is to be confined.
[0131] The volumes inside the various double walls 2.sub.1, 2, 2a,
2b and 3, 3a, 3b are defined by the inner and outer walls and by
the solid framing members 4.sub.3, 4.sub.6 that form compartments
which are leaktight relative to the outside, thus enabling them to
be filled with a fluid of density lower than that of sea water,
said fluid then acting as buoyancy material and compensating the
dead weight of the rigid structure constituting the sarcophagus
receptacle 1.
[0132] Said hull constituting the sarcophagus is advantageously
built dry in an open basin, and then the leaktight compartments 4
within the double walls 2.sub.1, 2, 2a, 2b and 3, 3a, 3b are closed
off in leaktight manner. After the open basin has been flooded, the
sarcophagus 1 floats, projecting well above water level because
said compartments 4 are filled with air. If there is any risk of
instability at this stage, it is advantageous to add ballast
temporarily to the bottom thereof.
[0133] The sarcophagus 1 is then towed to deep water where all of
the compartments 4 constituting the buoyancy volumes are filled
with the buoyancy fluid, for example gas oil of relative density
close to 0.85. The buoyancy volume is advantageously adjusted so
that the sarcophagus is in neutral equilibrium in water, with
overall equilibrium optionally being provided by means of
additional floats 19 capable of withstanding deep sea pressures,
i.e. about 350 bars for a depth of 3500 m. Said additional floats
19 may be made of syntactic foam, i.e. microspheres of glass held
captive in a binder of the polyurethane or epoxy resin type, but
they are advantageously constituted by a rigid or flexible casing
filled with liquefied gas, e.g. butane or propane, as explained
below.
[0134] The sarcophagus 1 is then towed to the site, and once in
position, at least two and preferably four ships 20 are connected
to the ends of the sarcophagus 1 as follows.
[0135] Each ship 20 has a winch 12.sub.1 provided with a cable 12,
preferably a steel cable, of length that is greater than the depth
of the water, e.g. 130% of said water depth. The end of said cable
12 is connected to a length of heavy chain 13, e.g. 100 m of chain
having a diameter of 6 inches (''), the end of said chain being
connected to a reinforced beam 10 constituting a fastener element
secured to the structure and projecting out from the sarcophagus 1,
as can be seen in FIGS. 1, 4, 5, and 8.
[0136] The heavy chains 13 have a self-regulating effect as the
sarcophagus is being lowered towards the sea bed 7, and their
operation is explained with reference to FIGS. 4, 4a, and 4b.
[0137] In FIG. 4, the cable 12 is in an intermediate position and
forms a catenary type curve, with a portion of the weight of the
chain 13 (F) being supported by the sarcophagus while the remainder
of the weight of the catenary is supported via the cable 12
directly by the ship 20 on the surface. Thus, the sarcophagus is
maintained in neutral equilibrium under the effect of this force
F.
[0138] When the winch 12.sub.1 on the surface ship 20 winds in the
cable 12, it raises the chain 13 as shown in FIG. 4a, thereby
reducing the weight of chain that is carried by the receptacle to a
weight F.sub.min, since the entire weight of the chain is then
supported by the surface ship 20: the sarcophagus 1 then presents
an apparent weight in water that is smaller and it rises in order
to come closer to an equilibrium position as shown in FIG. 4 and
stabilized in that position.
[0139] Conversely, when the winch 12.sub.1 on the surface ship 20
unwinds cable 12, it lowers the chain 13 as shown in FIG. 4b, thus
having the effect of increasing the weight carried by the
receptacle up to a weight F.sub.max. The apparent weight of the
sarcophagus 1 in water is then increased and it sinks in order to
approach the equilibrium position shown in FIG. 4 and be stabilized
therein.
[0140] Thus, under all circumstances, the configuration of the
chains 13 as catenaries produces a self-regulating effect on the
position of the sarcophagus while it is being lowered.
