US3742535A

US3742535A - Open ocean shallow water moor

Info

Publication number: US3742535A
Application number: US00129716A
Authority: US
Inventors: P Horrer; R Bridges
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1971-03-31
Filing date: 1971-03-31
Publication date: 1973-07-03
Anticipated expiration: 1990-07-03
Also published as: JPS5511552B1; CA933046A; GB1368533A

Abstract

An open ocean moor is disclosed for use at comparatively shallow ocean depths. The moor consists of a buoy floating on the surface which is fastened to an anchor on the bottom by means of a flexible tether formed of a plurality of linked sections of highly elastic material such as rubber of relatively large crosssectional area. The elastic sections are formed with heavy loops or eyelets at each end, and adjoining sections are connected by means of a link formed of two mating double grommet assemblies which, preferably, are also formed of mating configuration with respect to the loops to minimize stress concentrations. An electrical cable which is connected to various underwater instruments extends from the buoy to the anchor. This cable is supported on the flexible tether line by means of separate cable clamps on the links. A substantial amount of slack must be maintained in the electrical cable to allow for stretching during periods of high wave action without danger of pulling the cable taut. The electrical cable is fastened to the anchor and to the buoy by means of cable termination devices of a type known in the art.

Description

United States Patent [191 Horrer et a1.

[451 July 3,1973

[ OPEN OCEAN SHALLOW WATER MOOR [75] Inventors: Paul L. Horrer, La Jolla; Robert M.

Bridges, Northridge, both of Calif.

[73] Assignee: The Bendix Corporation, Southfield,

Mich.

221 Filed: Mar.31, 1971 21 Appl. No.: 129,716

Primary Examiner-Duane A. Reger Assistant Examiner-Gregory W. OConnor Atlorney-Robert C. Smith and Flame, Hartz, Smith & Thompson [5 7] ABSTRACT An open ocean moor is disclosed for use at comparatively shallow ocean depths. The moor consists of a buoy floating on the surface which is fastened to an anchor on the bottom by means of a flexible tether formed of a plurality of linked sections of highly elastic material such as rubber of relatively large crosssectional area. The elastic sections are formed with heavy loops or eyelets at each end, and adjoining sections are connected by means of a link formed of two mating double grommet assemblies which, preferably, are also formed of mating configuration with respect to the loops to minimize stress concentrations. An electrical cable which is connected to various underwater instruments extends from the buoy to the anchor. This cable is supported on the flexible tether line by means of separate cable clamps on the links. A substantial amount of slack must be maintained in the electrical cable to allow for stretching during periods of high wave action without danger of pulling the cable taut. The electrical cable is fastened to the anchor and to the buoy by means of cable termination devices of a type known in the art.

8 Claims, 4 Drawing Figures OPEN OCEAN SHALLOW WATER MOOR BACKGROUND OF THE INVENTION There are many applications for bottom-mounted moors that tether a buoy in place on the surface of the ocean. For oceanographic studies, it is frequently desired toplace instruments in the ocean which will provide readings of underwater temperatures, current flow, etc., which readings are converted to electrical signals and which must then be brought to a buoy on the surface and relayed through radio means in the buoy to shore stations. Where such buoys are moored in very deep water (of the order of 10,000 feet or more), it has been established practice to tether the buoy to the moor by means of a very strong, but somewhat elastic, connection such as a nylon rope. This rope will normally be tensioned to some extent, even in calm seas, to avoid generating slack and then sudden tightening which would result in excessive wear on the rope. In the case of very heavy seas, wave heights of the order of 100 feet are possible and should be planned for. In the case ofa very deep moor, this would involve a stretching of the nylon rope by an amount even including some lateral displacement of the buoy, which is actually a very small percentage of the length of the unstretched rope. The nylon ropes which have been used for this purpose easily accommodate this kind of stretching, and the buoys usually ride out heavy seas without any damage. Where it has been desired to locate instruments in relatively shallow water, however, a much more difficulty problem is presented. By shallow water, in this instance, is meant water of the normal depth on the various continental shelves and which might be of the order of 600 feet or less. Even in water of this depth, severe storm conditions can result in waves of the same height as that of the open sea or nearly so, and therefore it again becomes necessary to design for l-foot wave action. Given this relationship and the lateral displacement of the buoy which occurs in severe storms, it now becomes necessary to deal with a mooring means which may need to stretch up to 2% times its length rather than, perhaps, one onehundredth or one fiftieth, as in the case of the deep water moor previously referred to. This percentage of elongation is not within the capability of the typical nylon rope used in connection with deep water moors. Since such moors should be designed for a minimum life of one year irrespective of the weather conditions encountered, it will be recognized that thousands of elongation cycles must be withstood for acceptable life. In addition to withstanding the very substantial stretching required, the cable material must be stable in sea water for the requisite period of time, and it must have a spring rate sufficient to adequately support the conductor carrying the instrumentation signals to the buoy. 1

The means for attaching the tethering structure to the anchor, to the buoy, and to the electrical cable also becomes very important in this application. It will be apparent that sufficient slack must be placed in the electrical cable so that it does not become taut and accept mooring stresses during operation in this adverse environment. If the latter condition should occur, the moor will rapidly destroy itself by very high loads delivered through the cable into the buoy and the anchor.

