US3390408A - Long spar buoy structure and erection method - Google Patents

Description

Filed May 9, 1966 1968 s. s. LOCKWOOD, JR.. ET AL 3,390,408

LONG SPAR BUOY STRUCTURE AND ERECTION METHOD 2 Sheets-Sheet 1 Armin H45 July 2, 1968 5, og woon, JR" ET AL 3,390,408

LONG SPAR BUOY STRUCTURE AND ERECTION METHOD Filed May 9, 1966 2 Sheets-Sheet 2 INVENTORS.

6mm; 6 Z My t/e fxm Wm w =z/ BY Mm M r United States Patent 3,390,408 LONG SPAR BUOY STRUCTURE AND ERECTION METHOD George S. Lockwood, .lr., Los Augeles, Thad Vreeland,

Jr., Arcadia, and Nick Koot, South Laguna, Calif assignors to Global Marine, Inc., Los Angeles, Calif., a corporation of Delaware Filed May 9, 1966, Ser. No. 548,610 Claims. (Cl. 9-8) ABSTRACT OF THE DISCLOSURE A long spar buoy having an elongate, positively buoyant body which is many times greater in length than its maximum transverse dimension, in which the body is defined by a plurality of serially arranged body sections connected together in moment-free connector means which isolate bending moments developed in any one section from the adjacent sections of the body. The body sections have structures and buoyancy so related to each other than the buoy floats freely with the sections disposed vertically relative to each other.

This invention relates to novel marine buoy structures of the type known as long spar buoys. More particularly, it relates to an articulated long spar buoy and to a novel method for constructing and erecting such a buoy.

Proper instrumentation of the ocean is a major problem in acquiring reliable data regarding the ocean and its Weather. Such data is required for military purposes, such as for improving or predicting sonar performance, as well as for commercial purposes, such as locating undersea mining and farming areas and for predicting optimum shipping routes. Ideally, the oceanographic instrument platform or vehicle should be relatively motionless even in a severe sea, rugged, and low in cost. Also, the platform should be moorable without the use of complex and expensive mooring systems.

Long spar buoys have been proposed for use as instrument platforms in oceanographic instrumentation projects; such buoys preferably are fabricated of a number of sealed lengths of oil well drill pipe or oil well casing pipe and are of substantially constant diameter over their lengths. A long spar buoy may have a length of several thousand feet, if desired. Such buoys are ideally suited for use in oceanographic research since they have very little heave even in extremely high seas and are inexpensive in comparison with more conventional surface buoys. Originally, it was proposed that the adjacent pipe lengths in such a long spar buoy be rigidly connected together.

The construction of a rigid long spar buoy requires the use of highly skilled personnel and complex equipment, and such a buoy must be assembled in a vertically progressive manner at its intended location of use if the imposition of damaging bending moments in the buoy is to be avoided. Also, it has been found that wind and wave action upon the upper end of a rigid long spar buoy and the action of ocean currents upon other portions of a rigid long spar buoy combine to produce significant bending moments in the buoy. Such moments cause the material on the convex side of the buoy to be placed in tension and the material on the opposite concave side of the buoy to be placed under compression. Since a long spar buoy usually is not constrained from rotating by its mooring structure, the buoy is free to rotate even while subject to bending moments. Therefore, the loads developed in the buoy by imposed bending moments vary cyclically at a rate corresponding to the rate at which the buoy rotates. Where the buoy is rigid or substantially rigid over its entire length, these loads, whether "ice static or cyclic, produce undesirably large stresses in the buoy; the cyclic nature of these stresses is even more undesirable because they rapidly lead to fatigue fractures in the buoy.

.This invention provides an articulated long spar buoy useful in oceanographic instrumentation projects. The articulation of the buoy significantly reduces the bending moments which may be imposed upon the buoy. The buoy, therefore, is not subjected to the stress levels which would be encountered in a rigid long spar buoy of the same length and diameter. The invention also provides a novel method for constructing and erecting such a buoy without the use of specially trained personnel or complex and costly equipment.

Generally speaking, this invention provides along spar buoy which includes an elongate, positively buoyant body having a length many times greater than its maximum transverse dimension. The body is comprised of a plurality of substantially identical tubular members arranged in end-to-end relation to define a plurality of serially arranged buoy body sections. Moment-free connectors are provided between adjacent body sections for positively interconnecting the body sections and for isolating from one section any bending moments developed in an adjacent section. Preferably, the moment-free connectors are double universal joints.

In terms of procedure, this invention provides a method for fabricating and erecting a long spar buoy. The method includes the step of fabricating a long spar buoy Without ballast on shore in a substantially horizontal attitude from a plurality of substantially identical lengths of pipe or the like, the body of the buoy being articulated at selected locations along its length. The method also includes the step of towing the unballasted fabricated buoy body to a desired location at sea by a towing vessel. The method also includes the steps of ballasting at least a selected one of the pipe lengths adjacent the intended lower end of the buoy so that said end of the buoy sinks until the buoy is submerged to the extent desired and the buoy is disposed in a substantially vertical position.

The above-mentioned and other features of the present invention are more fully set forth in the following detailed description of presently preferred embodiments of the invention, which description is presented with reference to the accompanying drawings, wherein:

FIG. 1 is an elevation view of a long spar buoy;

FIG. 2 is an enlarged cross-sectional elevation view of a portion of the buoy shown in FIG. 1;

FIG. 3 is an elevation view illustrating an initial step in a method of fabricating and erecting the long spar buoy shown in FIG. 1; and

FIGS. 4, 5 and 6 show successive steps in the method illustrated in FIG. 3.