Nevertheless, it is still appropriate to synchronize the unwinding
of the cables 12 from all of the winches 12.sub.1 involved in the
maneuver in a manner that is very accurate so as to ensure that the
sarcophagus 1 is lowered while remaining substantially horizontal.
In addition, the ship 20 must remain at a substantially constant
distance from the axis of the receptacle, and preferably the two
ships 20a and 20b connected to opposite fastener elements 10 (FIG.
1) should be situated in substantially the same vertical plane as
includes the points where the chains 13 are attached to the beams
10 of the sarcophagus 1, which means that it is advantageous for
the ships to make use of dynamic positioning techniques relying on
a radiolocating system of the GPS type (global positioning
system).
[0141] The sarcophagus 1 is preferably lowered continuously down to
a distance where it is close to the wreck 6, for example 50 m from
the sea bed. The sarcophagus is then positioned relative to the
axis of the wreck 6 and is oriented in the proper direction by
moving the ships 20 on the surface. Said movements of the ships 20
produce an effect that is delayed by several minutes to several
tens of minutes on corresponding movements of the sarcophagus
situated several thousand meters below. In order to facilitate this
operation, it is advantageous to install steerable thrusters 16,
preferably at the ends of the structure, and more particularly at
the four corners of the roof, said thrusters 16 being powered by an
umbilical cord 16.sub.1 delivering power and control signals and
connected to a surface ship 20.
[0142] In the variant shown in FIGS. 1 and 2, winches 14.sub.1 are
installed on the side peripheral walls of the sarcophagus, and once
said sarcophagus 1 is close to the wreck, an automatic underwater
remotely operated vehicle (ROV) 22 controlled from the surface
connects the cables 14 of said winches 14.sub.1 to anchor points
15.sub.1, 15.sub.2 that have been previously installed in the
vicinity of the wreck, e.g. constituted by suction anchors 15.sub.1
or by deadweight blocks 15.sub.2.
[0143] Once the sarcophagus has been put finally into place, the
heavy chains rest on the sea bed 7 as shown in FIG. 2, and the
additional floats 19 are detached by means of the ROV 22, with
these floats then rising freely to the surface where they are
recovered. Care is taken to ensure that each of them is fitted with
an acoustic beacon, thus enabling their upward travel to be
followed by means of sonars on board the ship 20, and consequently
making it possible to move the ships so as to avoid any collision
when the floats surface. The sarcophagus 1 is then stable on the
sea bed, but its stability can be further improved by recovering
its buoyancy material, e.g. gas oil, as shown in FIG. 2. For this
purpose, a ROV 22 is used under control from the surface to connect
a preferably flexible pipe 23, preferably having an S-shaped
configuration, to an orifice that is provided with an isolating
valve 4.sub.4 and situated in the top of the compartment 4, with
care being taken to begin by opening a valve 4.sub.5 situated at
the bottom of the same compartment 4 so as to allow sea water to
penetrate therein as the buoyancy fluid rises to the surface.
[0144] After the buoyancy compartments 4 have been emptied of their
buoyancy fluid, the top valves 4.sub.4 at least are closed and the
sarcophagus then presents its maximum weight which provides it with
a high degree of stability, even in the event of large amounts of
leakage from the wreck. The effluent escaping from the wreck via
said leakage collects in the top portion of the internal volume of
the sarcophagus, thereby creating significant buoyancy, however
this buoyancy is much less than that of the fluid that was in the
compartment 4, which is generally gas oil presenting relative
density of 0.85. With highly viscous crude oils, relative density
is generally greater than 0.95 and is often close to 1.02, thereby
creating little buoyancy and running no risk of destabilizing the
sarcophagus.
[0145] After the buoyancy compartments 4 have been emptied, the
chains may be recovered, however if it is preferred to improve the
stability of the sarcophagus, it is advantageous to raise the
chains 13 so that their opposite ends are also carried by the beam
already carrying their first ends, or else they are raised and
merely placed on top of the sarcophagus, so that their entire
weight contributes to stabilizing said sarcophagus.
