BUOYANCY DEVICE AND METHOD

,. ___ - BfiCKGR0UND OF THE INVENTION UJhen submarine cabls .or pipe is paid out from a barge or other vessel, particularly into deep water, it is désirable to support the meight of cable or pipe in the mater by means of buoys or floats so that the entire length of cable or pipe does not present a tension load to the cable or pipe itself at its uppermost point. This is particularly important uihere the cable or pipe has discontinuities such a-s splices or joints that may be damaged by an extreme tension. A particular problem exists ".

for the laying of submarine poiuer cable, uihich is considerably heavier than communication cable. Experience has shown that splices in such cable, even when the diameter of the splices is only slightly larger than that of the cable . itself, may develop cracks in the lead sheath under the armor or distortion of the insulation when high,tension is encountered mhile taking bends at the cable laying capstan or.-boiu sheave, even though these splices can take tfte sameibends without difficulty at lom ten¬ sion. The tensile load encountered in submarine pouier cable be¬ ing laid to depths exceeding 500 meters, and in recovering such cables for repair and re-laying may uiell be 20-30 metric tons or greater if the cable is not properly buoyed. Under such tension.

particularly in the case of paper-insulated, power cables, sudden longitudinal movement of the conductor may occur with respect to the rest of the cable structure. Such movements are, of course, very damaging, particularly at splices and terminations. In rel- atively shallow water, it has been known, especially in the lay¬ ing of pipe, to reduce the load by buoying the pipe with hollow spheres or drums spaced at distances sufficiently large to permit the pipe to sink, dragging the buoys down with it. At a suffic¬ ient depth, however, the strongest of hollow buoys that are light enough in intrinsic weight to have a lifting effect, would be collapsed by external water pressure. Even were this not the case it would be undesirable to support more flexible articles such as electric cables at great depths and when the articles are substantially horizontal, with the same initial buoyancy as was appropriate for the steep angle of descent a cable usually assumes immediately adjacent to the laying vessel. For highly buoyant floats that are attached at widely spaced points to a flexible article would raise the article at these points and cause it to festoon in the lengths between supports.

It has been suggested to buoy an elongated article from a ser¬ ies of boats or buoys floating at the surface and equipped with winches. The disadvantages of this system are that, in deep water, it requires an excessive quantity of supporting line, and that the small boats will transmit the vertical movement of waves and swells to the suspended article along with horizontal effects created by wind. For very long installations surface floats might constitute an intolerable interruption of normal surface navigation. It would appear desirable, therefore, to utilize a buoy that neither remains on the surface nor retains its full buoyancy while sinking to the sea bottom with the art¬ icle being laid. It might be thought that a buoy in the form of ' 1073SÎ25 a bell, open at the bottom, would supply the desired means since the equalization of pressure inside the bell would prevent its collapse and the compression of air in the bell would reduce its buoyancy as it descended. This simple expedient would be useless in deep water, however, since the loss of buoyancy, with the air volume having in the first ten meters of descent, is too rapid.

The vertical contour taken by a cable or pipe underwater as it is being laid is determined by the water depth, the speed of the laying vessel, and the rate of descent. This latter can be controlled by the selection of buoyancy devices and their spac¬ ing. The bottom contour of the ground underwater is known. But the vessel speed is subject to weather conditions. It would be of great advantage to make provision in the buoyancy devices themselves for differences in descent rates as required for diff- erent laying conditions. Under certain circumstances it will also be desirable to permit divers or submarines to control the release of buoying devices from an article being laid, at some precise moment.

SUMMARY I have invented a buoyancy device for at least partially sup¬ porting a submerged article and particularly an elongated article such as a cable or pipe being laid from a moving vessel, which comprises walls defining a submersible chamber, a substantial volume of gas enclosed in the chamber, and access means to the lower portion of the chamber for the water that surrounds the buoyancy device. This water will rise within the chamber and compress the gas as the depth of submergence of the buoyancy de¬ vice increases. My buoyancy device also comprises a supply of flexible line which it holds in support. One end of the line is supportingly fastened to the submerged article and this end may be heavier than the trailing end of the line. Means within i 'the chambor grip the line and pay it out, thereby changing the [distance betiuesn the buoyancy dauice and the article. ffly buoy- ancy device advantageously comprises a cylindrical capstan mhich may advantageously be rotatably interlocked with propeller means projecting into the surrounding uiater and providing a braking ieffect. Preferably the length of the supply of flexible line is essentially shorter than the desired final distance between the jbuoyancy device and the article, and the trailing end of the line is not attached permanently to the buoyancy device so that, when the entire supply of line has passed around the capstan, the buoyancy device u/ill be free to rise from the article, whence it may ba recovered.

