US3883912A

US3883912A - Submerged hose arm stabilizing means for single point mooring systems

Info

Publication number: US3883912A
Application number: US424958A
Authority: US
Inventors: Kristen I Pedersen
Original assignee: Sofec Inc
Current assignee: Sofec Inc
Priority date: 1973-12-17
Filing date: 1973-12-17
Publication date: 1975-05-20
Anticipated expiration: 1992-05-20

Abstract

In a single anchor leg mooring system, the submerged hose arm pivotally connected to the upstanding fluid cargo pipe is provided with a buoyancy tank and ballast weight located substantially outwardly from the pipe and beneath the center line of the buoyancy tank. As the pipe oscillates due to wind and wave action on the mooring buoy, the tendency of the hose arm to rock correspondingly is counteracted by the tendency of the ballast weight to remain in or return to its stable position vertically beneath the supporting buoyancy tank. This stabilizing means prevents excessive strains on the attached hose as the arm may otherwise droop too far down or rise too far above the optimum position.

Description

Pedersen May 20, 1975 SUBMERGED HOSE ARM STABILIZING MEANS F OR SINGLE POINT MOORING SYSTEMS [75] Inventor: Kristen l. Pedersen, Scarsdale, NY.

[73] Assignee: Sofec, lnc., Houston, Tex.

[22] Filed: Dec. 17, 1973 [21] Appl. No.: 424,958

[52] US. Cl. 9/8 P [51] Int. Cl B63b 21/52 [58] Field of Search 9/8 P, 8 R;114/121, 123, 114/124, 126

[56] References Cited UNITED STATES PATENTS 3,641,602 2/1972 Flory et al. 9/8 P 3,651,525 3/1972 Rutten et al 9/8 P Assistant Examiner-Stuart M. Goldstein Attorney, Agent, or FirmBertram H. Mann; Frank B.

Pugsley Primary ExaminerDuane A. Reger [57] ABSTRACT In a single anchor leg mooring system, the submerged hose arm pivotally connected to the upstanding fluid cargo pipe is provided with a buoyancy tank and ballast weight located substantially outwardly from the pipe and beneath the center line of the buoyancy tank. As the pipe oscillates due to wind and wave action on the mooring buoy, the tendency of the hose arm to rock correspondingly is counteracted by the tendency of the ballast weight to remain in or return to its stable position vertically beneath the supporting buoyancy tank. This stabilizing means prevents excessive strains on the attached hose as the arm may otherwise droop too far down or rise too far above the optimum position.

2 Claims, 6 Drawing Figures SUBMERGED HOSE ARM STABILIZING MEANS FOR SINGLE POINT MOORING SYSTEMS BACKGROUND OF THE INVENTION This invention relates to so-called single point or single anchor leg mooring systems and consists particularly in novel means for stabilizing the hose arm pivotally connected to the upstanding cargo pipe and projecting laterally therefrom.

A single anchor leg mooring system as illustrated, for instance, in Flory et al. US. Pat. No. 3,641,602 provides for mooring of very large vessels such as super tankers in the open sea and for transfer of cargo, as petroleum, to and from the vessel through a floating hose or hoses and vertical pipes and/or hoses extending to a pipeline on the seabed. As the buoy and the upstanding pipe shaft oscillate and tilt due to wave and wind action, the pivotally attached hose arm, which is aupported by a buoyancy tank at its outer end, tends to correspondingly rock and may strike the buoy or cause excessive strains in the attached hose. Without the stabilizing arrangement described herein, the hose arm has no vertical stability at all, except for the relatively ineffective restraint provided by the stiffness of the attached hose leading to the water surface. This hose is usually extremely flexible and the proper alignment at the arm and hose often cannot be maintained satisfactorily even under calm weather conditions. This lack of stability causes the hose arm to droop too far down or to rise too high for satisfactory function of the hose arm.

Consequently, the main object of the present invention is to provide means for avoiding excessive swivelling and oscillation of the hose arm in a single anchor leg mooring system and to maintain the arm substantially in its optimum position.

SUMMARY OF THE INVENTION In accordance with the invention, the hose arm, which is pivotally connected to the upstanding pipe extending between the mooring buoy chain and the seabed anchor and extends laterally therefrom, is provided with distal buoyancy tank means for supporting the arm and hose connected thereto. In addition, a ballast weight is carried by the arm near its outer extremity and substantially beneath the longitudinal center line of the arm so that as the arm pivots in a vertical plane, the tendency of the weight to remain stably positioned vertically beneath the buoyancy tank tends to counteract the forces tending to produce such arm pivoting.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings which illustrate the invention,

FIG. 1 is a perspective view of a single anchor leg mooring and cargo transfer device.

