US2579703A - Submersible tank for supporting offshore structures - Google Patents

Description

Dec. 25, 19151 H. c. RUTLEDGE ETAL ,7 3

SUBMERSIBLE TANK FOR SUPPORTING OFFSHORE STRUCTURES Filed Oct. 3, 1949 3 Sheets-Sheet l ,i is

I IN VEN TORS RICHHRD M HDLEIZ ripe/van Howmeo c. .QUTLEDGE 1951 H. c. RUTLEDGE ETAL 2,579,703

SUBMERSIBLE TANK FOR SUPPORTING OFF SHORE STRUCTURES Filed Oct. 5. 1949 I 5 Sheets-Sheet 3 Zinnentors HOWflED 6. 07 1.45065 ,elalfiza M. 401.452

1 5 W/fm Gllomegs Patented Dec. 25, 1951 SUBMERSIBLE TANK FOR SUPPORTING )FF SHOEE STRUCTURES Howard 0. Rutledge and Richard M. Adler, Birmingham, Ala, assignors to The Ingalls Shipbuilding Corporation, a corporation of Delaware Application October 3, 1949, Serial No. 119,324

6 Cla ms- 1 Our present invention relates to a submersible tank or vessel for supporting off-shore structures such for instance as apparatus fordrilling and pumping oil wells, and has for an object the provision of a tank or vessel of the char acter designated which may be constructed and outfitted in a suitable way or in a dock'or the like adjacent the shore and then floated to the well location and sunk to the floor or bottom of the body of water, thereby firmly supporting the well rigging above water.

Another object is to provide a supporting tank of the character designated which shall be stable while being transported and while being submerged, the tank being so constructed, ballasted and compartmented that the free liquid surface therein during the submerging operation is reduced to a minimum, whereby during the critical stage in the submerging operation the metacenter remains sufficiently above the center of gravity to make the vessel stable.

A more specific object is to provide a submersible tank for supporting ofi-shore structures which is divided vertically into at least two compartments, the wall or deck defining the two compartments being so located that when the lower compartment is completelyfiooded the upper deck of the tank is full above water, together with means dividing the upper compartment into sub-compartments whereby the final submergence of the tank is caused by selectively flooding the sub-compartments.

Further objects are to provide a platform for supporting the well drilling equipment, living quarters and the like, in turn supported from the tank by columns and to make the unsupported lengths of such columns as short as possible by means of readily installed cross bracing; to provide a columnar support which shall have minimum resistance to wave action; to provide a support which can be submerged or raised for removal to a different location without loss of materials such as is usually incident to the erection and removal of pilingtype supporting structures; and in general to provide means of the character designated which shall be economical of construction, require a minimum number of auxil a y s rv esse s such. a tu s, bar es a d t e l e an wh n ud s m ans for storin oil pumped from the well.

Apparatus illustrating the ieatures of our invention is shown in the accompanying drawings forming a part of this application in which:

F g. 1 is. a d a ramma ic, isometric view of a ub e s b e tank howin t platfo m in p ace Fig. 4 is a sectional view taken generally along line IV-rIV of Fig. 3;

Fig. 5 is a wholly diagrammatic view illustrating the pumps, conduits and valves for flooding and pumping out the various compartments of the tank; and,

Figs. 6 and 7 are diagrammatic views illustrate ing the forces-tending to hold the entire struc.-.

le in upright position while floating and durs the su mers ns oper n- Referring now to the drawings for a better understanding o our invention, and more par-.

ticularly to Fig. 1, we show our improved form of s p rt n tank indica ed ra ly y t m1 meral l0 and having secured to the upper deck ll thereof a plurality of columns l2. Supported on the upper ends of the columns 12 is a deck or platform I .3 on which in turn is mounted the well derrick l4, living quarter I6, cranes l1, and other machinery, not shown, incidental to the drilling of oil wells, For the sake of clarity substantially all of the internal strengthening members are omitted from the drawin s, as well as crossbracing for the columns 12.

As best shown in Figs. 2 3 and l, the tank I0 is generally circular as viewed plan. More particularly, the tank is shown in the form of a. Gylinder having an outer wall l8 and an inner oy-.- lindrical wall i9 concentric with the outer wall,

both of which extend from top to bottom of the tank. The bottom of the tank is indicated at 2|. It will be understood that the walls l8 and 69 are joined by welding or otherwise to pro vide water and oil tight joints.

