US3710582A

US3710582A - Unique subsea storage vessel and unique method of lowering same

Info

Publication number: US3710582A
Application number: US00143798A
Authority: US
Inventors: L Anderson; W Bliss; R Hills; J Adams; J Murphy; F Hamren; H Honath
Original assignee: R Hills; J Adams; L Anderson; H Honath; J Murphy; W Bliss; F Hamren
Current assignee: PITTSBURGH-DES MOINES Corp
Priority date: 1971-05-17
Filing date: 1971-05-17
Publication date: 1973-01-16
Anticipated expiration: 1990-01-16

Abstract

A subsea storage vessel and a method of lowering same comprising, a roofed shell, at least one separate and independent tank means carried by the roofed shell, means connected with at least one of said tank means to control the amount of liquid or other ballast therein to submerge the roofed shell, said at least one tank means singly or in combination being incapable of statically floating the roofed shell with all gas removed from beneath said roofed shell, auxiliary buoyancy means carried by said roofed shell imparting buoyancy thereto, said auxiliary buoyancy means alone being incapable of statically floating the roofed shell with all gas removed from beneath the roofed shell, said at least one tank means and said auxiliary buoyancy means together being of such size and buoyancy as to statically float the roofed shell with all gas removed from beneath the roofed shell.

Description

United States Patent [191 Hills et al. 1 Jan. 16, 1973 s41 UNIQUE SUBSEA STORAGE VESSEL 2,631,558 3 1953 Harris ..|14 .5 T

AND UNIQUE METHOD OF 3,159,130 l2/l964 Vos R G S ME 3,507,238 4/l970 Chow v.l l4/.5 T [75] Inventors: f gz z f' gigzhgr fggg i g Primary ExsakzninerzJacotgI iliiapiro i An tt derson, ,lr., Pittsburgh; Woodrow E. omey oema er an a are Bliss, Jr., Pittsburgh; Fred W. Hamren, Jr., Sewickley; Harry F. [57] ABSTRACT Honath, Coraopolis; John C. A subsea storage vessel and a method of lowering Murphy, Pittsburgh, all of Pa. same comprising, a roofed shell, at least one separate [73] Assignee: Pittsburgh-Des Moines Steel Comand independent tank mans earned by any Pittsburgh Pa shell, means connected with at least one of Sdld tank p means to control the amount of liquid or other ballast [22] Filed: May 17, 1971 therein to submerge the roofed shell, said at least one 21 A L N 143 798 tank means singly or in combination being incapable 1 pp 0 of statically floating the roofed shell with all gas removed from beneath said roofed shell, auxiliary [52] US. Cl. ..6l/46.5, 114/5, 220/18 buoyancy means carried by said roofed She" imparting [51] Int. Cl ..B65d 89/10, E02b 17/00 buoyancy thereto, Said auxiliary buoyancy means [58] held of Search "61/46, 46-5; T; alone being incapable of statically floating the roofed 220/13 18 shell with all gas removed from beneath the roofed shell, said at least one tank means and said auxiliary [56] References cued buoyancy means together being of such size and UNITED STATES PATENTS buoyancy as to statically float the roofed shell with all gas removed from beneath the roofed shell. 34,426 2/1882 Howard ..6l/46.5 3,429,128 2/1969 Stafford et al ..61/46 52 Claims, 31 Drawing Figures PATENTEDJAH 16 1975 sum 01m 11 LLOYD E.AN

OW E BL E HARRY F JOHN 0.

HAMRENJ: HO

MURPH PATENTEDJAH 16 I915 SHEET 02 HF 11 PATENTEDJAN 16 ms SHEET 0U HF 11 PATENTEUJAH 16 I975 3.710.582

sum 06 [1F 11 FIG/3.

PATENTEU JAN 1 6 I975 SHEET 07 [1F 11 PATENTEDJAH 15 I975 SHEET 08 0F 11 PATENTEUJM 16 I975 SHEET OSUF 11 N in) UNIQUE SUBSEA STORAGE VESSEL AND UNIQUE METHOD OF LOWERING SAME BACKGROUND OF THE INVENTION This invention relates to a unique subsea storage vessel and unique method of lowering same, wherein said vessel is used for storing liquids such as crude oil and the like at offshore locations.

Both subsea and surface storage vessels are known in the art for storing liquid at offshore locations, but all such prior art devices have certain inherent disadvantages and undesirable characteristics. For example, some such prior art devices rely on a single means or tank for controlling the buoyancy and submergence of the vessel, and in the event of a malfunction in such systems, there is a danger of uncontrolled sinking of the vessel. Further, in such prior art devices, there is no means for trimming the vessel during floatation in order to correct for listing of the vessel due to structural variations and the like. Still further, such systems, due to the necessary :large size of the single means for controlling the buoyancy and submergence of the vessel, have less storage space than the present invention due to the volume occupied by the single means. Moreover, in these prior art devices, less control over stability of the vessel is possible than with the present invention due to the large size and placement of the buoyancy means and ballast or submergence means in the prior art devices.

in the prior art a situation arises during submergence, at a time when the roofed shell is partially submerged, where inherent instability causes a violent rolling of the vessel. This violent rolling produces a pronounced belching of the gas under the roofed shell and a consequent rapid submerging of the vessel due to loss of buoyancy. The invention described herein eliminates this violet reaction and is inherently stable at all times during towing and submergence.

Also in the prior art, submergence and control thereof depends upon maintaining freeboard through a large diameter standpipe to above the surface. This standpipe limits the depth to which this prior art device is useable. The subsea storage vessel described herein has no such depth limitation.

Another disadvantage of prior art in which standpipes or the like extend to above the surface of the body of water is the increased amounts of wind, wave and current loads these standpipes introduce into the roofed shell. The increased loads require additional structural rigidity and increased pile supports. The present invention, by eliminating the need for standpipes or the like and by having a removable lowering means, minimizes the structure required to resist wind, waves and currents. Several additional advantages in the invention disclosed herein are attributable to the lack of any parts of the vessel extending upwards toward the surface of the body of water. it is a known fact that due to oxygen depletion, corrosion rates lessen with depth. Hence, lower maintainance costs are an advantage of the present invention. Additionally with the advent of supertankers of great draft, collision damage is unlikely if the top of the subsea storage vessel is removed from near the surface of the body of water.

Additionally, in some prior art devices, the means-for controlling the buoyancy and submergence of the ves- 0 offshore storage vessel, floatable with inherent stability at all times and having a plurality of independent and separate means for controlling the buoyancy and submergence of the vessel. Auxiliary buoyancy means are provided on the vessel, which in cooperation with a trim control means and a compensator means or submergence means, provide sufficient buoyancy to statically float the vessel with all air or gas removed from beneath the roofed shell. In other words, the auxiliary buoyancy means, the trim control means, and the compensator means all taken together have a buoyancy at least as great as the total submerged weight of the vessel. The vessel is not capable of being statically floated with all gas removed from beneath the roofed shell with any of the compensator means, trim control means or auxiliary buoyancy means taken individually or in combinations of less than all, but all are required acting together to statically float the vessel. MOreover, with the plurality of individual buoyancy means, compensator means and trim control means and the placement thereof, relatively little volume in the storage space defined by the roofed shell is occupied and more liquid may be stored for a given size roofed shell. Further, the plurality of means renders the vessel more dependable in operation since a malfunction in one or more of the individual means does not render the vessel uncontrollable, and the remaining means may be used to float or submerge the vessel with stability. Still further, the compensator means, trim control means and auxiliary buoyancy means are removable from the vessel once the vessel is in position on the floor of the body of water and may subsequently be used on other vessels, if desired, thus rendering the vessel more economical than prior art systems.

