US 3525312 A
Description (OCR text may contain errors)
United States Patent Inventors Robert W. Beck Richard P. Knapp, Houston, Texas Appl. No. 673,510 Filed Oct. 6, 1967 Patented Aug. 25, 1970 Assignee Esso Production Research Company a corporation of Delaware STORAGE 0R SIMILAR VESSEL 8 Claims, 3 Drawing Figs.
US. Cl 114/.5, 9/8 Int. Cl B631 21/00, 1363b 3 5/00 Field of Search 1 14/0.5,
 References Cited UNITED STATES PATENTS 3,407,768 10/ l 968 Graham 114/230X 1,458,134 6/1923 Constan 114/235 3,191,201 6/1965 Richardson et a1. 114/230 3,335,690 8/1967 Busking 1 14/230 3,365,734 1/1968 Petrie et a1 1 14/200X Primary Examiner--Trygve M. Blix Attorney-James A. Reilly and James E. Reed Patented Aug. 25, 1970 Sheet ATTORNEY Rbberf w Beck INVENTORS Richard P. Knapp STORAGE OR SIMILAR VESSEL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to floating storage vessels and similar ships which must be moored in unprotected waters.
2. Description of the Prior Art Many offshore oil fields are located in areas where the construction of pipelines is impractical and tankers have to be used for transporting the crude oil to refineries. This normally requires that storage facilities of sufficient capacity to permit continuous oil production and rapid tanker loading be provided at the offshore locations. Although underwater facilities can sometimes be used, floating storage vessels connected to the underwater gathering system by flexible risers are often more practical. The mooring of such vessels so that they can remain on location during bad weather poses serious problems.
The method generally suggested for mooring storage vessels requires the use of lines which extend from the bow and stem to a system of buoys, chains, and anchors so that the vessel is held on a fixed heading, normally in the direction of the prevailing winds and waves. This system, referred to as multibuoy or spread mooring, is generally satisfactory only in sheltered areas where high winds, heavy seas, and strong currents are not apt to be encountered. In unprotected locations where LII the direction of the wind and waves may change, it is usually necessary to drop the mooring lines and move the vessel when a storm approaches. This requires that the risers be dropped or tied off to buoys and reconnected when the vessel is returned to location. It may be several days after the vessel returns before normal operations can be resumed.
An alternate method, the single point mooring system, requires the use of a moored buoy to which the risers are connected. The storage vessel is moored to this buoy by a line from the bow and is loaded through a hose extending from the vessel to a swivel on top of the buoy. As the direction of the wind and waves changes, the vessel tends to swing about the buoy and thus always heads into the wind. Such a system enables a storage vessel to withstand more severe weather than the spread mooring system but has disadvantages in that the vessel may tend to override the buoy in heavy seas. This may damage the buoy and risers and may endanger the vessel itself. Moreover, the floating hose extending between the vessel and buoy may fail under the stresses induced by relative movement between the vessel and buoy even though overriding does not take place. For this reason, both of the conventional systems leave much to be desired.
SUMMARY OF THE INVENTION This invention provides an improved storage vessel or similar ship which alleviates the problems outlined above. The vessel of the invention includes a bow section containing a well extending vertically through the hull of the vessel, a cylindrical turret mounted in the well and rotatable with respect to the bow section, means for connecting mooring lines to the turret, an elongated stern section, and means for detaching the stern section from the bow section without disturbing the mooring lines. This arrangement permits the entire vessel to pivot about the turret in response to changes in direction of the wind and waves without the overriding problems encountered with single point mooring systems, permits disconnection of the stern section in the event of heavy seas that might otherwise endanger the safety of the vessel, simplifies the resumption of normal operations following severe storms, and largely eliminates the difficulties encountered with floating hoses in conventional systems. It therefore has many advantages over systems advocated in the past.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 in the drawing is a side elevation of a floating storage vessel constructed in accordance with the invention; FIG. 2 depicts a plan view of the storage vessel of FIG. 1; and FIG. 3
shows a cross-sectional view through the detachable bow section of the vessel of FIGS. 1 and 2 taken about line 3-3 in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The vessel of the invention as depicted in FIG. I of the drawing comprises an elongated hull including a bow section 11 and a detachable stern section 12. The two sections are provided with water-tight bulkheads which abut against one another along bulkhead lines 14 and 15. Each section is sufficiently buoyant to float independently of the other. Mechanical dogs, latches, or similar coupling devices 16 hold the sections together during normal producing operations. These devices may be hydraulically or electrically actuated if desired. The positions of the coupling devices are shown more clearly in FIG. 2 of the drawing. Although FIG. 2 depicts the bow and stem sections as engaging one another along bulkhead lines which converge, other configurations may be used. To render the stern section more seaworthy, it may be preferred in some cases to join the two sections along bulkheads which extend at right angles to the longitudinal axis of the vessel or converge in the opposite direction from that shown.
The bow section of the vessel shown in FIGS. 1 and 2 contains a vertical well 17 which extends through the hull of the vessel and is thus open at its lower end. The arrangement of this well is shown in a FIG. 3 of the drawing. As depicted in FIG. 3 the well extends vertically through the upper deck 18 of the bow section, but this is not always necessary. In some cases it may be preferable to locate the upper end of the well on a lower deck so that the equipment associated therewith is protected from the weather. The well is normally of circular cross section. A turret assembly which includes an elongated cylindrical sleeve 19 extends downwardly in the well from a rotatable table 20 mounted on roller bearings 21. The bearings are housed in circular tracks 22 on the deck surrounding the upper end of the well. A flange 23 at the lower end of the sleeve is held in place by collar 24 and bearings 25 to restrain lateral movement of the sleeve within the well. Seals not shown will normally be provided to retard corrosion and fouling of the bearings.
