US3803942A

US3803942A - Pawls

Info

Publication number: US3803942A
Application number: US00279657A
Authority: US
Inventors: J Duggan
Original assignee: Drexel Equipment UK Ltd
Current assignee: National Oilwell Varco UK Ltd
Priority date: 1971-08-10
Filing date: 1972-08-09
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16
Also published as: JPS4827486A; NO134978B; NO134978C; DE2239183A1; GB1367358A; FR2148606A1; FR2148606B1; NL7210899A

Abstract

A collapsible pawl applied to emergency release of a mooring chain or cable of a ship or rig acts either directly on a chain guided over a bowstopper or wildcat, or indirectly, via a toothed ring, on a chain or cable extending around a wildcat, winch, or windlass. The pawl has two parts arranged one after the other therealong and articulated to each other by a toggle and also by two lateral links. The toggle is operated by a hydraulic ram connected to a central pin of the toggle. To collapse the pawl to release the chain or cable, the toggle is operated to cause the two pawl parts to turn about transverse axes.

Description

nit etl States Patent I191 Duggan Apr. 16, 19M

[54] PAWLS 1,226,731 5/1917 Wheeler 114/200 [75] Inventor: James Daniel Duggan, London,

England Primary Examiner-Benjamin W. Wyche [73] Assignee: Drexel Equipment (U.K.) Limited, Amstam Exammer F Shoemaker London, England; a part interest Attorney, Agent, or FirmEric H. Waters [22] Filed: Aug. 9, 1972 21 Appl. No.: 279,657 [57] ABSTRACT a A collapsible pawl applied to emergency release of a [30] Foreign Application Priority Data mooring chain or cable of a ship or rig acts either di' Au 10 1971 Great Britain 3759 1/7 1 rectly on a chain guided over a bowstopper or wildcat, or indirectly, via a toothed ring, on a chain or cable extending around a wildcat, winch, or Windlass. The [52] Cl 74/577 2 i a? pawl has two parts arranged one after the other there- [511 Int Cl Fl6d 41/12 along and articulated to each other by a toggle and [58] Fieid 577 R 520 also by two lateral links. The toggle is operated by a I hydraulic ram connected to a central pin of the toggle. 226/147 254/150 1 Ill/I99 200 To collapse the pawl to release the chain or cable, the [56] References Cited toggle is operated to cause the two pawl parts to turn UNITED S S PATENTS about transverse axes.

3.l44,776 8/1964 Minke.... 74/520 X 13 Claims, 11 Drawing Figures Z6 F J l Z5 29 O 15a r "F w 4 l 3/ L2 I I F"- v PATENTEUAPR 16 1974 SHEET 5 OF 7 PEG] PAWLS BACKGROUND OF THE. INVENTION 1. Field ofthe Invention This invention relates to a collapsible pawl. The pawl is particularly applicable to emergency release of mooring chains or cables of ships and marine figs.

2. Description of the Prior Art Onships and marine rigs, it is known to prevent additional paying-out of mooring chains or cables by equipping chainstoppers, Wildcats, winches and windlasses with pawls which act either directly on the chains at the chainstopper or Wildcats, or indirectly, via toothed rings, on the chains or cables at the winches or wind lasses. I

Under normal circumstances, when it is desired to heave in the chains or cables, these pawls are simply released and the winches or windlasses heave in the chains or cables.

Experience has shown that emergency situations can arise requiring immediate release of the moorings. For example, when there is a well blow-out, a marine rig may need to move immediately from the well location. In a case where the blow-out has ignited or has caused the sea to reduce in density so that the rig tends to sink, the speed with which the rig is moved maybe a vital factor in averting a disaster. In certain of-these situations, it has proved impossible to release the moorings. For example, a storm has created a tension in the chains or cables greater than the pulling capacity of the winches or windlasses, so that the winches or windlasses cannot even heave in the chains or cables to the smallextent required to allow release of the pawls.