In the present invention, the three separate means consisting of the compensator tank means, the trim control means and the auxiliary buoyancy means, are each used for a separate and independent function in the operation of submergence of the vessel. The auxiliary buoyancy means are sealed and no means is provided for adding or controlling liquid therein, and the buoyancy means function only to impart buoyancy to the vessel. They are adviseably located at a position high on the roofed shell so as to raise the center of buoyancy of the submerging vessel, thus increasing stability. They are removably attached to the subsea storage vessel for reuse on other vessels and are not intended for storage in connection with an installed vessel. However, after installation, the auxiliary buoyancy means could be interconnected with the roofed shell to act as additional storage. In form, the auxiliary buoyancy means could comprise any suitable means imparting buoyancy such as compartments filled with gas, or other buoyant materials.

The trim control means have means for independently controlling the amount of air or liquid or other ballast therein, independent of either the buoyancy means or compensator means, or with respect to one another, and are used only to trim the vessel prior to submergence of the vessel. They are adviseably equally spaced outwardly on the roof shell and should number at least three. In form, said trim control means could comprise any shape compartment to which ballast might be added. For example, a sealed container to which any liquid ballast might be added as by pumping or any open container to which any solid ballast might be added as by use of a crane or chute, or any means of attaching weights to the vessels as for example by bolting or clamping. The trim function could also be performed by removing parts or pieces from various areas of the vessel as by removing weight from the roofed shell. The said removed weight then becomes the trim control means. The ballast could be of any metallic or non-metallic, solid or non-solid material suitable for the purpose such as water, concrete, lead, etc.

The compensator means have means for controlling the amount of air and liquid or other ballast therein and are used only for submerging the vessel and are independent from the auxiliary buoyancy means and trim control means. They are adviseably spaced high and inwardly on the roofed shell. In form, said compensator means could comprise any suitable container in which ballast might be controlled. For example, a closed compartment into and out of which liquid ballast might be moved as by pumping could be used, or an open compartment to which solid ballast might be added as by a crane or chute might be used. The ballast used could be any metallic or metallic, solid or non-solid, material suitable for the purpose, such as water, concrete, lead etc. Further, the large size of the vessel and the thick side wall provide a large water plane area while the vessel is floating, thus substantially increasing the stability of the vessel while under tow or while floating. The side wall could be filled with a light material which contributes to the vessels buoyancy and further increase the stability of the vessel by raising the center of buoyancy; and the weight and location of the footer thereon results in a lowered center of gravity, further insuring stability of the vessel.

In operation, the vessel is assembled on shore and then floated with the volume under the roofed shell filled with any suitable pressurized gas such as air, nitrogen, etc. The auxiliary buoyancy means is filled with either gas or other suitable material of light density and sealed; and the compensator means and trim control means are empty of ballast. At this time, the vessel is floating with a light or shallow draft. Sufficient ballast might be selectively added to the trim control means to adjust the vessels level trim. Thereafter, the trim control means are sealed for the towing operation.

During towing, after the vessel has been moved offshore, the vessel is lowered in the water a slight amount by releasing some of the pressurized gas from under the roofed shell in order to prevent loss of the pressurized gas from under the edge of the roofed shell due to roll of the vessel caused by waves in the water. The auxiliary buoyancy means, compensator means and trim control means remains sealed and the amount of gas or liquid contained therein remains unchanged.

Once the vessel is at the site ofits intended use, dome vent valves in the roofed shell are opened, releasing the pressurized gas from beneath the roofed shell and the vessel is lowered in the water until the trim control means are disposed at least partially in the water. At this time, the gas under the roofed shell is at atmospheric pressure, and in the event the vessel has a list, due to structural variations or the like, the trim control means are used to right the vessel and adjust its level in the water by admitting ballast to the trim control means. Once the vessel is adjusted, the trim control means are sealed and thereafter remain sealed. Ballast is then added to the compensator means to submerge the vessel in a controlled manner to the floor of the body of water. Once the vessel is on the floor of the body of water and secured thereto, if desired, by pilings or the like, the auxiliary buoyancy means, trim control means and compensator means may be removed. It is important to note that in this system, each of the auxiliary buoyancy means, trim control means and compensator means have a completely separate and independent function, and none of them acting independently will statically float the vessel with all gas removed from beneath said roofed shell; but all are required acting in cooperation to statically float the vessel with all gas removed from beneath the roofed shell. With the vessel on the bottom, liquid to be stored, such as crude oil or the like, is pumped thereinto, said stored liquid displacing water in the vessel through means at the bottom of the vessel establishing communication between the inside of the vessel and the surrounding body of water. This open communication between the inside of the vessel and the surrounding body of water insures equalization of the pressure within the vessel and the pressure on the vessel from the surrounding body of water.

OBJECTS OF THE INVENTION It is an object of this invention to provide a unique subsea storage vessel for storing liquid such as crude oil and the like at offshore locations.

It is another object of this invention to provide a subsea storage vessel of simple and economical construction.

A still further object of this invention is to provide a subsea storage vessel for storing liquid, such as crude oil and the like, which is floatable with inherent stability and which has reliable means for controlling the buoyancy and submergence of the vessel.

An even further object of this invention is to provide a subsea storage vessel for storing liquids, wherein the vessel has a plurality of separate means for controlling the submergence of the vessel and for trimming the vessel.

A still further object of this invention is to provide a subsea storage vessel which has separate auxiliary buoyancy means, trim control means and compensator means, each functioning independently of the other to impart buoyancy to the vessel, to trim the vessel, and to submerge the vessel, respectively, none of said means having sufficient size and buoyancy, if acting independently or individually, to statically float the vessel; but all of said means acting together being of such size and buoyancy as to statically float the vessel with all gas removed from beneath the roofed shell.

Yet another object of this invention is to provide a subsea storage vessel having auxiliary buoyancy means, trim control means and compensator means wherein the auxiliary buoyancy means, trim control means and compensator means are removable from the vessel.

An even further object of this invention is to provide a unique method of lowering or submerging a roofed shell or subsea storage vessel.

A still further object of this invention is to provide a unique method of submerging a subsea storage vessel wherein a plurality of independent and separate means are used for separate stages or operations in submerging said vessel.

An even further object of this invention is to provide a method of lowering a subsea storage vessel which is not limited as to depth of water at installation site by standpipes or the like.

Another object of this invention is to provide a subsea storage vessel wherein no violent rolling or pitching occurs during the submergence due to inherent instabilities.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top perspective view of a first form of subsea storage vessel according to the present invention.

FIG. 2 is a top perspective view of a second form of subsea storage vessel.

FIG. 3 is a top view, partly broken away, of th storage vessel shown in FIG. 2.

FIG. 4 is a sectional view taken along the line 4-4 in FIG. 3.

FIG. 5 is a top perspective view of a third form of subsea storage vessel according to the present invention.

FIG. 6 is a top perspective view, broken away, of a portion of the apparatus forattaching the auxiliary buoyancy means and trim control means to the vessel.

FIG. 7 is an end view in section taken along the line 77 in FIG. 3

FIG. 8 is a detailed sectional view taken along the line 8-8 in FIG. 7.

