US3378086A

US3378086A - Stationary overwater platform

Info

Publication number: US3378086A
Application number: US550031A
Authority: US
Inventors: Kivisild Hans Robert
Original assignee: GEOCON Ltd
Current assignee: GEOCON Ltd
Priority date: 1966-05-13
Filing date: 1966-05-13
Publication date: 1968-04-16
Anticipated expiration: 1985-04-16

Description

April 16, 1968 H. R. KIVISILD STATIONARY OVERWATER PLATFORM 5 SheetsSheet 1 Filed May 13, 1966 INVENTOR HRK/V/S/LD A rromeys April 16, 1968 Filed May 13, 1966 H. R. KIVISILD STATIONARY OVERWATER PLATFORM 5 Sheets-Sheet 2 Fig. 4.

'INV'ENTOR H. R K/V/S/LD Arromeys April 16, 1968 H. R. KlVlSlLD STAT IONARY OVERWATER PLATFORM Filed May 13, 1966 5 Sheets-Sheet 1 Fly. 5.

87 as as 80 2 Hg. 6 r

- LNVENTOR H. R K/I/IS/LD A Horneys April 16, 1968 H. R. KlVlSlLD STATIONARY OVERWATER PLATFORM 5 heets-s t 4 Filed May 13, 1966 //3 in ToR ws/Lp W A faffley April 1968 H. R. KIVISILD 3,378,086

STATIONARY OVERWATER PLATFORM Filed May 13, 1966 5 Sheets-Sheet 5 INVENTOR H. R. KIVISILD Attorneys United States Patent 3,378,086 STATIONARY OVERWATER PLATFORM Hans Robert Kivisild, Willowdale, Ontario, Canada, assignor to Geoeon Ltd., a corporation of Canada Filed May 13, 1966, Ser. No. 550,031 43 Claims. (Cl. 175-7) This invention relates to apparatus for suspending a load-bearing platform a substantially fixed vertical distance above the bed of a body of liquid. The invention is particularly applicable to the support of a drilling platform having drill driving means thereon and arranged to drive a drill which is being used to bore in the bed of the body of liquid. The invention is also concerned with method of supporting a load bearing platform above the bed of a body of liquid, and also with a method of drilling in the bed of a body of liquid.

At the present time, elf-shore drilling for exploration or production is carried out by any one of the following methods:

(1) 'The drilling is carried out from rigid structures firmly supported on the bed of the body of liquid; or

(2) The drillin is carried out from a substantially submerged buoyancy chamber which is anchored to the bed;

(3) The drilling is carried out directly from a floating vessel.

The first method is limited for reasons of economy to use in relatively shallow water while the second method, due to its elaborate anchoring system and the expense involved, is practically limited to permanent or semipernianent installations. The third, and cheapest, method has the disadvantage that during vertical movements of the vessel, which may occur due to tides and wave action, the pressure on the drill bit will vary and difliculties in drilling will therefore result.

It is an object of the invention to provide apparatus which may be used for off-shore drilling and which may be used in deep water on temporary installations and which does not have the disadvantage of the third method but which maintains a substantially constant pressure on the drill bit.

A further object of the invention is to provide, when the apparatus is used for drilling, a guide for the drill string when the latter extends between the vessel and the bed to be drilled.

A further object of the invention is to provide apparatus which will allow the drill hole to be abondoned rapidly if necessary and which will enable the hole to be re-entered.

These objects are obtained by supporting the platform on an elongated member which extends between the vessel arid the bed and which is continuously tensioned during vertical movement of the vessel. Where the platform is used for drilling it will carry the drill driving means, and the drill casing will be guided by the tensioned elongated member.

A number of embodiments of the invention will now be described in detail by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of drilling apparatus embodying the invention mounted on the stern of a floating vessel;

3,378,086- Patented Apr. 16, 1968 "ice FIGURE 2 is a detail view of the platform supporting arrangement of the apparatus of FIGURE 1;-

FIGURE 3 is a side elevation of a second embodiment of the invention;

FIGURE 4 is a plan view of the embodiment of FIG- URE 3;

FIGURE 5 is a side elevation of a third embodiment of the invention;

FIGURE 6 is a side elevation of a fourth embodiment of the invention;

FIGURE 7 is a side elevation of a fifth embodiment of the invention;

FIGURE 8 is a side elevation of a sixth embodiment of the invention;

FIGURE 9 is a detail end elevation of the embodiment of FIGURE 8 on a larger scale;

FIGURE 10 is a side elevation of a seventh embodimerit of the invention;

FIGURE 11 is a side elevation of an eighth embodiment of the invention;

FIGURE 12 is a detail plan of the tensioning and support means for the elongated member of FIGURE 11; and

FIGURE 13 is a perspective view, partly broken away, of a detail of the elongated member of the embodiment of FIGURE 11.

