fig1 illustrates at 10 an off - shore well drilling platform which is intended to extend directly horizontally and is supported by a ` jacket ` 11 forming a framework resting on the sea bed 12 . jacket 11 as illustrated includes a number of tubular legs 13 extending downwardly through the water to the sea bed and each of which may be formed of a series of large diameter pipe sections welded together in end to end relation . the piles for connecting the jacket to the earth formation beneath the body of water 14 may extend downwardly through legs 13 or may be driven downwardly through a series of pile guides such as those represented at 15 . one or more jacking devices 16 constructed in accordance with the invention may be utilized in conjunction with piles driven downwardly through either legs 13 or guides 15 to raise one side of the jacket and platform slightly relative to the other in order to attain the desired precisely horizontal condition of the platform . in the drawings , it is typically assumed that the jacking device 16 is used in conjunction with one of several skirt piles 17 driven downwardly through one of a number of pile guides 15 secured rigidly to one of the jacket legs 13 . as seen in fig1 the legs and pile guides of the jacket are in most instances inclined to advance slightly laterally outwardly as they advance downwardly , in order to assure stability of the installed jacket and platform . for simplicity of illustration , however , fig2 through 7 do not attempt to illustrate this inclination of the legs , guides and piles , and the jacking tool , but instead show these elements in directly vertically extending positions . as seen in fig1 and 4 , the pile guides 15 normally have main straight cylindrical portions 18 to the upper ends of which flaring bells or centering guides 19 are secured to direct a pile into centered relation within the guides . in a jacket which is to be leveled by a jacking mechanism of the present invention , one or more of the pile guides 15 near the lower end of the jacket may be formed without the usual centering bell 19 , and in lieu of that bell have an extension sleeve 20 which projects upwardly above the main portion 18 of that guide and is annularly welded thereto at 21 . this skirt sleeve extension 20 may be formed of a length of pipe of the same diameter as the main portion 18 of the guide , the pipe being internally and externally cylindrical and preferably having a number of circularly spaced openings 22 near its lower end through which excess grout may discharge . above openings 22 , the tubular sleeve 20 carries a number of circularly spaced support lugs 23 , which may be welded to the outer surface of sleeve 20 and have upper surfaces 24 lying in a common plane 25 disposed transversely of the main longitudinal axis 26 of sleeve 20 and jack 16 . surfaces 24 of lugs 23 engage an annular undersurface 27 at the bottom of the jack mechanism disposed transversely of axis 26 to support the jack about sleeve 20 in the position shown in the drawings . as seen best in fig2 the jack 16 includes an upper gripping unit 28 which is adapted to engage and grip the outer cylindrical surface 29 of a pile 17 at a location above the upper end of sleeve 20 , and includes also a second and lower gripping unit 30 adapted to be received about and grip the outer cylindrical surface of sleeve 20 . several piston and cylinder mechanisms 31 extend between these two gripping units and act to move them vertically relative to one another , and may be attached to a sleeve 32 vertically between units 28 and 30 . upper gripping unit 28 includes an essentially annular rigid body 33 shaped to function as a slip bowl structure for engaging and locating a number of circularly spaced slips 34 . at the location of each of the slips 34 , body 33 has an upwardly conically tapering camming surface 35 engaging a correspondingly upwardly conically tapering camming surface 36 of the associated slip 34 to cam the slip radially inwardly against the outer surface 29 of the pile in response to upward movement of the slip relative to the slip bowl body 33 . the slips may be appropriately retained in engagement with camming surfaces 35 , and for upward and inward sliding movement relative thereto , by any conventional type of slip guiding structure typically illustrated as including a rod 37 rigidly secured to body 33 and inclined in correspondence with surfaces 35 and 36 and slidably received within guide openings in the slips . slips 34 have inner gripping faces 56 which engage the outer cylindrical surface of pile 17 in the fig5 and 6 gripping positions of the slips , and which curve essentially cylindrically in correspondence with the pile surfaces and have gripping teeth acting to lock the slips aggainst either upward or downward movement relative to the pile in the fig5 and 6 condition . the slips are power actuable between their released non - gripping condition of fig2 and their active gripping position of fig6 by powered means controllable from the surface of the body of water within which the platform is located , and preferably including a number of circularly