FIG. 9 is a sectional view, partly broken away, of a portion of the auxiliary buoyancy means and is taken along the line 99 in FIG. 7.

FIG. 10 is a detailed sectional view showing a modified means for joining or connecting together adjacent compartments in the torus connected to the roofed shell.

FIG. 11 is a sectional view of one of the trim control means of the present invention showing the manner in which ballast is added thereto.

FIG. 12 is a side view, partly in section, of one of the trim control means of FIG. 5.

FIG. 13 is a top view, partly broken away, of a form of one of the auxiliary buoyancy means of FIG. 5.

FIG. 14 is a top plan view of the trim control means of FIGS. 5 and 12. v

FIG. 15 is a vertical sectional view of the compensator means showing the manner of their connection to the roofed shell.

FIG. 16 is a sectional view of the compensator means taken along line 16-16 in FIG. 15.

FIG. 17 is a top plan view of the compensator means in FIG. 15, showing their arrangement in the attachment plate for joining them to the roofed shell.

FIG. 18 is a vertical sectional view showing details of the attachment means for connecting the compensator means to the roofed shell.

FIG. 19 is a sectional view of a collection dome placed on the roofed shell in place of the compensator means.

FIG. 20 is a detailed sectional view of the manner of attachment of the collection dome to the roofed shell.

FIG. 21 is a vertical sectional view of a portion of the footer means and a portion of the side wall means of the vessel and showing vent means extending through the side wall means.

FIG. 22 is a top plan view of a modification of the invention shown in FIGS. 1, 2 and 5 wherein means are provided establishing communication between the compensator means and the auxiliary buoyancy means.

FIG. 23 is a sectional view of a portion of the structure shown in FIG. 22, taken along line 2323.

FIG. 24 is a schematic view of a control system used for controlling the ballast in the compensator means to submerge the vessel.

FIG. 25 is a schematic view of the vessel floating with shallow draft in a body of water with the center of gravity above the center of buoyancy.

FIG. 26 is a view similar to FIG. 25, showing the vessel lowered slightly in the body of water for towing and with the center of gravity above the center of buoyancy.

FIG. 27 is a view similar to FIG. 26, showing the vessel partially submerged in the body of water and with the center of gravity and center of buoyancy coincidmg.

FIG. 28 is a view similar to FIG. 27, showing the vessel with a list in phantom lines and in a level position in full lines, with the center of buoyancy above the center of gravity.

FIG. 29 is a view similar to FIG. 28, showing the vessel completely submerged and in its descent to the seafloor.

FIG. 30 is a schematic view similar to FIGS. 25 through 28 with the vessel fully submerged and resting on the floor of the body of water with the auxiliary buoyancy means, trim control means and compensator means removed and the collection dome placed thereon.

FIG. 31 is a schematic view of a subsea storage vessel having a different type of auxiliary buoyancy means.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, wherein like reference numerals refer to like parts throughout the several views, the subsea storage vessel is indicated generally at 1 in FIG. 1 and comprises a roofed shell having a roof R and a cylindrical side wall S depending from the periphery thereof. A footer F of concrete, steel or other suitable strong and heavy material is secured to the lower marginal portion of the side wall S for lowering the center of gravity of the vessel and for providing a foundation for the vessel during assembly and when the vessel is installed on the floor of the body of water. The roof R may be made of any suitable flexible or non-flexible material, such as steel alloy, aluminum, reinforced concrete, wood, rubber, nylon or other material having sufficient structural strength and may be either dome shaped, as shown, or flat or conical or any other suitable shape of sufficient structural rigidity. Further, the roof R may be reinforced by means of radially extending rafters 2 and circumferentially extending braces 3 or other suitable means.

The side wall S is adviseably of double wall construction comprising an inner wall 4 and outer wall 5 spaced from the inner wall. A plurality of circumferentially spaced, vertically extending pile sleeves 6 are disposed between the inner and outer walls 4 and 5. The space between the walls 4 and 5 may be filled with a reinforcing material such as foam, perlite concrete, or regular concrete or the like as seen in FIG. 4. The inner and outer walls 4 and 5 may be omitted if the side wall is constructed of a material such as reinforced concrete or the like, if desired. The side wall S is suitably connected at its upper marginal edge to an annular frame or box beam 8 of steel or the like. If the vessel is to be used to store liquid having a density less than the density of water, the bottom may be open as shown. If desired, a bottom (not shown) may be provided on the vessel for lowering the center of gravity of the vessel and for providing a mat foundation for the vessel when the vessel is installed or when liquids having a density greater than the density of water are to be stored in the vessel. A plurality of vents V are provided in the side wall S adjacent the lower marginal edge thereof for establishing communication between the interior of the vessel and the surrounding body of water when the vessel is resting on the floor of the body ofwater.

One or more suitable dome vent valves DV are provided in the roof R for venting the gas from beneath the roofed shell in order that the vessel may be submerged. A torus T is connected to the roofed shell on top of the annular box beam 8 by means of a plurality of annular connecting rings 9. The torus T comprises a plurality of completely separate and independent auxiliary buoyancy means A and trim control means B. The auxiliary Buoyancy means A are sealed compartments separated from one another by means of bulkheads 10 (see FIGS. 6 and 7) welded or otherwise suitably secured at the ends of the auxiliary buoyancy means A. The auxiliary buoyancy means A are filled with gas, perlite concrete or any other suitable material of light density and are used solely to impart a predetermined buoyancy to the vessel, but the auxiliary buoyancy means A do not have sufficient size and buoyancy to statically float the vessel with all gas removed from beneath the roofed shell. Each of the trim control means B is constructed similarily to the auxiliary buoyancy means A, except that a pair of

valves

11 and 12 are provided thereon suitably controlled as by manual or automatic means for admitting liquid ballast to the trim control means B and for venting gas therefrom, respectively, for trimming the vessel in the body of water (See FIGS. 11 and 28). The trim control means B serve both to provide a buoyancy to the vessel and to provide a means for trimming the vessel, and once the vessel is trimmed, as in FIG. 28, the trim control means B are sealed and no more ballast is added thereto. The trim control means B do not have sufficient size and buoyancy to statically float the vessel with all gas removed from beneath the roofed shell, nor does the combination of buoyancy means and trim control means acting together have sufficient size and buoyancy to statically float the vessel with all gas removed from beneath the roofed shell. Three separate and individual compensator means 13 are connected in the center of the domed roof R, although one or more could be provided, as desired. The compensator means 13 comprise elongate cylinders having rounded ends 14 and 15 and are held in fixed assembled relationship in a connecting plate 16 for connecting the compensator means 13 to the roof R (see FIGS. l5, l6 and 17).

