GB2220900A

GB2220900A - Vessel mooring system having chain between vessel and chain table

Info

Publication number: GB2220900A
Application number: GB8814065A
Authority: GB
Inventors: E Lindsey Meadows; H E Anderson
Original assignee: HOULDER OFFSHORE ENGINEERING; NORTH SEA TERMINALS Ltd
Current assignee: HOULDER OFFSHORE ENGINEERING; NORTH SEA TERMINALS Ltd
Priority date: 1988-06-14
Filing date: 1988-06-14
Publication date: 1990-01-24
Also published as: GB8814065D0

Abstract

A mooring system for a vessel comprises a chain table 31 secured below a vessel 11 from which a plurality of lines 32 extend to anchoring points on the sea bed, the vessel being formed with a vertical hollow shaft 21 through which a chain 17 extends from a fixing point on the vessel to the chain table 31. <IMAGE>

Description

VESSEL MOORING SYSTEM Vessels moored in the open sea should be able to move about their mooring position in order to align themselves with prevailing winds - this is known as weathervaning. In order that the vessel can change its alignment by rotation about this single portion, it has been proposed that the mooring line should have at least one portion which is single.

In one known mooring system, the single portion is a rigid member, secured at its lower end at a table to a plurality, such as eight, of cables fanning out over the sea bed to anchoring points. The vessel is formed with a vertical hollow shaft, which contains a second rigid member,' connected to the top of the first rigid member by a swivel joint. Pipes leading from oil sources on the sea bed enter the vessel through the second rigid member. This arrangement is hard to adjust because adjustment requires the rigid menbers to be withdrawn and new ones of a different length substituted.

According to the present invention, adjustment is easier because it does not use the two rigid members between the table and the fixing point on the vessel. The present invention provides a mooring system for a vessel comprising a chain table secured below the vessel from which a plurality of lines extend to anchoring points on the sea bed, the vessel being formed with a vertical hollow shaft through which a chain extends from a fixing point on the vessel to the chain table. Preferably pipes from oil sources on the sea bed are connected to the vessel by passing up the shaft independently of the chain, and preferably in small groups. such as groups of three.

The system is readily adjustable by raising or lowering the chain, any surplus chain being easily storable on the vessel for example within a locker within the vertical hollow shaft.

Lifting the chain will increase the chain tension, raising the chain table accordingly.

The pipes can pass from the oil sources to a gravity point Can anchoring point) on the sea bed and thence to the vessel; they can be provided with buoys intermediate the gravity point and the vessel in order to provide loops which can accommodate sea currents and movement of the vessel without unduly stressing the pipes which might occur if they were tightly stretched between their ends.

An example of the invention will now bed decribed with reference to accompanying drawings, in which Figure 1 is a side elevation of the hull of a vessel moored over the sea bed, and Figure 2 is a vertical cross section through the turret of the vessel of Figure 1.

The vessel 11 has a turret 12 lining a vertical hollow shaft 13 extending through the whole height of the hull. The turret is rotatable about the axis of the shaft and has radial bearings 14 at the top and bottom of its body and a vertical bearing 15 on an upper flange 16 which retains the turret and transfers the vertical loads, from both the mooring system and the oil pipes, to the vessel. In this embodiment, the turret is about 10 metres in diameter, to accommodate the mooring chain 17 and the desired number of pipes 18.

The turret 12 is formed with a plurality of vertical passages which have flared lower ends to accomodate the change in direction of the member extending therefrom; one passage 21 is for a mooring chain 17 which is secured in position at the top of the turret. The turret is formed with a locker 22 adjacent the passage 21 for storage of surplus chain. The lower end of the mooring chain is secured to a chain table 31, from which cables 32 extend to a plurality of anchoring points on the sea bed. The other passages 23, of which only one is shown in Figure 2, contain the pipes 18 from the oil sources. These pass singly or in groups of three to a quick connect and disconnect (QCDC) joint 24 at the top of the passages 23, from which the pipes pass to a swivel distribution joint, which is the subject of our co-pending application (Ref P 11070 > .

Three channels is the greatest number usually available in a multi-channel QCDC unit. QCDC units are used, to allow a ship to cast off all its connecting lines in an emergency. The pipes in a group remain together below the hull, being suspended in an arch 33 by a buoy 34 to allow for changes in position of the hull relative to the sea bed, and being connected to a single anchoring point 35 on the sea bed. From the anchoring point 35, the pipes 18 extend individually to their respective oil sources.

It will be seen that the mooring chain 17 and the pipes 18 are kept independent, by passing up the turret in separate passages.

Figure 1 shows the vessel in three different positions. It only has one turret, and only one chain and one pipe group are shown descending from the hull. The central position A is that the vessel would take up if no wind, wave or current force were acting on the vessel. The positions B,C on either side of the mid position demonstrate the positions the vessel would take up when wind, wave and current forces were acting on the vessel from either left or right of the figure. In the latter cases the chain tensions will increase, tending to raise the chain table. It will be seen that the chain table 31 moves in the same direction as the vessel, although to a smaller degree.

The position of the turret 12 remains independent of the direction in which the ship lies, the motorised turret being turned in the hull as the hull turns relative to the sea bed.

The mooring chain 17 and the pipes 18 do not therefore twist or come into contact at any time.

Claims

CLAIMS:

1. A mooring system for a vessel comprising a chain table secured below a vessel from which a plurality of lines extend to anchoring points on the sea bed, the vessel being formed with a 5 vertical hollow shaft through which a chain extends from a fixing point on the vessel to the chain table.

2. A system as claimed in Claim 1 wherein pipes from oil sources on the sea bed are connected to the vessel by passing up the shaft independently of the chain.

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3. A system as claimed in Claim 2 wherein said pipes pass up the shaft in groups.

4. A system as claimed in Claim 3 wherein each group comprises three pipes.

A A mooring system substantially as herein described with 15 reference to the accompanying drawings.