SUMMARY OF THE INVENTION According to the present invention, there is provided a collapsible pawl, comprising first'and second parts which extend one after the other along the longitudinal axis of the pawl and which are articulated to each other so as to be able to turn about axes transverse to said longitudinal axis, and means displaceable between a first condition in which said means prevents said parts from turning about said axes under the action of a compressive force along said longitudinal axis and thus prevents collapse of said pawl by said force and a second condition in which said means does not prevent said parts from turning about said axesunder the action of said force. i

The invention has the advantage that, by equipping a chainstopper, wildcat, winch or windlass on board a ship or marine rig with the present pawl, it is'possible to provide simply and cheaply for immediate release of a chain or cable in any emergency situation.

' BRIEF DESCRIPTION OF THE DRAWING FIG. 4 shows a perspective view of another part of the pawl,

FIG. 5 shows a plan view of a first toggle link of the pawl,

FIG. 6 shows a side elevation of the first toggle link,

FIG. 7 shows a plan view of a second toggle link of the pawl,

FIG. 8 shows a side elevation of the second toggle link,

FIG. 9 shows a diagrammatic sectional side elevation of a wildcat equipped with the collapsible pawl,

FIG. 10 shows a diagrammatic sectional side elevation of a modified version of the wildcat of FIG. 9, and

FIG. 11 shows a diagrammatic sectional side elevation of a windlass equipped with the collapsible pawl.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 to 8 of the drawings, the bowstopper serves to carry the tension in an anchor chain 1 of which the left-hand end in FIG. I is connected to a which and the right-hand end to the anchor. The bowstopper includes two side plates (of which one is seen and referenced 2) between which is pivotally mounted a lever 3 to which is fixed a guide channel 4 for the chain 1. One arm of the lever 3 has at its outer end a load cell 5 which is used to indicate the tension in the portion of the chain 1 between the bowstopper and the anchor, while the other arm of the lever 3 has pivotally mounted thereon at its outer end the pawl 6 which stops movement of the chain 1 through the bowstopper towards the anchor. An arm 7 fixed to the pawl 6 is used to swing the pawl upwardly into an inoperative position when it is desired to pay out the chain 1.

I Under certain circumstances, for example in stormy conditions, the tension in the portion of the chain 1 between the bowstopper and the anchor may increase above the pulling capacity of the winch, so that the winch is unable to draw in the chain sufficiently for the pawl 6 to be released by means of the arm 7. To cope with such circumstances, the pawl 6 is made collapsible. For this reason, it consists of two

parts

8 and 9 which extend one after theother along the longitudinal axis ll of the pawl. The

parts

8 and 9 are articulated to each other by means of lateral lines 12 which are connected to the

parts

8 and 9 by means of horizontal pins 13 which have their axes l4 transverse to the axis 11. The

parts

8 and 9 are formed in the underneath of their inner ends with recesses I5 and 16 which receive

toggle links

17 and 18 which are pivotally mounted at their outer ends on

pins

19 and 20 provided in

slots

21 and 22 in the

parts

8 and 9, and are pivotally connected at their inner ends to a common pin 23. The slots 2I and 22 have their axes of elongation extending parallel to the protruding top surface and 16a of the

recesses

15 and 16. The pin 23 is received in an eye 24 of a piston rod 25 connected to a piston 26 reciprocable in a hydraulic cylinder 27. The piston rod 25 extends in a bore 28 provided fractionally in the part 8 and fractionally in the part 9. The top of the part 8 has a projecting lip 29 which enters a recess 30 in the top of the part 9. The cylinder 27 rests freely on a surface portion of the part 8 in this region. The items 17 to 24 form a toggle which is movable through a dead-centre position in which the axes of the

horizontal pins

19, 20 and 23 are co-planar. In the position shown in FIG. 2, the axis of the pin 23 is just below the common plane, but is prevented from moving downwards because the piston 26 is at the lower end of its stroke in the cylinder 27. Thus the toggle prevents the

pawl parts

8 and 9 from hinging about a horizontal axis 31, which is the apex of meeting of the recesses and 16 and extends above the axis 11, under the action of compressive force applied along the axis 11. Thereby, collapsing of the pawl under the action of such force is prevented. However, when it is desired to collapse the pawl, the cylinder 27 is fed with hydraulic fluid to lift the piston 26 and thus to lift the axis of the pin 23 to above the plane containing the axes of the

