Patent Publication Number: US-8985045-B2

Title: Chock insert for a maritime craft

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. §371 National Phase Entry Application from PCT/GB2009/000988, filed Apr. 15, 2009, and designating the United States, which claims the benefit of Great Britain Patent Application No. 0806822.3, filed Apr. 15, 2008, the disclosures of which are incorporated by reference. 
     The invention relates to a chock insert for a maritime craft, particularly a ship but also for use in rigs and floating platforms. 
     Chocks on ships, rigs, floating platforms and other maritime craft or installations generally comprise a flared aperture through which mooring ropes can pass. The flared nature of the chock is intended to prevent the mooring rope from passing over a small radius which would increase the level of wear on the rope. The mooring ropes are held under tension against the surface of the chock and the chock and rope running through it move relative to each other due to the movement of the craft, for example due to swell, the tides, wind and other phenomena. 
     Mooring ropes for large vessels such as tankers, gas carriers and container ships have typically been made from steel wire. However, these ropes are heavy which makes them difficult and time consuming to handle, placing an additional burden on crew and increasing time at berth. Also, as the wire ropes become worn individual wires break away and they can cut the hands of rope handling personnel. Also, in the salt water environment steel ropes can be subject to corrosion. Accordingly, synthetic fibre ropes have been offered as an alternative to steel. Generally these synthetic fibre ropes are made from a high modulus polyethylene fibre, aramid fibre or liquid crystal polyester fibre, all of which combine high strength with good resistance to stretch and make their performance largely equivalent to steel wire rope. The ropes are lighter and easier to handle. They tend not to present sharp fibres as they wear. Also, steel ropes are prone to sparking as they drag along the deck and that risk, which is significant when it occurs on a tanker or gas carrier, is eliminated with the synthetic fibre rope. 
     One issue with the synthetic fibre ropes in relation to steel ropes is that they have a relatively poor wear resistance. The chocks on vessels are generally made of sand cast steel. Whilst the sand cast steel surface does not present a wear problem for steel wire rope, the surface is rough enough to accelerate wear in fibre ropes. Chocks are also prone to rust which increases the abrasive qualities of the chock when the fibre rope is passing over it. 
     It is an object of the invention to provide an improved chock insert for a maritime craft. 
     According to one aspect of the invention there is provided a chock insert for a maritime craft comprising a body arranged to be received within or mounted to a chock, the body having a passageway therethrough to allow passage of a rope the body defining a rope running surface over which rope passing through the passageway can run, the rope running surface comprising a plastics material. 
     In that way, the fibre rope runs over a plastics material surface which is less abrasive. 
     The outer surface of the body of the chock insert is preferably arranged to conform to part of the inner surface of the chock. Most preferably, the outer surface of the body of the insert conforms substantially to the entire inner surface of the chock. 
     The body may be formed in two parts. The two parts of the body are preferably secured together compressively, for example by screw threaded fastener means, such as a series of nuts and bolts. Any gap that exists between the two parts of the body may be filled with a filler material. The two parts of the body may comprise an inner part and an outer part, the inner part being arranged to conform to the onboard side of the chock and the outer part being arranged to conform to the outboard side of the chock. 
     The passageway may be bounded on all sides by the body of the chock insert. The passageway may be circular, elliptical or obround. 
     The rope running surface preferably extends around the entrance to the passageway, the exit to the passageway or both sides of the passageway. The rope running surface may comprise the entire surface of the passageway. The plastics material of the rope running surface may comprise a removable plastics insert. 
     The plastics material may be one selected from the group of polyamide, polyester, epoxy or polyurethane. The plastics material may comprise a composite material comprising a plastics material matrix with a filler of different materials. The fillers may be provided so as to alter the performance of the rope running surface. The fillers may reduce the surface friction of the rope running surface. The fillers may improve the wear properties of the rope running surface. The fillers may be selected from the group of PTFE, FEP or graphite particles. Alternatively or in addition to the fillers, the plastics material matrix can have fibrous or other strengthening materials added to it. The fibrous materials may be glass, aramid or carbon fibre or other suitable fibre reinforcing material. 
     The body may be made by casting. Where the rope running surface comprises a separate plastics insert, the insert should be made by casting. Although it is less preferred, the body or insert could also be made by rotomoulding or injection moulding the plastics material. 
    
    
     
       An embodiment of the invention will now be described in detail by way of example and with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a chock insert in accordance with the invention, 
         FIG. 2  is a perspective view of the first part of the chock insert, 
         FIG. 3  is a perspective view of the second part of the chock insert, 
         FIG. 4  is a schematic sectional view through a chock with the chock insert of  FIGS. 1 to 3  installed thereon, 
         FIG. 5  is a schematic illustration of a chock liner test rig, 
         FIG. 6  is a table showing results of cycle testing of synthetic fibre rope. 
     
