This is a continuation of co-pending application Ser. No. 566,319 filed on Dec. 28, 1983, abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to offshore working platforms which are self-propelled or towed to a shallow water well site and can be jacked-up above the water surface for use in drilling and production activities, and more particularly to cranes used on such platforms. 
     2. Description of the Prior Art 
     Typically, self-elevating lift barges or other self-elevating or jack-up platforms are used in offshore shallow water drilling and production activities. These self-elevating platforms or rigs typically incorporate a deck-mounted crane. These cranes are essential to the operation of such vessels or platforms and often become more important to the end user of these boats or platforms than the boat or platform itself. 
     The cranes typically used on jack-up boats or platforms in the past have included hydraulic cranes employing a box boom and using hydraulic cylinders to lift the boom. These cranes are very popular due to their short swing radius. However, in the recent past jack-up boat and platform sizes have increased substantially resulting in an increased demand being placed on a deck mounted crane which frequently exceeds the lifting capabilities of a typical cylinder lift crane. Since cylinder lift cranes rely on the strength of the boom to suspend and support the load, the heavier the load, the stronger or heavier the crane boom must be to support it. The heavier crane booms create several problems for a jack-up boat or platform, the most significant of which is listing while the boat or platform is underway. 
     In order to economize on weight, the alternative to a cylinder lift crane has been a conventional lattice-type boom which is tip supported. Although the boom on tip supported cranes is much lighter, all lattice boom cranes suffer from a major drawback of a very large overhanging gantry which increases the swing radius thereby taking up valuable deck space. 
     In contrast to cylinder lift cranes, which can raise their boom to almost a vertical position thereby enabling a load to be placed only a few feet from the crane base on the deck, conventional lattice boom cranes are not capable of raising the boom to a near vertical position. Accordingly, a tip-supported lattice boom crane which is mounted on deck suffers from an additional drawback of not being able to turn a full 360° due to interference from the long, extended legs mounted on the periphery of the platform or deck of the jack-up boat. 
     SUMMARY OF THE INVENTION 
     A new and improved crane adapted to be rotatably mounted about the guide tower of a vertically movable leg of an offshore jack-up platform. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective of a jack-up boat showing the crane of the present invention mounted on the guide tower; 
     FIG. 2 is a schematic, perspective, sectional view of a tower section designed to be mounted above a guide tower, illustrating the placement of the bearing tube which supports the crane; 
     FIG. 3 is a sectional, elevational view of a king-post type crane mounting on a guide tower, taken along lines 3--3 of FIG. 2; 
     FIG. 4 is a plan view of the crane of the present invention mounted on a guide tower; 
     FIG. 5 is an elevational view showing the crane of the present invention mounted on top of the guide tower using hook rollers; and, 
     FIG. 6 is an elevational view showing a crane mounted on top of a guide tower using a combination bearing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The platform P of the present invention may be part of a small offshort jack-up rig (not shown) or may be a jack-up boat B as shown in FIG. 1. It is understood that although the following detailed description will refer to a jack-up boat B having a deck or platform 10a any other platform which is designed for use in well operations in shallow offshore locations is within the field of the invention. 
     The jack-up boat B shown in FIG. 1 is self-propelled so that it may easily be maneuvered to any shallow water offshore location adjacent an oil and gas well. Having brought the jack-up boat adjacent an oil and gas well, it is necessary to stabilize the boat B by supporting it from the sea bottom rather than from the water surface. 
     In order to shift the weight of the boat B to the subsea floor three guide towers 20a two of which can be seen in FIG. 1 are positioned around the periphery of the deck 10a. Typically the guide towers are mounted on deck extensions defined by surfaces 10b, 10c and 10d or surfaces 10e, 10f and 10g as shown in FIG. 1. As seen in FIG. 6 each guide tower 20a has a central axis perpendicular to deck 10a. 
     Guide towers 20a also have a central bore 201 (FIGS. 5 &amp; 6) to accommodate a leg 30a which is slidably mounted through the central bore of the guide tower 20a. Each leg has a pad 30b connected to its base for the purposes of distributing the weight on each leg 30a along the sea floor. Each leg 30a includes two vertically mounted racks 30c and 30d positioned 180° apart on its outer periphery and designed to pass through the central bore 201 of guide tower 20a as leg 30a is raised or lowered relative to deck 10a. 
     Each guide tower 20a has a first vertical row of hydraulic motors 20b, 20c, 20d and 20e and a second row of hydraulic motors 20f, 20g, 20h and 20i. Each hydraulic motor 20b through 20i drives a pinion gear (not shown). The pinion gears are attached to hydraulic motors 20b, 20c, 20d and 20e are in contact with rack 30d. Similarly the pinion gears connected to hydraulic motors 20f, 20g, 20h and 20i are in contact with rack 30c. Accordingly, through the use of a hydraulic control system, of a type well known in the art, the pinion gears, attached to hydraulic motors 20b through 20i and meshing with racks 30c and 30d, can be used to drive each leg 30a up or down with respect to deck 10a. Therefore, in order to stabilize jack-up boat B on the sea floor, hydraulic motors 20b through 20i on each guide tower 20a are activated to drive each of legs 30a downwardly through the central bore of each guide tower 20a until pad 30b at the bottom of each leg 30a contacts the sea floor. It should be noted that although FIG. 1 illustrates the usage of three legs 30a with three corresponding guide towers 20a, designs incorporating the usage of additional legs 30a and guide towers 20a are within the purview of the invention. Similarly designs having more than two racks on a leg 30a with corresponding additional rows of hydraulic motors on a guide tower 20a are within the contemplation of the platform of the present invention. 
