GB2174055A - Anchor chaser - Google Patents

Abstract

A chaser device, which may be used for deployment of an anchor of a water-borne vessel such as a sea-going ship or drilling rig, in the form of a continuous closed metal loop 5 having attachment means 6 on the outside edge of the loop and also having a pivoted section 10 having a portion 9 of reduced cross-section. The chaser device may be moved along a mooring cable without excessive frictional wear and may be retained adjacent to the vessel itself when the anchor is mooring the vessel. <IMAGE>

Description

SPECIFICATION Device for the deployment and recovery of anchors The present invention is a device for the deployment and recovery of anchors of water-borne vessels, especially of large vessels such as sea-going ships and in particular drilling rigs and platforms. It is of the type of devices known as "chasers", which can be irremovably or detachably fitted around an anchor cable to afford manipulative assistance in the processes of deploying and recovering anchors.

Chasers of known type are generally formed as a closed loop of such dimensions as to fit easily around the anchor mooring cable and to be a sliding fit thereon. When the anchor is in position, the chaser may be left in situ adjacent to the anchor, with its position marked at the surface by a buoy to which it is linked by a suitable operating cable.

When it is desired to move the anchor to a new position, the anchor and mooring cable are lifted by means of the chaser and its associated operating cable. Thus each chaser requires a buoy to mark its position and permit its retrieval. It would be convenient to remove the chaser to a position adjacent to or upon the vessel itself when the chaser is not in active use but that would entail passing the chaser along the full length of the mooring cable. Since the mooring cable is usually a steel wire rope, often in combination with steel chain, the resultant frictional wear on the chaser is considerable and therefore conventional chasers are not used in this way.

It is an object of the present invention to provide an improved chaser, which is less susceptible to wear in use and therefore allows the adoption of modified operating procedures.

The device according to the present invention for the deployment and recovery of anchors comprises a continuous closed metal loop having attachment means on the outside edge of the loop and also having a section of said loop pivoted within or substantially within the profile of the loop, which section has within its axial length a portion of reduced cross-section.

The continuous closed metal loop may be generally circular or preferably oval in elevation but it is particularly preferred that it be tapered towards one end of the loop, thus being generally pearshaped in appearance. When the loop is oval in shape, the attachment means and the pivoted section are preferably disposed at opposite narrow ends of the oval loop. When the loop is pearshaped, it is preferred to locate the attachment means at the narrower end and the pivoted section at the wider end of the loop.

The attachment means affords a facility for attaching to the loop a wire or chain by means of which the chaser device is manipulated so as to control in turn the movement of the mooring cable and the anchor. To this end, the attachment means may conveniently be an attachment eye, for example an upstanding, apertured flange forming a padeye designed to accept the pin of a shackle to which the operating wire or chain is attached.

A key feature of the chaser device according to the present invention is the pivoted section of the loop. As indicated above, this section is pivoted within or substantially within the profile of the loop. Thus the pivot may be displaced by a small amount laterally from the continuous profile of the loop but, in a preferred form of the invention, the pivot lies within the loop profile.

The pivoted section may be generally cylindrical and pivoted to rotate about its axis, a portion of its axial length being of reduced cross-section. It is strongly preferred that the pivoted section be smoothly curved from its widest cross-sectional dimension towards the portion of reduced cross-section. The latter portion may be of circular crosssection but in a preferred form of the invention the reduction in cross-section is greater at one or more parts of its circumference, for example in the form of transverse recesses or grooves at opposite sides of its circumference. In a particularly preferred form, the pivoted section is generally cylindrical and the portion of reduced cross-section has an oval cross-section.

The pivot for the pivoted section may advantageously be a removable bolt. Thus by removal of the bolt the pivoted section may in turn be separated from the loop so as to open the loop and assist its initial installation around the mooring cable or its susbsequent removal therefrom. The bolt may engage an internally-threaded socket in the loop but is more preferably retained in place by a nut engaging its free end. In a less preferred form of the invention, the pivoted section is pivoted upon a fixed pin, welded in place, or upon a bolt secured by shrink-fitting in a socket in the loop.

As already explained above, one important advantage of the device according to the present invention is that frictional wear in normal use is reduced. A further advantage is that, if such wear has taken place to an extent rendering the device unsuitable for further use, the wear will normally have been confined to, or largely confined to, the pivoted section, which latter may be replaced so as to restore the chaser to a fully usable condition.