[0146] By increasing the distance between the double walls defining
the compartments 4, and by using light metals, e.g. aluminum for
the structure, it is possible advantageously to replace gas oil
with fresh water as the buoyancy fluid.
[0147] The relative density of sea water is about 1.026 at the
surface and about 1.045 at a depth of 4000 m and at 3.degree. C.,
whereas the relative density of fresh water is 1 at the surface and
1.016 at a depth of about 4000 m and a temperature of 3.degree. C.,
so the buoyancy provided by fresh water per cubic meter (m.sup.3)
thus lies in the range 26 kilograms force (kgf) at the surface and
29 kgf at a depth of 4000 m. The total volume of the compartments 4
in the following example enable the dead weight of the sarcophagus
structure described below to be balanced. A sarcophagus having
aluminum walls, a length of 180 m, a width of 40 m, and a height of
35 m, with a distance of 3 m between its inner and outer double
walls represents a mass of aluminum equal to 3000 (metric) tonnes
(T), i.e. an apparent weight in sea water of 1850 tonnes. The total
volume of the compartments is 73,125 m.sup.3, giving a buoyancy of
1480 tonnes when filled to 75% with fresh water. Additional
buoyancy of 470 tonnes is applied in the form of floats distributed
along the structure, and the stabilizing chains for lowering
purposes are constituted by four identical lengths of chain each
weighing 50 tonnes, each of them being installed at a corner of the
sarcophagus.
[0148] For a sarcophagus having the same dimensions and made of
steel, it is necessary to use a fluid of lower density than fresh
water, e.g. gas oil, and the total volume of the buoyancy
compartments requires the distance between the inner and outer
walls to be 2.5 m. The sarcophagus then presents a mass of 7500
tonnes, i.e. an apparent weight in sea water of 6300 tonnes. The
total volume of the compartments is 60,200 m.sup.3, giving buoyancy
of 6320 tonnes when filled to 70% with a fluid presenting relative
density of 0.85, e.g. gas oil. The additional floats (280 T) and
the stabilizing chains (50 T.times.4) remain the same as for the
aluminum sarcophagus.
[0149] In an advantageous variant shown in FIGS. 5 and 6, it is
advantageous to install a horizontal diaphragm or web 21 that is
tensioned between the side walls 2, 2a, 2b, and 2.sub.1 in such a
manner as to isolate the top portion of the inside volume of the
sarcophagus, which top portion is advantageously filled with fresh
water. This generates additional buoyancy, thereby contributing to
the buoyancy of the sarcophagus as a whole, and making it possible
to reduce correspondingly the volume of the main buoyancy fluid
such as gas oil that is used for filling the internal compartments
4 within the structure of the sarcophagus. By way of example, for
the two cases described above, a diaphragm situated at half height
serves to confine 126,000 m.sup.3 of fresh water, thereby
contributing overall buoyancy of 3400 tonnes and enabling the
buoyancy compartments to be reduced correspondingly, particularly
if the structure is made of steel, thus correspondingly reducing
the volume of gas oil. In addition, in those zones of the structure
that do not have buoyancy compartments, it becomes possible to
simplify the structure, thereby reducing its weight by locally
omitting one of its walls, preferably the inner wall. This
diaphragm 21 is secured mechanically to the walls, e.g. by means of
straps. There is no need for the connection to be entirely
leaktight, since the role of the diaphragm 21 is mainly to ensure
that stirring created by the current during towing to the site does
not cause the fresh water to mix with sea water, which would lead
to a large fraction of said fresh water being lost quickly by being
dispersed in the sea water, thereby losing a large portion of the
buoyancy of the structure as a whole. Once the sarcophagus 1 has
been lowered to the immediate vicinity of the wreck 6, and prior to
it being placed on the sea bed, the diaphragm 21 is removed, either
by means of the ROV 22, or by using automatic release systems of
the hydraulic actuator or explosive bolt type, and then the
sarcophagus is lowered into its final position on the wreck. At the
end of installation, a top drainage orifice 9 through the roof of
the sarcophagus is advantageously opened so that the fresh water
can escape and the stability of the sarcophagus can be improved.