Advantageously my buoyancy device will comprise means, such as a float, that is responsive to the level of uiater tuithin the chamber, for controlling the braking means. Advantageously also the braking means will comprise a friction brake and the float will be fastened to a lover arm that will release the brake and pay out line when the water level rises within the chamber. In some preferred embodiments my buoyancy device will comprise a pair of threaded posts passing' through matching threaded holes in the float, and gear means, driven by the capstan, for rotating the posts to raise the float relative to the laver arm as line is paid out by the capstan. This has the 'effect of allowing more water into the chamber and reducing the lifting effect of the buoyancy device as the article being supported approaches bottom.

In some embodiments my buoyancy device comprises a release line connecting the braking means and the article and sheave means paying out the release line. A centrifugal clutch supports the sheave means within the chamber in such a manner that the release line can pay out slowly without affecting the braking means but A- I<y73335 mill release the brake upon a sudden application of tension.

I hav/e invented a method of louiering an elongated article un- !der water which comprises the steps of paying the article from a supply of the same aboard a moving vessel and fastening a plural¬ ity of lines to spaced" locations along the length of the article.

The lines are individually connected to buoyancy devices and I isubmerge the article, along mith the buoyancy devices until the buoyancy devices have reached a depth uihere they are unaffected by mave motion or passing vessels. Thereafter I pay out the lineè from the buoyancy devices so as to lower the elongated article at a speed substantially greater than any speed of lowering of the buoyancy devices, although my method may comprise a step of reducing the buoyancy of the buoyancy devices in the final stage of descent of the article.

BRIEF DESCRIPTION OF THE DRAUJINGS FIGURE 1 shows a front viem of my buoyancy device.

FIGURE 2 shoius an enlarged section through the line 2-2 of FIGURE 1.

FIGURE 3 shoius an enlarged section through the line 3-3 of FIGURE 1 . ' " FIGURE 4 shoius a section through the line 4-4 of FIGURE 2, exposing my float apparatus.

FIGURE 5 shoius an elevation of a vessel laying a cable in ac¬ cordance mith one embodiment of my invention; FIGURE 6 shoius another embodiment of the float apparatus of FIGURE 4.

FIGURE 7 shoms an elevation of a vessel laying a cable in ac¬ cordance with another embodiment of my invention.

FIGURE 8 shouis an elevation of one embodiment of the line used in my invention.

DETAILED DESCRIPTION OF PREFERRED EiïlBODiniENT Referring first to FIGURE 1 my buoyancy means or device in¬ dicated generally by the numberal 10 is seen to have a generally spherical hollow bell 11 of glass-reinforced plastic and lower cylindrical portion 12 in the form of a skirt, of steel. The wall 13 of the bell extends downwardly in a cylindrical shape at the area 14 to cover and grip a cylindrical wall 16 of the skirt 12. The walls 13 and 16 combine to define a chamber 17 for the entrapment of air or other gas 18 which may be compressed by the pressure of a mass of water 19 free to enter the chamber 17 through an open bottom 2.1 of the cylinder 12. Although the use, of steel for the wall 16 as opposed to plastic for the wall 13, and the concentration of heavy elements, to be described, at the lower portion of the device 10 will usually suffice to prevent the device from turning bottom side up and permit escape of the gas 18, where conditions such as difficulty in launching or tur¬ bulent currents may be encountered, the opening 21 may be cover¬ ed by a suitable bulkhead provided with a check valve for the entrance of water, or by a membrane designed to burst when suff¬ icient depth is reached by the device 10 to remove the danger of its capsizing.