spaced piston and cylinder mechanisms 38 , whose cylinders 39 may be connected to a slip actuating ring 40 centered about axis 26 . the cylinders 39 are movable along individual axes 41 relative to the pistons of mechanisms 38 , and the pistons 41 of mechanisms 38 may have double ended piston rods 42 rigidly connected at first ends to a flange 43 of body 33 and at second ends to a ring 44 of a diameter to be received about skirt sleeve extension 20 . ring 40 actuates the slips 34 through a number of links 45 , which may be pivotally connected at their opposite ends to ring 40 and the slips to cause upward and downward movement of the slips in correspondence with upward and downward movement of ring 40 while permitting the slips to move radially inwardly and outwardly with respect to the ring as the slips move from their gripping positions to their retracted positions of fig2 . the rods 42 of the pistons of course extend along the different axes 41 to locate and guide cylinders 39 for movement along those axes . connected to the upper end of slip bowl body 33 of gripping unit 28 , there is provided a pile centering guide or bell structure 46 , having an internally straight cylindrical portion 47 of a diameter to be received closely about outer surface 29 of pile 17 , and a portion 48 having an upwardly conically flaring annular inner surface engageable with a pile to direct its lower end into centered relation within jack 16 . guide structure 46 may have an annular wall 49 disposed transversely of axis 26 and welded to the other portions 47 and 48 of the structure , and appropriately rigidly secured to slip bowl body 33 as by extension of reduced diameter threaded end portions 50 of piston rods 42 through openings in wall 49 and flange 43 and connection of nuts 150 onto portions 50 . lines 51 for retrieving jack 16 after a platform leveling operation are connected to upper guide structure 46 , as by means of shackles or other connectors 52 to which the lower ends of the lines may be secured . these lines may be suspended at their upper ends from a crane 53 mounted on a barge or other support vessel 54 , with the lines being windable on a drum 55 to raise jack 16 to the surface after completion of a leveling operation . the lower gripping unit 30 may be identical with the above discussed upper gripping unit 28 , except that slips 34a in their gripping condition have a greater effective internal diameter than do slips 34 , and are cammed to their gripping condition by downward rather than upward movement . the slip bowl structure or body 33a of the lower gripping unit has at the location of each of the slips 34a an inner camming surface 35a which tapers conically downwardly and engages a correspondingly downwardly conically tapering camming surface 36a of the associated slip . the inner gripping faces 56a of slips 34a curve essentially cylindrically about axis 26 at a diameter corresponding to the outer surface of sleeve 20 , and have gripping teeth acting to support the weight of sleeve 20 and the jacket through the slips in the lower active positions of the slips relative to body 33a . slips 34a are actuable by piston and cylinder mechanisms 38a corresponding to mechanisms 38 of the upper gripping unit and having their cylinders connected to a ring 40a attached to the slips by links 45a each pivoted at its opposite ends to the ring and one of the slips . the piston rods of mechanisms 38a are rigidly connected at their opposite ends to flange 43a of body 33a and a ring 44a . in the upper retracted position of ring 40a and the connected parts , slips 34a are withdrawn upwardly relative to body 33a and are retracted slightly radially outwardly away from engagement with the outer surface of sleeve 20 to allow upward and downward movement of gripping unit 30 relative to the sleeve . the main piston and cylinder mechanisms 31 for applying the jacking force to the gripping units have their cylinders 57 connected at their upper ends 58 to brackets 59 projecting downwardly from the upper guide structure 46 . there preferably are four of the piston and cylinder mechanisms 31 , having their axes 60 disposed parallel to axis 26 and at evenly circularly spaced locations thereabout . the cylinders 57 may also be rigidly connected to sleeve 32 , as by members 61 extending radially between sleeve 32 and the cylinders and appropriately welded or otherwise secured to these parts . sleeve 32 has an inner cylindrical surface 62 which is a close fit about sleeve 20 and is preferably of a diameter approximately the same as the inner diameter of straight cylindrical portion 47 of guide structure 46 . the pistons 63 within cylinders 57 have their rods 64 connected at their lower ends to bracket lugs 65 formed on a rigid essentially annular lower body part 66 . this lower body part 66 may be constructed of a number of parts rigidly welded together , and including top and bottom annular walls 67 and 68 joined by vertical connectors . the top wall 67 is rigidly secured to slip bowl body 33a of the lower gripping unit , as by connection of nuts 150a onto reduced diameter threaded end portions of the piston