After the fresh water has been exhausted, said top orifice 9 is
closed so as to recover any leakage coming from the wreck.
[0150] The same top orifice 9 is advantageously used for recovering
the effluent 9 that escapes from the wreck 6 over time, which
effluent collects in the top of the inside volume of the
sarcophagus underneath its roof 3, 3a, 3b. By making a connection
with this top orifice 9 and after opening the isolating valve, the
oil 8 that has accumulated since the preceding campaign is
advantageously transferred either by means of a pipe 23 connecting
the top orifice 9 to a recovery ship situated on the surface, or
else by using a recovery device between the sarcophagus and the
surface ship, e.g. a device of the kind described in French patent
application No. FR 2 804 935, or indeed a shuttle type device as
described in yet-to-be-published European patent application No.
03/358003.6.
[0151] In a version of the invention shown in FIG. 7, a hangar type
load-carrying structure is made built up from beams of steel or
other metal 24 assembled together by welding or bolting, and
leaktight compartments are incorporated therein, being distributed
continuously or otherwise, either on the side walls 2, 2a, 2b or in
the roof 3, 3a, 3b, or in both of them. The structure as a whole is
made leaktight against a fluid that tends naturally to escape
upwards by means of diaphragms or webs 25 fixed outside the
structure and against it in leaktight manner, so as to recover all
leakage from the wreck and direct it towards a high point where it
can be stored while waiting to be recovered, either by means of a
bottom-to-surface connection 23 or by means of a recovery device or
shuttle as mentioned above.
[0152] In a version of the invention shown in FIG. 8, the
sarcophagus structure is made of lightweight concrete 26 that is
reinforced and prestressed, and it contains compartments 4 which
are filled in the same manner as before with a fluid of density
lower than that of sea water. The concrete 26 is advantageously
made using lightweight aggregate, such as expanded clays for
example, associated with high-strength mortars, thus giving
excellent behavior at great depth, even at depths of 3000 m to 4000
m, or even more. Expanded clays are substantially spherical in
shape leaving gaps that are filled with air or gas, thus giving
them very low density; when taken within a matrix constituted by
high strength mortar, it is the matrix proper which provides
overall strength. When the structure is subjected to very high
pressures, e.g. the pressure of 400 bars that exists at a depth of
about 4000 m, water will migrate over time into the mass of
concrete and will, little by little, invade the expanded clay
aggregate, thereby considerably increasing the apparent weight of
the sarcophagus. Since this migration process is relatively slow it
is not a disadvantage during installation since after being towed
to the site, the critical operation of lowering said sarcophagus
from the surface to its final position resting on the sea bed over
the wreck will occupy a maximum duration of 12 hours (h) to 24 h.
Once in place, the dead weight of the sarcophagus increases day by
day, thereby increasing its stability, with the water migration
phenomenon continuing over a period of several weeks or even
several months. In order to retard water migration phenomena into
the porous aggregate, it is advantageous to cover the walls of the
concrete structure that come into contact with water completely in
a layer of elastomer type paint, thereby creating an effective
sealing barrier. This layer is advantageously also applied to the
inside of the buoyancy compartments integrated in the concrete
structure in order to minimize migration of buoyancy fluid into
said aggregate.
[0153] It is advantageous to use a fluid of very low density, thus
reducing the overall volume of the buoyancy compartments. For this
purpose, it is advantageous to use butane, propane, ammonia, or any
other similar gaseous compound whose relative density in the liquid
state lies in the range 0.55 to 0.70. These compounds are gaseous
at atmospheric pressure and at a temperature of 20.degree. C., but
they liquefy once they have been compressed to a few bars. It is
thus highly advantageous to use them as buoyancy fluid since their
efficiency (in terms of buoyancy per m.sup.3 of fluid) is much more
advantageous than that of gas oil or fresh water, however the
compartments then need to be filled in a particular manner in order
to avoid any risk of accidents or difficulties.