The cylindrical wall 16 is formed from a single strip, folded round and bolted at a flange 22 (FIGURE 3). Internal steel chord beam members 23 and 24 are bolted to the wall 16 and to another beam 26 while a beam 25 is bolted between the wall 16 and the beam 23 to support the elements to be described. A pair of groov¬ ed capstans 27, 28, terminating in spur gears 29, 30 are mounted on respective shafts 31, 32 between the beams 26, 25. The gears 29, 30 intermesh with a braking pinion 33 keyed to a shaft 34.

The shaft 34 passes through bearings 36, 37 on the beams 25, 26 respectively and through a bushing 38 on the wall 16. A propel¬ ler 39 is fixed to the shaft 34 at a point external to the walls of the device 10. The purpose of the propeller 39 is to brake the rotation of tha capstans 27, 28 and it will ba undarstood that, in lieu of a propellar, a paddle, turbine or hydraulic motor might be used to serve the same purpose ujithin the scope of my invention. At the opposite end of the shaft 34 from the prop¬ eller 39 a brake drum 41 is fastened in contact tuith a brake band 42 mhich is connected at both ends to a lever arm 43 pivot¬ ing on a pin 44 projecting from the beam 26. A flexible rope line 46 pays into a groove 47 of the capstan 27 from a supply 48 coiled in a bin 49 from vuhich it passes upiuardly to a ring guide 51 and domn through a holloui cylinder 52 in the center of the bin 49. The ring guide 51 is supported from the cylinder 52 by upright rods 53, 54. A floor 56 of the bin 49 has perforations 57-57 for the entrance of water so that the bin, of itself, uùil have no buoyancy. It will, however, be understood that other storage means for the line 46, such as a pail rigidly suspended below the capstans 27, 28 or a rotatable spool might be used in the practice of my invention with guides being provided, where necessary, for directing the line into a desired groove of the capstans.

At the right extremity 'of the lever arm 43, as seen in PIGURE 2 there is hingedly mounted a float 58 of low density foam plas¬ tic bonded to a rigid dense plastic or metal plate 59 having two tapped bores 61, 62 through which are engaged two oppositely threaded plastic posts 63, 64 to the bottomsof which plastic spur gears 66, 67 are locked by means of integral collars 68, 69 and appropriate set screws, not shown. The posts 63, 64 are ro- tatably mounted in bearings in the top of a gear reducer 71 through which one of the rods is driven slowly as the gear redu¬ cer is driven through a flexible shaft 72 extension of the shaft 34. The direction of rotation is such that thei float 58 rises slowly on ths posts 63, 64 as the capstans 27, 28 pay out the line 46. This line is fastened to a cable 73 or other article being laid, and as the line 46 is paid out the distance between the buoyancy device 10 and the cable 73 is increased. The gear reducer 71 is mounted onto the lever arm 43 through a support member 74 and locking pin 76 and the combined weight of the ele¬ ments 63, 64, 58, 59, 71, 74 is such that their moment around the pivot 44 is sufficient to put enough tension in the brake band 42 to prevent the capstans 27, 28 from turning and paying out any of the line 46. The device 19 will therefore sink along with the cable 73. As it sinks, however, the increased water pressure will cause water to enter the opening 21 and begin to compress the pocket of air 18. The water will also lift the fl¬ oat 58, reducing tension in the brake band 42, so that the line 46 will be paid out and allow the device 19 to rise until it reaches a point such that the water level within the chamber 17 no longer buoys the float 58 sufficiently to release line 46 and the device 10 will sink again until the process is repeated.

Some restraint is required against paying out of the line 46 when the brake band 42 is relaxed to prevent the buoyant units frome repeatedly bobbing up in a series of jerking motions that would terminate the shocks to the cable 73. This restraint is provided by the propeller 39 which prevents too rapid rotation of the capstans. As the line 46 is paid out and the float 58 raised on the rods 63, 64 the device 10 will gradually reduce in buoyancy due to the fact that increasing quantities of water will be required toenter the chamber 17 before the brake band 42 is loosened. This reduced buoyancy will prevent the festoon¬ ing of very flexible cables, as shall be explained, but, where festooning presents no problem because of a greater stiffness in the article being lowered, the short distance between buoy at- - 8 •>f ia 1.073225 tachments, or a rapid perniissable rate of descent, an alterna¬ tive mounting of the float is illustrated in FIGURE 6. Here a foam plastic float 77 is fixed to a perforated metal or plastic strip 78 tuhicb passes upwardly through a slot (not shown) in the center of the float, the strip being piv/otally attached to the lever arm 43. By means of attachment perforations 79 in the strip 78, and a pin 80-, the float can be fixed in a preselected position uihich mill determine the effective buoyancy of the de¬ vice 10 in operation. With the use of the float structure of FIGURE 6 the flexible shaft 72 tuill be omitted along with the gear reducer 71, the float 77 having sufficient weight, in air,.

