GB2098944A

GB2098944A - Moorings

Info

Publication number: GB2098944A
Application number: GB8110257A
Authority: GB
Original assignee: CRYSTAL JOHN DONALD WATSON
Current assignee: CRYSTAL JOHN DONALD WATSON
Priority date: 1981-04-01
Filing date: 1981-04-01
Publication date: 1982-12-01

Abstract

A mooring comprises a mooring buoy 1 and a flexible mooring cable extending down from the buoy to an anchorage point 3. The upper run of the mooring cable is located within a length of flexible tubular hose 11, the upper end of the hose being secured to the tail 8 of the buoy with the hose- end axis substantially upright. The lower end of the hole 11 is secured to a buoyancy assembly 9 which is anchored to the anchor point 3 by the lower run 6 of the cable. The hose is chosen such that its natural torsion stiffness resists relative twisting between its ends, thereby avoiding kinks in the cable and the need for swivels in the cable. Localised flattening of the hose is avoided by arranging the inner diameter of the hose to be not much greater than the envelope diameter of the cable, and, particularly, in deeper water, by providing access for water to enter the hose, for example at one or both ends, so that local hydrostatic pressures over the inner and outer walls of the hose are equalised. The buoyancy assembly may be distributed along the length of the lower run 6. <IMAGE>

Description

SPECIFICATION Moorings The present invention relates to moorings.

According to one aspect of the present invention there is provided a mooring comprising a mooring buoy and a flexible mooring cable extending down from the buoy to an anchorage point, wherein the mooring cable is located within a length of flexible tubular hose extending from the buoy to the anchorage point. Preferably the upper end of the hose is secured to the buoy with the hose-end axis substantially upright.

The hose is chosen such that its natural torsion stiffness resists relative twisting between its ends, thereby avoiding kinks in the cable and the need for swivels in the cable.

Localised flattening of the hose can be avoided by arranging the inner diameter of the hose to be not much greater than the envelope diameter of the cable, and, particularly in deeper water, by providing access for water to enter the hose, for example at one or both ends, so that local hydrostatic pressures over the inner and outer walls of the hose are equalised.

The hose may be provided with buoyancy to counteract some of the weight of the cable.

The cable may be normal mooring chain.

According to another aspect of the invention there is provided a mooring comprising a mooring buoy and flexible mooring cable extending down from the buoy to a buoyant anchorage at a level at which water movement due to surface wave action and tides is insignificant, and the buoyant anchorage is itself moored to an underwater bed by a lower mooring cable, the buoyancy of the buoyant anchorage together with that of any additional buoyancy members distributed along the lower mooring cable being greater than the apparent weight of the lower mooring cable. With this arrangement, the lower mooring cable tends to remain substantially vertical especially when nothing is moored to the mooring buoy, thereby reducing the range of drift of the latter.

The two mooring cables may be formed by upper and lower runs of a continuous length of cable (typically mooring chain).

Two embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figs. 1 and 2 are diagrammatic elevational views of two mooring arrangements in accordance with the invention.

In the mooring arrangement shown in Fig. 1, a mooring and buoy 1 carries a mooring point 2C for example of conventional crucifix form) which is connected to anchor blocks 3 (or other suitable sea bed anchorage) on the sea bed 4 by upper and lower runs 5, 6 of mooring chain. The upper run extends downwards from the anchorage 2 through the interior of the main floatation part 7 of the buoy 1, down through a tail portion 8 of the buoy 1 and on down to an anchorage float assembly 9 to emerge from the lower end of the latter as the lower run 6.

The buoyancy of the assembly 9 is chosen to be somewhat greater than the apparent weight of the total length of the lower run 6 so as to keep the latter taut and substantially vertical. The assembly 9 is situated at a level, such as about 30 metres below the surface 10 of the water, where the effects of tides and wave action are effectively negligible.

