GB2131380A - Collapsible chain stopper - Google Patents

Abstract

A collapsible pawl 6 in a bowstopper comprises two parts 8 and 9 articulated together by a pivot pin 10, the part 9 having two parallel arms 17 embracing an arm 18 of the part 8. In its normal, rigid, condition of use, the pawl 6 has the axis 11 of its pin 10 just below the dead centre position and has the free ends of its arms 17 and 18 abutting the parts 8 and 9. Acting between the part 9 and an extension 15 of the part 8 and along a line 14 is a pawl-collapsing, hydraulic, piston-and-cylinder device 16. Carried by the arm 18 and arranged between eyes 19 carried by the respective arms 17 is a double, hydraulic, piston-and-cylinder arrangement 20 whereof piston rods 21 releasably engage outwardly in the eyes 19 in the rigid condition of the pawl 16. <IMAGE>

Description

SPECIFICATION A collapsible pawl According to one aspect of the present invention, there is provided a collapsible pawl, comprising a first part including one extremity of said pawl, a second part including the other extremity of said pawl and articulated to the first part so as to be turnable relative to the first part about a single axis transverse to the pawl, and means arranged to displace said pawl from a first condition in which said second part is prevented from turning about said axis relative to said first part under the action of a compressive force along said pawl and thus collapse of said pawl by said force is prevented to a second condition in which said second part is able to turn about said axis relative to said first part under the action of said force, said means being arranged to turn the second part relative to the first part by acting between the first and second parts along a line of action transverse to said pawl and said axis and spaced along said pawl from said axis.

According to another aspect of the present invention, there is provided a collapsible pawl, comprising a first part including one extremity of said pawl, a second part including the other extremity of said pawl and articulated to the first part so as to be turnable relative to the first part about an axis transverse to the pawl, and a safety device comprised of a safety member carried by one of the parts and a hole in the other of the parts arranged to receive said safety member to prevent undesired collapse of said pawl, said safety member being automatically releasable from said hole.

In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 shows a sectional side elevation of a bow-stopper for a ship, and Figure 2 shows a sectional plan view of a collapsible pawl of the bow-stopper.

Referring to the drawing, the bow-stopper serves to carry the tension in an anchor chain 1 of which the left-hand end in Figure 1 is connected to a winch and the right-hand end to an anchor.

The bow-stopper includes two side plates (of which one is seen and referenced 2) between which is arranged a guide channel 4 for the chain 1 and also between which is pivotally mounted for turning about a horizontal axis a 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.

Under certain circumstances, for example in stormy conditions, the tension in the portion of the chain 1 between the bow-stopper 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 rigid parts 8 and 9 which include the respective inner and outer extremities of the pawl. The parts 8 and 9 are articulated to each other by means of a single horizontal pivot pin 10 which has its axis 11 transverse to the longitudinal axis 5 of the pawl 6.

Fixed to the part 9 are keepers 1 2 which engage in respective grooves in the pin 10 to prevent axial displacement of the pin 1 0. Mounted on the part 9 adjacent to the free end thereof is an hydraulic piston-and-cylinder device 13, the line of action 14 of which is perpendicular to the axes 5 and 11 and is spaced along the pawl from the axis 1 The part 8 includes an extension 1 5 which extends above a piston rod head 1 6 of the device 13. The part 9 includes two parallel arms 1 7 which embrace between them an arm 1 8 of the part 8 and which carry respective eyes 1 9 aligned parallelly to the axis 11.Carried by the arm 1 8 and arranged between the eyes 1 9 is a double pistonand-cylinder arrangement 20 whereof piston rods 21 are co-axial with each other and are arranged to engage outwardly in the eyes 1 9 in the rigid condition of the pawl 6 shown in the drawing. The pistons can be hydraulically displaced between respective abutment rings near the ends of the cylinder and a common abutment ring 22 at the middle of the cylinder, inward displacement of the pistons being achieved by feeding hydraulic fluid to respective outer hydraulic connections 23 of the cylinder, and outward displacement of the pistons being achieved by feeding hydraulic fluid to a common hydraulic connection 24 at the middle of the cylinder.

In the normal condition of use, the pawl is in the rigid condition shown in full lines in Figure 1.

