Technical Field

This invention relates to systems for transferring peo- pie between two spaced platforms subject to relative move¬ ment during the transfer process, and more particularly to an articulated ramp providing a temporary bridge connecting the platforms.

Background Of the Invention

To extract oil from offshore deposits, it is common practice to erect a platform above the drill sites or well¬ heads from which workmen may tend the machinery used to drill for the oil, or to pump the oil from the wellhead on the ocean floor to a tanker on the water surface above or through a pipeline to shore. The platforms may be free floating on the water surface above the drill site or well¬ head, or tied to the ocean floor by tether line, or elevated above the water surface on stilts reaching down to the ocean floor below. In any case, the platforms are subject to more or less constant motion due to the forces of wind and waves acting on the structure, complicating such tasks as the loading and unloading of supplies and workmen.

Some oil platforms are equipped with a heliport to per- mit supplies and workmen to be transported between the plat¬ form and the mainland by helicopter. However, the high

costs and inherent dangers involved in the use of helicop¬ ters for transporting personnel and supplies to and from offshore oil platforms has led others to search for better ways to perform these functions using ocean going transport vessels or ships. Where such platforms are serviced by ship there is a problem in providing a safe link or bridge between the ship and platform during loading and unloading operations: due to the nearly constant motion of either or both", the; ship and platform. To overcome this problem, vari- ous schemes have been proposed such as that shown in U.S. patent 4,011,615 which discloses a form of telescoping ramp. Additional examples of prior art for transferring personnel or cargo between spaced platforms subject to relative move¬ ment, such as between a ship and an oil platform, are described in U.S. patents 3,808,625; 4,180,362; and 4,412,598.

The amount of relative movement which telescoping ramps such as shown in U.S. patent 4,011,615 can safely accept is somewhat limited, and they are restricted as to use with oil platforms of different height. Moreover, like hoist systems such as shown in U.S. patents 4,180,362 and 4,412,598, in order to make a good hook-up, the ship platform must maneu¬ ver closer to the oil platform than is desirable for safety, particularly in open waters under high sea state conditions.

Summary of the Invention

The present invention employs two ramps, a main ramp and an outer ramp. The main ramp in its preferred form is swingably maintained on a rotatable pedestal secured to the deck of the ship. The outer ramp is connected to the main ramp through an intermediate or mid-ramp platform which is stabilized with respect to the deck of the ship or platform on which the main ramp is mounted through the use of a par¬ allelogram linkage which includes the main ramp and main ramp handrails. The outer ramp is movable about two right axes to accommodate movement of the ramp assembly between a stowed position and a bridge forming position connecting the ship or other platform on which the main ramp is mounted and a relatively movable platform such as an offshore oil plat- form.

A principal object of the present invention is to pro¬ vide an articulated ramp which is capable of making and maintaining a bridge between two spaced platforms at least one of which is subject to substantially continuous movement relative to the other within a wide envelope of such move¬ ment in any direction due to waves and wind or other forces. Another object of this invention is to provide a ramp which has substantial reach and which is useable on ships in high sea state conditions. Still another object of this invention is to provide a ramp which is capable of adjusting to platforms of different

and varying heights, including the capability of reaching to a platform of much greater height than the ship on which it is mounted.

Further and other objects and advantages will become apparent from the following detailed description in which like numerals refer to like parts, especially when read in conjunction with the accompanying drawings.

Brief Description of Drawings Figure 1 is a fragmentary isometric view showing the articulated ramp assembly of this invention in a system in which the preferred embodiment is intended to be used.

Figure 2 is an isometric view of the articulated ramp assembly. Figure 3 is a fragmentary isometric view of the interme¬ diate platform on the articulated ramp showing anchor line reeved as well as the drive mechanism for the outer ramp.

Figure 4 is a fragmentary isometric view showing the pedestal drive and anchor line winches for the articulated ramp.

Figure 5 is a side elevation view of the articulated ramp with the outer ramp extended normal to the main ramp and showing the main ramp parallelogram linkage pivot points.

Figures 6 and 7 are fragmentary isometric views showing the station structure on an oil platform for releasably cou¬ pling the articulated ramp to the oil platform.

Figure 8 is a partial cross section elevation through the bottom portion of the main ramp showing the self level¬ ing steps and their parallelogram actuation linkage. The main ramp is shown in its elevated position in solid links and in its horizontal position in phantom lines.