[0154] For this purpose, the procedure is as follows. After the
sarcophagus has been built and taken out of the open basin, its
compartments 4 still being empty, the compartments are filled with
sea water and the assembly is made buoyant by means of barges 27,
preferably two or four barges floating on the surface as shown in
FIG. 9a.
[0155] The sarcophagus is connected to each of said barges 27 by a
cable 28 connected to a winch 28.sub.1, in association with a
pounding compensator 29 seeking to ensure that the cable 28 does
not break. The assembly is then towed to the site, and then as
shown in FIG. 9b, the sarcophagus is lowered to a depth of 30 m to
60 m which corresponds to a pressure of 3 bars to 6 bars, at which
pressure the gas that is to be injected into the compartments 4 is
in liquid form. A pipe 23 is then lowered and connected to the high
point 4.sub.4 of the buoyancy compartments and liquid gas stored on
board a specialized gas tanker ship 31 (known to the person skilled
in the art), is injected under pressure. The bottom orifice 4.sub.5
of the compartment is left open so the liquid gas expels the sea
water therein and fills the compartment 4 completely, little by
little. At the end of filling, the top valve 4.sub.4 is closed in
leaktight manner. Once all of the compartments have been filled,
the barges 27 used during towing can be released after the
retaining cables 28 have been disconnected. The sarcophagus can
then be lowered as explained above. In FIG. 9b, the right-hand
compartment is full of gas in the liquid state, whereas the
left-hand compartment is being filled, with sea water escaping
through the bottom valve 4.sub.5 which is in the open position.
[0156] At the end of installation, it can suffice to open the top
orifice 4.sub.4 situated at the top of each of the
buoyancy-compartments to a small extent so as to allow the gas to
escape in liquid form: it then rises naturally towards the surface,
initially in liquid form and finally in the form of gas close to
the surface where it becomes diluted in the atmosphere. These gases
are not dangerous for the environment or for personnel, insofar as
the instantaneous quantities thereof remain reasonable, i.e.
constituting a few tens or a few hundreds of kilograms per hour,
but it is nevertheless preferable to recover the cargo of liquefied
gas. For this purpose, a bottom-to-surface connection 23 is
installed as described above with reference to FIG. 2, which
connection connects the top orifice 4.sub.4 of each compartment to
the gas tanker ship and enables nearly all of the gas cargo to be
recovered in a very short length of time since the gas in liquid
form is very fluid and the pressure difference between the sea bed
and the surface is very high, particularly when the wreck is at a
depth of 3000 m to 4000 m.
[0157] In each of the variants of the invention described above,
the leaktight compartments are positioned and dimensioned in such a
manner as to comply with the rules applicable to ship-building, and
in particular with the .rho.-a rule which consists in ensuring that
the center of vertical thrust due to buoyancy remains above the
center of gravity of the structure. It is common practice to
consider that for a value of .rho.-a>1 m, the structure can be
considered as being stable and not in danger of turning over by
pivoting about its axis XX'. For this purpose, it is advantageous
to add external floats 19 which are preferably situated above the
structure of the sarcophagus, and possibly also to ballast its
bottom portions.
[0158] In each of the variants of the invention, a structure is
described which covers the wreck completely down to the sea bed,
however it would remain within the spirit of the invention to make
use of a structure that remains at a distance of a few meters from
the sea bed, standing on posts constituted by posts provided at
their bottom ends with support plates, so as to limit penetration
into the sea bed. This disposition makes it possible,
advantageously to access the wreck under the sarcophagus by means
of an ROV 22 in order to inspect it or indeed in order to operate
valves, drill holes to release crude oil for recovery purposes, or
indeed to place destructive explosives in order to create localized
openings in the wreck.
