Anchor-line laying device and operating method

Abstract: This invention concerns a line-laying device (10) used for platform mooring systems, consisting of two pairs of claws (11, 12) with twin hooks, swivelling about a spindle (13), one (12) of which claws is solid (at 18) where it swivels upon the spindle and is provided with a shoulder (19) engaged by a spring biased latch (20) provided with a small wheel (22) at its free end and mounted on said claw (11) by means of a spindle (23), said one claw (11) also being provided with a stop (24) to limit travel of said latch and with a ring (25) to which the cable to be dealt with is tied. This invention also covers a method of operating said line-laying device.

Description: This invention concerns a line-laying device used in a platform mooring system, and also its operating method. The device is useful in lowering the chain part of a line into the sea, down to the sag level of the line since, owing to the great weight involved, failure to use it might lead to damage to not only the platform but also the line itself, while use of the device can prevent any slipping or drop of the line after each platform chain has been fastened to the previously laid line. US-A-3967572 discloses a platform mooring system which needs a line-laying device because, as the platform approaches the vessel which holds the line that has been laid beforehand, an end of the chain (from the platform) is transferred to the vessel. By means of an auxiliary winch the vessel locates the transferred chain and holds it down on the deck of the vessel, and then fastens it to the chain of such previously laid line. After being fastened, the line must be lowered into the sea down to its sag level, without slipping or falling. US-A-3967572 also discloses a chain stopper for clamping one link of a chain. Our EP-A2-0438258 discloses an improved chain laying device which consists of a support, and a sheave with a crown and fixed to such support by a spindle, there being slots in the flanges at the side of the crown which act as guides for breakable ropes, which are fixed in the following way: at one end, to a central common lug kept off by a guide mounted on the spindle, and at the other end, to individual turn-buckles which enable the links of a chain to be fastened to the crown at different angles. Thus, as the line is lowered down to its sag level, the chain around the crown tends to reduce its wrap angle and initially this pushes away from the crown the links on the topmost side of the sag. Thus, when the last breakable rope breaks the line will be practically at its sag level and any sliding or slipping of the laying device will not harm the platform or the winch in any way. However, in spite of the fact that the improved laying device referred to above is extremely efficient, there is a need for a laying device which is less rugged but more in keeping with the kind of handling available on conventional craft dealing with anchors. Accordingly, the device of this invention is defined in claim 1. The method of the present invention is defined in claim 2. In order that the present invention may more readily be understood the following description is given, merely by way of example, with reference to the accompanying drawings, in which:- FIGURE 1 is a front, partly sectioned, view of the line-laying device of this invention; and FIGURE 2 is a side perspective view of the line-laying device shown in Figure 1. The invention consists of a line-laying device 10 made up of two claw members, 11, 12 each having twin hooks, and pivoting relative to one another on a spindle 13. The claw member 12 is solid at part 18 where it swivels on the spindle 13 and it has a shoulder 19 against which a latch 20 is biased by a spring 21. This latch 20 is mounted on the claw 11 by means of spindle 23 and is fitted with a small wheel 22 at its end. The claw 11 is also fitted with a stop 24 to limit travel of the latch 20, and with a ring 25 to which an associated cable is fastened. The line-laying device employed for the mooring of platforms has the twin hooks of its two claws 11 and 12 able to grip the outside of link 14 by its ends. The claws 11 and 12 are such that the forward link 15 and the next link 16 following upon the gripped link 14 of the chain lie in between the spaced hooks and are free to turn about the end parts 17 of the link 14. This method of operating the line-laying device 10 is as follows:- firstly, for operating the line-laying device, fasten a cable to a winch on the line-laying vessel, by means of the ring 25, and put the line-laying device 10 on to a chain link 14, between a part locked on deck and a free end of the chain; latch 20, biased by the spring 21 automatically fits against shoulder 19 when the claws 11 and 12 close on the link 14, and holds the claws 11, 12 engaged on the link 14; after thus fastening the mooring line and the laying device 10, the mooring line is pulled to release the deck locks and allow the lowering operation to begin, controlling the lowering rate by the pull on the supporting cable attached to ring 25, and go on down to the sag level of the chain; during lowering, the claws 11, 12 will close around the link 14, due to the weight of the chain acting upon claw 12 and the pull exerted by the supporting cable through the ring 25; when the chain ceases to fall vertically after having first of all hung from the laying device 10, the laying device 10 unlocks, as a result of the cable now adjusting itself to the sag of the chain so that the forward link 15 turns about upper end part 17 of the gripped link 14 until it contacts and lifts the small wheel 22 of the latch 20; the latch 20 lifts as the link 15 continues to turn, and releases itself from the shoulder 19 until it gets to shoulder 24 whereupon unlatching is complete; and the claw 11, which had been pulled upwardly by the link 15, lifts and the chain is released after its sag level has been reached, because of transfer of the weight of the travelling chain run between the platform and the link 15, to the platform, thereby relieving the ring 25 from its supporting task. As can be seen from Figure 2, the link 15 lies in the run of the chain coming from the platform, and the link 16 lies in the run to the end at which the previously laid line is fastened. The chain from the platform is held on the deck of the line-laying craft, and a certain number of links (at the tail end) are left free, behind the place where the chain is held down, for the purpose of fastening to the previously laid line. During the lowering, the weight acting upon the claw 12 and the pull exerted by the holding cable through the ring 25, create forces that tend to close the claws 11 and 12 about the link 14, thereby reducing the force acting upon latch 20, which happens all the more as the weight supported by the device 10, acting on claw 11, is gradually transferred to the platform as the link sinks lower. Unlocking occurs when the chain, which was originally hanging from device 10 along with the cable, starts to shift away from its vertical position in following the sag of the chain, and the link 15 turns the link 14 as described above. As lowering proceeds from this point, the link 15 begins to press against the stop 24 and tends to lift up (open) the claw 11 resisted by the weight that acts upon the claw 12 and the holding force exerted by the device 10, at ring 25. Upon getting down to the sag level, the weight of the chain acting upon link 16 is transferred to the platform, thus relieving the holding force at ring 25 and therefore enabling claw 11 which had been pulled by link 15 to lift and release the chain.