Referring now to FIGURES 1 and 2, the apparatus comprises a drilling platform which is supported from the stern of a vessel indicated generally at 21; the vessel floats on a body of liquid 22. The platform is supported by means of a boom 23 which is pivoted about a generally horizontal shaft 25 mounted in trunnions 26 secured to the deck 27 of the vessel. The free end 28 of the boom is connected by cables 29 to a leg 30 which itself is pivoted about a horizontal shaft 31 held in the trunnions 26. The angular position of the leg 30 about its shaft 31 is controlled by means of cables 32 which are led to Winch means 36 controlled by drive means 34.

At its end 28, the boom 23 is provided with a pair of guide pulleys 35 for a pair of flexible cables 36. The ends of the cables 36 are connected to winch drums 37 which are mounted on a common shaft 38 and are driven by drive means 39. Also mounted on the shaft 3 8 is a further drum 40 around which is wrapped a flexible cable 41 which passes over a guide pulley 42 mounted on a horizontal shaft 43 at the top of a tower 44 extending vertically from, and secured to, the deck 27. The tower is braced by guy-ropes 45.

Mounted for vertical sliding motion in the tower 44 is a counterweight 46. The other end of the cable 41 is connected to the counterweight at 47. The

drums

37 and 40 may be separately driven by the drive means 39; they may be independently braked; and they may be locked to the shaft 38 to rotate together.

Below the guide pulleys 35, the flexible cables 36 pass around guide pulleys and through clamps on a yoke member 48 most clearly indicated in FIGURE 2. The yoke member carries an inner pair of pulleys 49 and an outer pair of pulleys 50. Mounted on the upper surface of the yoke member are two hydraulic clamps 51 with which are associated abutments 52, each cable 36 passing between a clamp 51 at its associated abutment 52. It can be seen from FIGURE 2 that each cable 36 passes between a clamp 51 and its abutment 52 and then beneath one of the pulleys 49 and over one of the pulleys 50. Referring now to FIGURES l and 2, each cable 36 on leaving its pulley passes under a pulley 53 on the upper surface of the platform 20 and then over a pulley 54 at the edge of an aperture 55 in the platform and then extends downwardly until the lower end of the cable is connected to a ring 56. The ring 56 is connected by two rigid stays 57 to a generally cylindrical weight indicated at 58 and having a central bore 59.

The platform 20 is supported from the yoke member 48 by means of four cables 60 which are connected at their upper ends to an eye 61 supported on a hook 62 rigidly secured to the yoke member. The platform carries drill driving means indicated generally at 63 which may be of any conventional type. The upper end 65 of a drill string 64 is engaged with the drill driving means 63, and the lower end 66 of the drill string carries a drill bit (not shown).

An outer casing 67 for the drill string has secured thereto clamps 68 at spaced intervals, the clamps carrying two pairs of spaced rollers 69, each cable 36 extending between one of the pairs of rollers 69 so that the cables 36 can guide and support the outer drill casing 67. The outer drill casing is secured to the platform 20 by a suitable device 70. An inner drill casing (not shown) is mounted within the outer drill casing.

The platform 20 is connected to the vessel 21 by means of a walkway 71.