Between the bottom 2| and deck II is an intermediate deck 23 which may consist of an annular plate and which is joined along its inner and outer edges 24 and 26 to the inner and outer sides respectively of the walls I 8 and [9. This n rmedi deck d vides the tank in o uppe d lo er c ar m n s in cat generally y the letters A and B respectively. A circular deck 2'! made up of plates and which may be located at the same level as the deck 23, divides the central part of the tank into upper and lower corn. partments 28 and 29.

T e upp r com a tme A s subdivided in o compartments 3| through 38 inclusive by means of a plurality of radially extending bulkheads 39 to 46 inclusive. The bulkheads 40, 42, M and 46 extend the entire height of the vessel, being joined at their upper and lower ends in water tight manner to the deck H and bottom 2|. Thus, the compartment B is subdivided by the bulkheads 4U, 42, M and 4% into sub-compartments 4? to 5! inclusive as is more particularly illustrated in Fig. 4.

As shown in Figs. 3 and 4, the entire bottom of the tank included within the compartments 5! to 50 inclusive, and 29, is covered with a layer 5| of reinforced concrete material or the like to serve as ballast in the manner later to be explained and to stifen the bottom and distribute the vertical load of the superstructure equally over the bottom of the vessel. Beneath each of the columns I 2 other than those connected to the deck over the inner and outer walls l9 and through the supplementary columns 30.

The compartment 28 at the center of the vessel or tank may be utilized as a pump room. Likewise, it may be utilized as a general control room for the various valves which are used for submerging the vessel l0, pumping out the compartments, and pumping oil thereinto. In each of the compartments 4! through 50, and 29 we provide a sea valve 52 having a horizontally disposed control rod 53 and a vertically disposed control rod. 54 having an operating wheel 56 thereon. The valve 52 for compartment 2!! has a conduit 29a leading through the outer wall l8. Similarly, in each of the compartments 3! through. 38 inclusive, immediately above the deck 23, we provide sea valves 5'! having an operating rod 58 therefor with an operating wheel 59disposed in the control compartment 23. By means of the sea valves 52 and 5'! the several compartmentsmay be selectively flooded in the mannerlater to be explained, thus to submerge the vessel Ill. Access to the compartment 28 may be obtained by means of a tubular hatchway 6! having therein a ladder 62.

Referring particularly to Figs. 2 and 5, within the compartment 28 we provide a pump 56 which may be operatedby any suitable motive power, for instance an electric motor 61. The discharge side of the pump 65 is connected by a line 63 which leads to the outside of the tank. The in-- take side of the pump is connected by a line 59 to amanifold conduit H. The manifold is in turn connected by a conduit 12 to each of the compartments 3| through 38, inclusive, 4'! through 58. inclusive, and 29'. Each of the conduits 12 has .therein a valve 13, also located in the pump compartment 28. By this means it will be apparent that the several compartments may beiplismped out selectively thus to refloat the vesse Referring now particularly to Fig. 5, we show means for also pumping oil into the compartments selectively to store the same as it is produced from the well. As illustrated, we provide a' second pump 14 having its intake side connected to a conduit 76 under control of a valve H. The conduit 18 leading to the intake side of the pump is provided with avalve l9, and the discharge conduit 8! leading from the pump M is provided with a valve 82. A by-pass line 85 having therein a valve 84 connects the conduits l8 and 8|. Likewise, there is provided in the line 68 associated with the pump 66 a valve 86, and a valve 81 is interposed in the line 69 leading from the manifold pipe H to the intake connection of pump 66. By the arrangement shown it will be deck l3 under the well derrick l4.

seen that the several conduits 12 leading to the various compartments may be utilized either to pump water therefrom or to pump oil therein-to. When pumping oil'irito the compartments the sea valves may be opened to permit the water therein to be displaced by the oil. While not shown in the drawings, the compartments may be provided with vent connections and control valves therefor. Thus, by closing valve 81, valve 32, and valve 19 oil from a suitable source deliv-' ered to the pump 14 through the line 16 passes through the cross conduit 83 and into the mani fold pipe H. By suitable manipulation of the valves 13, 52 and 5'! it will be apparent that a selected compartment may be filled with oil and the water therein displaced. v