At least the upper run 5, over its length between the lower end of the mooring buoy tail 8 and the floatation assembly 9, is located in the interior of a flexible tubular hose 11. Typically, the hose 11 has an outer wall of runner or like material within which may be a tubular filling of foamed plastics material providing some buoyancy. The space within the inner wall of this hose (which may also be lined with a wall of rubber or like material) surrounding the mooring chain run 5 is in communication, for example through one or both ends of the hose, with the surrounding water to ensure pressure equalisation between the interior of the hose and the surrounding water.The upper end of the hose 11 is fixed to the tail 8 to ensure, in conjunction with the latter, that there is no risk of the hose and mooring chain getting sufficiently near the surface 10 for possible fouling of ships endevouring to moor to the buoy 1.

Similarly, the lower end of the hose 11 is preferably secured to the top surface of the buoyancy assembly 9 to prevent chafing on the upper surface of the buoy 9 under slack conditions such as low tide.

It can be seen from Fig. 1 that one advantage of the arrangement is that the anchorage point is effectively raised from the position of the anchor blocks 3 at a depth at say 120 metres or more to a depth of only say 30 metres. The lower run of the chain 6 remains taut and does not therefore require swivels. The upper run 5, which is normally slack when no vessel is moored to the buoy 1, again requires no swivels and is prevented from kinking by the hose 11.

In the modified arrangement shown in Fig. 2, the buoyancy assembly 9 is in effect distributed along the length of the lower run 6, in the form of smaller spaced buoyancy elements 1 9. Also, a different form of mooring buoy 21 is shown which may include an internal radar reflector 22 to assist vessels in finding the mooring buoy.

Suitable products for forming both the hose 11 and the buoyancies 9 and 19 are available under the Trade Mark RESINEX.

The mooring arrangements shown in the drawings may be used either singly as single point moorings, for example one on each side of an oil rig, or they may be used in pairs or greater multiples such that a vessel moors to two or more of the mooring buoys.

Claims (Filed 1 April 1982) 1. A mooring comprising a mooring buoy and a flexible mooring cable extending down from the buoy to an anchorage point, wherein the mooring cable is located within a length of flexible tubular