The operation of the embodiment of FIGURES l and 2 will now be described. When the vessel 21 arrives above the part of the bed 72 to be drilled, the platform 20 and the weight 58 are stowed on the deck 27 of the vessel and the counterweight 46 also rests on the deck of the vessel. In this stowed position the drill string 64 and the drill casing 67 will not be in position, the sections of the drill string and of the casing being stored in some convenient part of the vessel. Similarly, the clamps 68 will not be engaged with the cable 36 and the latter will have been shortened by being wound onto the drums 37 so that there is a convenient length of cable between the platform 20 and the weight 58. To commence operations, the cables 36 are tightened by winding on the drums 37. The clamps 51 are operated to hold fast the platform 20 to the cables 36, and the platform and the weight are swung out by the boom 23. The yoke member 48 is then connected by a chain 73 shown in chain-dotted lines in FIGURE 2 to the boom, and the clamps 51 are released so that the platform is suspended directly by the boom 23. The

cables 36 are then payed out by the drums 37 until the weight 58 is just clear of the bed of liquid 72. The clamps 51 are then operated to reconnect the platform to the cable 36, and the chain 73 is disconnected from the platform. The cables 36 are then lowered until the weight 58 sits firmly on the bed 72.

The drum 40 is then rotated by the drive means 39 to raise the counterweight 46 to a convenient position in its guiding tower 44, and when the vessel is at a relatively high position (such as at high tide and/ or when the vessel is on the crest of a wave), the drum 40 is locked to the shaft 38 and to the drums 37 and is disconnected from the drive 39. The counterweight 46 will then move down the tower 44 until it has taken up all the slack in the cables 36. It will achieve this by rotating the drum 40 which in turn will rotate the drums 37 and take up the slack in the cables 36. The counterweight is of a mass such that it will exert a continuous tension on the cables 36 during vertical movement of the vessel but is of insutficient mass to raise the weight 58 from the bed 72. It will be seen, therefore, that so long as the counterweight 46 is provided with enough room for vertical movement, the cables 36 will be continuously tensioned during vertical movement of the vessel. The boom 23 may have its position varied to provide the best location for the counterweight 4 travel or to partially adjust for the rise and fall of any tide on which the vessel is floating.

The walkway 71 can be placed in position and the drill driving means 63, may if not permanently fixed to the platform, be mounted thereon. Sections of the outer drill casing 67 are then brought onto the platform 20 and are screwed together in sequence and lowered. As the sections of the outer casing are lowered the clarnps 68 which are in two parts are secured thereto so that they embrace the cables 36, and the outer casing is thus guided by the cables 36. When the appropriate length of outer casing has been assembled onto the cables 36, its upper end is made fast to the platform 20 by the dew'ce 70. The

inner casing is then inserted into the outer casing and is driven into the bed, and finally the drill string 64 is engaged with the drive means 63 and is lowered down the casing whereupon drilling can commence.

Due to the fact that the cables 36 are continuously tensioned during vertical movement of the vessel 21, the platform 20 will remain a constant vertical distance above the bed 72. Since the drill string extends between the platform and the bed it will be possible to maintain a substantially constant pressure on the string because there will be no variation in distance between the bed which is being drilled and the drive means at the top of the.

string. It will be appreciated that, if the vessel falls into the trough of a wave the counterweight 46 will fall relative to the deck 27 thus taking up the slack in the cables 36 and keeping them tensioned. Conversely, if the vessel 21 rides on the crest of the Wave the counterweight 46 will rise in its tower 44 and will allow further lengths of the cables 36 to be payed out thus maintaining the cables tensioned but without lifting the weight 58 from the bed. The counterweight cannot lift the Weight 58 from the bed because of the relative masses of the weight and of the counterweight as described above.

If the hole being drilled in the bed has to be abandoned temporarily during drilling, the platform 20 may be attached to the boom 23 by means of the'chain 73 and the cables 36 may be disconnected from the drums 37 and may be buoyed so that they may be recovered and the hole re-entered when the vessel returns to the drilling position. The inner and outer drill casings may either be left attached to the cables 36 or they may be pulled.

It will be seen that the tensioned cables 36 do not only maintain the platform at a constant distance above.

the bed 72 and therefore allow constant pressure to be applied to the drill string. They also .provide lateral support to the drill casing, thus reducing the stresses induced in the drill casing by wave action and/or by currents in the liquid. As a further function, the cables guide the drill string from the drill into the bed.

In FIGURES 1 and 2, the vessel 21 is moored by means of anchors, one of the anchor cables being indicated at 74. Referring now to FIGURES 3 and 4, these show an arrangement which is identical to that shown in FIGURES 1 and 2 except that there are four anchor cables 75 which extend from the platform 20 to anchor weights 76 on the bed 72. The anchor cables 75 together with the elongated member comprising the cables 36 thus fixedly locate the platform 20 since the platform is maintained at a constant height above the bed 72 by the cables 36 as described in relation to FIGURES 1 and 2 and is located against horizontal movement by means of the anchor cables 75. The anchor cables 75 preferably are connected at their upper ends to winches (not shown) on the platform 20 so that the tensions in the cables 75 may be adjusted.