The actual drilling operation takes place through a plurality of tubes 88 passing'vertically through the decks H and 2'! and bottom iii of the tank and which may extend up through the While show tubes 88 for this purpose it will be apparent that by suitable means a portion of the central opening maybe made water tight from theremainder thereof by means of plates, thus to leave an arcuate opening for passing the drilling tools.-

From the foregoing the method of constructing and using our improved apparatus may now be explained and understood. As is understood in the art to which this invention relates the principal criterion of stability of floating and submerged vessels is the vertical distance between the metacenter and the center of gravity. By definition the metacenter is the point of'intersection M of the vertical through the center of buoyancy B of a body floating or suspended in a liquid with the vertical through the new center of buoyancy B when the body is angularly displaced however little. See Figs. 6 and 7. When the point M is above the center of gravity G" of the body the'position of the body is stable when below it, unstable; when coincident with it, neutral. When the upper deck or surface of a vessel passes beneath the surface of a maid: or in other words when the vessel is suspended in the liquid, the metacenter is, except as affected by factors such as free liquid surface, at the center of buoyancy B'. When there is free liquid surface within the vessel the metacenter is lowered by a determinable amount. Thus, with a free liquid surface in a vessel being submerged the point M moves downwardly, resulting in a loss of metacentric height GM, Figs. 6 and '7, and consequently lowering the degree of stability of the vessel. Should the intermediate decks 23 and 27 of our improved vessel be located so high that at the time of submergence there exists a large amount of free liquid surface within the lower compartments the stability of the vessel would be of a low order. To overcome this we locate the intermediate decks 23 and 21 at a point vertically between the upper deck H and bottom 2! so that when the lower compartments are all.

merged conditions by the ballasting material 5!. We-have found that the metacentric height is maintained positive and of a'suiflcient magnitude to assure stability by 1ocating the deck at the height just explained and by subdividing the upper and lower compartments. This vertical and horizontal subdivision of the vessel in addi tion to reducing free liquid surface loss in metacentric height, further increases metacentric height by permitting the ballast water to be placed as low as possible and thus contributes to the lowering of the center of gravity G. Without the intermediate decks 23 and 27, to decrease the free liquid surface loss in metacentric height, the compartments necessary to lower the vessel to the, degree accomplished by flooding all the lower sub-compartments would have to extend up to the deck II, thus raising the center of gravity G. During the time until the deck ll of the tank remains just above the water line W the free surface loss in metacentrio height is kept low by subdivision of the lower compartment 13. As is understood, the loss in metacentric height when free liquid surface is present is directly proportional to the sum of the moments of inertia of the individual surfaces in the compartments. With the tank remaining just above water, the flooding to completely submerge the same is restricted to the required number of the small compartments above the intermediate deck 23. The net result of the construction shown including the ballasting material 5| is the provision of a vessel of the character designated which is stable in floating condition and which also is stable at the critical point during the submergence thereof, namely, when the upper deck H passes beneath the water line. Thus, by locating the intermediate deck 23 at a point whereby when the lower compartments are flooded without causing complete submergence of the vessel, dividing the upper compartment into sub-compartments, and selectively flooding the latter to complete submergence, we have provided a vessel which is stable in all conditions. The dead weight and moments of the platform 13, the derrick and other structures and equipment on the platform can be effectively counterbalanced by the weight of the vessel itself with the aid of the ballasting material 5| so that the center of gravity of the whole system, including water ballast, will remain always below the metacenter.

While we have shown means for selectively flooding all of the upper compartments 3| through 38 inclusive it may well be found that some of these compartments will not be needed for this purpose and may be utilized for the storage of fuel or wet or dry supplies for use in the drilling operation. As will be apparent, whether or not these are available for purposes other than flooding can be readily determined by calculations and considerations which take into account the design of the vessel and the superstructure therefor.