Claims: A chain-stopper device (10) for laying platform mooring systems, consisting of means for clamping a chain link, characterised in that said clamping means comprise two claws (11, 12) each having two hooks and relatively pivotable about a spindle (13), one said claw being solid at the part (18) where it swivels on said spindle and being fitted with a shoulder (19) engaged by a latch (20) biased by a spring (21) said latch (20) being provided with a small wheel (22) at its end and being mounted on one said claw (11) by means of spindle (23), and wherein the other said claw is also fitted with a stop (24) to limit the travel of said latch and with a ring (25) to which the cable to be dealt with can be fastened; wherein said claws (11, 12) are so arranged that they grip the outside of a chain link (14) by its ends, and that the forward link (15) and next the successive link (16) to said clamped link (14) of the chain lie within the claws (11 and 12) and are free to turn about parts (17) at the ends of said clamped link. A method of laying a line using a chain-stopper device according to claim 1, including the steps of securing a link (14) of a chain to the chain stopper device (10); paying out a winch cable from a craft; and fastening said winch cable to the chain; characterised by the steps of fastening the winch cable to the chain by fastening the winch cable to the chain-stopper device (10) by means of said ring (25) of the chain-stopper device (10), the link (14) of said chain being between locks on the deck of the craft and the free end of the chain; automatically fitting said spring biased latch on said abutment shoulder (19), so that the claws close upon the link; after fastening, pulling the mooring line with the aid of said laying device, thus enabling the deck locks to be released and allowing the lowering operation down to the sag level of the line to begin; closing the claws (11, 12) of the laying device about the chain link during lowering, due to forces arising from the weight exerted upon the claw (12) and the pull exerted by the winch cable at the ring (25); unlocking the laying device as the chain shifts away from the vertical position, after having initially hung from the laying device together with the winch cable, to follow the sag of the chain, while the forward link (15) turns about the upper end part (17) of the clamped link (14), until it contacts the small wheel (22) of the latch; raising the latch by the action of the forward link (15) continuing to turn, and releasing from said shoulder (19) and eventually engaging said stop (24), so completing the unlocking; and after having arrived at the sag level, lifting the claw (11) which had been pressed upon by the clamped link (14), to free the chain because of the transfer of the weight of the chain bearing upon link (14) to the platform, thereby relieving the holding force of the ring (25).

Inventors: FUJITA TOKUME, FUJITA, TOKUME
Applicants: PETROLEO BRASILEIRO SA, PETROLEO BRASILEIRO S.A. - PETROBRAS
Application year: 1991
Main classification: B63B21
IPC codes: F16B45, F16G15, B63B21