If desired, each anchor weight 76 could be connected to the platform by two anchor cables connected to the platform at opposite sides thereof. In the embodiment shown in FIGURES 3 and 4, the vessel 21 may be positioned by means of the cables 36 since these are connected to the platform 20 by means of the clamps 51 and the cooperating abutments 52, and the platform 20 is itself located by means of the elongated member and by means of the anchor cables 75. In this arrangement, therefore, the vessel 21 can locate itself relative to the platform in a position in which it offers least resistance to wave action and/ or current.

Referring now to FIGURE 5, this shows an arrangement in which the platform 20, the flexible cables 36, the weight 58 and the boom 23 are precisely as described in relation to FIGURE 1. However, in FIGURE 5 the flexible cables 36 are taken directly to a winch 77 and the winch is connected to a constant torque drive means in the form of a hydraulic power actuator 78 having an accumulator 79. Any convenient form of actuator may be used and by way of example the actuator 78 may act on the spindle of the winch 77 by means of a rack and pinion operated by a hydraulic jack which in turn is supplied with hydraulic fluid from a pump via the accumulator 7 9. The winch 77 has conventional drive means independent from the hydraulic power actuator 78, whereby the initial length of the cables 36 upon the commencement of the drilling operation can be adjusted. The winch 77 and its constant torque drive take the place of the counterweight 46 and its guiding tower 44 in FIGURE 1, and the arrangement is particularly suitable where large vertical movements of the vessel 21 may make the counterweight system of FIGURE 1 cumbersome.

Referring now to FIGURE 6, this again is similar to FIGURE 1 so far as the weight 58, the cables 36, the platform 20 and the boom 23 are concerned. In the arrangement of FIGURE 6, however, the upper ends of the cables 36 are taken to a winch 80 having a conventional drive and are anchored thereto. However, between the platform 20 and the winch 80 the cables pass around guide pulleys 81 mounted on the end of the piston rod 82 of a hydraulic jack 83 and also around guide pulleys 84 on a sheave fixed to the boom 23; the cylinder of the jack 33 is fixed to the boom 23. The jack 83 is fed from a hydraulic accumulator 85 which is kept charged with hydraulic fluid from a reservoir 86 by means of a pump 87. The pressure in the jack 83 is thus adjusted to keep the cables 36 under tension during vertical movements of the vessel 21 without lifting the weight 58. The embodiment of FIGURE 6 may be considered to be a variation of the embodiment of FIGURE 5 and has the advantage that the inertia of the drum of the winch 77 is eliminated;

Referring now to FIGURE 7, this shows a somewhat different arrangement in which a vessel 88 is provided with a well 89 therein. The arrangement of the weight 58, the cables 36 and the platform 20 is as in FIGURE 1. However, the cables 36 extend up through the well 89, pass over guide pulleys 90 at free end of a boom 91 and pass over guide pulleys 92 at the top of a guide tower 93 within which is mounted a counterweight 94 to which the upper ends of the cables 36 are connected. The boom 91 is pivoted about a horizontal shaft 95 and a leg 96 is provided whereby the position of the boom 91 can be adjusted.

1n FIGURE 7, the counterweight 94 directly tensions the cables 36 continuously without lifting the weight 58, and the operation of the embodiment is otherwise similar to the operation of the embodiments previously described, The well is provided with an upper part 97 in which the platform 20 can be stowed when not in use, and the lower part 98 of the well is dimensioned so as to receive the Weight 58 and the ring 56.

The arrangement illustrated in FIGURES 8 and 9 uses the weight 58, the elongated cables 36 and the platform 20 as already described in relation to FIGURE 1. As shown in FIGURE 9, the cables 36 after having passed around the

pulleys

54 and 53, pass around pulleys 99, 100 and 101 on one end of a boom 102. The platform 20 is supported from the boom 102 by means of cables 103 secured to the platform and to a hook 104 on the end of the boom.