From the foregoing it will be apparent that we have devised an improved tank or vessel for supporting cit-shore structures. While we have shown our invention as especially adapted for the support of oil well drilling equipment it will be apparent that the same may be used for other purposes if desired. It will also be apparent that by suitable manipulation of the valves and pumps shown diagrammatically in the drawing the vessel may be refloated by pumping out the compartments. If desired the water in the compartments may be displaced by pumping thereinto oil from the well;- thus simultaneously keeping the vessel submerged and affording storage space for the oil. Our invention is particularly characterized by the fact thatit can be moved from place to placewithoutloss of material such as piling or the'like; Due to the 'fact that it is stable both during towing and during the submerging operation our improved apparatus is capable of use in water ofupwards of feet in depth. Also, the cross bracing of the columns 12, not shown in the drawings may be installed and repaired with case since when the vessel is afloat these columns are out of the water. Thus the unsupported length of such columns l2 may be reduced to the optimum. The circular shape of the vessel has, among others, the structural advantages of strength, simplicity of construction and high strengthweight ratio. Hydrodynamically this shape has the advantage of offering minimum resistance to the varying forces due to waves, currents and winds, regardless of direction and magnitude.

While we have shown our invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications, without departing from the spirit thereof, and we desire therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims. I

What we claim is:

1. In means for supporting oiT-shore structures, a tank, a horizontal deck in the tank dividing the same into upper and lower water tight compartments, vertical bulkheads dividing the upper compartment into a plurality of water tight sub-compartments, said upper compartments having suflicient buoyancy when substantially empty to float the tank when the lower compartment is substantially completely flooded, and means to flood the lower compartment and a sufficient number of the upper compartments to submerge the tank.

2. In means for supporting off-shore structures, a tank having an upper deck on which the structure to be supported is mounted in spaced relation thereto, an intermediate horizontal deck defining with the upper deck and bottom of the tank a pair of water tight compartments, the relative volume of said compartments being such that when the lower compartment only is flooded the upper deck remains above water, water tight bulkheads dividing the compartments vertically into upper and lower sub-compartments, means to flood all of the lower sub-compartments thereby reducing to zero the liquid free surface therein, and means to selectively flood a suflicient number of the upper compartments to cause the tank to submerge with its upper deck below the water line.

3. In means for increasing the stability of a submersible vessel having sides and upper and lower decks, an intermediate deck dividing the vessel into upper and lower water tight compartments, said deck being located vertically at a point whereby when the lower compartment is flooded the vessel remains afloat, a quantity of ballasting material distributed substantially equally over the bottom of the vessel, vertically disposed bulkheads dividing the upper and lower compartments into sub-compartments, means to flood the lower sub-compartments, and means to flood at least one of the upper compartments to submerge the vessel.

4. In a submersible vessel for supporting off- 7 shore structures; a cylindrical water tight tank having sides and; upper and lower decks, columns secured to the upper deck and disposed to support the structure above water, an intermediate deck parallel with the upper and lower decks dividing the interior of the body into upper and lower compartments, said intermediate deck being located at the point whereby when the lower compartment is flooded the upper deck remains above water, radially disposed bulkheads dividing the upper and lower compartments into sub-compartments of substantially equal size, other radially disposed bulkheads above the intermediate deck dividing the upper sub-compartments into smaller substantially water tight compartments, means to flood all of the lower compartments, and means to admit water selectively to a sufficient number of the upper smaller compartments afterv all of the lower compart- V ments are fully flooded to'submerge the tank.

heads extending between the top and bottom of the vessel sub-dividing the upper and lower compartments into sub-compartments of substantially equal size, other vertical radially disposed bulkheads dividing the upper sub-compartments into smaller compartments, a layer of ballast material distributed evenly over the bottom of the vessel, and means to selectively flood the lower sub-compartments and upper smaller compartments.

6. A submersible vessel as defined in claim 2 in which the bottom of the tank has distributed substantially evenly thereover ballasting material sufiicient to counterbalance the weight of the structure supported in spaced relation to the upper deck of the tank.

HOWARD O. RU'I'LEDGE. RICHARD M. ADLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 5 Number Name Date 2,187,871 Voorhees Jan. 23, 1940 2,399,656 Armstrong May 7, 1946 2,430,014 Hansen Nov. 7, 194'? 2,482,788 Moon Sept. 27, 1949

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