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Moorings The present invention relates to moorings. According to one aspect of the present invention there is provided a mooring comprising a mooring buoy and a flexible mooring cable extending down from the buoy to an anchorage point, wherein the mooring cable is located within a length of flexible tubular hose extending from the buoy to the anchorage point. Preferably the upper end of the hose is secured to the buoy with the hose-end axis substantially upright. The hose is chosen such that its natural torsion stiffness resists relative twisting between its ends, thereby avoiding kinks in the cable and the need for swivels in the cable. Localised flattening of the hose can be avoided by arranging the inner diameter of the hose to be not much greater than the envelope diameter of the cable, and, particularly in deeper water, by providing access for water to enter the hose, for example at one or both ends, so that local hydrostatic pressures over the inner and outer walls of the hose are equalised. The hose may be provided with buoyancy to counteract some of the weight of the cable. The cable may be normal mooring chain. According to another aspect of the invention there is provided a mooring comprising a mooring buoy and flexible mooring cable extending down from the buoy to a buoyant anchorage at a level at which water movement due to surface wave action and tides is insignificant, and the buoyant anchorage is itself moored to an underwater bed by a lower mooring cable, the buoyancy of the buoyant anchorage together with that of any additional buoyancy members distributed along the lower mooring cable being greater than the apparent weight of the lower mooring cable. With this arrangement, the lower mooring cable tends to remain substantially vertical especially when nothing is moored to the mooring buoy, thereby reducing the range of drift of the latter. The two mooring cables may be formed by upper and lower runs of a continuous length of cable (typically mooring chain). Two embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figs. 1 and 2 are diagrammatic elevational views of two mooring arrangements in accordance with the invention. In the mooring arrangement shown in Fig. 1, a mooring and buoy 1 carries a mooring point 2C for example of conventional crucifix form) which is connected to anchor blocks 3 (or other suitable sea bed anchorage) on the sea bed 4 by upper and lower runs 5, 6 of mooring chain. The upper run extends downwards from the anchorage 2 through the interior of the main floatation part 7 of the buoy 1, down through a tail portion 8 of the buoy 1 and on down to an anchorage float assembly 9 to emerge from the lower end of the latter as the lower run 6. The buoyancy of the assembly 9 is chosen to be somewhat greater than the apparent weight of the total length of the lower run 6 so as to keep the latter taut and substantially vertical. The assembly 9 is situated at a level, such as about 30 metres below the surface 10 of the water, where the effects of tides and wave action are effectively negligible. At least the upper run 5, over its length between the lower end of the mooring buoy tail 8 and the floatation assembly 9, is located in the interior of a flexible tubular hose 11. Typically, the hose 11 has an outer wall of runner or like material within which may be a tubular filling of foamed plastics material providing some buoyancy. The space within the inner wall of this hose (which may also be lined with a wall of rubber or like material) surrounding the mooring chain run 5 is in communication, for example through one or both ends of the hose, with the surrounding water to ensure pressure equalisation between the interior of the hose and the surrounding water.The upper end of the hose 11 is fixed to the tail 8 to ensure, in conjunction with the latter, that there is no risk of the hose and mooring chain getting sufficiently near the surface 10 for possible fouling of ships endevouring to moor to the buoy 1. Similarly, the lower end of the hose 11 is preferably secured to the top surface of the buoyancy assembly 9 to prevent chafing on the upper surface of the buoy 9 under slack conditions such as low tide. It can be seen from Fig. 1 that one advantage of the arrangement is that the anchorage point is effectively raised from the position of the anchor blocks 3 at a depth at say 120 metres or more to a depth of only say 30 metres. The lower run of the chain 6 remains taut and does not therefore require swivels. The upper run 5, which is normally slack when no vessel is moored to the buoy 1, again requires no swivels and is prevented from kinking by the hose 11. In the modified arrangement shown in Fig. 2, the buoyancy assembly 9 is in effect distributed along the length of the lower run 6, in the form of smaller spaced buoyancy elements 1 9. Also, a different form of mooring buoy 21 is shown which may include an internal radar reflector 22 to assist vessels in finding the mooring buoy. Suitable products for forming both the hose 11 and the buoyancies 9 and 19 are available under the Trade Mark RESINEX. The mooring arrangements shown in the drawings may be used either singly as single point moorings, for example one on each side of an oil rig, or they may be used in pairs or greater multiples such that a vessel moors to two or more of the mooring buoys. Claims (Filed 1 April 1982)

1. A mooring comprising a mooring buoy and a flexible mooring cable extending down from the buoy to an anchorage point, wherein the mooring cable is located within a length of flexible tubular hose extending from the buoy to the anchorage point.

2. A mooring comprising a mooring buoy and flexible mooring cable extending down from the buoy to a buoyant anchorage at a level at which water movement due to surface wave action and tides is insignificant, and the buoyant anchorage is itself moored to an underwater bed by a lower mooring cable, the buoyancy of the buoyant anchorage together with that of any additional buoyancy members distributed along the lower mooring cable being greater than the appararent weight of the lower mooring cable.

3. A mooring according to claim 2, wherein the two mooring cables are formed by upper and lower runs of a continuous length of cable.

4. A mooring according to claim 2 or 3, wherein the mooring cable is located with a length of flexible tubular hole extending from the buoy to the anchorage point.

5. A mooring according to claim 1 or 4, wherein the upper end of the hose is secured to the buoy with the hose-end axis substantially upright.

6. A mooring according to claim 1, 4 or 5, wherein the inner diameter of the hose is not much greater than the envelope diameter of the cable, and access is provided for water to enter the hose, so that local hydrostatic pressures over the inner and outer walls of the hose are equalised.

7. A mooring according to claim 1 or any of the claims 4 to 6, wherein the hose is provided with buoyancy to counteract some of the weight of the cable.

8. A mooring according to any of the preceding claims, wherein the cable is normal mooring chain.

9. A mooring substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the drawings.