to hold the brake drum 41 against rotation. In lieu of suffi¬ cient weight of the float 77 additional weights or spring means may ba added to activate the brake, within the scope of rny in¬ vention. Ulhils the braking mechanism of the drawings has the advantages of simplicity and low cost, it will be understood that other braking mechanisms are known, mechanical, hydraulic, and magnetic that might be activated by the floats 58 or 77, within the scope of my invention. The line 46 must, of course, be cap¬ able of transmitting the lifting effect of the buoyancy device to the article 73. This line is, however usually expendable • and, moreover, it takes up significant space in the chamber 17 and adds weight counter to the desired buoyancy. Where the de¬ vice ID is designed to have a reduced buoyancy as the cable 73 descends, the high initial strength of the line 46 is no longer required. Referring to FIGURE 8 a line 81 has a maximum section in a leading length 82 that is fastened to the cable 73 and a much lighter trailing end 83, having a much smaller section, which is not paid from the capstan until the buoyancy device hasfdescsnded to a point where its buoyancy is a minimum. Inter¬ mediate weights of line are represented in the drawing by theri .9'» length 84. A further advantage of the tapered line 81 resides in the fact that, should the mechanism within the buoyancy device fail to raise the float and reduce buoyancy, the smaller por¬ tion of the line would break, freeing the buoy and avoiding the formation of a loop in the cable. The line 46 is not positively tied to the buoying device 10 and is designed to be fully paid out before the cable 73 is deposited on the submarine bottom.

When the end of the line has passed through the capstans 27, 28 there is no longer any connection to the cable and the device is free to rise. To make sure that sufficient grip is maintain¬ ed by the capstans on the iline until the end of the line is rea¬ ched, a roller 86 hingedly mounted to the beam 25 applies pres¬ sure against the line in one of the grooves of the capstan, be¬ ing urged by a tension spring 87 (FIGURE 3). A release line 88 is also tied between the cable 73 and the buoyancy device 10 for the purpose of releasing the brake by the hand of a diver or by means of a submarine with articulated grasping means. The pur¬ pose of tying the release line 88 to the cable is merely to aid a diver to locate thé former. The line 88 takes a few turns around a sheave 89 which constitutes the outer rim of a centri¬ fugal clutch 91. Such clutches are well known articles of com¬ merce and will permit the sheave 89 to turn slowly but will en¬ gage and lock against rotation when rapid turning is attempted.

A supply of the release line 88 is held in a rigidly suspended pail 92. From the sheave 89 the release line pays over a pulley 93 with the effect that a sharp tug on the release line 88 at any point below the device lO will turn the lever arm 43 counts; erclockwise (as seen in FIGURE2) around the fulcrum 44 and re¬ lease the brake band 42. This means will enable a diver to re- lease any buoyancy devices the release mechanisms of which have otherwise malfunctioned, and to deposit the cable 73 or other article into a precise position such as a prepared trench.

It will be understood that my buoyancy device, hereinabove described, incorporates a "fail safe" feature in that, should the braking device of one of the buoyancy devices supporting a cable fail so that no line is paid out, the device will simply follow the cable down and soon lose so much buoyancy that it will not affect the way the cable comes to rest at the ocean bed.

OPERATION The operation and method of my invention is best illustrated lO with the aid of FIGURES 5 and 7. A cable laying ship 101 car¬ rying a cable capstan 102 ,and bow sheave 103 pays the cable 73 with the buoyancy devices 10 into a body of water 104 to deposit it on a botton surface 106. Because of the adjustability of the floats 58 or 77 the depths at which the buoyancy devices will start to pay out line rather than sink at the same rate as the cable can be preselected and, if necessary, be varied from one buoyancy device to another with variations in laying conditions.

