Abstract:
An apparatus for efficiently guiding the legs of a lift boat. Roller assemblies are used to guide the legs. The rollers may be placed at any location or in any number either vertically or around the leg to adequately center the leg. The roller can either have a metal surface that rolls along the leg or be coated with a resilient material. The base of the roller can either be rigidly mounted to the vessel or incorporate resilient material between the roller and the vessel. A means of adjusting the clearance between the leg and roller may be incorporated in the roller assembly.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention is generally related to a lift boat or jack-up rig and more particularly to the mechanism for raising and lowering the legs of a lift boat or jack-up rig.  
           [0003]    2. General Background  
           [0004]    In offshore work related to the search for and production of oil and gas, a variety of vessel types are used. One type is a lift boat. A lift boat is a vessel that can elevate itself out of the water so as to provide a stable platform at the appropriate elevation to perform a number of marine construction tasks. Lift boats are equipped with retractable legs that each has a footing at the bottom. The footings contact the bottom and are of sufficient size to support the vessel on the seabed. The number of legs can vary from three to as many as six. One or more cranes are fixed to the deck of the vessel and are used to lift equipment onto or off of oil drilling or production platforms. A larger version of the lift boat called a jack-up rig typically is outfitted with drilling equipment. From this point on all mention of lift boats shall also be understood as including jack-up rigs.  
           [0005]    At least one gear rack is typically incorporated into each leg of a lift boat. The legs of a lift boat are either constructed as a lattice type or as a tubular type. One or more pinion assemblies operate along each gear rack. A pinion assembly typically consists of a pinion, gear box, braking mechanism and either an electric or hydraulic motor. The pinion assemblies are either rigidly fixed to the vessel or can be of the floating type. As the pinions of the lift boat rotate, the lift boat is either raised out of the water or lowered toward the surface of the water depending upon the direction of pinion rotation.  
           [0006]    The legs can be somewhat self-centering if multiple gear racks are used on the legs and if the gear racks are arranged properly. Even if the racks are ideally numbered and positioned some side loading of the legs will occur due to sea, wind, and vessel loading conditions. The current generation of lift boats employs a linear metal bearing guide to restrict leg movement. This guide system consists of metal bearing strips attached to the vessel or to the jacking apparatus. The guides may ride along the gear rack, the leg cords, or attachments to either the leg or gear rack. Smaller lift boats have leg towers constructed from tubular members and have tubular legs with outside diameters slightly smaller than the inside diameters of the leg towers. The leg tower is the sole guide. The shortcomings of these types of guide apparatus are that friction between the leg and guides increases the jacking force required to operate the lift boat and much of the lubricant used on the guides is dropped into the sea.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention addresses the above needs in a straightforward manner. What is provided is an apparatus for efficiently guiding the legs of a lift boat. Roller assemblies are used to guide the legs. The rollers may be placed at any location or in any number either vertically or around the leg to adequately center the leg. The roller can either have a metal surface that rolls along the leg or be coated with a resilient material. The base of the roller can either be rigidly mounted to the vessel or incorporate resilient material between the roller and the vessel. A means of adjusting the clearance between the leg and roller may be incorporated in the roller assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    For a further understanding of the nature and objects of the present invention reference should be made to the following description, taken in conjunction with the accompanying drawings in which like parts are given like reference numerals, and wherein:  
         [0009]    [0009]FIG. 1 is an isometric view of a lift boat.  
         [0010]    [0010]FIG. 2 is a detail view of a jacking and guide apparatus.  
         [0011]    [0011]FIG. 3 is an isometric view of the guide roller assembly.  
         [0012]    [0012]FIG. 4 is an exploded view of the guide roller assembly.  
         [0013]    [0013]FIG. 5 illustrates an alternate embodiment of the invention.  
         [0014]    [0014]FIG. 6 is a detail view of the alternate embodiment of FIG. 5.  
         [0015]    [0015]FIG. 7 is a detail view of another alternate embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Referring to FIG. 1, it is seen that a typical lift boat is generally indicated by the numeral  10 . For ease of illustration the lift boat&#39;s deckhouse, cranes and all deck equipment have been omitted. The lift boat is generally comprised of a hull  12  and a plurality of legs  14 . The hull  12  is a buoyant hull that has sufficient buoyancy to support the hull, legs, and any equipment placed on the hull. As seen in FIG. 1, the lift boat is elevated above the water&#39;s surface  30 . As seen in FIG. 2 each leg  14  is received through a leg well  34  provided near each corner of the hull  12 . The outer diameter of each leg  14  is less than the diameter of the leg well  34  so as to be movable through the hull  12 . Although only a tubular column  20  is shown, it should be understood that the legs  14  may be formed from either a tubular or lattice column. Each leg  14  is provided with a rack  22  and a footing  24 . The legs  14  may have singular or multiple racks  22 . The leg  14  is raised and lowered through the hull  12  by a pinion tower  18 . Each rack  22  may have singular or multiple pinions  32 . Multiple pinion towers  18  may be separately attached to the hull  12  or may be integrated into a unit attached to the hull  12 . The footings  24  are of sufficient size to provide resistance to the seabed  28  to allow the pinion tower  18  to elevate the hull  12  above the surface of the water.  