[0159] Thus, in a preferred version of the invention as shown in
FIG. 10, the sarcophagus is provided at each of its corners with a
post 40 having a support plate 40.sub.1 so that the structure does
not rest directly on the sea bed but stands above it, e.g. by 2 m,
thereby leaving access around its entire periphery for the ROV 22
to perform inspection and other operations. Given the considerable
dimensions of the structure, it is advantageous to install
intermediate posts 41 along each of its faces, with said posts then
being in a high, retracted position 41a during transport and
lowering of the sarcophagus. Thus, once the sarcophagus has been
lowered onto the wreck and is resting on the sea bed, it initially
stands only on the corner posts 40, thereby conferring
quasi-isostatic trim thereto. At this stage, with buoyancy still
being at a maximum in the buoyancy compartments and the additional
floats, the apparent weight of the structure is small and can be
supported by the structure. The ROV then acts on each of the posts
to operate bolts 42 for releasing the posts so that under their own
weight they move away from the high, retracted position 41a into
the low, deployed position 41b. Thereafter, the ROV again actuates
the bolts 42 so as to lock said posts relative to the structure of
the sarcophagus. By acting in this way one each of the posts so as
to cause them to go from the retracted position to the deployed
position, and by locking them in the deployed position, the trim of
the sarcophagus structure is greatly improved, and this applies
regardless of the nature of the sea bed and any obstacles that
might be present beneath each of the posts. This ensures that none
of the posts are left hanging while others have too great a
fraction of the overall load concentrated thereon, running the risk
of leading to significant damage or even total loss of the
structure. This disposition thus makes it possible to have
quasi-isostatic trim over the entire surface via a large number of
posts, and to achieve this regardless of the nature of the sea bed
and any obstacles that might be encountered. Once all of the posts
have been deployed, it is possible to empty the buoyancy material
from the buoyancy compartments so that the structure then presents
its maximum weight and rests safely on the sea bed even if the sea
bed itself is highly non-uniform.
[0160] The buoyancy compartments are described above as having a
top orifice and a bottom orifice each fitted with an isolating
valve, however it would remain within the spirit of the invention
if the compartments were to be open-based, with the buoyancy fluid
remaining in place solely because of its difference in density.
[0161] For buoyancy compartments having bottom orifices fitted with
respective valves, it is preferable to keep said valves closed
while the structure is being towed to the site, however it is
advantageous for them to be opened while the structure is being
lowered towards the bottom so that variations in the volume of the
buoyancy fluid due to ambient pressure and temperature do not give
rise to unacceptable deformation of the structure of said
compartment, since that would run the risk of damaging the
structure of the sarcophagus.
[0162] It is advantageous to fit square openings having a size of 2
m or 3 m halfway up the side walls 2, 2a, 2b, 2.sub.1 so as to
facilitate access for ROVs 22 for the operations described above.
These openings are advantageously closed under normal conditions by
hinged flaps that are locked in place in leaktight manner so as to
avoid losing any polluting substances coming from the wreck.
[0163] FIGS. 11a to 11d and 12 show a shuttle tank 32 of the type
serving to recover effluent from a wreck on the sea bed by lowering
and raising said shuttle tank respectively when empty and when
full, between the surface and the bed of the sea. The shuttle tank
32 is constituted by a side wall 34 that is flexible and leaktight,
e.g. made of strong reinforced plasticized fabric, said side wall
being secured at its top portion to a dome 33 having a circular
horizontal section and having a bullet-shaped profile in vertical
section, and that is made of a strong and rigid material,
preferably a composite material, and said side wall being secured
at its bottom portion to a plane, solid, strong, rigid, and
preferably circular bottom wall 35, which is itself also preferably
made of composite material so as to represent a minimum apparent
weight in water, while guaranteeing extreme rigidity and strength.
Said bottom wall 35 is pierced at its center by a main orifice
35.sub.1 and is fitted with a valve, preferably a draw-off valve,
e.g. of the guillotine type, said valve being fitted with a flange.