Referring to FIGS. 6, 7, 8 and 9, details of construction of the connecting rings 9 for removably joining the torus T to the roofed shell can be seen. A ring 9 is provided at each end of each of the auxiliary buoyancy means A and trim control means B and comprises an annular web 17 welded to the said means A and B and an annular, right angularly extending stiffening flange l8 welded to the web 17 and extending in surrounding relationship to each of the said means A and B. The web 17 increases in width at the bottom of the torus, defining a wide section 19 having a flat, planar bottom edge 20. A flat, rectangular bottom plate 21, of the same width as the flange 18, is welded to the bottom of the surface 20 and extends from one end of the surface to the other end thereof. An elongate slot 22 is formed in the bottom plate 21 and a notch 23 is cut in the widened portion 19 of web 17 for receiving a complementally shaped connecting plate 24 welded or otherwise suitably secured along the edge to the top surface of annular box beam 8. An opening 25 is formed through the connecting plate 24 adjacent opposite ends thereof for receiving connecting pins 26. A hole is also formed through the web 17 on opposite sides of the center of torus T, spaced upwardly and outwardly from the connecting plate 24, and pins 27 are received therein. Two pairs of

tumbuckles

28, 29 and 30, 31 are received at their opposite ends over the opposite ends of each of the pairs of

pins

26 and 27 on the opposite sides of the web 17 for connecting the ring 9 and the torus T to the plate 24 and roofed shell. The torus T is lowered onto the top of the annular box beam 8 with the connecting plate 24 received through the slots 22 and into the notches 23.

Pins

26 and 27 are then placed through the openings in the plate 24 and web 17 and the

tumbuckles

28, 29 and 30, 31 are placed on the

pins

26 and 27. The tumbuckles are then tightened, securely holding the torus to the roofed shell. The torus may be removed from the roofed shell by removing the tumbuckles. This may be accomplished either by loosening the tumbuckles and slipping them off the pins or by knocking the pins out or by cutting or burning the tumbuckles or pins. Alternatively, remote means may be provided for explosively releasing the tumbuckles from the pins in order to release the torus from the vessel.

Referring now to FIGS. 15, l6, l7 and 18, the manner in which the compensator means 13 are connected to the roof R is shown. Each of the compensator means 13 is received in an opening 32 in the connecting plate 16, the openings 32 being equally spaced and symmetrically arranged in the connecting plate 16. A plurality of equally spaced bolt holes 33 are formed about the marginal edge of the connecting plate 16 for connecting the plate 16 and the compensator means 13 to an annular stiffening ring 34 having a square crosssection and suitably joined to the roof R to define a central opening 35 in the roof. A plurality of bolts 36 are extended through the holes 33 into the stiffening ring 34 for holding the plate 16 and compensator means 13 to the ring 34.

A plurality of bracing webs or

flanges

37 and 38 are welded or otherwise suitably secured along one side to the top surface of the plate 16 and extend vertically upwardly and are joined at their upper side or edge to an annular I-section bracing ring 39 spaced upwardly from the plane of the plate 16 and disposed in close surrounding bracing relationship to each of the compensator means 13. An annular groove 40 is formed in the bottom surface of plate 16 spaced radially inwardly from the bolts 36 and an annular sealing ring 41 of rubber or the like is disposed in said groove for sealing the plate 16 to the annular stiffening ring 34. Additionally, if desired, an annular groove 42 may be formed in the bottom surface of plate 16 with a plurality of openings 43 in communication therewith so that an epoxy sealer or the like may be put in said groove to provide a further seal for sealing the plate 16 to the stiffener ring 34.

As best seen in FIGS. and 16, the lower ends 15 of the compensator means 13, which extend downwardly into the vessel 1, are braced against lateral movement by means of an annular ring 44 disposed about the lower ends of the compensator means 13 and having a plurality of guy wires or the like 45 extending from the ring radially outwardly to the side wall S of the vessel 1.

A collection dome 46 is shown in FIGS. 19, and 29 and is adapted to be placed over the opening in the roof R when the compensator means 13 are removed from the opening. A pipe 47 extends into the collection dome 46 for removing liquids from the roofed shell. The collection dome 46 could be placed on the roof R at other locations, but the central location shown at the highest point in the roof R is desirable when liquids having a density less than water are stored in the vessel.

As seen in FIG. 20, the manner of connecting the collection dome 46 to roof R is similar to the manner in which the compensator means 13 are connected to the roof R. An annular connecting plate 16' is welded or otherwise suitably secured to the bottom marginal edge of the collection dome 46 and is bolted to the annular stiffening ring 34 by means of a plurality of bolts or the like 36 extended through holes 32 in connecting plate 16' and in the stiffener ring 34. A groove is provided in the bottom surface of a connecting plate 16 for receiving a resilient sealing gasket 41 therein and an annular channel or groove 42 as formed in the underside of connecting plate 16 adjacent channel or groove 40 and has a plurality of openings 43 in communication therewith for placing an epoxy sealer or the like in the channel or groove 42 to effect a seal between a plate 16' and stiffener ring 34.

Referring now to FIG. 24, the control system for lowering or submerging the vessel in the body of water is shown schematically. Each of the compensator 11168113113 has at least one inlet pipe 48 in communication with the bottom thereof for admitting liquid ballast to the compensator means, and at least one outlet pipe 49 for exhausting or blowing liquid ballast from the compensator means 13. A pump 50 is disposed in the inlet pipe 48 for pumping liquid through the pipe into 49 to the surrounding body of water.

Valves

51 and 52 may be any suitable type of control valves, such as electro-hydraulically operated valve or the like, and the liquid ballast may be derived from the surrounding body of water or from any other suitable source. Preferably, the pump 50 runs continuously and the flow of ballast into and out of the compensator means is controlled by the operation of

valves

51 and 52, valve 51 being open when valve 52 is closed, and vice versa. Opening and closing of

valves

51 and 52 is accomplished by means of a controller 53 which is placed on board a surface vessel or the like for controlling submergence of the subsea storage vessel. The controller 53 operates automatically in response to a signal from a sensor 54 which indicates the actual depth of the vessel, said signal being compared with a set point or desired depth signal provided to the controller. This set point signal is provided and adjusted by means of a knob 55. The controller 53 includes means for operating one or the other of

valves

51 or 52 to either admit or exhaust liquid ballast to or from the compensator means 13 to submerge the vessel to the desired depth selected at the controller 53 by knob 55. Each of the means 13 is filled with pressurized gas; and as the liquid ballast is added to the said means, this gas is compressed. When it is desired to exhaust liquid ballast from the tank, valve 51 is closed and valve 52 is opened and the pressurized gas in the tank blows or forces the liquid ballast from the compensator means through the line 49 and valve 52. More than one pump and associated piping may be provided for each compensator means, if desired.

Alternatively, the two

valves

51 and 52 may be replaced by a single 3 way remotely operated control valve, or the like, (not shown) placed in the inlet pipe 48. Ballast is supplied to the compensator means 13 from the pump 50 through the 3 way valve. Ballast is forced from the compensator means, when desired, by the compressed gas therein via the said pipe 48 and said 3 way valve with the valve positioned so as to vent. Pipe 49 is thus eliminated. Control of the 3 way valve is on signal from the controller as before.

It is thus seen possible to hover the subsea storage vessel 1 at any selected depth as indicated by the set point introduced by the knob 55 to the controller 53. To hover, the control system automatically varies the amount of ballast in the compensator means, 13. Said variation of ballast changes the state of buoyancy of the vessel which causes a motion of the vessel. For example, if the vessel is at a depth greater than the set depth, this deviation would cause the compensator means to expel ballast. The then lighter vessel would start to rise thus decreasing the deviation. As the deviation approaches zero, the system will add sufficient ballast to the compensator means to attain neutral buoyancy at the set point depth.