         [0017]    Referring to FIG. 2- 4 , it is seen that the invention is generally indicated by the numeral  26 . Guide roller apparatus  26  is generally comprised of a support box  36 , a pivot arm  38  and a roller  40 .  
         [0018]    The support box  36  is formed from two or more support box side plates  42  that are attached to a support box back plate  46  and a support box bottom plate  44 . A support box pin  48  connects the pivot arm  38  to the support box  36 . A keeper  50  prevents the support box pin  48  from sliding out of the support box  36 . The keeper  50  is attached to the support box  36  by any suitable means such as by welding, mechanical fastener, or by the use of an adhesive.  
         [0019]    The pivot arm  38  is of suitable shape to transfer forces from the leg  14  to the hull  12 . The pivot arm  38  is formed from two or more pivot arm side plates  52  that are attached to a pivot arm back plate  68 . A pivot arm pin  56  connects the roller  40  to the pivot arm side plate  52 . A keeper  51  prevents the pivot arm pin  56  from sliding out of the pivot arm side plates  52 .  
         [0020]    The roller  40  is of suitable shape to transfer forces from the leg  14  to the hull  12 . A bushing  58 , an inner core  60 , and an outer core  62  are assembled together to make up the roller  40 . The bushing  58  is of suitable shape and material to allow it, the inner core  60 , and the outer core  62  to rotate around pin  56 . The bushing  58  may be constructed of non-lubricated or lubricated material. The bushing  58  is attached to the inner core  60  by interference fit, bonded, or keyed to prevent relative movement. The inner core is constructed of suitable rigid material such as steel and attached to the outer core  62  by interference fit or bonded to prevent relative movement. The outer core  62  is formed from a suitable resilient material such as neoprene.  
         [0021]    One or more spacer plates  64  are of suitable shape and material to transfer forces from the leg  14  to the hull  12 . Resilient plate  66  is of suitable shape and material to transfer forces form the leg  14  to the hull  12 . Spacer plates  64  may be of varying thickness and number to adjust the nominal distance between the roller  40  and the leg  14  from a clearance to a compressed pre-load. In a pre-load condition the resilient outer roller  62  and the resilient plate  66  are deformed so that during normal operating conditions there is no clearance between roller  40  and leg  14 .  
         [0022]    The guide roller apparatus  26  may be securely attached to either the hull  12 , pinion tower  18  or, as seen in FIG. 2, to a guide roller tower  16 . The guide roller apparatus  26  may be the sole means of guiding the leg  14  or may be used in conjunction with bearing strips or any other suitable guide apparatus. The guide roller apparatus  26  may be set to a desired clearance or pre-load to the leg column  20 , rack  22 , or any attachment to either. The roller apparatus  26  is of sufficient size, number and location to adequately restrict the leg  14  to movement with the hull  12 . The guide roller tower  16  may be attached directly to the hull  12  or incorporated into the hull  12 , pinion tower  18  or other parts of the lift boat  10 .  
         [0023]    In operation, as the legs  14  are moved up or down through the hull  12 , the guide roller apparatus  26  on each leg  14  confines each leg  14  to a near perpendicular orientation relative to the deck of the hull  12 . The advantage this provides is that it prevents any out of alignment movement, which decreases the efficiency of the driving system and increases the possibility of damage.  
         [0024]    An alternate embodiment of the invention is generally indicated by numeral  70  in FIG. 5 and  6 . Track guide apparatus  70  is generally comprised of track  92 , rail structure  90 , idlers  76  and rollers  86 . For ease of illustration, the hull and pinion tower are not shown.  
         [0025]    A leg tower  74  is attached to the lift boat and is sized to allow movement of the leg  14  therethrough. The leg tower  74  is provided with an elongated opening  72 . Track guide apparatus  70  is attached to the leg tower  74  and contacts the leg  20  through the elongated opening  72  in the leg tower.  
         [0026]    As best seen in FIG. 6, the track  92  is comprised of link plates  88 , link pins  78 , and track pads  84  traveling around idlers  76 . The force exerted upon the track  92  by the leg  20  is transferred to the rail structure  90  via the rollers  86 . The rollers may be of a similar design as shown in FIG. 4 or of any other design suitable to transfer the force. The rail structure generally indicated by numeral  90  is comprised of a rail  82  and rail flanges  80 . The rail flanges  80  are attached to the leg tower  74 .  
         [0027]    [0027]FIG. 7 illustrates a second alternate embodiment of the invention. The alternate track guide apparatus is generally indicated by the numeral  102 . The link  94  and pins  96  are similar to the link and pin shown in FIG. 5 and  6 . Roller  98  contacts the rail  100  and the leg, not shown. Roller  98  may be incorporated with the pin  96  as one component. For clarity, the rail flanges that attach the rail to the tower are not shown.  
         [0028]    Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein re to be interpreted as illustrative and not in a limiting sense.