GB2383317A

GB2383317A - Submerged friction mooring device

Info

Publication number: GB2383317A
Application number: GB0130698A
Authority: GB
Inventors: Baan Jacob De
Original assignee: Bluewater Terminal Systems NV; Bluewater Energy Services BV
Current assignee: Bluewater Energy Services BV
Priority date: 2001-12-21
Filing date: 2001-12-21
Publication date: 2003-06-25
Anticipated expiration: 2021-12-21
Also published as: GB2383317B; GB0130698D0

Abstract

An apparatus and method are described for mooring two vessels (10,28) together. The apparatus comprises a submerged rigid arm (14,Fig 1) rotatably attached at one end to the first vessel (10). A variable buoyancy means (24) is mounted at the other end. The buoyancy can be altered to submerge the second end of the arm to a greater or lesser extent. A fender system (26) is mounted on the variable buoyancy means (24). The variable buoyancy means (24) can be submerged deeply as a second vessel (28) approaches, and then raised until the fender system (26) contacts the hull of the vessel (28) with sufficient force to create friction between the two and to keep the fender system (26) in contact with the hull of the vessel (28).

Description

MOORING DEVICE The present invention relates to an apparatus for mooring vessels, particularly for mooring two vessels together temporarily in open sea.

In the off-shore mooring of floating vessels, particularly in the temporary mooring of vessels to other vessels, it is often difficult to achieve a sufficiently high level of strength in the means employed to establish such mooring, without resorting to dedicated structures and reinforcements on both vessels.

For a temporary mooring between vessels such structures are difficult to realise because, in offshore loading, such vessels are connected to one another in open sea for relatively short periods of time, such as during a transfer of an oil cargo between them, and often under weather conditions which are not conducive to human activities.

Therefore, there is a need to provide an improved means and method to establish a temporary mooring between two vessels, which avoids the need for special reinforcements on the visiting vessel, while increasing the allowable weather conditions in which the vessel can remain moored, and avoiding manual intervention in establishing the mooring.

Accordingly, the present invention provides apparatus for mooring a first vessel to a second vessel, comprising a submerged, rigid arm which is rotatably attached at its proximal end to the first vessel, variable buoyancy means mounted at the distal end remote from the first vessel and operable to selectively increase and decrease the depth of the

distal end, and fendering means mounted at the distal end to contact the hull of the second vessel.

Preferably, the arm is suspended from the from first vessel by means of at least one tension member.

Preferably, the arm is bifurcated and comprises two arm portions joined at the distal end and diverging so as to be spaced apart at the proximal end.

In this embodiment, a respective tension member is provided on either side of the stern of the first vessel for attachment to each arm portion.

Preferably, the arm is constructed from a plurality of tubular members.

The variable buoyancy means may comprise a tank and means to supply air to the tank to drive out water contained therein and thereby to increase the buoyancy of the tank, and means to release air from the tank and allow water to return thereby to decrease the buoyancy thereof.

The means to supply air may provide low pressure, high volume air.

In this case, air may be provided from the first vessel via at least one of the tubular members making up the arm.

The apparatus may further comprise flexible hoses provided across the rotatable connection of the arm to the first vessel, to provide a conduit for the air.

Alternatively, the means to supply air may provide high pressure air to storage containers integrated

with the tank.

The present invention also provides a method of mooring a first vessel to a second vessel using the apparatus described above, comprising the steps of: (a) reducing the buoyancy of the variable buoyancy means to increase the depth at which the distal end is submerged, (b) moving the second vessel into a location with a portion of its hull above the distal end, and (c) increasing the buoyancy of the variable buoyancy means to decrease the depth at which the distal end is submerged until the fendering means contacts the hull of the second vessel.

Preferably, step (a) includes reducing the buoyancy until the distal end is submerged at a depth of approximately 15-20 metres below the waterline.

Preferably, step (c) includes increasing the buoyancy until the fendering means contacts the hull of the second vessel with a load of approximately 500-1500 tonnes.

The invention will now be described in detail by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic side view of a mooring device in accordance with a first embodiment of the present invention; Figure 2 is a plan view of Figure 1; Figure 3 is a schematic side view of the mooring device of Figure 1 shown in engagement with a visiting vessel; and

Figure 4 is a detail view of the distal end of the mooring device in Figure 3.

With reference to Figures 1 and 2, a first vessel 10 is permanently moored out at sea by means well known in the industry, but not shown in these figures.