It can be seen that it is important that all parts of the tether assembly he as lightweight as possible to reduce the amount of supported load and consequently the amount of prestretch of the elastic mooring member. The amount of supported weight is affected by the amount of stretch designed into the elastic member, since its design is governed by the loads placed on the buoy, wave motion and downward forces of the tether, plus cross-current forces on the tether assembly. Stretch, therefore, must not be excessive since slack in the electrical cable is determined by the maximum amount of stretch permitted in the elastic tether membet.

The spring rate of the elastic member is significant since enough stretch must be designed into the elastic member to allow for the orbital motion of the surface buoy on the surface as it follows the wave in addition to the static stretch produced by wind forces on the buoy and current forces on the tether assembly. This design consideration places a maximum constraint on the spring rate while the supported weight of hardware and electrical cable places a minimum constraint on the spring rate (i.e., excessively long stretch results in excessively large cable weights).

Since it is impractical to mold a rubber or rubberlike tether member of several hundred feet in one piece, and also because it is necessary to attach the electrical cable at several points along the tether, means must be supplied for linking the tether sections together as well as supporting the cable at various points. Such link means should be designed to avoid concentrated stress on the ends of the tether sections.

SUMMARY OF THE INVENTION By means of this invention, a mooring arrangement is provided which includes a plurality of elongated elastic members which are terminated at each end in eyelets of substantial thickness and strength. These are tied together through lightweight links in the form of double grommet assemblies which are bolted together to contain the eyelets. Also fastened to the links are separate cable clamp means which secure the electrical cable to the flexible tether line. Preferably, the grommet assemblies include mating spacer portions which, when bolted together, produce a support of mating configuration for the eyelets to thereby equalize the stress on the eyelets during severe stretching.

A certain amount of preload is introduced in the tether assembly so that in calm seas the load of the cable assembly, the mounting link and the weight of the elastic members can be supported without producing slack near the anchor which could result in kinking or twisting of the electrical cable with resulting fatigue and possible failure. Thus the spring rate or stiffness must be such as to supply this support, while at the same time it must not be so stiff as to cause the buoy to be submerged in heavy weather.

The electrical cable is attached at each link and must have substantial slack between the links to accommodate the stretching of the elastic member. This cable is sufficiently strong to carry a substantial load in tension but must not be exposed to the shock which would occur if it were to be repetitively snapped taut and loose because its length was insufficient to tolerate the maximum wave action experienced. Because of the slack in the cable, it is necessary that it be protected against extreme bending angles at the upper side of each attachment link. This protection has been provided by means of a wire rope support means fastened as a sleeve at each link which stiffens the cable at that point to limit the radius of curvature which it can experience.

The buoy which is tethered may be of a type which has a weathervane action, thus seeking always to be headed into the wind. To attach the cable to such a buoy requires that a swivel mechanism, which may include electrical slip rings, be used to prevent twisting of the cable and the tether line. This cable is then fastened to the swivel through a cable termination device. A similar termination device is used to attach the cable to the anchor.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawing showing a typical open ocean shallow water moor according to my invention;

FIG. 2 is a side plan view showing the elastic tether sections, the electrical cable and the linking devices for connecting said sections and for attaching the electrical cables to the tether;

FIG. 3 is an enlarged top plan view, with the center broken away, of one of the elastic tether members shown in FIG. 2; and

FIG. 4 is an enlarged side plan view, in partially exploded form, of the link and cable clamp arrangement shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT A typical open ocean, shallow water buoy for gathering underwater data and transmitting the data through radio means to shore stations is shown in FIG. 1. Various

underwater instrumentation devices

10, 12 and 14 are attached to an underwater electrical cable 16 which is supported at some substantial distance off the ocean bottom by means of a float 18 anchored to the bottom by means of an anchor 20. Cable 16 is fastened to anchor 20 by means of a cable termination device 22 which may be of the type shown in Maddux US. Pat. No. 3,288,913 and which is tied to a lug 21 on anchor 20. Cable 16 then extends along the bottom to a second anchor 24 which has attached to it a similar cable termination device 26. The cable 16 passes through the cable termination device 26 which is otherwise attached to a lug 28 on the anchor 24. It will be observed that cable 16 extends a short distance from the termination structure 26 and then is clamped into a link 30 which includes a double grommet structure for attach ing one end of a flexible tether section 32. The opposite end of tether section 32 is attached to a similar link 34 which also includes a cable clamp means supporting cable 16. A number of identical tethering links, including