The cables 36 run back along the boom 102 to a winch 105 mounted thereon. The boom is pivoted at 106 about a substantially horizontal axis to a tower 107 mounted on a vessel 108. The left-hand end of the boom 102 in FIGURE 8 is provided with a counterweight 109. In this arrangement, therefore, the flexible cables 36 are tensioned by pivoting of the boom 102 about its axis 106, this pivoting being brought about by means of the counterweight 109 which is so arranged to have a moment about the axis 106 which will continuously tension the cable 36 without lifting the weight 58 from the bed 72 during vertical movements of the vessel 108.

Referring now to FIGURE 10, this embodiment utilizes a vessel 110 having a central well 111 therein. A weight 112 is connected by flexible cables 113 to winches 114 on a platform 115. The platform itself is slidable vertically in guides on vertical towers 116 which contain counterweights 117 which also are slidable vertically in the towers. The platform is connected to the counterweights 117 by flexible cables 118 which pass over guide pulleys 119 at the tops of the towers. In this arrangement, the initial lengths of the flexible cables 113' are adjusted by means of the winches 114 and the cables 113- are then tensioned by means of the counterweights 117 which tend to raise the platform 115 and thus tension the cables 113. The operation of the embodiment is otherwise similar to that of the embodiments described above.

Referring now to FIGURES 11 to 13 inclusive, these show an embodiment which utilizes a vessel 120 from which is suspended an elongated member indicated generally at 121 and comprising an upper rigid sleeve 122 and a plurality of interconnected sections 123, each section being formed of two lengths 124 of flexible cable connccted at their ends to

collar

125 and 126 as clearly shown in FIGURE 13. The

collar

125 and 126 carry complementary screw-threaded formations indicated generally at 127 and the sections are assembled, as shown in FIGURE 11, so that the cable lengths 124 in adjacent sections lie in perpendicular planes.

A platform 123 is rigidly secured to the top of the sleeve 122 and carries drill driving means 129 and a gantry 130 whereby drill sections can be fed to the drill driving means.

The sleeve 122 passes through an aperture 131 in a guide platform 132 secured to the side of the vessel. The sleeve is guided by means of four rubber tired wheels indicated at 133 and spaced equiangularly about the axis of the sleeve 122 and freely rotatable about horizontal axes. The lower ends of flexible cables 135- are connected at 136 to the sleeve 122 at positions below the guide platform 132, as shown in FIGURE 11. The other ends of the cables 135 are connected to winches 13 7 on the vessel, which winches are provided with constant torque drive means 138.

The lower end of the elongated member 121 is connected to a weight 139 and this in turn is connected by means of a flexible cable 140 with a separate winch 141 in the vessel. A platform 142 is provided on the side of the vessel to receive the weight 139 when the drilling rig is not in use.

To set up the embodiment shown in FIGURES 11 to 13, the vessel 120 is brought to the desired location and soundings are taken of the depth of the bed beneath the vessel. An appropriate number of sections 123 is then connected to the bottom of the sleeve 122 and the end section is connected to the weight 139. The weight 139 is then lowered by means of the flexible cable 140 until it rests on the bed 72. The winches 137 are then operated to apply a tension to the rigid sleeve 122 and therefore to the elongated member 121 continuously during vertical movements of the vessel, the tensioning being such as not to raise the weight 139 from the bed.

The outer casing and the drill string are then passed down the elongated member substantially as described in relation to FIGURE 1 except that, as shown in FIGURE 7 13, the outer casing 143 of the drill string is guided in the

collars

125 and 126.

It will be seen that the invention provides various means whereby an elongated member may be tensioned between the bed of the body of liquid and a load-bearing platform and whereby a load-bearing platform may be used for drilling in the bed of the liquid and, since it is suspended at a fixed vertical distance above said bed, a constant pressure can be applied to the drill bit.

What I claim as my invention is:

1. Apparatus for suspending a load-bearing platform a substantially fixed vertical distance above the bed of a body of liquid and comprising, in combination with the load-bearing platform, a vessel floating on said liquid, a weight resting on the bed, an elongated member extending between the weight and the platform, means for securing A one end of the member to the weight, tensioning means on the vessel acting on the member to tension the member continuously during vertical movements of the vessel without lifting the weight from the bed, and means connecting the platform to the member so that the platform is vertically located by the member.