pins

19 and 20. The pawl does not yet collapse however, because the abutting inner end faces of the

parts

8 and 9 are in compression against each other and because the

slots

21 and 22 allow a limited amount of movement of the pins 19 and therealong until the

pins

19 and 20 reach the inner ends of the slots. Thereupon, continued lifting of the pin 23 by the piston 26 begins to turn the

parts

8 and 9 anticlockwise, and clockwise, respectively, in FIG. 2 until the compressive force along the axis 11 acts to jack-knife the pawl 6. J ack-knifing of the pawl 6 suddenly lifts the piston rod and thus lifts the cylinder 27 off the part 8. The collapsed pawl swings clockwise until it is captured by a spring-loaded plunger (not shown) which prevents the pawl from rebounding back onto the chain 1.

The collapsible pawl 6 is also applicable to a wildcat, as shown in FIG. 9, wherein the anchor chain 1 extending over the wildcat 40 is prevented from moving to the right by the pawl 6. A hydraulic piston-and-cylinder device 41 serves the same purpose as the arm 7 in FIG. 1.

In the version shown in FIG. 10, instead of the pawl 6 acting directly on the chain 1, which might damage the chain links, the pawl acts indirectly thereon via the teeth of a ratchet wheel 42 fixed co-axially to the wildcat 40.

FIG. 11 shows the pawl 6 applied to a windlass 43 over which extends the chain 1. The windlass 43 includes a driving pinion 44 which meshes with a ring of teeth 45 on the windlass wildcat. The pawl 6 has teeth 46 at its free end for engaging with the teeth 45 to prevent rotation of the windlass wildcat.

I claim:

1. A collapsible pawl, comprising first and second parts which extend one after the other along a longitudinal axis of the pawl and which are articulated to each other so as to be able to turn about axes transverse to said longitudinal axis, and means displaceable between a first condition in which said means prevents said parts from turning about said axes under the action ofa compressive force along said longitudinal axis and thus prevent's collapse of said pawl by said force and a second condition in which said means does not prevent said parts from turning about said axes under the action of said force, said means comprising a toggle device having first, second and third axes of pivoting, of which the second axis is disposed between the first and third axes and, when said means is in said first condition, is disposed at one side of a plane containing the first and third axes and, when said means is in said second condition, is disposed on the other side of said plane.

2. A pawl according to claim I, wherein said means further comprises a fluid-operated piston-and-cylinder device connected to said toggle device for displacing the second axis of pivoting between said one side and said other side of said plane.

3. A pawl according to claim 1, wherein said means further comprises a piston rod extending from the piston of said piston and cylinder device to said second axis and connecting said piston to said toggle device, and wherein the cylinder of said piston-and-cylinder device bears freely on a surface portion of said first part when said means is in said first condition and is spaced from said surface portion when said means is in said second condition, said piston rod extending through a hole formed through said surface portion.

4. A pawl according to claim 1, wherein said first and third axes of pivoting are provided by respective pins of first and second pin-and-slot couplings connecting said first and second parts, respectively to said toggle device, said couplings providing a limited amount of play between said toggle device and said first and second parts, whereby displacement of said second axis through said plane from said one side to said other side is accompanied by the taking-up of said play until said second axis has reached a predetermined distance from said plane.

5. A pawl according to claim 1, and further compris- -ing respective recesses formed in the inner ends of said first and second parts and receiving said toggle device.

6. A pawl according to claim 1, wherein said means in said second condition applies to said first and second parts forces tending to turn said first and second parts about said axes in senses to collapse said pawl.

7. A pawl according to claim 1, and further comprising lateral link means interconnecting said first and sec ond parts.

8. In combination, a chain, a wildcat guiding longitudinal movement of said chain and a collapsible pawl for engaging said chain to prevent longitudinal movement of said chain in one direction, said pawl comprising first and second parts which extend one after the other along the longitudinal axis of the pawl and which are articulated to each other so as to be able to turn about axes transverse to said longitudinal axis, and means displaceable between a first condition in which said means prevents said parts from turning about said axes under the action of a compressive force along said longitudinal axis produced by said chain and thus prevents collapse of said pawl by said force and a second condition in which said means does not prevent said parts from turning about said axes under the action of said force.