Figure 9 is a cross section taken along line 9-9 of Fig- ure 8 showing the self leveling steps.

Figure 10 is a fragmentary isometric view of the outer end of the outer ramp showing the ball joint and mechanism for actuating the outer ramp gate.

Description of the Preferred Embodiment

The system as shown in FIG 1 comprises a first platform such as ship 10 on which is mounted articulated ramp assem¬ bly 11, illustrated in detail in FIGS 2 through 5, ^" and 8 through 10, and a second platform such as an offshore oil platform 12. Articulated ramp assembly 11 when extended and connected to oil platform 12 at station 13 forms a secure bridge between ship 10 and platform 12 for the safe transfer of passengers and personnel as well as small cargo. The construction of station 13 is shown in FIGS 6 and 7. FIG 1 illustrates the ramp just prior to being positioned for the transfer operation.

Referring particularly to FIGS 2 through 5, a vertical kingpost 14 projects through ship deck 16 to support pedes¬ tal 17 for rotation about the vertical axis of the kingpost. Pedestal 17 is provided with a base plate 18 which forms the lower landing for spiral stairway 19. Spiral stairway 19 wraps around pedestal 17 to an upper landing 21 at the top of the pedestal.

To control the rotational movement of pedestal 17, a pair erf; redundant slewing drive motors 15 and 15' are car¬ ried on base plate 18 as shown in FIG 4. These drive motors engage a ring gear 20 on kingpost 14.

A pair of posts 22 and 23 extend upwardly from the base of pedestal 17 beyond the upper landing to hingedly support ramp assembly 11 through pins as at 24 for movement about an axis normal to the axis of pedestal rotation (FIG 5) . Ramp assembly 11 comprises a main ramp 26, an intermediate or mid-ramp platform 27 and an outer ramp 28.

Main ramp 26 is hingedly connected to a pair of verti¬ cally extending arms 29 and 31 on mid-ramp platform 27 through pins as at 30. Main ramp handrails 32 and 33 are similarly hingedly connected at one end to mid-ramp platform arms.2-9T and 31 through pins 34 and 36 and at their opposite ends; to pedestal arms 22 and 23 through pins 37 and 38 form¬ ing a parallelogram linkage with arms 22 and 23 and arms 29 and 31, and main ramp 26, which maintains mid-ramp platform 27 parallel with the plane of ship deck 16 as main ramp 26

is raised or lowered about the main ramp swing axis defined by pins 24.

A pair of hydraulic actuators 39 and 41 each connect at one end to pedestal arm 22 or 23 through pins as at 43 near pedestal base plate 18 and to a fitting as at 42, through pins at 44 on either side of main ramp 26. Actuators 39 and

41 move main ramp in elevation as directed by ramp control operator 90 stationed at the upper landing 21 on pedestal 17 at ramp control console 46 (FIG 1) . Handrails 32 and 33 on main ramp 26 may be suitably braced as shown in FIGS 2 and 5 by support stanchions 47. The stanchions should be swingably connected to the main ramp and to the handrails so as to provide added support for the handrails, but not resist the limited angular changes they must undergo as the main ramp is swung in elevation.

Referring to FIG 5, line 55 acting between arms 22 and 29 or 23 and 31 through pins 57 and 58 serves as a tension member in the preferred embodiment to eliminate compression in handrail 32. To adjust the tension in line 55, a turn- buckle 59 or the like may be employed.

The main ramp is intended to function at elevation angles as high as 35 to 45 degrees or more above horizontal. To enable its safe use at these high elevation angles, the pedestrian floor of the main ramp is segmented to form self-leveling stair steps as the ramp is raised in ele¬ vation. As best shown in FIG 8 and 9, step segments 48 are

each hinged to the ramp by pins as at 49, and to a pair of links 54, one on either side of the step segments, by pins as at 51. Links 54 each extend the full length of main ramp

26 to connect at one end with arm 22 or 23 on the pedestal as at pin 53 and similarly at its opposite end with arm 29 or 31 on midramp platform 27,' and with each step segment therebetween. Links 54 and main ramp 26, together with arms

22, 29 and.23, 36 function as a second parallelogram linkage causing each, step segment 48 to remain generally parallel with ship deck 16 throughout movement of the main ramp in elevation. The steps are formed as the main ramp is moved up in elevation.