2. Apparatus according to claim 1 including releasable clamp means associated with the platform and with the elongated member whereby the platform may releasably be connected with said member.

3. Apparatus according to claim 1 wherein the elongated member comprises a flexible cable and the apparatus includes a boom, means pivoting the boom to the vessel about a generally horizontal axis and guide means .on the boom adjacent one end thereof for said flexible cable.

4. Apparatus according to claim 3 including drum means on the vessel around which said flexible cable is wrapped and a further flexible cable also wrapped around the drum means and connected to the tensioning means.

5. Apparatus according to claim 3 wherein the pivot means for the boom is located so that said one end thereof can overhang the body of liquid.

6. Apparatus according to claim 1 wherein the elongated member comprises a flexible cable and is connected directly to the tensioning means.

7. Apparatus according to claim 6 including releasable clamp means associated with t1 e platform and with the member whereby the platform may releasably be connected with said member.

8. Apparatus according to claim 7 wherein the elongated member comprises an upper rigid sleeve, the ap paratus including guide means for the sleeve overhanging said liquid and connected to the vessel and wherein the tensioning means includes winch means on the vessel, flexible cables connected to the winch means and to the sleeve, guides for the cables on the guide means and constant torque drive means for the winch means.

9. Apparatus according to claim 8 wherein there is a recess in the hull of the vessel to receive the weight when the latter is lifted from the bed.

10. Apparatus according to claim 8 wherein the guide means comprise a plurality of guide wheels rotatable about generally horizontal axes, the guide wheels being connected to pulleys constituting the guides for the flexible cables.

ll. Apparatus according to claim 10 wherein the lower part of the elongated member comprises a plurality of interconnected sections, each section comprising a col-' lar at each end and at least two flexible cable lengths interconnecting the collars.

12. Apparatus according to claim 11 wherein adjacent collars of adjacent sections have mutually complementary screwthreaded formations.

'13. Apparatus according to claim 12 including drill driving means on the platform and a drill string extending downwardly from the platform to the bed, the drill string extending through the apertures in the collars so as to be guided thereby.

'14. Apparatus according to claim 6 including a boom, means pivoting the boom to the vessel about a generally horizontal axis and guide means on the boom adjacent one end thereof for said flexible cable.

15. Apparatus according to claim 14 wherein the tensioning means includes a winch to which the other end of the elongated member is connected and a constant torque drive for said winch.

16. Apparatus according to claim 14 wherein the pivot means for the boom is located so that said one end thereof can overhang the body of liquid.

-17. Apparatus according to claim 14 wherein the tensioning means comprises means for anchoring the flexible cable adjacent the other end of the elongated member, means for forming a loop in said cable adjacent said other end and a fluid-operated jack engaged with said loop to provide said continuous tension in the member.

'18. Apparatus according to claim 17 wherein the pivot means for the boom is located so that said one end thereof can overhang the body of liquid.

19. Apparatus according to claim 14 wherein the tensioning means includes a counterweight connected to the other end of said member and means mounting the counterweight on the vessel for vertical movement relative thereto.

20. Apparatus according to claim 19, wherein the vessel is provided with a well open to the liquid on which the vessel floats and wherein the elongated member extends up through the well.

21. Apparatus according to claim 6 including a boom, means pivoting the boom intermediate its ends to the vessel about a generally horizontal axis, guide means adjacent one end of the boom for the cable, means anchoring the cable at the other end of the member to the boom and a counterweight adjacent the other end of the boom to continuously tension the member.

22. Apparatus according to claim 21 wherein the platform is connected to the boom'adjacent said one end.

23. Apparatus according to claim 22 wherein the pivot means for the boom is located so that said one end thereof can overhang the body of liquid.

24. Apparatus according to claim 23 including drill driving means on the platform, a drill string extending downwardly from the platform to the bed, and guide means for the drill string connected to the elongated member at intervals along its length.

25. Apparatus according to claim 1 wherein the elongated member is connected to the platform, the apparatus including flexible cables connecting the platform to the tensioning means.

26. Apparatus according to claim 25 wherein the tensioning means includes a counterweight and means mounting the counterweight on the vessel for vertical movement relative thereto.

27. Apparatus according to claim 25 wherein the vessel is provided with a well open to the liquid on which the vessel floats and wherein the elongated member extends up through the well.

28. Apparatus according to claim 25 wherein the vessel is provided with a well open to the liquid on which the vesssel floats and the elongated member extends through the well, the apparatus including two towers mounted on opposite sides of the well, a counterweight mounted for vertical movement in each tower and means connecting the flexible cables with the counterweights to tension the member.

29. Apparatus according to claim 28 including drill driving means on the platform, a drill string extending downwardly from the platform to the bed, and guide means for the drill string connected to the elongated member at intervals along its length.

30. Apparatus for suspending a load-bearing platform a substantially fixed vertical distance above the bed of a body of liquid and comprising, in combination with the load-bearing platform, a vessel floating on said liquid, a .weight resting on the bed, an elongated member comprising a flexible cable extending between the weight and the platform, means for securing one end of the member to the weight, releasable clamp means associated with the platform and with the cable whereby the platform may be releasably connected to said cable, a boom, means pivoting the boom to the vessel about a generally horizontal axis, means for controlling the position of the boom about its pivot axis, guide means on the boom adjacent one end thereof for said flexible cable, the pivot means for the boom being located so that said one end thereof can overhang the body of liquid, drum means on the vessel around which the flexible cable is wrapped, a further flexible cable also wrapped around the drum means, a counterweight connected to said further flexible cable, and means mounting the counterweight on the vessel for vertical movement relative thereto to tension the elongated member continuously during vertical movements of the vessel without lifting said weight from the bed.

"31. Apparatus according to claim 30 including drill driving means on the platform, a drill string extending downwardly from the platform to the bed, and guide means for the drill string connected to the elongated member at intervals along its length.

32. Apparatus according to claim '30 and including a plurality of anchoring means extending between the platform and the bed and radiating from the elongated member so as, with said member, positively to locate the platform.

'33. Apparatus for suspending a load-bearing platform a substantially fixed vertical distance above the bed of a body of liquid and comprising, in combination with the load-bearing platform, a vessel floating n the liquid, a weight resting on the bed, an elongated member comprising a flexible cable and extending between the weight and the platform, means for securing one end of the member to the weight, releasable clamp means associated with the platform and with the cable whereby the platform may be releasably connected with said cable, a boom, means pivoting the boom to the vessel about a generally horizontal axis, means for controlling the position of the boom about its pivot axis, guide means on the boom adjacent one end thereof for said flexible cable, the pivot means for the boom being located so that said one end thereof can overhang the body of liquid, a winch to which the flexible cable is connected, and a constant torque drive for said winch to tension the elongated member continuously during vertical movement of the vessel without lifting the weight from the bed.

'34. Apparatus according to claim.33 including drill driving means on the platform, a drill string extending downwardly from the platform to the bed, and guide means for the drill string connected to the elongated member at intervals along its length.

35. Apparatus for suspending a load-bearing platform a substantially fixed vertical distance above the bed of a body of liquid and comprising, in combination with the load-bearing platform, a vessel floating on said liquid, a weight resting on the bed, an elongated member comprising a flexible cable and extending between the weight and the platform, means for securing one end of the member to the weight, releasable clamp means associated with the platform and with the member whereby the platform may be releasably connected with said member, a boom, means pivoting the boom to the vessel about a generally horizontal axis, means for controlling the position of the boom about its pivot axis, guide means on the boom adjacent one end thereof for the flexible cable, the pivot means for the boom being located so that said one end thereof can overhang the body of liquid, means for anchoring the cable adjacent the other end of the elongated member, means for forming a loop in said cable adjacent said other end, and a fluid-operated jack engaged with said loop to provide a continuous tension in the member during vertical movements of the vessel without lifting the weight from the bed.

36. Apparatus according to claim including drill driving means on the platform, a drill string extending downwardly from the platform to the bed, and guide means for the drill string connected to the elongated member at intervals along its length.

'37. Apparatus for suspending a load-bearing platform a substantially fixed vertical distance above the bed of a body of liquid and comprising, in combination with the load-bearing platform, a vessel floating on said liquid, a weight resting on the bed, an elongated member comprising a flexible cable and extending between the weight and the platform, means for securing one end of the member to the weight, releasable clamp means associated with the platform and with the member whereby the platform may be releasably connected with said member, a well in the platform open to the liquid on which the vessel floats and through which the elongated member extends, a boom, means pivoting the boom to the vessel about a generally horizontal axis, guide means on the boom adjacent one end thereof for the flexible cable, a counterweight connected to the other end of said memher to tension the member continuously during vertical movement of the vessel without lifting the weight from the bed, and means mounting the counterweight on the vessel for vertical movement relative thereto.