     As distinguished from jack-up boats in the prior art, which feature a deck mounted crane, the platform P of the present invention features a crane 40 supported on a guide tower 20a. The crane 40 shown in FIGS. 1-6 is a lattice boom tip supported crane. However, other types of cranes can be mounted to the guide tower 20a without departing from the spirit of the invention. Having the crane 40 mounted on a guide tower 20a frees up space on deck 10a adjacent front surface 10i of the jack-up boat B. Furthermore, when the crane 40 is mounted guide tower 20a it can easily rotate 360° as opposed to a deck mounted crane mounted adjacent to a guide tower 20a which may encounter interference with an adjacent leg 30c in any attempt to rotate 360°. Since the larger jackup-up boats B employ lattice boom tip supported cranes having an high capacity which further require a substantial turning circle, mounting the crane 40 on guide tower 20a frees up additional space on deck 10a which normally would have been consumed in providing turning clearance for the crane 40. Since the guide towers 20a with the crane 40 mounted thereon are disposed on extensions to deck 10a as indicated by surfaces 10b, 10c and 10d or 10 e, 10f and 10g in FIG. 1, little, if any, valuable space on deck 10a is taken up by the turning clearance required for the crane 40. 
     There are several ways to attach the crane to the guide tower three of which are shown in FIGS. 2, 3, 5 and 6. FIGS. 2 and 3 relate to a king post type crane mounting system. FIG. 5 shows a hook roller mounting system. FIG. 6 illustrates a combination load bearing mounting assembly. Although these three types of mounting systems have been illustrated in the figures, different means to mount a crane 40 on a guide 20a can be used without departing from the spirit of the invention. 
     Referring to FIGS. 2 and 3 which illustrate the king-post method of mounting the crane 40 onto the guide tower 20a, a tower section 40a is attached to the upper end of a guide tower 20a above the hydraulic motors 20b through 20i. The tower section 40a is a tubular member which when placed above and attached to the guide tower 20a has a tower section central bore 40b in substantial alignment with the central bore 201 of guide tower 20a  thereby allowing a leg 30a to travel up and down simultaneously, through tower section 40a and guide tower 20a. 
     Tower section 40a has a lower tower flange 40c with an upper surface 40d which acts as a bearing surface in supporting crane movement as will be more fully discussed hereinbelow. Upper surface 40d is essentially parallel to deck 10a. Upper tower flange 40e is disposed above lower tower flange 40c. Upper tower flange 40e is essentially parallel to lower tower flange 40c and is attached to tower section 40a via a series of bolts 40f which secure upper tower flange 40e to a mounting angle 40g which is in turn secured to tower section 40a. A resilient strip 40i is attached to tower section 40a slightly below upper tower flange 40e. A second resilient strip 40j is connected to tower section 40a adjacent lower tower flange 40c. A resilient thrust segment 40k extends from tower section 40a radially, between upper surface 40d of lower tower flange 40c and lower flange 50b of bearing tube 50a. The lower end of resilient strip 40j is adjacent to resilient thrust segment 40k. 
     Lower tower flange 40c can optionally have gear teeth 401 disposed along its outer periphery. When so equipped lower tower flange 40c functions as a stationary sprocket which can be used in rotating crane 40, mounted on bearing tube 50a, around the periphery of tower section 40a. 
     Bearing tube 50a has a lower flange 50b and an upper flange 50c. The upper flange 50c is assembled to bearing tube 50a after the crane 40 has been lowered onto lower flange 50b. Having lowered the crane onto lower flange 50b of bearing tube 50a, the upper flange 50c is then welded to bearing tube 50a so that it is essentially parallel to upper tower flange 40e. Having placed the crane 40 only lower flange 50b of bearing tube 50a, and secured the upper flange 50c to bearing tube 50a, upper tower flange 40e can be secured to tower section 40a via bolts 40f and mounting angle 40g. As can readily be seen from FIG. 3, resilient thrust segment 40k supports the bulk of weight of the crane 40 which is resting on top of lower flange 50b of bearing tube 50a. Furthermore, resilient strips 40i and 40j resist overturning moment from loads picked up by the crane 40 and permit bearing tube 50a to rotate about the outer periphery of tower section 40a. Similarly, resilient thrust segment 40k facilitates rotation of bearing tube 50a around the outer periphery of tower section 40a. 