Mid-ramp platform 27, as shown in FIG 3 includes an out¬ er ramp support drum 61 supported on the platform under its deck 64 for rotation about shaft 60 on an axis generally parallel with the axis of rotation of pedestal 17. Posi¬ tioning of drum 61 about its axis of rotation is controlled by motor 62 through gearing 63.

Outer ramp 28 is cantilevered intermediate its ends from drum 61 on shaft 65 and is movable on the shaft about an axis normal to the drum axis of rotation as shown in FIG 3, whereby the outer ramp may be swung on shaft 65 between a stowed position (not shown) along side main ramp 26 to an extended position for connection with an oil platform as illustrated in FIG 1.

Still referring to FIG 3, a hydraulic actuator 66 acting between mid-ramp platform 27 and outer ramp 28 may be pro¬ vided to selectively control the movement of the outer ramp about shaft 65, to clamp its movement, or permit it to rotate freely as directed by commands inputted by the ramp operator at control station 46.

To near balance outer ramp 28 on shaft 65 for purposes to be hereinafter more fully explained, a counter weight 68 may be added as best shown in FIGS 2 and 3. Outer ramp 28 connects the articulated ramp assembly to oil platform 12 through a ball joint 69 carried on tubular guide or shaft 70 which projects from outer ramp 28 below the walkway as best shown in FIG 10. To absorb shock loads, and to actuate loading gates 93, shaft 70 is slidably sup- ported in bearings 102 and 103 permitting limited axial movement of the shaft and ball joint. .Compression spring and shock absorber packs 97 and 98, acting between flange 99 on outer ramp 28 and arms 104 and 106 extending from shaft 70, normally urge the ball joint 69 and shaft 70 towards an extended position projecting forwardly of the outer ramp. Tension springs 109 and 110 each connect at one end to arms 104 and 106, respectively, and at their opposite end to levers 112 and 113 formed on gate 93. Bearing tubes such as 114, one on either side of gate 93, support the gate for swinging movement between open and closed positions on outer ramp 28 while coil spring 116, one for each bearing tube

114, normally urge the gate closed. Stops 117 and 118 pro¬ jecting from ramp 28 prevent gate overtravel in the closed position by limiting the movement of levers 112 and 113. The gate is opened by springs 109 and 110 when ball joint 69 and shaft 70 are retracted, ^' causing springs 109 and 110 to overpower the gate closing force exerted by coil spring 116. Referring now to FIGS 6 and 7, ramp station 13 on oil platform 12 includes a deck threshold 73 adapted to overlap the end 71 of outer ramp 28 and provide solid footing for those being transferred between the ship and oil platform when the ramp is secured to the platform. Below threshold 73 is a rigid box-like structure 74 having a slit 76 formed therein which extends through the threshold and communicates with a centrally located opening through the box-like struc- ture forming a socket 77 on one side of the box-like struc¬ ture. Socket 77 is adapted to mate with ball joint 69 on outer ramp 28. On the opposite side of box-like structure 74, the opening therethrough forms a seat 78 for an anchor line stop fitting 79. Ball joint 69 on outer ramp 28 is drawn into mating engagement with socket 77 for securing the outer ramp to oil platform 12 by anchor lines 81 and 82 carried on articulated ramp assembly 11. As shown in FIG 4, anchor lines 81 and 82 are each tied to separate constant tension winches 83 and 84 mounted on pedestal plate 18 and suitably reeved along the underside of ramp assembly 11 such as by guide pulley 86 on

outer ramp 28 as shown in FIG 3. The free end of anchor lines 81 and 82 extend through opening 87 formed in ball joint 69 to connect with anchor line stop fitting 79. By passing anchor lines 81 and 82 through slit 76 in oil plat- form station structure 74 as indicated in FIG 7 to position anchor line stop fitting 79 on seat 78, and then drawing the anchor lines in with winches 83 and 84 until ball joint 69 is firmly seated in socket 77, articulated ramp assembly 11 is cinched to oil platform 12 providing a secure bridge between ship 10 and the oil platform.