Referring now to FIGS. 22 and 23, a means for relieving the pressure in compensator means 13 when ballast is added thereto is shown. A pipe 56 is in communication at one end with the upper end of each of the compensator means 13 and is in communication at the other end with the auxiliary buoyancy means A in the torus T. Each of the pipes 56 is connected at said one end with a compensator means 13 through a flanged coupling 57 welded or otherwise suitably secured to the means 13. Each pipe 56 is connected at its said other end through a flanged coupling 58 with an annular manifold pipe 59, which is in communication with each of the buoyancy means A through a plurality of short, radially extending pipes 60. In this form of the invention, the auxiliary buoyancy means A serve as accumulator tanks for the compensator means 13 for relieving the pressure in means 13 when liquid ballast is added thereto, thus tending to compress the gas in the means 13 and increasing the pressure in said means. This prevents the pressure in the compensator means 13 from reaching a value wherein the pump 50 is incapable of pumping more liquid ballast into the compensator means 13. A float trap or other suitable means 61 is disposed in each of the pipes 56 for permitting the flow of gas through the pipes but for preventing the flow of liquid therethrough. The construction and operation of the system is otherwise the same as the system described and illustrated with reference to FIG.

The torus T, manifold 59 and radially extending pipes 60 are removable as a unit from the vessel once it is submerged, and the compensator means 13 and flanged coupling 57 are removable as a unit from the roof. The pipes 56 are connected to the roof R by pipe hangers or clamps 62, and may be removed, if desired, by disconnecting the pipe hangers or clamps 62 which secure the pipes 56 to the roof R.

The pump 50 and associated pipes and valves for the means 13 may be confined in a housing attached to the bottom of each of the compensator means 13 which would serve as an extension of the compensator means 13.

Referring now to FIGS. 2, 3 and 4, a further modification of the invention shown in FIG. 1 is illustrated, and in this form of the invention, the torus T is comprised completely of auxiliary buoyancy means A, filled with either gas, perlite concrete or other suitable material of light density. The trim control means B are mounted vertically on the side wall S at equally spaced points about the circumference of the vessel 1. Three trim control means B are shown in this figure, but any number of said means could be provided as desired in order to trim the vessel. The trim control means B are connected to the side wall S by means of a T-section connecting member 63 welded along one flange 64 to the side of the trim control means B and bolted through the other flanges 65 to the side wall S by means of a plurality of bolts or the like 66 extended through the flanges 65 into the side wall. A valve 11 is provided adjacent the lower end of each of the trim control means B for admitting liquid ballast to the said means for trimming the vessel, and a valve 12 is provided adjacent the upper end of each of the trim control means B for venting air from the said means when liquid ballast is added thereto. The construction and operation of this form of the invention is identical in all other respects with the form of the invention illustrated in FIG. 1, and the auxiliary buoyancy means A in the torus T may be utilized as accumulator tanks for the compensator means 13, such as described and illustrated with reference to FIGS. 22 and 23, if desired.

When the vessel 1 according to this fomi of the invention is completely submerged, the torus T, compensator means 13 and trim control means B may be removed, if desired, such as in the previous embodiment.

Referring now to FIGS. 5, 12, 13 and 14, a further modification of the invention is shown. In this form of the invention, buoyancy means A and trim control means B" are completely separate from one another and are independently connected to the vessel 1. Each of the means B or A has at least two connecting rings 9 thereon for securing the units to the vessel, and each of the trim control means B" has a pair of

valves

11 and 12 thereon for admitting liquid ballast to the said means and venting gas therefrom, respectively. Except for the complete separation of the means A and B, the operation and construction of the vessel 1 in this form of the invention is identical to the operation and construction of the vessel shown in FIG. 1. Further, the means A may be used as accumulator tanks for the compensator means 13 as illustrated and described with reference to FIGS. 22 and 23.

As shown in FIG. 5, the means B are smaller than the units A, but they could be of the same size, if desired; and any number of means A and B" could be provided on the vessel so long as the means A and B, together with the compensator means 13, provide sufficient buoyancy to the vessel to statically float the vessel with all gas removed from beneath the shell. Neither the buoyancy means A, the trim control means B nor the compensator means 13, if taken separately, are capable of statically floating the vessel with all gas removed from beneath the roofed shell. All of the means must be taken together in order to have sufficient size and buoyancy to statically float the vessel with all gas removed from beneath the roofed shell.

As seen in' FIG. 13, the means A may comprise several individual auxiliary buoyancy means welded or otherwise suitably connected together as in FIG. 9, with a connecting ring 9 welded at the end of each of the buoyancy means.

A modified construction of the torus T is shown in FIG. 10, wherein the torus comprises several sections joined together, each section consisting of one or more means A and/or B welded together, the sections being separable and independently removed from the vessel, if desired. As seen in this figure, one of the means A or B in the torus would have a bulkhead 10 closing the end thereof and extending at its margin beyond the edge of the means A or B to form the web 17 for the connecting ring 9, and an annular ring 18 would be welded or otherwise suitably secured around the web 17 for stiffening the connection. A plurality of bolt holes 67 would be provided through the web 17 for receiving bolts or the like (not shown) to secure the means A or B to an adjacent means A or B, having an open end 68 and an annular flange 69 welded thereto with a plurality of bolt holes 70 therein for receiving the bolts extended through web 17 to secure the adjacent means A or B together.

Referring now to FIGS. 25 through 30, the various steps in towing and submerging the storage vessel according to any one of the above described modifications is shown. In FIG. 25, the vessel 1 is shown assembled and floating on the surface of a body of water W with a light draft and the volume under the roofed shell is filled with pressurized gas. Neither the auxiliary buoyancy means A or trim control means B in the torus T, nor the compensator means 13 in the roof R have any ballast therein and dome vent valves DV are closed. Because of the large diameter of the peripheral wall and the large moment of inertia of the water plane produced by the wall, the vessel has a high metacenter and is very stable while on the surface. The gas under the roofed shell serves only to support the vessel and provides no stabilizing effects. In this position, the center of gravity is spaced above the center of buoyan- Some amount of ballast may now be added to the trim control means B so as to adjust the floating attitude of the vessel. After addition of ballast the means B are sealed for the towing operation.

In FIG. 26, dome vent valves D have been opened for a short period of time to release some of the pressurized gas from under the roofed shell to lower the vessel a slight amount in the water for towing since the elevation of the water surface under the roofed shell is close to the bottom of the side wall, and it is desirable to lower the vessel into the water before towing so as to allow for some degree of roll of the vessel due to waves without the possibility of losing any of the gas under the roofed shell. The side wall continues to provide a large water plane during this stage of operation with increased draft and the vessel remains very stable. The means A and B in the torus T and the compensator means 13 remain sealed and the amount of ballast contained within these means is unchanged and the center of gravity is still spaced above the center of buoyancy.

In FIG. 27, the vessel is shown at the site at which it is intended to be used and the dome vent valves DV have been opened, venting the gas from beneath the roofed shell to allow the vessel to settle or sink in the body of water. No change has been effected in the means A and B and the compensator means 13 still do not have any ballast therein, but the center of gravity and center of buoyancy coincide. In this position, wherein the center of gravity coincides with the center of buoyancy, enough freeboard of the vessel is provided so that the water plane area creates a sufficient metacentric height to insure stability. The gas under the roofed shell is vented to atmospheric pressure.