FIG. 2 is a schematic top view showing the hose arm portion of the device.

FIG. 3 is a side view of the structure in FIG. 2.

FIGS. 4, 5, and 6 are schematic views showing the hose arm in its optimum position and swivelled to various positions vertically and illustrating the compensating effect of the invention.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT OF THE INVENTION FIG. 1 illustrates a single anchor leg mooring apparatus including a base portion 8 firmly anchored 'to the seabed and into which the seabed pipeline 9 extends. Pipeline 9 communicates with an upstanding pipe shaft 10 connected to the base by a universal joint 11 and extends to a buoy chain 12 which at its upper end is attached to a buoy 13 having a bracket 14 to which the vessel mooring line 15 may be attached. At the top of the pipe shaft 10 there is provided a horizontally rotable coupling 16 having horizontally opposed

swivel joints

17 and 18 from which project the yoke 19 form ing the laterally projecting hose arm to which is connected the hose 20 leading to the tanker or other vessel to be serviced. This mooring and cargo transfer arrangement, as more fully described and claimed in Flory et al. US. Pat. No. 3,641,602, enables the vessel secured by mooring line 15 to rotate about the mooring apparatus under the influence of wind and waves with minimum mooring line forces and without the danger of fouling or damaging the hose 20, or other components of the mooring facility.

A buoyancy tank 24 is mounted on hose arm 19 near the outer extremity thereof. However, in case of severe rocking or tilting of pipe shaft 10 or in case there is a change in the specific gravity of the cargo inside the hose 20, the attitude of yoke-arm l9 and the hose 20 may be altered such that the hose may drop or rise excessively, possibly causing the arm to strike the buoy or pipe 10 or otherwise endanger hose 20 or the hose arm. In order to avoid such dangerous conditions, the ballast weight 25 is rigidly supported beneath the center line of arm 19 and at a substantial distance outwardly from pipe 10. While ballast weight 25 is shown supported substantially vertically beneath the buoyancy tank 24, this arrangement is not essential. Rather the weight should be positioned so that in its normal stable position the arm will be in its optimum position relative to pipe 10 and its connected hose 20. Preferably, the

Operation As arm 19 tends to pivot above (FIG. 5) or below (FIG. 6) its optimum position (FIG. 4), the effective moment arm of ballast weight 25 will be, respectively, increased or decreased by the value a sin a (FIGS. 5 and 6). This results in a restoring or stabilizing force substantially equal to Q a sin a where Q is the submerged weight of ballast 25, a is the distance between the center of the buoyancy force and the ballast weight 25 (FIG. 4), and a sin a is the moment arm increment upon tilting of the hose arm. The relationship of buoyancy tank 24 and ballast 25 may be varied, particularly in order to vary the optimum positioning of the hose arm from that shown in FIG. 4.

The particular form of mooring apparatus is not essential and others may be substituted; for instance, the swivelling hose and anchor line connections may be provided in the base of the apparatus. The invention may be modified in various respects as will occur to those skilled in the art, and the exclusive use ofall modifications as come within the scope of the appended claims is contemplated.

I claim:

1. In a single point mooring system of the type having a buoy with means for mooring of a vessel thereto, a base anchored to the sea bottom, an upstanding cargo pipe shaft pivotally connected to said base and extending upwardly therefrom, a hose arm projecting laterally from the upper portion of said pipe shaft, a hose extending from said arm for carrying cargo to and from a vessel moored to said buoy, buoyancy tank means for supporting said arm in substantial alignment with said hose, and a pivotal connection between said arm and said pipe shaft permitting vertical swivelling of said arm relative to said pipe shaft, and hose arm stabilizing means comprising a ballast weight carried by said arm substantially laterally outwardly of said pipe shaft and substantially beneath the center of buoyancy of said arm and buoyancy tank means thereby causing a stabilizing effect which counteracts external forces tending to dislodge the arm from its proper position.

2. In a single point mooring system of the type having a buoy with means for mooring of a vessel thereto, a base anchored to the sea bottom, a structure pivotally connected to said base and extending upwardly therefrom, a hose arm projecting laterally from said structure, a hose extending from said arm for carrying cargo to and from a vessel moored to said buoy, buoyancy tank means for supporting said arm in substantial alignment with said hose, a pivotal connection between said arm and said pipe shaft permitting vertical swivelling of said arm relative to said pipe shaft, and hose arm stabilizing means comprising a ballast weight carried by said arm substantially laterally outwardly of said pipe shaft and substantially beneath the center of buoyancy of said arm and buoyancy tank means thereby causing a stabilizing effect which counteracts external forces tending to dislodge the arm from its proper position.