members

36, 38 and 40, are tied together and to cable 16 by means of

link members

42, 44 and 46. Obviously, many more sections will normally be involved in spanning a depth of 500 or 600 feet. Cable 16 is supported by clamp means at each of the links in such manner as to retain a substantial amount of slack in the electrical cable in quiet weather. At the upper end, cable 16 is attached to the floating buoy 48 by means of an additional cable termination device 50 which may be similar to devices 22 and 26. The buoy 48 will normally contain electronic equipment for transmitting electrical signals received from the

instrumentation devices

10, 12 and 14 to shore stations.

FIG. 2 shows a typical length of electrical cable and the supporting flexible tether sections which are attached together through the use of the link members, as described. This figure shows, in somewhat greater detail, the structure of the individual elements and the manner in which they are assembled to provide the desired flexible moor device. A link 30 which corresponds to the link of the same number shown on FIG. 1 is attached through cable 16 to the cable termination device 26 as shown in FIG. 1 and provides a clamp for the electrical cable 16. This clamp also supports a somewhat stiff wire rope sleeve 52 which is of tapered stiffness to support cable 16 in such a way that its radius of curvature leaving the link member is limited so that it cannot bend back sharply on itself. The loop at one end of the flexible tether member 30 is securely positioned between the bolted-together halves of the link 30 which form a spool-like structure which is of mating configuration relative to the inside of the loop in order to minimize the stress concentrations on the loop. Link 44 connects two such

flexible tether members

38 and 40 and also supports a section of cable 16 in the manner described and also secures a sleeve member 54 to preventa sharp bending of the cable. Flexible tether member 40 is terminated at link 46 and cable member 16 passes through the clamp and the termination 50 and to the buoy 48. It will be recognized that with this arrangement there will be substantial tension load on the cable 16 below link 30 and above link 46, but with the flexibility imparted by the flexible tether members 32-40, etc., this tension load will be essentially continuous and not subject to sudden release and reapplication with corresponding danger of kinking or buckling. Should a limited number of flexible tether members break in operation, the corresponding cable sections will receive a tension load, but there will be sufficient compliance remaining in the tether to handle large wave action.

FIG. 3 is a plan view, with a portion of the center broken away, of a typical elastic tether member. Each of these members is essentially like member 32 and is formed with large loops or eyelets 32' and 32" at each end. The diameter of the rubber material in the eyelet is essentially the same as that in the center of the member. Although there would normally be a considerable degree of latitude in this respect, the length of the tether members used by applicant was approximately 16 feet. The use of unduly long lengths would load the connecting links excessively because of the amount of slack cable to be supported. The diameter or thickness of the center section used was approximately 1% inch. This thickness, of course, is controlled by the spring rate required for a given application. The diameter of the eye of the loop was approximately the same as the diameter of the rubber member, or 1% inches. Again, this dimension may vary, depending upon loading conditions. Initial attempts to produce a flexible tether member of this type involved the use of a member having a round cross-section and flattened on the ends so that they could be drilled and bolted to a link or splicing member. As a result, forces were concentrated around the area where the bolt penetrated the flexible member and the connection failed because the bolt ultimately pulled out through the flattened portion of the rubber member. The present design is much superior and has withstood hundreds of thousands of elongations of 2 to 2% times its unloaded length. Applicant's members 32 were made of natural rubber and were not molded with reinforcements of any type built into the end loops. Under tension, the rubber flows smoothly around the support which passes through the eye of the loop andis able to withstand very substantial loads.

FIG. 4 shows a plan view, partially exploded, of the link structure used for tying together the individual tether sections and also for clamping the electrical cable 16 to the tether. Since the link member is the same as that shown in FIG. 2 at numeral 44 (as well as the several others), it will be considered an enlarged view of the structure 44. The

tether members

38 and 40 are identical to those shown in FIG. 3 and are tied together by means of the link member 44 which consists of two mating

double grommet members

56 and 58 having side plates which contain the end loops of

elastic tether members

38 and 40. These members should be of lightweight material chosen to withstand the sea water environment, and may be any of several plastics. Member 56 has attached thereto a block 60 which cooperates with a mating block 62 to form a clamp for supporting and restraining the electrical cable 16 and its supporting sleeve 54. Each of the

double grommet members

56, 58 includes a pair of

mating grommet sections

64, 66 which are in the shape of a low filleted cylindrical attachment to the corresponding plate, and each is drilled as at 68 and 70 to receive a through

bolt

72, 74, respectively. It will be observed that the grommet section 66 includes an upstanding collar 76 which mates with a corresponding depression 78 in the adjoining grommet section. This, of course, preserves the alignment between the mating grommet sections as the nuts 80 and 82 are tightened on the

bolts

72 and 74, respectively. Clamping

plates

60 and 62 are also drilled to accommodate a plurality of other bolts 84 which are threadedly engaged with plate 60 to secure the cable 16 and sleeve 54 to the link 44. It may be desired to safety-wire these bolts as shown at numeral 86 to assure their remaining secured in operation.