The anchor line is a key element in system safety, and therefore two separate anchor lines 81 and 82 and winches 83 and 84 are preferably employed to increase system reliabil¬ ity through redundancy. It should also be noted that the anchor lines, in passing through the ball and socket are subject to being pinched under extreme angular movement. To prevent shearing of the anchor lines under such conditions, the opening through ball 69 and socket 77 should be free of sharp cutting edges. These parts are preferably either coated with a resilient liner or fabricated using a material which is somewhat compliant, yet of sufficient strength to carry the loads to which it will be subjected.

The controls and lines for the ramp drive motors and linear actuators are old in the crane art and except for the reference to ramp control station 46 are omitted from the

disclosure for simplicity since they form no part of this invention.

In operation, after ship 10 maneuvers into its preferred position near oil platform 12, articulated ramp assembly 11 is unfastened from its stowed position and prepared for deployment. A messenger line 91 is passed between the oil platform and the ship by rig man 96. The ramp operator identified in FIG 1 by reference numeral 90 catches the mes¬ senger line and connects it to anchor line pendant 92, which is that short portion of anchor lines 81 ^' and 82 which extend beyond anchor line stop fitting 79. He then assumes his station at ramp control console 46 atop pedestal 17 and pro¬ ceeds to elevate main ramp 26 to the height of oil platform 12. He simultaneously rotates outer ramp 27 so that it points towards the oil platform. During the same time, using messenger line 91, the rig man pulls anchor lines 81 and 82 up through ball joint 69 from constant tension winch¬ es 83 and 84. Anchor lines 81 and 82 are fixed on the oil platform by dropping the anchor lines through slot 76 on the oil platform to position anchor line stop fitting 79 against seat 78 on box structure 74.

The ramp operator then activates the constant tension winches 83 and 84 to bring anchor lines 81 and 82 under load. The brake on slewing drive motor 62 for outer ramp 28 is released, and increasing tension on the anchor lines pulls the ramp into transfer position drawing ball 69 firmly

into engagement with socket 77, causing the springs in spring and shock absorber packs 97 and 98 to compress as shaft 70 and ball joint 69 retract to where outer ramp end

71 rests below and overlaps oil platform threshold 73. The movement of shaft 70 in retraction opens gate 93 by means of tension springs 109 and 110. The winches maintain tension on the anchor lines throughout the transfer operation. When this hook up is established, ship 10 is free to pitch, heave and roll and to move on the seaway as allowed by ramp assem- bly 11.

Before the transfer process begins, the rig man checks out the system and manually opens safety gate 95 on platform 13. Ramp gate 93 which forms a part of the handrail restraint system 94 on outer ramp 28, is automatically opened by the actuating mechanism shown in FIG. 10 through retraction of ball joint 69 after the ball is placed in platform socket 77. Gate 93 will automatically close if the ball should pull away from the socket due to relative move¬ ment between ship 10 and platform 12 which exceeds the capa- bility of the ramp, so that personnel will not step or fall off the end of the ramp if it is not in proper transfer position.

During the transfer operation, after hookup, no active actuation systems or power other than tension in winches 83 and 84 is required. Movement of the ramp system elements is caused by the relative motion of the ship and platform being

bridged. Main ramp 26 will be caused to rotate about the axis of kingpost 14, and outer ramp 28 will be caused to rotate relative to main ramp 26 about shafts 60 and 65, as outer ramp 28 is rotated relative to the loading platform 13 through the ball 69 and socket 77.

After the transfer operation is complete, the ramp oper¬ ator and the rig man make sure the ramp is clear. Thereaft¬ er the ramp operator effects closure of gate 93 by releasing tension on the anchor lines as the rig man disconnects the anchor lines and stop fitting 79 from box structure 74 on the oil platform. The ramp operator then rotates the ramp assembly away from the oil platform, slewing outer ramp 28 alongside main ramp 26, and stows the ramp as the ship pro¬ ceeds to its next transfer point. Although the invention has been shown and described in connection with a certain specific embodiment, it will be apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit require¬ ments without departing from the spirit and scope of the invention. For example, a pair of anchor lines 81 and 82 and a pair of winches 83 and 84 are disclosed when only one may suffice where the added safety of redundancy is not required. Moreover, winches 83 and 84, shown mounted on pedestal base plate 18, may conveniently be located else- where on ramp assembly 11 such as to serve partially or

wholly as the counterweight 68 on outer ramp 28, thus serv¬ ing a dual purpose within the scope of these teachings. Having described my invention, I now claim: