Ships – Mooring device – Having ship-mounted turret
Reexamination Certificate
2000-08-16
2001-11-13
Basinger, Sherman (Department: 3617)
Ships
Mooring device
Having ship-mounted turret
C114S293000
Reexamination Certificate
active
06314901
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for mooring a ship, in the open sea, especially an oil/gas production ship positioned above a submarine well, comprising three or more mooring chains/anchor lines extending from a turret disposed within the ship to anchors/anchoring points on the seabed.
Likewise, the invention relates to a mooring arrangement based on the use of said three or more mooring chains/anchor lines, and aims at achieving considerable simplifications and improvements in or indirectly relating to said turret, said simplifications manifesting themselves in significant savings, both economical and operational upon the establishment of the mooring.
Said turret has been disposed in association with a vertically through-going cavity in the ship, said cavity being formed i.a. for passage of a production riser string and/or other production accessory and, possibly, for the accommodation and temporarily attachment of a so-called STL buoy. The turret which has a substantially vertical axis, is freely rotatably mounted in the ship, for relative turning around said axis, so that the ship may turn dependent on wind and current conditions about the axis of the turret. The turret will be equipped with at least one pipeline portion which is connected to an underlying portion and which, uppermost, through a swivel device, is connected to a pipeline connected to the ship and may lead to its storage room for oil.
It is previously known to moor such a production ship to the seabed, so that it may turn about the axis of the turret.
First, according to previously known technique of this kind, e.g. eight anchor lines in the form of mooring chains or wires are positioned on the seabed and attached thereto through anchors or through other fastening by means of piles or the like, in order to, thereupon, to be drawn up via the free end portion through the turret. In known turrets of this kind, lowermost in the turret, is for each mooring chain disposed a rotary guide pulley which, normally, will be situated below the sea surface and, therefore, represents a considerable maintenance problem. For each anchor line, besides the guide pulley, at a higher situated level, a separate winch has been disposed, i.e. totally eight individual winches, each with a guide pulley assigned thereto. The winches serves to stretch and tension the individual mooring chain associated therewith, and these chains are locked in the tightened condition thereof.
This known mooring arrangement is expensive in purchase and operation, and it is relatively awkward in use.
SUMMARY OF THE INVENTION
The object of the invention has primarily been to simplify the mooring arrangement purely constructively and also such that the necessary number of mooring chains/anchor lines may be brought into active, stretched, tensioned and locked condition in a way only implying winch-based tightening of some of the mooring chains/anchor lines.
For the method, said object has been realized by proceeding in accordance with the steps/operations as defined in the claims.
The mooring arrangement distinguishes itself through con
5
structive detail features as appearing from the following claims.
When one is in the process of mooring a production ship to the seabed through the turret of the ship, so that the ship will become positioned substantially on the upward vertical projection of an underlying production well, the mooring chains have been placed on the seabed beforehand as well as anchored thereto at their one ends, the mooring chains/anchor lines having such a length that they in stretched, tightened, tensioned and locked condition will centre the turret and, thus, the ship above the production well.
According to the present invention, the turret, preferably at a lower portion, is equipped with hooks or other fasteners or attachment means for half the number of mooring chains of the total number, i.e. four hooks/fasteners in the exemplary case concerned. If in all three mooring chains are used only, one or two of these chains may be assigned thereto a fixed attachment means.
In conformity with the method according to the invention, each of these so-called ‘fixed’ anchor lines, possibly after the turret has been raised somewhat by means of a hoisting means so that the hooks/fasteners are exposed, is attached to a hook/fastener, whereupon the turret possibly can be lowered, each of the remaining mooring chains, as known per se, thereupon being connected with the winch belonging thereto, to carry out the final stretching/tensioning. When the mooring chains each tightened by means of its own winch are taut, the production ship is correctly positioned, simultaneously as the mooring arrangement then is correctly biased.
Upon the tightening of the “movable” anchor lines by means of a separate winch for each line, or by means of one common, displaceable winch, the stretching operations are made diametrically in relation to the opposedly positioned “fixed” anchor line.
In the method and in the mooring arrangement according to the invention, the mooring chains not assigned any winch beforehand, are allotted a fixed length between the anchoring point on the seabed and the turret. The remaining mooring chains assigned a winch have a changeable length. The last-mentioned mooring chains will have a length which will be oversized in relation to the active length, the respective winch being adapted to accommodate surplus chain length in the final position thereof. These anchor lines having adjustable length are each tightened and tensioned by means of the winches until also the anchor lines having fixed length are correctly stretched. Thereupon, the anchor lines can be locked as known per se, e.g. by means of locking devices carried by the turret.
REFERENCES:
patent: 3191201 (1965-06-01), Richardson et al.
patent: 3583354 (1971-06-01), Flickinger
patent: 3774562 (1973-11-01), Dean, III
patent: 4566398 (1986-01-01), Sasaki et al.
patent: 5359957 (1994-11-01), Asketsad
patent: 5381750 (1995-01-01), Pollack
patent: 60-146787 (1985-08-01), None
patent: 86/02329 (1986-04-01), None
patent: 96/26861 (1996-09-01), None
Andrus Sceales Starke & Sawall LLP
Basinger Sherman
Hitec Systems AS
LandOfFree
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