The mooring equipment associated with the turret assembly includes chains 26 stored in chain lockers 27 on table 20. The chains extend from the lockers over anchor windlasses 28 and chain stoppers 29 which are also mounted on the table. Each chain passes over an upper fairleader 30 near the top of the sleeve and a lower fairleader 31 located near the bottom of the sleeve to an anchor 32 as depicted in FIG. 1. Although six mooring lines are shown, a greater or lesser number may be provided, depending upon the size of the vessel and the conditions under which it is to be moored.
The bow section is connected to an underwater gathering system 33, shown in FIG. 1 as pipelines 33 and 34. These lines extend to flexible hoses or similar conduits 35 and 36 which pass upwardly through the well to manifold 37 positioned near the upper end of the assembly. A swivel joint 38 is mounted at the upper end of the manifold to permit rotation of the vessel with respect to the manifold and risers. Transfer line 39 extends from the swivel to the stern section of the vessel. A flanged joint 41 and valves 42 and 43 in the line are provided to permit breaking of the line when it becomes necessary to disconnect the stern section from the bow section of the vessel.
The stern section of the vessel depicted in FIGS. 1 through 3 is provided with storage tanks, a propulsion unit, crew s quarters, and other facilities necessary for the normal operation of the vessel. Separators, treaters, and other equipment may also be installed in the stern section if desired. Auxiliary thrusters, not shown, may be provided to assist in stabilizing the vessel and facilitate maneuvering it into and out of position adjacent the bow section. Where seagoing tugs are available and movement of the stern section over long distances at frequent intervals is not contemplated, the cost of the vessel can be reduced by omitting the main propulsion unit.
The initial mooring of the vessel is normally accomplished by positioning the bow of the vessel over the point at which the risers are to extend upwardly to the surface and then installing the mooring lines. The lines are lowered through the turret and attached to anchors which can be installed with the lines or placed by means of an auxiliary vessel. Divers can be used for attaching the lines to preset anchors if desired. After the connections have been made, slack is taken up by means of the anchor windlasses until the bow section is effectively moored in the desired position. The risers are then connected to the manifold in the turret and to the lines of the underwater gathering system. After the system has been tested, the production of fluids through the risers, manifold, and swivel and into the storage vessel can be initiated. The rotatable turret in the bow section permits the vessel to swing about the turret in response to changes in wind, waves, and currents without disturbing either the risers or the mooring lines. Because of the forward position of the turret, only slight changes are necessary to produce a response. Since the vessel will thus normally head into the wind and waves, it is able to withstand much rougher seas than if it were held in a fixed position by means of a spread mooring system. Even though the wind and waves change direction 180, there is no problem of overriding the mooring as in conventional single point mooring systems.
In the event that a severe storm necessitates removal of the I vessel into a sheltered location or removal to a dock is necessary to permit repairs, production can be halted by shutting in the individual wells or closing valve 42 in transfer line 39. Once this has been done, the flanged joint 41 in the transfer line can be broken. The dogs or similar coupling members between the bow and stem sections can then be disconnected and the stern section can be backed or towed away from the bow section without disturbing the risers or mooring lines. Since the bow section is unmanned and is capable of withstanding high seas without capsizing, it can be left on location with little danger. This avoids the necessity for dropping or tying off the risers to a buoy and simplifies the later resumption of production. The stern section can be reattached to the bow section and put back into operation with little difficulty.
Although the invention has been described in terms of a floating vessel for the storage of crude oil and similar products, it will be apparent that it has equal application to ships used for the generation of electrical power at offshore locations, vessels provided with separators and other equipment for the initial processing of crude oil and natural gas before they are transported through long distance pipelines, ships used in offshore mining operations, and similar vessels which must be moored in proximity to fixed ocean floor locations in unprotected areas.
1. A floating vessel comprising:
a. a hull including a bow section and an elongated, detachable stern section, said bow section containing a well extending vertically in said hull and open at its lower end and said bow and stern sections abutting against one another;
b. means for disconnecting said stern section from said bow section and reconnecting the two sections;
c. a turret mounted in said well and rotatable with respect to said bow section; and
d. means for attaching mooring lines to said turret to anchor said bow section to a submerged bottom.
2. A vessel as defined by claim 1 including propulsion means located in said detachable stern section.
3. A vessel as defined by claim 1 wherein said turret includes a rotatable table, bearings supporting said table in said bow section, and a cylindrical sleeve extending downwardly in said well from said rotatable table.
4. A vessel as defined by claim 3 including a manifold mounted in said sleeve and a swivel joint connected to the upper end of said manifold.
. A vessel as defined by cla1m 4 including a mooring Wlfldlass, a chain stopper, and a fairleader mounted on said rotatable table.
6. A floating storage vessel comprising:
a. a hull including a bow section containing a vertical well extending through said hull and an elongated separable stern section containing a storage compartment and said bow and stern sections abutting against one another;
b. means for disconnecting said stern section from said bow section and reconnecting the two sections;
0. a mooring turret including an elongated sleeve extending downwardly in said Well and a rotatable table supporting said sleeve in said bow section;
d. means including a swivel joint for conducting fluids upwardly through said sleeve in said mooring turret and into each storage compartment in said stern section; and
e. means for anchoring said mooring turret to the ocean floor.
7. A vessel as defined by claim 6 wherein said means for anchoring said turret includes fairleaders mounted near the upper and lower ends of said sleeve, mooring lines guided by said fairleaders, and mooring windlasses on said table to which said mooring lines are connected.
8. A vessel as defined by claim 1 wherein said detachable stern section includes means for propelling said stern section.