38. Apparatus according to claim 37 including drill driving means on the platform, a drill string extending downwardly from the platform to the bed, and guide means for the drill string connected to the elongated member at intervals along its length.

39. Drilling apparatus in which a drilling platform is suspended a substantially fixed vertical distance above the bed of a body of liquid to enable drilling to proceed in said bed and comprising, in combination With the drilling platform, drill driving means on the platform, a vessel floating on said liquid, a weight resting on the bed, an elongated member extending between the weight and the platform, a drill string, guide means for the drill string connected to the elongated member at intervals along its length, means for securing one end of the member to the weight, tensioning means on the vessel acting on the member to tension the member continuously during vertical movements of the vessel without lifting the weight from the bed, and means connecting the platform to the member so that the platform is vertically located by the member.

40. Drilling apparatus according to claim 39 wherein the elongated member comprises a pair of spaced flexible cables and wherein the guide means comprises a casing, clamps connected to the casing at spaced intervas1 and rollers carried by the clamps and engaging the ca es.

41. Apparatus according to claim 40 and including a yoke member above the platform, means suspending the platform from the yoke member, pulley means on the yoke member over which the cables are passed and releasable clamp means mounted on the yoke member to grip the cables.

42. A method of suspending a load-bearing platform a substantially fixed vertical distance above the bed of a body of liquid, comprising positioning an elongated member to extend substantially the whole distance between the bed and a vessel floating on the body of liquid, weighing the lower end of the member to maintain said lower end in a fixed vertical relation to said bed, applying a force to the upper end of the member to establish a tension in the member such that the member is continuously tensioned during vertical movements of the vessel without varying said fixed relation between 11 the lower end of the member and the bed, and connecting the platform to the member above the surface of the liquid so as vertically to locate the platform by the member.

43. A method of drilling in the bed of a body of liquid comprising positioning an elongated member to extend substantially the whole distance between the bed and a vessel floating on the body of liquid, weighing the lower end of the member to maintain said lower end in a fixed vertical relation to said bed, applying a force to the upper end of the member to establish a tension in the member such that the member is continuously tensioned during vertical movements of the vessel without varying said fixed relation between the lower end of the member and the bed, extending a drill casing downwardly from the platform to adjacent the bed, supporting the drill casing by the elongated member, in-

12 serting a drill string into the casing to extend between the platform and the bed and driving the drill from the platform.

References Cited UNITED STATES PATENTS 1,778,320 10/1930 Hansen 17510 X 2,512,783 6/1950 Tucker 175-7 X 3,004,612 10/1961 Kofahl 1757 3,114,420 12/1963 Wilde 175-7 X 3,196,958 7/1965 Travers et a1. 166.5 X 3,208,728 9/ 1965 Parks 175-5 X 3,221,817 12/1965 De Vries et al 166-.5

CHARLES E. OCONNELL, Primary Examiner.

RICHARD E. FAVREAU, Assistant Examiner.

Claims

1. APPARATUS FOR SUSPENDING A LOAD-BEARING PLATFORM A SUBSTANTIALLY FIXED VERTICAL DISTANCE ABOVE THE BED OF A BODY OF LIQUID AND COMPRISING, IN COMBINATION WITH THE LOAD-BEARING PLATFORM, A VESSEL FLOATING ON SAID LIQUID, A WEIGHT RESTING ON THE BED, AN ELONGATED MEMBER EXTENDING BETWEEN THE WEIGHT AND THE PLATFORM, MEANS FOR SECURING ONE END OF THE MEMBER TO THE WEIGHT, TENSIONING MEANS ON THE VESSEL ACTING ON THE MEMBER TO TENSION THE MEMBER CONTINUOUSLY DURING VERTICAL MOVEMENTS OF THE VESSEL WITHOUT LIFTING THE WEIGHT FROM THE BED, AND MEANS CONNECTING THE PLATFORM TO THE MEMBER SO THAT THE PLATFORM IS VERTICALLY LOCATED BY THE MEMBER.