US3726247A

US3726247A - Mooring system

Info

Publication number: US3726247A
Application number: US00044201A
Authority: US
Inventors: J Dalzell
Original assignee: Offshore Co
Current assignee: SONAT OFFSHORE DRILLING Inc
Priority date: 1970-06-08
Filing date: 1970-06-08
Publication date: 1973-04-10
Anticipated expiration: 1990-04-10

Abstract

A resilient mooring system for maintaining a vessel in a substantially fixed lateral position in a body of water wherein the system includes a float member for disposition on the surface of the body of water a distance away from the vessel, a first mooring line adapted to be coupled to the vessel and to the float member, a sinker member attached substantially midway between the ends of the first mooring line, and a second mooring line coupled to the float member and to an anchor member adapted to be secured to the floor beneath the body of water.

Description

United States Patent 1 Dalzell 1 MOORING SYSTEM [75] Inventor: John F. Dalzell, Berkeley Heights,

21 Appl. No.: 44,201

[52] US. Cl. ..114/206 R, 1 14/05 D, 114/230 [51] Int. Cl ..B63b 21/24, B63b 21/00 [58] Field of Search ..l14/206 R, 230, 0.5 D

[56] References Cited UNITED STATES PATENTS 10/1964 Collipp ..l14/206R 7/1930 Fountain ..1l4/206R 1 Apr. 10, 1973 3,111,926 11/1963 Shatto ..1l4/206R Primary ExaminerTrygve M. Blix Att0rneyCushman, Darby & Cushman 5 7 1 ABSTRACT A resilient mooring system for maintaining a vessel in a substantially fixed lateral position in a body of water wherein the system includes a float member for disposition on the surface of the body of water a distance away from the vessel, a first mooring line adapted to be coupled to the vessel and to the float member, a sinker member attached substantially midway between the ends of the first mooring line, and a second mooring line coupled to the float member and to an anchor member adapted to be secured to the floor beneath the body of water.

5 Claims, 1 Drawing Figure PATENTEI] APR 1 0 I973 ATTORNEYS MOORING SYSTEM The present invention relates to a mooring system and more particularly to a resilient mooring system for maintaining a vessel in a substantially fixed lateral position in a body of water.

Recently, offshore oil, gas and mineral exploration is being carried out in increasingly exposed areas. It is essential to the success of these operations to have platforms or vessels to house equipment and personnel which are both stable and which remain over the operating cite. Generally, in water depths up to approximately three hundred feet jack-up rigs are used. These rigs are vessels with legs which are lowered to the ocean floor at the operation cite so that the vessel is jacked out of the water. These vessels do not require mooring during operation; however, in water depths in excess of three hundred feet the jack-up rigs are not practicable and explorations are performed from floating vessels. Such vessels are expected to work in water depths as shallow as 200 feet in addition to being capable of operating in depths in excess of three hundred feet.

Conventional mooring equipment consists of four to mooring lines and anchors wherein the lines are composed of wire, rope, chain or nylon rope. Sometimes buoys are also included in the system. The inability of the conventional mooring system to maintain the vessel in the desired position is vividly demonstrated by the fact that many offshore drilling vessels must discontinue operations due to excessive horizontal motions even in moderate weather and many lose their moorings altogether. In order to provide an adequate conventional mooring system it would be necessary to have very large lines or many more lines and in this case the system would become extremely uneconomical and difficult for physical handling. Furthermore, as

the sizes and number of lines increase the weight of the mooring equipment also increases so that the vessels must carry this additional weight at the expense of being able to carry less of the material more vital to the earning power of the vessel. In addition, conventional mooring arrangements have not provided sufficient resiliency so that the tensions in the mooring lines rapidly increase when surge or horizontal excursion of the vessel occurs from the reference point so that the tensions created in the mooring lines in such conventional systems become much greater than actually required to merely hold the moored vessel in position.

Accordingly, the general purpose of this invention is to provide a mooring system for maintaining a vessel in a substantially fixed lateral position in a body of water which performs well even in rough weather. To accomplish this the present invention contemplates a unique arrangement whereby a sinker is attached to a mooring line which is coupled between a buoy and the vessel and an anchor is connected to a second mooring line coupled between the anchor and the buoy. A resilient mooring system is provided which even provides adequate resiliency for relatively shallow water moorings where only moderately severe wind and sea conditions can cause large surge excursions of the vessel when used with conventional mooring arrangements.

An object of the present invention is the provision of a resilient mooring system for maintaining a vessel in a substantially fixed lateral positionin a body of water.

Another object is to provide a resilient mooring system which is both practical and economical.

A further object of the invention is the provision of a resilient mooring system which provides adequate resiliency for both relatively shallow water moorings and for relatively deep water moorings.

Other objects and features of the invention will become apparent to those of ordinary skill in the art as the disclosure is made in the following description of a preferred embodiment of the invention as illustrated in the accompanying drawings in which:

The FIGURE shows a diagrammatic view of a preferred embodiment of the invention.

With reference now to the drawing, there is shown a semi-submerged vessel 10, such as a stabilized column platform, which is located in a body of water 12 covering a floor 14 and having a surface 16. A float member or buoy 18 is disposed on the surface 16 of the water 12 a distance away from the vessel. A first mooring line 20 has a first end which may be coupled to the vessel 10 at the point 22, for example, while a second end is coupled to the float member at the point 241. A sinker member 26 is attached to the first mooring line 20 and is located substantially between the ends 22 and 24 thereof for normally causing a substantially catenary curve in the mooring line 20. A second mooring line 28 has a first end 30 coupled to the float member 18 and a second end 32 coupled to an anchor 34 which is adapted to be secured to the floor 14.

The primary function of the mooring system of this invention is to maintain the vessel 10 in a substantially fixed lateral position in the body of water 12 and to provide for only a gradual increase in tension in the mooring lines during horizontal surge excursion of the vessel so that the tensions in the mooring lines become only as great as necessary to hold the vessel in the desired position. The location of the sinker member 26 substantially midway along the mooring line 20 greatly increases the resiliency of the mooring system. During surge or horizontal action of the vessel 10 as a result of movement of the water 12 the vessels movement causes the sinker member 26 to be raised in a vertical direction so that the horizontal component of force exerted by the mooring line 20 on the vessel 10 is gradually increased. Thus, the mooring system of this invention acts somewhat like a spring with slightly increasing tension occurring in the mooring line 20 depending upon the amount of horizontal excursion of the vessel from the desired position.

Clearly, a number of such arrangements as illustrated in the FIGURE can be provided so that a number of mooring lines 20 extend from various points on the vessel 10. The advantage of the present mooring system is further emphasized when a plurality of such mooring systems are utilized since conventional mooring arrangements are characterized by rapidly increasing tensions when surge excursion of the vessel increases so that the mooring line loads become much greater than actually required to hold the vessel in position and opposing mooring lines may actually tend to pull against each other to further increase the tension in the individual lines. However, with the mooring system of this invention wherein a more resilient mooring line 20 is provided in conjunction with thesinker member 26 the gradual increase in horizontal force with respect to in a substantially fixed lateral position in a body of water, said system comprising:

at least one float member for disposition on the surface of said body of water a distance away from said vessel;

at least one first mooring line having a first end adapted to be coupled to said vessel and a second end coupled to said float member;

at least one sinker member attached to and substantially midway between said ends of said first mooring line for normally causing a substantially catenary curve therein;

at least one second mooring line having a first end coupled to said float member and having a second end; and

at least one anchor means attached to said last-mentioned second end for securing to the floor beneath said body of water and for coacting with said float member, said sinker member and said first and second mooring lines to provide for gradually increasing tensions in said mooring lines during lateral or horizontal surge excursion of said vessel whereby said tensions in said mooring lines become only substantially as great as necessary to hold said vessel in said position.

2. A resilient mooring system as in claim 1 including a plurality of said float members, said first mooring lines, said sinker member, said second mooring lines and said anchor means for holding said vessel in said position.

3. A resilient mooring system as in claim 1 in combination with said vessel wherein said first end of said first mooring line is coupled to said vessel.

4. A resilient mooring system as in claim 2 wherein -each float member resides at the surface of the body of water and wherein each sinker member is submerged in the body of water at a location above and out of contact with the submerged floor.

5. In a resilient mooring system for maintaining a buoyant vessel in a substantially fixed lateral position in a body of water and above a submerged bottom, said system including a plurality of first mooring lines each having one of its ends secured to the vessel and extending outwardly from the vessel to its other end secured to a buoyant float member, and a plurality of second mooring lines each extending outwardly and downwardly from one of said float members to an anchor secured in the submerged bottom, the improvement comprising a sinker member carried intermediate the ends of each of said first mooring lines, each sinker member maintaining its respective line in a continuous curve extending from the vessel to the float member.

Claims

1. A resilient mooring system for maintaining a vessel in a substantially fixed lateral position in a body of water, said system comprising: at least one float member for disposition on the surface of said body of water a distance away from said vessel; at least one first mooring line having a first end adapted to be coupled to said vessel and a second end coupled to said float member; at least one sinker member attached to and substantially midway between said ends of said first mooring line for normally causing a substantially catenary curve therein; at least one second mooring line having a first end coupled to said float member and having a second end; and at least one anchor means attached to said last-mentioned second end for securing to the floor beneath said body of water and for coacting with said float member, said sinker member and said first and second mooring lines to provide for gradually increasing tensions in said mooring lines during lateral or horizontal surge excursion of said vessel whereby said tensions in said mooring lines become only substantially as great as necessary to hold said vessel in said position.

4. A resilient mooring system as in claim 2 wherein each float member resides at the surface of the body of water and wherein each sinker member is submerged in the body of water at a location above and out of contact with the submerged floor.