The vessel 10 is permanently fitted with a submerged mooring device 12 which comprises a rigid arm 14, which in this embodiment is bifurcated into two arm portions 15, 16. At the first, proximal end of the arm 14 the arm portions 15,16 are spaced apart from each other and each is suspended from the vessel 10 by means of a tension member 18. Each arm portion 15,16 is connected to a respective tension member 18 by an articulation allowing rotation about a substantially horizontal axis XX as seen in Figure 2.

The proximal end of the arm 14 is also provided with ballast means 20 such that there is a significant tension force in the tension members 18 and if the arm 14 is pushed or pulled away from its equilibrium position, it will automatically return to the equilibrium position. The attachment points of the tension members 18 to the arm portions 15,16 are preferably located some vertical distance above the ballast means 20 in order to create a stable position for the mooring device 12 when not in use.

The spaced proximal ends of the two arm portions 15,16 are suspended from the vessel 10 at spaced locations, for example from either side of the stern as shown.

The arm portions 15,16 are then arranged to converge towards one another so that their distal ends meet at a point remote from the vessel 10. At this distal end a spherical or cardanic joint 22 is provided above which is fitted a variable buoyancy device such as a

large tank 24. This tank 24 may be closed or open to the sea. On top of the tank 24 a substantial fendering system 26 is fitted.

In the inoperative condition of the mooring device 12, the arm 14 floats beneath the surface with the distal end at a depth of approximately 15-20 metres below the waterline. When a second visiting vessel 28 arrives to be moored to the first vessel 10, it positions itself with its forward hull above the tank 24. Once this position has been achieved the tank 24 is purged of sea water by injecting it with air. This increases the buoyancy of the tank 24 and causes the entire mooring device 12 to rotate upwardly about the axis XX seen in Figure 2, until the fendering system 26 makes contact with the underside of the hull of the visiting vessel 28, causing a contact load between the hull and the mooring device 12.

The displacement of the tank 24 is designed such that the magnitude of the contact load will be in the order of 500-1500 tonnes. This load will vary in operation due to the effects of waves and vessel motion but will generally be sufficient to create horizontal friction capacities between the hull and the fendering system 26 in the region of 500 tonnes, while the spherical or cardanic joint 22 allows the vessel 28 to pitch, roll and yaw without imposing these motions upon the arm 14.

The force is taken up by the existing hull structure of the visiting vessel 28, without requiring modifications, and is large enough to allow the vessel combination to ride out weather conditions well above anything practicable with known mooring devices.

When it is desired to disconnect the vessels 10,28,

air is allowed to escape from the tank 24 and seawater is allowed to return into the tank, reducing its buoyancy and moving the arm 14 downwardly to disengage the fendering system 26 from the hull of the vessel 28.

The air required to purge the tank 24 is preferably supplied from the first vessel 10 either directly as a low pressure, high volume supply or at high pressure to storage cylinders integrated within the tank 24.

The rigid arm 14 is preferably of a space frame type construction, consisting of a number of slender, tubular members and some of these may be used to convey low pressure-high volume air from the first vessel 10 to the tank 24. In this case, flexible hoses may be used to bridge the articulations between the tension members 18 and the arm 14.

Preferably, the tank 24 and the fendering system 26 are designed as such that there is ample space for the mooring device 12 to contact different underwater hull shapes of various tankers and no extreme precision in positioning the vessel 28 is required.

Thus, the present invention provides an improved mooring apparatus operable remotely, without direct human intervention, and without the need for additional structures or reinforcements on the visiting vessel. It will appreciated by those skilled in the art that a number of modifications and variations to precise details described may be employed. For example, the first vessel may in fact be an offshore structure, and a gas other than air may be supplied to the tank to vary its buoyancy. The particular configuration of the arms and tension members may also be altered. In particular, the

bifurcated arm may be replaced by a single arm supported from the centreline of the first vessel.

Claims

CLAIMS 1. Apparatus for mooring a first vessel to a second vessel, comprising a submerged, rigid arm which is rotatably attached at its proximal end to the first vessel, variable buoyancy means mounted at the distal end remote from the first vessel and operable to selectively increase and decrease the depth of the distal end, and fendering means mounted at the distal end to contact the hull of the second vessel.
2. Apparatus as claimed in claim 1, wherein the arm is suspended from the from first vessel by means of at least one tension member.
3. Apparatus as claimed in claim 1 or claim 2, wherein the arm is bifurcated and comprises two arm portions joined at the distal end and diverging so as to be spaced apart at the proximal end.
4. Apparatus as claimed in claim 3 when dependent on claim 2, wherein a respective tension member is provided on either side of the stern of the first vessel for attachment to each arm portion.
5. Apparatus as claimed any of claims 1-4, wherein the arm is constructed from a plurality of tubular members.
6. Apparatus as claimed in any preceding claim, wherein the variable buoyancy means comprises a tank and means to supply air to the tank to drive out water contained therein and thereby to increase the buoyancy of the tank, and means to release air from the tank and allow water to return thereby to decrease the buoyancy thereof.