rods 42a of assemblies 38a . the portions 75 of slip bowl 33 circularly between the slips have cylindrical centering surfaces 77 corresponding in diameter to the diameter of the external cylindrical surface 78 of sleeve 20 to accurately center sleeve 20 relative to the upper gripping unit . when a jacking mechanism such as that shown at 16 is to be utilized for leveling a marine platform , it is preferred that the jack be moved into position about the tubular member 20 of fig2 before the jacket is launched into the water . before thus positioning the jack on tube 20 , the slips 34 and 34a of both of the gripping units 28 and 30 are actuated to their released positions . with the jack in this condition , it is lowered to the position of fig2 in which the lower body part 66 is supported on lugs 23 of sleeve 20 , following which piston and cylinder mechanisms 38a of lower gripping unit 30 are actuated to move slips 34a downwardly from their retracted or inactive upper broken line positions of fig2 to their lower full line active gripping positions in which they are capable of transmitting upward force from slip bowl body 33a to sleeve 20 . with the jack thus positioned , and with the upper slips 34 still in their lower retracted positions , pile 17 is driven downwardly through jack 16 and through tube 20 and guide 15 into the sea bed to firmly anchor the pile relative to the sea bed . when the pile has been driven to a desired depth , the main piston and cylinder units 31 are actuated by fluid pressure to force their cylinders 57 and the connected parts including upper gripping unit 28 upwardly to a position such as that shown in fig3 and 4 and just far enough to enable the subsequent jacking operation as will be discussed to exactly level platform 10 . the amount of upward movement of the upper gripping unit is indicated to an operator located in barge 54 on a remote indicator diagrammatically represented at 69 in fig1 . this indicator may be controlled by signals from a sensing unit diagrammatically represented at 70 in fig3 as including an elongated rod 71 fixed to lower body 66 and movably engaging a coacting unit 71 carried by one of the cylinders 57 . unit 71 produces signals which may be conveyed in any appropriate manner to the indicator 69 to enable an operator by reference to indicator 69 to control precisely the amount upper gripping unit 28 is raised relative to lower gripping unit 30 . after the upper gripping unit has thus been elevated along the pile to the desired fig3 and fig4 position , the piston and cylinder machanisms 38 of upper gripping unit 28 are actuated to move slips 34 upwardly to their active gripping positions of engagement with pile 17 . with the slips of both gripping units held in their active gripping conditions , piston and cylinder mechanisms 31 are actuated to pull lower body part 66 and lower gripping unit 30 upwardly relative to upper gripping unit 28 , to thus forcibly elevate tubular part 20 and the remainder of the jacket and platform structure relative to the pile . this upward movement , represented in fig5 is continued until the upper annular transverse end edge 72 engages downwardly facing surfaces 73 on slips 34 to exert upward force against the slips . this engagement of the slips with tubular member 20 places that sleeve 20 and the slips and piston and cylinder mechanisms 31 in a heavily preloaded condition , preferably approximately a one - thousand ton preload very effectively retaining slips 34 against any possible downward movement relative to the engaged slip bowl structure 33 , and thus effectively locking the upper gripping unit against either upward or downward movement relative to the pile . because of the predetermination of the extent to which the upper gripping unit is moved upwardly relative to the lower gripping unit in the fig3 and 4 condition of the apparatus , the platform 10 is exactly horizontal in the fig5 locked preloaded condition of the equipment . with the platform held in this precisely horizontal condition and with the jack preloaded as discussed , grout is filled into the annular space radially between the outer surface of pile 17 and the inner surface of tubular pile guide 15 , with excess grout discharging through bottom openings 22 in sleeve 20 , and the apparatus is held in this condition while the grout sets . after the grout has hardened and set completely , the operator on barge 54 can reverse the pressure in piston and cylinder mechanisms 38 and 31 to release the upper gripping unit and raise the upper gripping unit relative to the lower gripping unit , and then similarly reverse the pressure in the cylinders of the lower gripping unit to release the bottom slips . the entire jack 16 can then be withdrawn upwardly by lines 51 from about the pile guide and pile , and retrieved onto barge 54 for subsequent use in leveling another platform . while a certain specific embodiment of the present invention has been disclosed as typical , the invention is of course not limited to this particular form , but rather is applicable broadly to all such variations as fall within the scope of the appended claims .