The present invention will now be further described with reference to the accompanying drawings, wherein: Figure 1 is a view in elevation of a first embodiment of the chaser device according to the present invention; Figure 2 is a sectional view of the device of Figure 1; Figure 3 is a view in elevation of a second embodiment of the chaser device according to the invention; and Figure 4 is a sectional view of the device of Figure 3.

The chaser shown in Figures 1 and 2 comprises a chaser body 5, which may be a steel or iron casting or a steel forging or a welded fabrication of steel components. The body 5 is, as shown, generally pear-shaped and has an upstanding apertured extension forming a pad-eye 6 which can accept the securing pin of a shackle (not shown) to which an operating wire or chain is attached.

At its wider end, the chaser body 5 is provided with two opposed flanges 7, 7 on opposite sides of its centre line. Between these flanges a rocker 8 is pivoted. The rocker 8 is slightly shorter than the distance between the flanges 7, 7 to afford at its ends a working clearance ailowing ready pivoting of the rocker. The rocker is a casting or a forging in steel, iron or a non-ferrous metal alloy. In end elevation it is circular but, intermediate its ends, it has a narrowed portion 9 of oval cross-section forming, in effect, a pair of opposed grooves 10, 10.

The pivot for the rocker 8 is formed by a steel bolt 11 having an unthreaded plain cylindrical central portion and threaded at its end remote from its head to engage a nut 12. The nut 12 may be square, hexagonal or round and may be of steel or non-ferrous metal alloy. Beyond the threaded portion of the bolt 11, adjacent to its end, a transverse bore is drilled to receive a locking pin 13. The pin 13 is of steel or non-ferrous metal alloy and may be a solid pin or a split cotter pin. Its function is to retain the nut 12 upon the bolt 11.

The chaser device 15 shown in Figures 3 and 4 has many similarities to the above-described chaser but differs in that its profile is modified to enable a rocker 14 to be located within the profile of the chaser. The rocker 14 is pivoted upon a bolt 16, secured by a nut 17, both the head of the bolt and the nut being disposed in recesses 18 in the chaser body. This form of chaser has the advantage of a smoother profile, free of projections corresponding to the flanges 7 and therefore less liable to foul the mooring cable or the anchor chain.

The illustrated chaser devices are assembled around the mooring cable of a sea-going vessel such as a drilling rig and remain in place around the cable throughout the use of the cable. The chaser is attached to an operating wire or chain by the eye 6 and the other end of the wire is secured to the deck of the vessel during passage of the vessel, the anchor of course being stowed at the vessel. When the vessel arrives at its mooring position, the operating wire is transferred to a support vessel and secured to the winch wire of that vessel.

The support vessel, using the chaser as a towing collar, tows the anchor to its intended dropping point and then lowers the anchor to the sea bed.

The anchor cable is now tensioned by the winch on the vessel being moored and then the chaser is taken back along the mooring cable by the support vessel, the operating wire being transferred back to the deck of the vessel being moored.

When the moored vessel is required to move away from the moored position, the operating wire or chain is passed to the support vessel and the chaser is towed along the mooring cable and into contact with the embedded anchor. The anchor is raised by the winch on the support vessel and the mooring cable, anchor and chaser are returned to the vessel to be moved and the operating wire or chain re-secured to the deck of that vessel.

Claims (10)

1. A device for deployment and recovery of an anchor, comprising a continuous closed metal loop having attachment means on the outside edge of the loop and also having a section of said loop pivoted within or substantially within the profile of the loop, which section has within its axial length a portion of reduced cross-section.

2. A device as claimed in claim 1, wherein said closed metal loop is oval or tapered.

3. A device as claimed in claim 2, wherein said closed metal loop is generally pear-shaped.

4. A device as claimed in claim 2, wherein the attachment means and the pivoted section are at opposite ends of the loop.

5. A device as claimed in claim 3, wherein the attachment means is at the narrower end and the pivoted section at the wider end of said generally pear-shaped loop.

6. A device as claimed in any of the preceding claims, wherein the pivoted section is mounted between flanges extending from the loop.

7. A device as claimed in any of the preceding claims, wherein the pivoted section is generally cylindrical and pivoted to rotate about its axis, a portion of its length being of reduced cross-section.

8. A device as claimed in claim 7, wherein the portion of reduced cross-section is of oval crosssection.

9. A device as claimed in any of the preceding claims, wherein the pivoted section is pivoted upon a removable bolt.

10. A device for deployment and recovery of an anchor, which device is substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.