9. In combination, a flexible elongate member, wheel means around which extends said flexible elongate member, a ring of teeth connected to said wheel means and a collapsible pawl for engaging said ring of teeth to prevent rotation of said ring of teeth in one sense and thus to prevent rotation of said wheel means in one sense, said pawl comprising first and second parts which extend one after the other along the longitudinal axis of the pawl and which are articulated to each other so as to be able to turn about axes transverse to said longitudinal axis, and means displaceable between a first condition in which said means prevents said parts from turning about said axes under the action of a compressive force along said longitudinal axis produced by said ring of teeth and thus prevents collapse of said pawl by said force and a second condition in which said means does not prevent said parts from turning about said axes under the action of said force.

10. A combination according to claim 9, wherein said wheel means comprises one of a wildcat and a wireline drum.

11. A combination according to claim 9, and including one of a winch and a Windlass which includes said wheel means and said ring of teeth.

12. In combination, a chain and chain-stopper, said chain-stopper comprising:

means guiding longitudinal movement of said chain,

pivot means fixed relative to said guiding means,

a collapsible pawl comprising two parts which extend one after the other along the longitudinal axis of the pawl, and of which one part is pivotally mounted at said pivot means at the end of said one part further from the other part so as to be turnable about an axis transverse to said longitudinal axis, and means articulating said parts to each other so that said other part is turnable relative to said one part about an axis transverse to said longitudinal axis, said other part at its end further from said one part engaging said chain to prevent longitudinal movement of said chain in one direction,

and a fluid-operated piston-andcylinder device disposed in the region of the two adjacent ends of said parts and acting at said region to displace said parts from a first condition in which said parts are prevented from turning relative to each other to a second condition in which said parts turn relative to each other and thus said pawl collapses.

13. A combination according to claim 12, wherein,

throughout the collapse of said pawl, turning of said pawl about said pivot means is substantially unhindered by said fluid-operated piston-and-cylinde'r device.

Claims

1. A collapsible pawl, comprising first and second parts which extend one after the other along a longitudinal axis of the pawl and which are articulated to each other so as to be able to turn about axes transverse to said longitudinal axis, and means displaceable between a first condition in which said means prevents said parts from turning about said axes under the action of a compressive force along said longitudinal axis and thus prevent''s collapse of said pawl by said force and a second condition in which said means does not prevent said parts from turning about said axes under the action of said force, said means comprising a toggle device having first, second and third axes of pivoting, of which the second axis is disposed between the first and third axes and, when said means is in said first condition, is disposed at one side of a plane containing the first and third axes and, when said means is in said second condition, is disposed on the other side of said plane.

2. A pawl according to claim 1, wherein said means further comprises a fluid-operated piston-and-cylinder device connected to said toggle device for displacing the second axis of pivoting between said one side and said other side of said plane.

5. A pawl according to claim 1, and further comprising respective recesses formed in the inner ends of said first and second parts and receiving said toggle device.

7. A pawl according to claim 1, and further comprising lateral link means interconnecting said first and second parts.

12. In combination, a chain and chain-stopper, said chain-stopper comprising: means guiding longitudinal movement of said chain, pivot means fixed relative to said guiding means, a collapsible pawl comprising two parts which extend one after the other along the longitudinal axis of the pawl, and of which one part is pivotally mounted at said pivot means at the end of said one part further from the other part so as to be turnable about an axis transverse to said longitudinal axis, and means articulating said parts to each other so that said other part is turnable relative to said one part about an axis transverse to said longitudinal axis, said other part at its end further from said one part engaging said chain to prevent longitudinal movement of said chain in one direction, and a fluid-operated piston-and-cylinder device disposed in the region of the two adjacent ends of said parts and acting at said region to displace said parts from a first condition in which said parts are prevented from turning relative to each other to a second condition in which said parts turn relative to each other and thus said pawl collapses.

13. A combination according to claim 12, wherein, throughout the collapse of said pawl, turning of said pawl about said pivot means is substantially unhindered by said fluid-operated piston-and-cylinder device.