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(11) | EP 0 079 404 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A single point mooring buoy with rigid arm |
| (57) The buoy (3) and rigid arm (15) are free to rotate about the vertical axis (A-A)
of the buoy. The rigid arm (15) is connected to the single point mooring buoy by a
hinge arrangement (9) and an axial rotational connection (10) to allow for independent
pitch and roll motions of the buoy in relation to the rigid arm. The vessel (1) is
connected to the rigid arm by two tension members (6,7), which could be chains, cables
or bars. The rigid arm is ballasted (13,14) at the vessel end. In addition, the vessel
and the single point mooring buoy may be connected using a conventional hawser (18).
The weight of the rigid arm and its ballast, and the loading on the tension members,
combine to produce a restoring force and moment which prevent the vessel from riding
up to the buoy or jack-knifing of the assembly when the rigid arm moves out of line
with the centre line of the vessel. |
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a single point mooring buoy with a vessel moored to it, floating on the surface of a body of water. This buoy is anchored by means of a number of anchor points and anchor chains to the floor of the body of water, while the vessel is coupled to the buoy by a rigid arm which serves to hold the vessel away from the buoy. This member is at one end pivotably hinged on the horizontally disposed pin affixed to the buoy, and at the other end it is coupled to the vessel in such a manner that the vessel is free to swing about the vertical axis of the buoy. Such a single point mooring buoy with rigid arm is known from the Dutch Patent Applications 6600321 and 7207903, laid open to public inspection.
[0002] In this known embodiment of the buoy, the rigid arm is pivotably hinged to the vessel. This connection is made by means of a horizontally disposed pivot. The buoy and vessel, the latter of which is in many instances a tanker, are subject to the motions of the waves within the body of water and the forces exerted by the wind. Consequently, the rigid arm needs to have considerable inherent strength and stiffness to cope with the forces exerted upon it by the vessel. These forces attempt to turn the buoy over or force it sideways in relation to the connected vessel or tanker. This situation implies that the rigid arm needs to have a relatively large hinge construction at the end which is connected to the vessel or tanker in order to provide adequate strength and stability, with the result that an expensive construction and/or extensive vessel modifications are necessary.
[0003] A structure which is subject to considerably reduced loads is achieved by attaching the rigid arm to the vessel by means of two pivotable tension members located at each side of the hull, including a pivot in the rigid arm which allows independent roll motions between the vessel and the buoy. Hence, the rigid arm does not require any torsional stiffness and the strength of the rigid arm does not need to exceed the forces necessary to transfer the anchoring forces of the vessel to the anchor chains.
[0004] The rigid arm is fitted to the vessel or tanker in a similar way as a wide swing is connected to its support beam. This implies that only the distance between the rigid arm and the vessel is maintained by the weight of the swing, whilst no other restriction in motion is implied. The buoy and rigid arm may tend to jack-knife when the vessel is pushed towards the single point mooring buoy by a reverse current, such as occurs during a change in tide.
SUMMARY OF A PREFERRED EMBODIMENT OF THE INVENTION
[0005] It is the general objective of the present invention to provide a novel type of apparatus for anchoring a vessel on the surface of a body of water to the floor of that body of water, which consists of a construction that allows the maximum of freedom of motion between the rigid arm and the vessel, and provides a sufficient restoring force and moment to restrict the jack-knifing of the arrangement or the horizontal displacement of the buoy and rigid arm in relation to the vessel, without any driving means. This is achieved through the provision of (a) adequate weight in the two arms forming the vessel end of the rigid arm, (b) two pivotable tension members between the rigid arm and the vessel, (c) a pivotable connection which can pivot about a horizontal axis and is located between the buoy and rigid arm, and (d) the axial rotational connection located in the rigid arm. Alternatively, the axial rotational connection in the rigid arm can be omitted entirely.
[0006] Since the tension members located at each side of the hull of the vessel are pivotably connected to the vessel or tanker, the weight of the rigid arm, including its ballast weight, provides a restoring force and a restoring moment when the vessel moves towards, away or out of line with the buoy and rigid arm. The restoring force is proportional to the weight of the rigid arm, inclusive of its ballast weight, the sine of the angle of inclination from the vertical of the tension members, and the length of the tension members. The value of the restoring moment is also proportional to the distance between the two tension members. The restoring moment can be altered by changing the length of the 'vertical' pivotable tension members, or by changing the weight of the rigid arm using ballast, depending on the demands imposed by the dimensions of the mooring arrangement, the expected weather and storm conditions, etc.
[0007] A preferred embodiment of the present invention would involve the rigid arm be g provided with a ballasting arrangement that could be emptied to erable the rigid arm to act as a floating unit. This would provide the mooring system with a stable buoyancy capacity should the vessel be disconnected.
BRIEF DESCRIPTION OF THE DRAWING
[0008] Further and additional objects and advantages of the present invention will become apparent to those skilled in the art when considering the following detailed description and accompanying drawing, wherein like elements have been fiven like numbers, in which FIGURE 1 is a general view of a preferred embodiment of the apparatus of the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0009] As may be seen from Figure 1, the vessel (1) is moored to the floor of a body of water (2) by means of two tension members (6)(7), a rigid arm (15), a standard type of single point mooring buoy (3), and one or more anchor chains (5). The single point mooring buoy (3) is of a type known to those skilled in the art, and consists of a buoy body (4) on which the turntable (8) is free to rotate about the vertical axis (A-A) of the buoy body (4). The buoy body (4) is attached to the floor of the body of water (2) by means of one or more anchor chains (5).
[0010] The rigid arm (15) is attached to the single point mooring buoy (3) by means of the hinges (9). These hinges (9) allow relative movement between the buoy (3) and the rigid arm (15) about the horizontal axis (B-B). The axial rotational connection (10) located in the rigid arm (15) allows axial rotational movements of the rigid arm (15) in relation to the buoy (3). The rigid arm (15) is Y-shaped, and the two arms (11)(12) incorporate ballasting arrangements (13)(14). This implies that the two arms (11)(12) can be ballasted or alternatively deballasted, in which case the rigid arm (15) can become independently buoyant. Two tension members (6)(7), which can be chains, cables or bars, connect the two arms (11)(12) to the vessel (1). In addition, a mooring hawser (18) connects the single point mooring buoy (3) to the vessel (1). This is to provide both an additional mooring facility and a factor of safety in the mooring arrangement.
[0011] The product fluid is carried to the single point mooring buoy (3) by means of the submarine riser (16). It is then transported to the vessel (1) by means of the floating hose string (17).
[0013] Furthermore, the invention is also applicable in combination with all other SPM (Single Point Mooring) apparatus such as the SALM (Single Anchor Leg Mooring) buoy, laid open to public inspection in the Dutch Patent Application 7600189.
[0014] The rigid arm (15) is attached to the single point mooring buoy (3) by means of the hinges (9). These hinges (9) allow relative movement between the buoy (3) and the rigid arm (15) about the horizontal axis (B-B). The axial rotational connection (10) located in the rigid arm (15) allows axial rotational movements of the rigid arm (15) in relation to the buoy (3). The rigid arm (15) is Y-shaped, and the two side arms (11, 12) incorporate ballasting arrangements (13, 14). This implies that the two side arms (11, 12) can be ballasted or alternatively deballasted, in which case the rigid arm (15) can become independently buoyant.- Two tension members (6, 7), which can be chains, cables or bars, connect the two side arms (11, 12) to the vessel (1) .These tension members (6, 7) run from the ballasting members (13, 14) upwards through hawses (19) to fixing points (22) on dock (21) of the vessel (1). Any rolling movement of the vessel (1) is thus smoothed out by the up-and-down movement of the side arms (11, 12) causing the middle leg of the Y-shaped rigid arm to oscillate about its axis. Nearly the same effect can be obtained when the rigid arm is not Y-shaped but instead T-shaped. Similar shapes can also be used.
[0015] In addition, a mooring hawser (18) connects the single point mooring buoy (3) to a fixing point (24) on deck of the vessel (1). This is to provide both an additional mooring facility and a factor of safety in the mooring arrangement.
1. A buoy for mooring a vessel floating on the surface of a body of water, said buoy
anchored to the floor of said body of water by means of one or more anchor points
and anchor chains, said vessel being connected to said buoy by means of a rigid arm,
said rigid arm being fitted to one end in either a fixed or a pivotable manner to
said buoy, said rigid arm being free to rotate about the vertical axis of said buoy,
said rigid arm being fitted to said vessel via two pivotable tension members which
are attached to the rigid arm at the vessel end, said pivotable tension members being
separated by a certain distance.
2. The buoy of claim 1, and furtlez comprising an axia- rotational connection which
is located in the rigid arm.
3. The buoy of claim 1 or 2, in which the rigid arm is Y-shaped.
4. The buoy of claim 1 and/or claim 2, and further comprising ballast weight(s) located
in the rigid arm.
5. The buoy of any of claims 1 to 4, wherein the tension members consist of chains
or cables which can be suspended through the anchor chain hawses of the vessel.
6. The buoy of any of claims 1 to 5, and further comprising hinges between the buoy
and the rigid arm.
7. The buoy of any of claims 1 to 6, and further comprising a buoyancy chamber in
the rigid arm.