Referring now to FIG. 28, most of the remaining gas under the roofed shell has been vented and the vessel has been submerged to a point where the torus T is nearly awash in the body of water and the compensator means 13 are submerged in the water approximately one-half their length. At this time, the center of buoyancy is above the center of gravity. If the vessel is listing, as shown in phantom lines, due to structural variations or the like, the

valves

11 and 12 in the trim control means B on the high side of the vessel are opened, admitting ballast to the units B to add weight to that side of the vessel to lower that side and level the vessel in the body of water to the position shown in full lines. Once the vessel is trimmed, sufficient ballast is added to all of the trim control means to lower the vessel in the water until the compensator means 13 are submerged exactly a predetermined amount. This amount might be one-half their length. Thereafter, the

valves

11 and 12 on all of the trim control means B are sealed and remain sealed for the duration of the lowering operation. The compensator means 13 are still empty of ballast. At this position in the body of water,

the spacing of the center of buoyancy above the center of gravity is important in order to impart stability to the vessel by providing a sufficient righting moment thereto since the side wall is submerged and there is little or no water plane area for righting the vessel.

The control system for the compensator means 13 is now activated, admitting ballast to the compensator means 13 to submerge the vessel in a controlled manner. By adding a certain amount of ballast to the compensator tanks 13, neutral buoyancy of the vessel is obtained. Thereafter, the addition of a small amount of ballast to the compensator means 13 causes the vessel to sink in the body of water at a controlled rate. The size and buoyancy of the auxiliary buoyancy means A, trim control means B and compensator means 13 is such that when taken together they will statically float the vessel, either partially or fully submerged, with all the gas removed from beneath the roofed shell.

During submergence of the vessel, ballast is added and subtracted to and from the compensator means as necessary in order to submerge the vessel to the floor of the body of water in a controlled manner, the control system being operated as previously described.

The vessel is shown hovering at a selected intermediate depth in FIG. 29. The hovering could continue indefinitely if the set point remains unchanged. This ability to hover is the result of the control system operating to vary the ballast in the compensator means 13. As the vessel approaches the floor F of the body of water, adjustments in the horizontal position of the roofed shell will be required to properly locate it. This vessels ability to hover facilitates this adjustment.

The vessel is shown in position on the floor of the body of water in FIG. 30 with the torus T and compensator means 13 removed and the collection dome 46 positioned on the roof R covering the opening 35 from which the compensator means 13 were removed. Piles P are installed through the pile sleeves 6 in the side wall S into the floor F of the body of water to anchor the vessel in position. Other means could be used for anchoring the vessel to the floor of the body of water, such as mooring lines or the like, or the weight and size of the footer and side wall could be such that the weight of the vessel would hold the vessel to the floor of the body of water without requiring any separate securing means such as piles P or mooring line or the like.

As seen in FIG. 30, the vessel is filled with a liquid to be stored such as crude oil L or the like, and the interface I between the stored liquid L and the surrounding body of water W is adjacent the lower edge of the side wall S. Vents V extending through the lower portion of the side wall S establish communication between the inside of the vessel and the surrounding body of water. This open communication between the inside of the vessel and the surrounding body of water results in an equalization of the pressure inside the vessel and the pressure on the vessel from the surrounding body of water since as stored liquid is added to or withdrawn from the vessel, the displaced water flows out of and into the vessel through the vents.

It is important to note that neither the compensator means 13, nor the trim control means B, nor the two taken together have sufficient size and buoyancy to statically float the vessel with all gas removed from beneath the roofed shell. Also, the auxiliary buoyancy means A, whether taken alone or with the compensator means 13 or the trim control means B, do not have sufficient size and buoyancy to statically float the vessel with all gas removed from beneath the roofed shell. All of the above mentioned means are required acting together to have sufficient size and buoyancy to statically float the vessel with all gas removed from beneath the roofed shell.

It is also important to note that the auxiliary buoyancy means A are uncontrolled, removable, non oil storing devices. Their only function is to provide a buoyant force advisably located at a high point on the roofed shell. Their function and nature remain unchanged during towing and submergence. They are not intended for liquid storage, and are removable for reuse in lowering additional subsea storage vessels.

It is important to note also that this subsea storage vessel is unencumbered in its lowering devices by the necessity of maintaining standpipes, floats or the like in communication with the surface of the body of water.

Also, this invention is noteworthy in its inherent stability at all times in the lowering process. Never does a tendency to roll caused by a lack of inherent stability occur.

Referring now to FIG. 31, an alternate form of auxiliary buoyancy means is shown.

In FIG. 31, the auxiliary buoyancy means comprises a double shell construction of the roof R wherein an inner shell 71 and an outer shell 72 define hollow volumes 73 filled with a suitable material of light density, such as gas or the like, imparting sufficient buoyancy to the vessel to statically float it when acting in concert with the trim control means and compensator means and with all gas removed from beneath the roofed shell.

By way of specific example, a vessel constructed in accordance with the present invention has a diameter of approximately 240 feet, the side wall is about 50 feet high, and the vessel weighs approximately 12,500 tons. The side wall is approximately 6 feet thick, and the compensator means 13 are on the order of 50 feet long and 13.5 feet in diameter. The trim control means B are about 40 feet long and have a diameter of about 15 feet. Similar dimensions apply to the buoyancy means A. Such a vessel is capable of holding 500,000 barrels of stored liquid. These dimensions are not to be taken as limiting on the invention, since the vessel could have any suitable size and shape.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents, are therefore intended to be embraced by those claims.

We claim:

1. A subsea storage vessel comprising: a roofed shell, separate and independent tank means carried by the roofed shell, means connected with said tank means to control the amount of ballast therein to completely submerge the roofed shell, said tank means having a buoyancy less than the total weight of the roofed shell and thus being incapable of statically floating the roofed shell with all gas removed from beneath said roofed shell, auxiliary buoyancy means carried by said roofed shell separate from said tank means and imparting buoyancy to said roofed shell, said auxiliary buoyancy means alone having a buoyancy less than the total weight of the roofed shell and thus being incapable of statically floating the roofed shell with all gas removed from beneath the roofed shell, said tank means and said auxiliary buoyancy means together having a buoyancy at least equal to the total submerged weight of the roofed shell so as to statically float the roofed shell with all gas removed from beneath the roofed shell.

2. A subsea storage vessel comprising a roofed shell, at least one tank means carried by the roofed shell, at least another tank means carried by the roofed shell, means connected with said at least one tank means and the said at least another tank means for individually controlling all the said tank means by supplying amounts of ballast thereto, all the said tank means singly or together being incapable of statically floating the roofed shell with all gas removed from beneath the roofed shell, auxiliary uncontrolled buoyancy means carried by the roofed shell, all the said tank means and the uncontrolled buoyancy means together being of such size and buoyancy to statically float the roofed shell with all gas removed from beneath the roofed shell, the said at least one tank means being of such size that the roofed shell together with said buoyancy means and said another tank means can be submerged by addition of ballast to the said at least one tank means.

3. A subsea storage vessel comprising a roofed shell, first tank means connected with said roofed shell, first means connected with said first tank means for controlling the amount of gas or ballast therein to submerge said roofed shell, second tank means connected with said roofed shell, second means connected with said second tank means for controlling the amount of gas or ballast therein, said first and second tank means having a buoyancy less than the total weight of the roofed shell, auxiliary buoyancy means connected with said roofed shell separate from said tank means for imparting a predetermined buoyancy thereto less than the total weight of the roofed shell, said first and second tank means and said auxiliary buoyancy means together having a buoyancy at least equal to the total submerged weight of the roofed shell so as to statically float the vessel with all gas removed from beneath the roofed shell.