    
    
     In  FIG. 1  a chock insert  10  comprises a first and second trumpet-shaped body parts  12 ,  14 . The body parts  12 ,  14  butt together at their respective narrow ends  12   a ,  14   a  and flare outwardly to flared ends  12   b ,  14   b . The parts  12 ,  14  are secured together by means of multiple nut and bolt fastener assemblies  16  which extend through apertures  18  and bores  20  formed respectively in each body part  14 ,  12 . 
     The body parts  12 ,  14  are made of plastics material, for example a polyamide, a polyester, epoxy or a polyurethane. 
     The inner surfaces of the body parts  12 ,  14  define a rope running surface over which mooring rope can run. The plastics material surface is less abrasive to synthetic fibre rope than the surface of a chock. 
     In  FIG. 2 , one side of the chock insert  10  is shown. 
     The body part  14  in  FIG. 2  is the craft side part of the chock insert. In other words, in use, that part is arranged to face towards the craft when installed on the chock. The body part  14  comprises an obround narrow end  14   a  and an obround wide end  14   b . A parabolically flaring wall  14   c  extends between the narrow end  14   a  and the wide end  14   b . Six fastener receiving apertures  18  are formed equally angularly spaced around the inside surface of the body part  14 . The apertures  18  extend through the body part  14  and emerge on the end face of the body part  14  at the narrow end  14   a . Only four apertures are shown in  FIG. 2 . Bolts  16   a  of the nut and bolt fastener assembly  16  are arranged in the apertures  18 . 
     Turning to  FIG. 3 , the chock body part  12  shown is the quay-side part of the chock insert. In other words, the part  12  is the part that, when arranged on the ship or other maritime craft, faces towards the quay. 
     Again, as with the part  14 , the part  12  comprises an obround narrow end  12   a , an obround wide end  12   b  and a parabolically flared wall  12   c  extending between the ends  12   a ,  12   b.    
     A series of bores  20  are formed in the end face of the narrow end  12   a  of the body part  12 . The bores extend through the body towards the wide end  12   b  and they receive a nut of the nut and bolt fastener arrangement  16 . Access apertures  22  extend from the outer surface of the body part  12  inwardly towards the bores  20  to enable either insertion or manipulation of a nut of the nut and bolt fastener arrangement  16 . 
     In  FIG. 4 , the chock insert  10  is shown, schematically, assembled upon a chock of a ship or other maritime craft. 
     In  FIG. 4 , a ship (not shown) has a ship wall  24  in which a chock  26  is mounted. The chock  26  is supported by chock mounting webs  28  which may be bolted or welded to the ship wall  24 . 
     The chock  26  defines an aperture generally indicated at  30  through the ship wall  24 , through which a rope R can run. The running surface of the chock  26  is rough and tends to wear synthetic fibre rope. In  FIG. 4 , the chock insert  10  is arranged within the chock  26  so as to cover the surface of the chock  26 . The chock insert  10  is secured on the chock by means of the nut and bolt arrangements  16  as shown in  FIGS. 1-3 . In the embodiment shown in  FIG. 4 , the narrow ends  12   a ,  14   a  of the chock insert body parts  12 ,  14  do not meet. The small gap between those ends  12   a ,  14   a  is filled using a known filler material  32 . A typical filler material may be a silicon sealant material or a room temperature vulcanising polyurethane. As can be seen in  FIG. 4 , the rope R runs over the inner surface of the chock insert  10  rather than the surface of the chock  26 . The inner surface of the chock  10  is considerably less wearing on synthetic fibre rope R than the surface of the chock. 
     In the chock insert of  FIGS. 1-3 , the quay-side part  12  is larger than the craft-side part  14 . However, they may be identical in size or the craft-side part may be larger than the quay-side part. Also, various shapes of chock inserts are possible. For example, the parts  12 ,  14  could be conical in shape. Likewise the aperture defined by the chock insert  10  could vary in shape from circular, through elliptical to obround. It is likely that the aperture will always have a rounded profile and the inner surface of the insert will flare convexly so as to maximise the radii over which the rope must pass. 
     The chock insert  10  in accordance with the invention was tested in a test rig as shown in  FIG. 5 . In  FIG. 5  a test rig  34  comprises opposite drive mechanisms  36 ,  38  which are spaced apart from each other and which drive away from each other. A rope R is secured between the drive mechanisms  36 ,  38  and passes over a first roller  40 , through a chock  42  and over a second roller  44 . The drive mechanisms  36 ,  38  are intended to pull the rope back and forth as illustrated by the arrow in  FIG. 5  through the chock  42 . Identical ropes were tested on an unfinished chock (A), on a smoothed chock (B) and then on a chock insert (C) in accordance with the invention. After 1500 cycles back and forth through the chock, the rope used on the unfinished chock retained just over 60% of its residual strength. The rope that was used in the relation to the smoothed chock had around 67% of its original strength. A series of ropes tested on the chock insert retained between 78% and 85% of their residual strength after 1500 cycles. Thus it can be seen that the use of the chock insert substantially improves the fatigue life of ropes passing through the chock insert in comparison to ropes passing through both finished and unfinished chocks. 
     An alternative chock comprises a framework of a first material, for example steel, with a plastics material insert received in the framework to define the rope running surface.