A complementary side orifice of smaller diameter is provided with a
valve 35.sub.2, thereby enabling sea water to be exchanged between
the inside of the shuttle tank and the marine environment, and in
particular enabling sea water to escape while the tank is being
filled with oil.
[0164] The dome 33 and the bottom wall 35 can present a diameter in
the range 5 m to 10 m, the dome 33 can present a height in the
range 2 m to 5 m, and the side wall 34 can present a height in the
range 10 m to 50 m, once deployed.
[0165] The apparent weight in water of the shuttle tank 32 is
advantageously adjusted by integrating buoyancy into the highest
portion of the dome 33, e.g. syntactic foam 33.sub.1 constituted by
microspheres of glass coated in epoxy, polyurethane, or other
resins.
[0166] The shuttle tank 32 is thus lowered to the wreck or tank 6,
or even to a sarcophagus 1 placed over a said wreck or tank, in the
collapsed position, and presents an apparent weight in water that
is very light and that can be adjusted both positively and
negatively, thereby making it easy to install directly by using an
ROV controlled from the surface and provided with manipulator
arms.
[0167] FIG. 11a shows that the raising of the shuttle tank 32 is
controlled by a connection cable 12 having a fraction of its bottom
portion 13 that is weighted, e.g. by metal blocks 31 secured to
said cable 30 by clamping at 31.sub.1 like a string of beads.
[0168] As shown in FIG. 11d, the beads 31 have a cylindrical
central body that is prismatic or circularly cylindrical, and
frustoconical ends, so that when the cable is curved, the
frustoconical ends of two adjacent beads thus come into abutment
against each other at 31.sub.2, thereby limiting the local radius
of curvature to a value that is greater than R.sub.0. Thus, the
connection cable 12, being fastened to the shuttle tank 32 at said
first fastener point 36 at the bottom of the tank, descends, then
moves away through an arc of a circle of radius R.sub.0, before
finally rising vertically or in a catenary configuration at a
distance of about at least 2R.sub.0 from the side wall 4 of said
shuttle tank, thereby avoiding any mechanical contact during
raising, and thereby preventing said connection cable from being
damaged by rubbing.
[0169] In FIG. 11a, the buoyancy of the shuttle tank filled with
hydrocarbons F.sub.v that corresponds to the buoyancy thrust that
is exerted on the tank and its cargo is compensated by the weight
of the cable up to the horizontal tangent point corresponding to
the bead 31.sub.i, added to the weight of the beads 31.sub.g
between the tank and the lowest bead 31.sub.i, i.e. 8.5 beads in
FIG. 11a, the overall weight P.sub.e thus corresponding to the
system being in equilibrium.
[0170] By way of example, in order to illustrate. FIG. 11a, the
shuttle tank having a volume of 250 m.sup.3 of oil of density 1011
kilograms per cubic meter (kg/m.sup.3), in sea water at 3.degree.
C. of density 1045 kg/m.sup.3, has a buoyancy of about 8.5
tonnes.
[0171] Each of the beads of the equilibrium device 30-31 thus has a
weight in water of about 1 tonne.
[0172] In FIG. 11b, the top end of the connection cable 12
connected to a winch installed on board a surface ship (not shown)
is raised, thereby bringing the bead 31.sub.g in FIG. 11 into the
bottom horizontal position, and thereby reducing the number of
beads hanging from the tank to 6.5 beads, the overall weight
opposing the F.sub.v thrust thus being reduced to P-. The resultant
F.sub.v+P- is thus upwardly positive and the shuttle tank can rise
until the force equilibrium of FIG. 11a is reached.
[0173] In addition, in FIG. 11c, the top end of the connection
cable 12 is veered (lowered), thereby bringing the bead 31.sub.k
into the bottom horizontal position, and thereby increasing the
number of beads hanging from the tank to 10.5 beads, with the
overall weight thus being equal to P+. The resultant F.sub.v+P+ is
thus downwardly positive and the shuttle tank can move back down
until the force equilibrium of FIG. 11a is reached.