It will be apparent to those skilled in the art that modifications may be made, depending upon the requirements of individual installations. Thus, while applicant has shown a specific manner in which the electrical instrumentation is deployed, other means may be used. While a given type of cable termination is shown and described, there are other termination arrangements which would be operative in this type of installation.

It will be apparent to those skilled in the art that modifications may be made, depending upon the requirements of individual installations. Thus, while applicant has shown a specific manner in which theelectrical instrumentation is deployed, other means may be used. While a given type of cable While applicants have shown elastic tether members of circular cross-section and a given size has been discussed, both size and crosssectional configuration are subject to change depending upon requirements. For instance, a cross-section in the form of a rounded square would be quite feasible for this purpose and might be used both in the main center section of the tether member as well as in the end loops. Depending upon the thickness and weight of the electrical cable 16 used, the sleeve structure for limiting the radius of curvature may or may not be required. There are a number of advantages to using the kind of buoy which has a weather vane action and which, therefore, tends always to turn into the wind action. This makes a swivealable connection at the buoy a mandatory requirement to avoid excessive twisting of the cable and tether. Another type of buoy which is not so subject to rotation may permit a less flexible type of connection between the cable and the buoy.

We claim:

1. An open ocean shallow water moor comprising a buoy;

an anchor on the ocean floor;

means generating electrical signals to be transmitted to said buoy;

an electrical cable for connecting said signals from said means to said buoy;

and a tether assembly for attaching said buoy to said anchor and for supporting said electrical cable, said assembly comprising a plurality of elongated elastic members of substantial thickness each of which is capable of being stretched to at least a substantial percentage greater than its unstretched length over a large number of cycles, said members being formed such that they terminate at each end in an eyelet of substantial thickness; and

a link for attaching saidelastic members together including a double grommet member formed with side plates and spacers such that, when said members are fastened together, support posts are formed of said spacers and said eyelets are contained on said posts;

and cable clamp means fastened to one of said plates.

2. An open ocean shallow water moor as set forth in claim 1 wherein said spacers are mating parts which, when fastened together, form support posts which substantially flll said eyelets and generally conform to the shape of said eyelets.

3. An open ocean shallow water moor as set forth in claim 2 wherein said elastic member and said eyelets are of essentially round cross-section.

4. An open ocean shallow water moor as set forth in claim 1 wherein the thickness of said elastic members is such as to produce a spring rate permitting the buoy to follow wave action while adequately supporting itself, said electrical cable and said links.

5. An open ocean shallow water moor as set forth in claim 4 wherein said tether assembly has a tension preload, even in quiet water, sufficient to prevent substantial slack in said electrical cable immediately above the said anchor.

6. An open ocean shallow water moor as set forth in claim 1 wherein said electrical cable is fastened to said cable clamp means such that said cable has sufficient slack between each of said clamp means that it does not pull taut at the maximum wave amplitudes experienced.

7. An open ocean shallow water moor as set forth in claim 1 wherein support meansis provided at each of said cable clamp means to limit the radius of curvature of said electrical cable upwardly of said clamp means.

8. An open ocean shallow water moor as set forth in claim 1 including an underwater float, a second anchor, means attaching said float to said second anchor, and wherein said electrical signal-generating means is suspended from said float.

Claims

1. An open ocean shallow water moor comprising a buoy; an anchor on the ocean floor; means generating electrical signals to be transmitted to said buoy; an electrical cable for connecting said signals from said means to said buoy; and a tether assembly for attaching said buoy to said anchor and for supporting said electrical cable, said assembly comprising a plurality of elongated elastic members of substantial thickness each of which is capable of being stretched to at least a substantial percentage greater than its unstretched length over a large number of cycles, said members being formed such that they terminate at each end in an eyelet of substantial thickness; and a linK for attaching said elastic members together including a double grommet member formed with side plates and spacers such that, when said members are fastened together, support posts are formed of said spacers and said eyelets are contained on said posts; and cable clamp means fastened to one of said plates.

2. An open ocean shallow water moor as set forth in claim 1 wherein said spacers are mating parts which, when fastened together, form support posts which substantially fill said eyelets and generally conform to the shape of said eyelets.

7. An open ocean shallow water moor as set forth in claim 1 wherein support means is provided at each of said cable clamp means to limit the radius of curvature of said electrical cable upwardly of said clamp means.