     The king-post mounted crane 40 has an engine driven pinion 40m (an example of which can be seen in FIG. 6) which is horizontally disposed and engages the gear teeth 401 on lower tower flange 40c. Accordingly, by selectively driving engine driven pinion 40m, the crane nestled within bearing tube 50a can be made to rotate around the outer periphery of tower section 40a. 
     Referring to FIG. 5, the hook roller method of attaching the crane 40 to the guide tower 20a is illustrated. A mounting section 60a having a mounting section central bore 60b is connected to the top of guide tower 20a. The mounting section central bore 60b of mounting section 60a is in substantial alignment with the central bore 201 of guide tower 20a thereby enabling leg 30a to be driven vertically up or down simultaneously through both central bores 60b and 201. Mounting section 60a has a support flange 60c connected at the upper end of mounting section 60a. Support flange 60c has an upper bearing surface 60d and an lower bearing surface 60e. A plurality of roller assemblies 60f are attached to the underside of crane 40 at spaced intervals along a circular pattern. As shown in FIG. 5 the roller assemblies 60f are spaced at 90° intervals although different spacing may be employed depending upon the load characteristics of the particular crane 40 involved. Each roller assembly 60f has a series of upper rollers 60g which bear on upper bearing surface 60d and a series of hook rollers 60h which bear on lower bearing surface 60e of support flange 60c.  Upper rollers 60g transfer the bulk of the weight of the crane 40 to the guide tower via upper bearing surface 60d of support flange 60c. Hook rollers 60h resist overturning moment placed on crane 40 due to loads picked up by the crane and the weight of the crane boom. The combination of upper rollers 60g and hook rollers 60h permits the crane 40 to rotate about the vertical axis of mounting section 60a. The crane 40 is rotated about the vertical axis of mounting section 60a due to the interaction of an engine driven pinion such as 40m (FIG. 6) or mounted to the crane and a stationary gear secured to or integral with the inside of mounting secton 60a just below support flange 60c (not shown). 
     FIG. 6 illustrates the combination bearing method of mounting the crane 40 to the guide tower 20a. A pedestal section 70a is mounted to the upper end of guide tower 20a. The pedestal section 70a has a pedestal section central bore 70b which is in substantial alignment with central bore 201 of guide tower of 20a thereby permitting leg 30a to move vertically up or down simultaneously through central bores 70b and 201. Pedestal section 70a has a mounting flange 70c at its upper end. Combination bearing 70d has a fixed segment 70e which is fixed to mounting flange 70c. Disposed within fixed segment 70e of combination bearing 70d is a rotating segment (not shown) which is adapted to be mounted to a mounting plate (not shown) on the base of crane 40. An engine driven pinion 40m is connected to crane 40 and meshes with gear teeth 70f located on the outer periphery of fixed segment 70e. Accordingly, the connection between the mounting plate (not shown) on the crane 40 and the rotating segment (not shown) of the combination bearing 70d enables crane 40 to rotate about central axis 10h. The position of the crane may be adjusted by selectively driving engine driven pinion 40m which due to its meshing with gear teeth 70f, selectively rotates crane 40 about central axis 10h. 
     By placing the crane 40 on a guide tower 20a additional load is placed on the guide tower which may tend to make the jack-up boat B list while underway. Accordingly, to offset the additional transfer of weight to the edge of the deck 10a, several pieces of on-board equipment such as water and oil storage tanks can be relocated to the opposite side of the jack-up boat B to counterbalance the additional load on the guide tower 20a which supports the crane 40. 
     As can readily be seen mounting the crane 40 on the guide tower 20a frees up additional space on deck 10a and eliminates the problem of leg interference in rotation of tip supported lattice boom deck mounted cranes. This is especially significant for jack-up boats B employing very large high-capacity cranes which have a tip supported boom as shown in FIGS. 5 and 6 as opposed to a hydraulically telescoping boom. Although the lower capacity cranes having a telescoping boom are able to raise the boom almost a vertical position, the heavier duty lattice boom tip supported cranes are not able to raise the boom to a vertical position. Accordingly, on the larger jack-up boats B employing a heavy duty tip supported crane, a deck mounted crane would be limited in rotation due to interference from an adjacent leg 30a. The platform of the present invention by mounting the crane 40 on a guide tower 20a has effectively solved the problem of interference with crane rotation posed by an adjacent leg 30a. 
     Accordingly, by mounting a tip supported lattice boom crane on a guide tower the problem of interference with an adjacent leg is eliminated. Furthermore, since the guide tower is located well above and off to the side of the deck (by virtue of its attachment to the top of the guide tower), no valuable deck space must be sacrificed in order to accommodate the large tail swing clearance normally required by such lattice boom tip supported cranes. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.
A new and improved crane adapted to be rotatably mounted about the guide tower of a vertically movable leg of an offshore jack-up platform. In one form, the crane is mounted for rotation about the leg tower section on a bearing tube having a thrust bearing interposed between a tower section flange and the lower end of the bearing tube. In a second form, the crane is mounted about the leg tower section utilizing upper rollers and hook rollers coacting with a support flange mounted with the tower section.