4. A subsea storage vessel as in claim 3, wherein said roofed shell includes a roof, said first tank means comprises compensator means mounted in the center of said roof and said second tank means comprises trim control means connected in an annular ring carried by said roofed shell.

5. A subsea storage vessel as in claim 3, wherein said roofed shell includes a roof and a side wall depending from the periphery thereof, said first tank means being mounted in the center of said roof and said second tank means and said auxiliary buoyancy means being connected in an annular ring secured to said roofed shell at the periphery of said roof.

Claims

6. A subsea storage vessel as in claim 5, wherein said annular ring is continuous, said second tank means and said auxiliary buoyancy means being joined iN end-to-end relationship to said ring.

7. A subsea storage vessel as in claim 3, wherein said roofed shell includes a roof and a side wall depending from the periphery thereof, said first tank means being mounted at the center of said roof, said second tank means being mounted on said side wall and said auxiliary buoyancy means comprising an annular ring of separate and individual means secured to said roofed shell at the periphery of said roof.

8. A subsea storage vessel as in claim 7, wherein said auxiliary buoyancy means comprise hollow compartments in said annular ring.

9. A subsea storage vessel as in claim 8, wherein said second tank means comprises a plurality of tank means spaced equidistantly about said side wall.

10. A subsea storage vessel as in claim 3, wherein said roofed shell has a roof and a side wall depending from the periphery of said roof, said first tank means being connected to said roofed shell at the center of said roof, said second tank means being connected to said roofed shell at the periphery of said roof, and said auxiliary buoyancy means being connected to said roofed shell at the periphery of said roof.

11. A subsea storage vessel as in claim 10, wherein said second tank means and said auxiliary buoyancy means are separate and independent from one another and are independently connected to said roofed shell.

12. A subsea storage vessel as in claim 11, wherein said second tank means and said auxiliary buoyancy means are spaced apart about the periphery of said roof.

13. A subsea storage vessel as in claim 12, wherein said auxiliary buoyancy means comprise sealed compartments filled with gas.

14. A subsea storage vessel as in claim 3, wherein said second tank means and said auxiliary buoyancy means are removably connected to said roofed shell.

15. A subsea storage vessel as in claim 14 wherein said means for removably connecting said second tank means and said auxiliary buoyancy means to said roofed shell comprises an annular connecting ring means disposed about said second tank means and said buoyancy means, and connecting means connecting said connecting ring means with said roofed shell.

16. A subsea storage vessel as in claim 14, wherein said first tank means are removably connected to said roofed shell.

17. A subsea storage vessel as in claim 3, wherein said first tank means are of such size and are capable of holding sufficient ballast to submerge said vessel, said second tank means being connected to said roofed shell in symmetrically spaced relationship thereto so that by addition of ballast thereto said second tanks are used to trim said vessel while floating, said second tank means being sealed prior to complete submergence of said vessel and remaining sealed subsequent to complete submergence of said vessel, and said auxiliary buoyancy means serving only to impart buoyancy to said vessel.

18. A subsea storage vessel as in claim 3, wherein said roofed shell has a roof and a side wall depending from the periphery thereof, said roof being made of any flexible material suitable for use therein.

19. A subsea storage vessel as in claim 3, wherein said roofed shell has a roof and a side wall depending from the periphery thereof, said roof being made of steel.

20. A subsea storage vessel as in claim 3, wherein said roofed shell has a roof and a side wall depending from the periphery thereof, said first tank means being connected to said roofed shell at the center of said roof and said second tank means and said auxiliary buoyancy means being connected to said roofed shell at the periphery of said roof, and means interconnecting and establishing communication between said first tank means and said auxiliary buoyancy means, said auxiliary buoyancy means serving as accumulator means for said first tank means.

21. A subsea storage vessel as in claim 3, wherein said first and second tank means and said auxiliary buoyancy means are removably connected to said roofed shell, said roofed shell having a roof and a side wall depending from the periphery thereof, said first tank means being connected to said roofed shell at the center of said roof, and means adapted to be connected to said roofed shell when said first tank means are removed therefrom.

22. A subsea storage vessel as in claim 3, wherein said roofed shell has a roof and a side wall depending from the periphery thereof, said first tank means comprising a plurality of tanks connected to said roofed shell, said second tank means comprising a plurality of separate and independent tanks connected to said roofed shell, and said auxiliary means comprise a plurality of separate and independent buoyancy means connected to said roofed shell.

23. A subsea storage vessel as in claim 22, wherein said plurality of said first tank means are connected to said roofed shell at the center of said roof, said plurality of second tank means and said plurality of auxiliary buoyancy means being connected to said roofed shell at the periphery of said roof.

24. A subsea storage vessel as in claim 23, wherein said second tank means and said auxiliary buoyancy means are connected together in an annular ring secured to said roofed shell at the periphery of said roof.

25. A subsea storage vessel as in claim 24, wherein said plurality of first tank means, said plurality of second tnak means and said plurality of auxiliary buoyancy means are removably connected to said roofed shell, said second tank means and said auxiliary buoyancy means in said annular ring being removable as a unit from said roofed shell.

26. A subsea storage vessel as in claim 24, wherein said annular ring comprises sections removably joined together.

27. A subsea storage vessel as in claim 26, wherein each of said sections includes at least an auxiliary buoyancy means and a second tank means rigidly interconnected therein.

28. A subsea storage vessel as in claim 2, wherein said means for individually controlling all the said tank means comprises first control means connected with said at least one tank means and second control means connected with said at least another tank means, said first control means comprising a first conduit connected with said at least one tank means, pump means in said first conduit means, electro-hydraulic valve means in said first conduit means between said pump means and said at least one tank means, second conduit means connected with said at least one tank means, electro-hydraulic valve means in said second conduit means, depth sensing means associated with said roofed shell for sensing the depth of said roofed shell in a body of water, and remote means having selectively operable means for selecting a predetermined desired depth connected with said sensing means and with said valve means for operating said valve means when said depth sensed by said sensing means is different from the predetermined depth selected at said remote means to admit or exhaust liquid ballast to said at least one tank means to control the depth of submergence of said roofed shell in said body of water.

29. A subsea storage vessel as in claim 5, in which said depending side wall of said roofed shell has a height and thickness and weight distribution, which in conjunction with the buoyant effect provided by the said annular ring, is such that no tipping of said roofed shell occurs upon lowering of said roofed shell in said body of water.

30. A subsea storage vessel as in claim 6, wherein said first tank means is a compensator means having means for automatically varying ballast therein for changing said vessel''s elevation in said body of water, and said second tank means is a trim control means having means for varying ballast therein to adjust the trim of said vessel in said body of water.

31. A subsea storage vessel as in claim 17, wherein said first tank means include means to change the rate of ascent or descent of the roofed shell in said body of water during submergence from the surface to the floor of the body of water to thus control the elevation of the vessel in the body of water.

32. A subsea storage vessel as in claim 2, wherein said means for individually controlling all the said tank means comprises first control means connected with said at least one tank means and second control means connected with said at least another tank means, said first control means comprising a first conduit connected with said at least one tank means, pump means in said first conduit means, valve means in said first conduit means between said pump means and said at least one tank means, sensing means associated with said roofed shell for sensing the depth of said roofed shell in a body of water, and means connected with said sensing means and with said valve means for operating said valve means to admit or exhaust liquid ballast to said at least one tank means to submerge said roofed shell in said body of water.