In the case of the float 77 (FIGURE 6) adjustment is made by in¬ serting the pin 80 through the desired perforation 79, and in the case of the float 58 (FIGURE 4) the flexible shaft 72 can be disengaged from the shaft 34 and rotated independently until the float assumes the desired position. In FIGURE 7 the buoyancy devices 10 are equipped with the float mechanisms of FIGURE 4 and the positions of the floats 58 on the rods 63, 64 have been initially established so that none of the line 46 will be paid out until the devices 10 have reaches a desired depth. It will be understood that, while I have shown operations in which the article being submerged is paid from the bow of a ship, my in¬ vention has equal application where, as is most common, for ex- ample, in pipe laying, the article and buoys are launched from the stern of a barge. Referring again to FIGURE 7 the lines 46 - 11 to the last three buoyancy devices being launched are of equal length because the water 19 (FIGURE 2) has not yet reached a le¬ vel to lift the float 58. The line at position indicated by the numeral 107 has, however, lengthed, and, in so doing has, through the turning of the capstans 27, 28 and the flexible shaft 72 raised, somewhat, the float 58 on the rods 63, 64. This pro¬ cess continues with the resialt that the devices lO descend along with the cable 73 but at a slower rate since the length of the lines 46 are progressively increased as the cable nears the bot- torn. Because the position of the cable becomes more horizontal as the cable sinks, the devices 10 become spaced further apart in the water and, between the buoyancy devices at positions 108 and 109 festooning of the cable is seen to occur as evidenced by a maximum sag 111 at a point between these two positions. The magnitude of the sag decreases from this maximum point because of the greatly lessened buoyancy of the devices 10 which now hold increased quantities of water. At a position 112, prior to the point where the cable is deposited on the bottom, the length of the line 46 has been exhausted and, the line having passed completely around the capstans 27, 28 the device 10 is beginning to rise freely to the surface. In FIGURE 5 the devices 10 have been spaced closely enough that, in combination with the stiff¬ ness characteristics of the cable 73, festooning does not pre¬ sent a problem. Here the float mechanism of FIGURE 6 has been employed in the devices 10 with the result that the buoyancy de¬ vices, once the water has reached a predetermined level within them, have remained at a substantially fixed depth characterized by position 113. The depths of devices 10 at alternate positions are shown to vary somewhat because the devices sink until the water has risen enough to lift the float 77 and release line 46 whereafter they rise again until pressure of the gas 18 within ths chamber 1? has forced out the water 19 against the reduced iambiant pressure, and again applied the capstan brake. At posi¬ tion 114, at a preselected depth of the cable 73, the line 46 has become exhausted and has released its buoyancy device.

The foregoing description has been exemplary rather than de¬ finitive of my invention for which I desire an award of Letters Patent as defined in the appended claims.

I claim:

1. A buoyancy device for at least partially supporting a submer¬ ged article comprising:

A. walls defining a submersible chamber, B. a substantial volume of gas enclosed in said chamber, C. access means to the lower portion of said chamber for water surrounding said buoyancy device, said water rising within said chamber and compressing said gas with increasing submergence of said buoyancy device, D. a supply of flexible line supported by said buoyancy device, one end of said line being supportingly fastened to said submer¬ ged article, E. means within said chamber gripping and paying out said line thereby changing the distance between said buoyancy device and said article, and F. means braking said paying out means.

2. The buoyancy device of claim 1 wherein said paying out means comprises a cylindrical capstan.

3. The buoyancy device of claim 2 wherein said braking means comprises, at least in part, propeller means rotatable in the water surrounding said buoyancy device and means rotatably in¬ terlocking said capstan and said propeller means.

4. The buoyancy device of claim 1 comprising means controlling said braking means, said controlling means being responsive to the level of the water within said chamber.

5. The buoyancy device of claim 4 wherein said controlling means comprises a float.

6. The buoyancy device of claim 5 comprising a friction brake for said capstan, lever means controlling said friction brake, and a float, said float being carried on the surface of water in said chamber, said float being fastened to said lever means