[0174] Thus, the stabilizing device of the invention presents a
stabilizing effect while the shuttle tank is being raised. When the
surface ship moves excessively under the effect of swell or moves
away from the vertical above the position of the shuttle tank, the
movements have an instantaneous effect on only the zone of the
beads surrounding the beads 31.sub.g to 31.sub.k, the bead 31.sub.i
corresponding to the mean value of the oscillations.
[0175] Thus, in order to control the raising of the shuttle tank
32, it suffices to wind the connection cable onto the winch
situated on board the surface ship 20 at a speed that is compatible
with the natural rate of rise of said shuttle tank, with said
shuttle tank naturally always seeking to, return to its equilibrium
position shown in FIG. 11a. In the event of difficulties, it
suffices to slow down or stop winding onto the winch, the shuttle
tank then finding its position of equilibrium almost immediately,
while waiting for the winch to restart.
[0176] FIG. 12 shows a shuttle tank 32 installed in register with
of an emptying device 9 fitted with a valve provided on the top
wall of a sarcophagus 1 to which said shuttle tank is connected by
a connection 50. When the valve is in its open position, it passes
through the crude oil that has accumulated inside said sarcophagus,
after flowing out from the tanks of the ship 6. It can thus be
collected in the shuttle tank, which can be raised to the surface
once full and once the connection 50 has been broken, with the rise
to the surface being performed under the control of a device of the
invention for stabilizing and controlling raising and lowering. The
sarcophagus 1 is fitted with a stabilizing and control device of
the invention having connection elements 12 constituted by cables,
each having a bottom portion that comprises a string of metal
blocks 31.
[0177] The device for controlling the lowering or raising of a
heavy or massive structure is described above as being constituted
either by a cable provided with blocks or beads clamped onto said
cable, or by a chain having links that are modified so as to create
the minimum radius of curvature R.sub.0 merely by abutment between
links. But, it is not beyond the ambit of the invention for said
heavy portion of said connection elements to be constituted by a
string of heavy bars that are hinged together so that deformation
of the string of hinged bars creates a load imbalance of P+ or P-
relative to the equilibrium load Pe, as described above with regard
to FIGS. 11a, 11b and 11c, said bars advantageously presenting
mechanical abutments at the hinges, making it possible to limit the
curvature to a minimum value R.sub.0.
[0178] FIG. 13 shows a heavy structure consisting of a device 1 for
placing and anchoring a base 52 on the wall 54 of a tank and/or of
a shipwreck on the sea bed. The device 1 comprises a support
structure 54 constituted by a rectangular machine-welded stand,
itself supporting:
[0179] a drill body 54.sub.1 comprising means for actuating a crown
saw 55 both in translation and in rotation, which saw, through a
corresponding opening provided in said base, enables a large
orifice to be pierced in said wall 6 so as to allow fluid contained
in said tank to be evacuated; and
[0180] side carriages 56 comprising means for actuating crown saws
57 both in translation and in rotation that are capable of piercing
holes in said wall 6 in order to anchor the base 52 to said wall,
the crown saws 57 being displaced through orifices 58 in said
base.
[0181] FIG. 13 shows the lowering of a structure 1 consisting of an
anchoring and piercing device controlled by a stabilizing chain 12,
13 of the invention, and by a buoyancy element 19. The bottom
lefthand portion of the base 52 is shown in section in order to
show the cutting means 57 inside an orifice 58 provided in said
base.
[0182] The device 1 is suspended by a connection 59 from a buoyancy
element 19. A connection element 12 of the cable type, having a
bottom portion 13 comprising weighting blocks 31 disposed in a
string as mentioned above, and extending from a surface-floating
support to a fastener element 36 at the base of a buoyancy element
19, makes it possible to control the speed at which the device 1 is
lowered and raised, and where appropriate, makes it possible to
stabilize it in the vicinity of the wall 6, in accordance with the
present invention.
* * * * *