In this condition, the axis 11 is slightly below dead centre relative to the line of the compressive force applied by the chain 1 to the pawl 6. In this condition, irrespective of the size of that force, the pawl does not collapse of its own accord, because the free ends of the arms 1 7 and 18 abut against complementary surfaces on the parts 8 and 9 respectively. Should an emergency arise such that it becomes necessary to collapse the pawl to release the chain 1, then hydraulic fluid is fed into the connections 23 to retract the piston rods 21 and hydraulic fluid is fed into the device 1 3 to cause the device 1 3 to act between the parts 8 and 9 in such a manner as to turn them away from each other about the pin 10 until the axis 11 has just gone above dead centre relative to the line of the compressive force.Thereupon, the compressive force applied by the chain 1 to the pawl 6 causes the part 9 to continue to turn relative to the part 8 in the same sense so that the parts move suddenly into the collapsed condition indicated by means of the chain lines 8', 9', 1 3', and 15' in Figure 1. As the pawl 6 collapses clockwise in Figure 1, an anti-rebound counterweight 25 moves from the inner end of the arm 7 to the outer end thereof, as indicated in chain lines at 25'.

Some means for causing the collapse of the pawl other than the piston-and-cylinder device 13 can be employed. For example, the device (13) can be replaced by a screwthreaded pin extending along the line 1 4 and provided with radially projecting lugs and screwed into one of the parts 8 and 9. In such an arrangement, to cause collapse of the pawl, the lugs are hit with a sledge hammer to cause the screwthreaded pin to turn in an unscrewing manner in order to turn the parts 8 and 9 away from each other about the axis 11.

If desired, the pawl 6 can be held in its chainengaging position by a pin passed through transverse holes (of which one is seen and referenced 26) in the side plates of the bowstopper.

As in the case of the collapsible pawl disclosed in British Patent Specification 1367358, the present pawl is not restricted in its application to bowstoppers but can also be applied to a wildcat or a windlass, for example.

Claims (11)

1. A collapsible pawl, comprising a first part including one extremity of said pawl, a second part including the other extremity of said pawl and articulated to the first part so as to be turnable relative to the first part about a single axis transverse to the pawl, and means arranged to displace said pawl from a first condition in which said second part is prevented from turning about said axis relative to said first part under the action of a compressive force along said pawl and thus collapse of said pawl by said force is prevented to a second condition in which said second part is able to turn about said axis relative to said first part under the action of said force, said means being arranged to turn the second part relative to the first part by acting between the first and second parts along a line of action transverse to said pawl and said axis and spaced along said pawl from said axis.

2. A pawl as claimed in claim 1, wherein said second part includes two substantially parallel arms which embrace between them an arm of the first part, and said single axis extends through those three arms.

3. A pawl as claimed in claim 1 or 2, wherein said first part has an extension, and said means acts between said extension and said second part along said line of action.

4. A pawl as claimed in any preceding claim, wherein said means comprises an hydraulic piston-and-cylinder device.

5. A pawl as claimed in any preceding claim, and further comprising a safety device comprised of safety means carried by one of the first and second parts and hole means in the other of the parts arranged to receive said safety means to prevent undesired collapse of said pawl, and automatic release means for automatically releasing said safety means from said hole means.

6. A pawl as claimed in claim 5, wherein said automatic release means comprises hydraulic piston-and-cylinder means whereof piston means is connected to said safety means.

7. A pawl as claimed in claim 5 or 6, wherein said safety means comprises two safety members and said hole means comprises two holes arranged to receive the respective safety members.

8. A pawl as claimed in claim 7, wherein said safety members and said holes are all substantially co-axial with each other.

9. A collapsible pawl comprising a first part including one extremity of said pawl, a second part including the other extremity of said pawl and articulated to the first part so as to be turnable relative to the first part about an axis transverse to the pawl, and a safety device comprised of a safety member carried by one of the parts and a hole in the other of the parts arranged to receive said safety member to prevent undesired collapse of said pawl, said safety member being automatically releasable from said hole.

10. In combination, a chain-guiding device, and a pawl as claimed in any preceding claim for engaging a chain in the chain-guiding device.

11. A collapsible pawl, substantially as hereinbefore described with reference to the accompanying drawings.