33. A subsea storage vessel as in claim 20, wherein said means interconnecting and establishing communication between said first tank means and said auxiliary buoyancy means allows only the flow of gas therebetween.

34. A subsea storage vessel comprising a roofed shell, compensator means connected with said roofed shell, first means connected with said compensator means for controlling the amount of gas or ballast therein, trim control means connected with said roofed shell, second means connected with said trim control means for controlling the amount of gas or ballast therein, auxiliary buoyancy means connected with said roofed shell for imparting a predetermined buoyancy thereto, said compensator means and said trim control means and said auxiliary buoyancy means together being of such size and buoyancy as to statically float the vessel with all gas removed from beneath the roofed shell.

35. A subsea storage vessel as in claim 34, in which said auxiliary buoyancy means are flexibly connected as by a cable or the like to the roofed shell.

36. A subsea storage vessel as in claim 34, in which the auxiliary buoyancy means comprise sealed hollow volumes integrally mounted within the structure of said roofed shell.

37. A roofed shell, a plurality of separate and independent compensator means and trim control means carried by the roofed shell, means connected with at least one of said means to control the amount of ballast therein to submerge the shell, said plurality of compensator means and trim control means singly or together being incapable of statically floating the roofed shell with all gas removed from beneath said roofed shell, auxiliary buoyancy means carried by said roofed shell imparting buoyancy thereto, said auxiliary buoyancy means alone being incapable of statically floating the roofed shell with all gas removed from beneath the roofed shell, said plurality of compensator means and trim control means and said auxiliary buoyancy means together being of such size and buoyancy as to statically float the roofed shell with all gas removed from beneath the roofed shell.

38. A roofed shell, at least one compensator means carried by the roofed shell, at least one trim control means carried by the roofed shell, means connected with said compensator means and said trim control means for individually controlling the said compensator and trim control means by supplying predetermined amounts of ballast thereto, auxiliary uncontrolled buoyancy means carried by the shell, the said controlled compensator and trim control means singly or together being incapable of statically floating the roofed shell with all gas removed from under the roofed shell, the compensator and trim control means and the uncontrolled auxiliary buoyancy means together being of such size and buoyancy to statically float the shell, the said compensator means being of such size that sufficient ballast can be added thereto so as to submerge the roofed shell with said uncontrolled buoyancy means, said compensator means and said control means thereon.

39. A roofed shell, a plurality of separate And independent tank means carried by the roofed shell, means connected with at least one of said tank means to control the amount of liquid or other ballast therein to completely submerge the roofed shell and said tank means, said plurality of separate and independent tank means having a buoyancy less than the total weight of the roofed shell and thus being incapable of statically floating the roofed shell with all gas removed from beneath said roofed shell, auxiliary buoyancy means carried by said roofed shell separate from said tank means and imparting buoyancy to said roofed shell, said auxiliary buoyancy means having a buoyancy less than the total weight of the roofed shell and thus being incapable of statically floating the roofed shell with all gas removed from beneath the roofed shell, said plurality of separate and independent tank means and said auxiliary buoyancy means together having a buoyancy at least equal to the total submerged weight of the roofed shell so as to statically float the roofed shell with all gas removed from beneath the roofed shell.

40. A roofed shell as in claim 39, wherein at least some of said tank means and said auxiliary buoyancy means are connected in an annular ring secured to said roofed shell.

41. A roofed shell as in claim 40, wherein said roofed shell has a roof and a depending side wall about the periphery thereof, said annular ring being secured to said roofed shell at the periphery of said roof.

42. A roofed shell as in claim 39, wherein said auxiliary buoyancy means comprise sealed compartments, said sealed compartments being filled with gas.

43. The method of submerging a subsea storage vessel comprising, providing a roofed shell, providing a plurality of separate and independent tank means carried by said roofed shell, providing means connected with at least one said tank means for controlling the amount of ballast in said tank means to submerge the roofed shell, providing said plurality of tank means with a size and buoyancy less than that required to statically float the roofed shell with all gas removed from beneath said roofed shell, providing auxiliary buoyancy means carried by said roofed shell for imparting buoyancy to said roofed shell, providing said auxiliary buoyancy means with a size and buoyancy less than that required to statically float the roofed shell with all gas removed from beneath the roofed shell, filling the volume defined beneath said roofed shell with pressurized gas, floating the roofed shell in a body of water to a site of intended use of the roofed shell, releasing the pressurized gas from beneath the roofed shell to lower the roofed shell in the body of water, controlling the amount of ballast in at least some of said tank means to level said roofed shell in the body of water, and controlling the amount of ballast in at least some of said tank means to submerge said roofed shell in said body of water and lower said roofed shell to the floor of the body of water.

44. The method as in claim 43, including the steps of removing said plurality of said separate and independent tank means and said auxiliary buoyancy means when said roofed shell is on the floor of the body of water.

45. The method as in claim 44, including the step of securing said roofed shell to the floor of the body of water.

46. The method of submerging a subsea storage vessel comprising the steps of: providing a roofed shell, providing first tank means on said roofed shell, providing first control means for controlling the amount of ballast in said first tank means, providing second tank means on said roofed shell, providing second control means for controlling the amount of ballast in said second tank means, providing auxiliary buoyancy means on said roofed shell, floating said roofed shell on a body of water to a site in said body of water where said roofed shell is to be used for storage, lowering said roofed shell in said body of water until said second tank means are awash in said body of water, controlling thE amount of ballast in said second tank means to level said roofed shell in the body of water, sealing said second tank means, and controlling the amount of ballast in said first tank means to submerge said roofed shell to the floor of the body of water.

47. The method as in claim 46, including the steps of providing pressurized gas under said roofed shell to aid in floating said roofed shell and then releasing said pressurized gas from beneath said roofed shell to lower said roofed shell in said body of water.

48. The method as in claim 47, including the steps of removing said first and second tank means and said auxiliary buoyancy means when said roofed shell is on the floor of said body of water.

49. The method as in claim 46, wherein said first and second tank means and said buoyancy means together are provided with such size and buoyancy as to statically float the vessel with all gas removed from beneath the roofed shell, said first tank means, said second tank means and said auxiliary buoyancy means being incapable of individually statically floating said roofed shell with all gas removed from beneath said shell.

50. The method of submerging a roofed shell, comprising, providing a roofed shell, providing a plurality of separate and independent tank means carried by the roofed shell, providing means connected with at least one of said tank means to control the amount of ballast therein sufficient to submerge the roofed shell, said plurality of tank means being incapable of statically floating the shell with all gas removed from beneath said roofed shell, providing auxiliary buoyancy means carried by said roofed shell for imparting buoyancy thereto, said auxiliary buoyancy means being incapable of statically floating the shell with all gas removed from beneath the roofed shell, providing said plurality of tank means and said auxiliary buoyancy means with such size and buoyancy that said tank means and said buoyancy means together will statically float the roofed shell with all gas removed from beneath the roofed shell.

51. The method as in claim 43, including the steps of providing such amounts of weight and buoyancy and distributing them relative to said roofed shell such that no tipping occurs as the vessel''s position in the body of water is changed from that of light draft to that of complete submergence.

52. The method as in claim 43, including the step of providing the said means connected with at least one of said tank means with such capability that it can maintain the approximate elevation of said roofed shell in the body of water at any given depth for any desired period of time.