<Desc/Clms Page number 9>
7. Apparatus as claimed in claim 6, wherein the means to supply air provides low pressure, high volume air.
8. Apparatus as claimed in claim 6 or claim 7, when dependent upon claim 5, wherein air is provided from the first vessel via at least one of the tubular members.
9. Apparatus as claimed in claim 8, further comprising flexible hoses provided across the rotatable connection of the arm to the first vessel, to provide a conduit for the air.
10. Apparatus as claimed in claim 6, wherein the means to supply air provides high pressure air to storage containers integrated with the tank.
11. A method of mooring a first vessel to a second vessel using the apparatus of any preceding claim, comprising the steps of: (a) reducing the buoyancy of the variable buoyancy means to increase the depth at which the distal end is submerged, (b) moving the second vessel into a location with a portion of its hull above the distal end, and (c) increasing the buoyancy of the variable buoyancy means to decrease the depth at which the distal end is submerged until the fendering means contacts the hull of the second vessel.
12. A method as claimed in claim 11, wherein step (a) includes reducing the buoyancy until the distal end is submerged at a depth of approximately 15-20 metres below the waterline.
13. A method as claimed in claim 11 or claim 12,

<Desc/Clms Page number 10>

wherein step (c) includes increasing the buoyancy until the fendering means contacts the hull of the second vessel with a load of approximately 500-1500 tonnes.
14. Apparatus for mooring a first vessel to a second vessel substantially as hereinbefore described and with reference to the accompanying drawings.
15. A method of mooring a first vessel to a second vessel substantially as hereinbefore described and with reference to the accompanying drawings.

15. A method of mooring a first vessel to a second vessel substantially as hereinbefore described and with reference to the accompanying drawings.

<Desc/Clms Page number 11>

Amendments to the claims have been filed as follows

1. Apparatus for mooring a first vessel to a second vessel, comprising a submerged, rigid arm which is rotatably attached at its proximal end to the first vessel, variable buoyancy means mounted at the distal end remote from the first vessel and operable to selectively increase and decrease the depth of the distal end, and fendering means mounted at the distal end to contact the hull of the second vessel.

2. Apparatus as claimed in claim 1, wherein the arm is suspended from the first vessel by means of at least one tension member.

3. Apparatus as claimed in claim 1 or claim 2, wherein the arm is bifurcated and comprises two arm portions joined at the distal end and diverging so as to be spaced apart at the proximal end.

4. Apparatus as claimed in claim 3 when dependent on claim 2, wherein a respective tension member is provided on either side of the stern of the first vessel for attachment to each arm portion.

5. Apparatus as claimed any of claims 1-4, wherein the arm is constructed from a plurality of tubular members.

6. Apparatus as claimed in any preceding claim, wherein the variable buoyancy means comprises a tank and means to supply air to the tank to drive out water contained therein and thereby to increase the buoyancy of the tank, and means to release air from the tank and allow water to return thereby to decrease the buoyancy thereof.

<Desc/Clms Page number 12>

7. Apparatus as claimed in claim 6, wherein the means to supply air provides low pressure, high volume air.

8. Apparatus as claimed in claim 6 or claim 7, when dependent upon claim 5, wherein air is provided from the first vessel via at least one of the tubular members.

9. Apparatus as claimed in claim 8, further comprising flexible hoses provided across the rotatable connection of the arm to the first vessel, to provide a conduit for the air.

10. Apparatus as claimed in claim 6, wherein the means to supply air provides high pressure air to storage containers integrated with the tank.

11. A method of mooring a first vessel to a second vessel using the apparatus of any preceding claim, comprising the steps of: (a) reducing the buoyancy of the variable buoyancy means to increase the depth at which the distal end is submerged, (b) moving the second vessel into a location with a portion of its hull above the distal end, and (c) increasing the buoyancy of the variable buoyancy means to decrease the depth at which the distal end is submerged until the fendering means contacts the hull of the second vessel.

12. A method as claimed in claim 11, wherein step (a) includes reducing the buoyancy until the distal end is submerged at a depth of approximately 15-20 metres below the waterline.

13. A method as claimed in claim 11 or claim 12,

<Desc/Clms Page number 13>

wherein step (c) includes increasing the buoyancy until the fendering means contacts the hull of the second vessel with a load of approximately 500-1500 tonnes.

14. Apparatus for mooring a first vessel to a second vessel substantially as hereinbefore described and with reference to the accompanying drawings.