A surface-piercing, positively buoyant long spar buoy 10 is shown in FIG. 1, floating vertically in a body of water 11 having a free surface 12. The buoy has an elongate substantially hollow body 13 comprised of an indeterminate number of similar elongate tubular elements 14. Preferably, the tubular elements are defined by convenient lengths, say 20 to 40 foot lengths, of oil well drill pipe or oil well casing pipe of selected diameter. The buoy, when in place at sea, has an upper section 15 which extends through water surface 12; buoy section 15 is shown to be defined by a number of pipe Sections which have a diameter greater than the pipe sections used in the remainder of the buoy. It will be understood, however, that the upper section of a buoy according to this invention may have a diameter the equal to or less than the remaining sections of the buoy Without departing from the scope of the invention. All of the pipe lengths in the upper section of the buoy are rigidly interconnected in endto-end relation by means of pipe coupling collars 16. The ends of the pipe lengths in the upper section of the buoy as well as in the other buoy sections are preferably welded to each other via welding collars. Alternatively, the ends of the pipe lengths may be accurately machined to define precision threads which are screwed into similar threads machined on the interior surface of a threaded coupling collar. When threaded couplings are used, an epoxy thread-sealing compound preferably is applied to the threads just before the joints are made up; the compound cures in the assembled joints. As a result, the joints between adjacent pipe lengths are made up watertight.

The lower end of buoy upper section is connected to a second buoy section 17 by a moment-free connector 18 shown in more detail in FIG. 2. Buoy section 17 is rigid along its length. The remainder of the length of the buoy is defined by an indefinite number of rigid sections 19, each comprised of a number of pipe lengths rigidly connected together. Buoy sections 17 and 19 are serially interconnected by additional moment-free connectors 18.

As shown in FIG. 2, the lowermost pipe length in upper buoy section 15 carries a conical end fitting 20 secured to the pipe length by a threaded pipe collar 16. The upper end of second buoy section 17 carries a similar conical fitting 20. Moment-free connector 18 is comprised of a double universal joint 21 connected between the adjacent end fittings along the axis of the buoy. The relatively movable parts of the double universal joint are housed within a protective rubber sleeve 22. The opposite ends of the double universal joint define stub shafts 23 which are welded to the opposing end fittings. The opposite ends of the rubber sleeve are bonded to the adjacent stub shafts close to the end fittings. The double universal joints permit the adjacent sections of the buoy to move pivotally relative to each other in response to dilferential lateral loads on the adjacent body sections. The body sections can move in any desired direction about a point intermediate the sections and lying on the axis of the buoy. The joints, however, prevent the adjacent buoy sections from moving axially relative to each other. If desired, lengths of woven wire cable or swivels, for example, may be used as moment-free connectors in accord with this invention.

An access platform 25 is mounted to the upper end of upper buoy section 15 above water surface 12 and mounts a radio antenna 26. The antenna is coupled to a suitable transmitter, not shown, located within the buoy adjacent the platform for transmission of radio signals to a remote receiving station. A plurality of oceanographic instrument transducers 27 are strapped to the buoy at selected locations along its length. If desired, however, and if compatible with the nature of a given transducer, the transducers may be located within the buoy. The transducers preferably provide electrical output signals which are applied to the radio transmitter via a suitable cable 28 extending along the length of the buoy and secured at desired locations to the buoy by suitable straps 29.

As shown in FIG. 2, a bulkhead plate 30 is disposed across each pipe length used in the construction of the buoy adjacent each of its ends. Each bulkhead plate is welded about its periphery to the interior of the adjacent pipe length to provide a watertight seal across the interior of the pipe length. In the event that the connection between the adjacent end of the pipe length and the next pipe length (or the connection between the pipe length and a conical end fitting) should leak, the seal provided by the bulkhead plate holds flooding of the buoy to a minimum.

A long spar buoy may have a length of from about 100 or 3000 feet or more. The pipe lengths from which the buoy is constructed may have diameters of from 4 to 24 inches. Where the buoy is of considerable length, the lower portions of the buoy are fabricated from stronger sections of pipe than are used for the upper portions of the buoy. This practice is followed so that the weight of the buoy is kept as low as possible, yet the buoy is sufficiently strong at all points along its length to withstand the external water pressures which tend to crush the hollow buoy body. The lower end of the buoy carries a mooring ring 31 to which a mooring cable 32 is secured for mooring the buoy at a desired location in body of water 11.

The upper section of buoy 10 must be sufficiently long that this section of the buoy, together with any payload carried by it, has positive buoyancy when the section is vertically disposed and a selected portion of its length (preferably about 25 feet) lies above water surface 12. The positive buoyancy of the upper section of the buoy may be slight relative to the total buoyancy of the buoy; preferably, however, the upper section of the buoy is the most buoyant section of the buoy. For the reasons set forth below, it is desired that the uppermost section of the buoy not be unduly long, but it is desired that the uppermost section be as long as possible in order that its angular motion be minimized. Therefore, in order that the length of buoy section 15 may be held within workable limits, it is preferred that the pipe lengths used in the fabrication of buoy section 15 be of greater outer diameter than the pipe lengths which are used in the fabrication of the remainder of the buoy.

A floating long spar buoy is subjected to lateral loadings at its upper end by wind and wave related forces. Particularly where the buoy is of extreme length, the lower reaches of the buoy are subjected to transverse shear loads when the buoy extends through a region of relatively fast moving water into a region of relatively slow moving water. If the buoy were essentially rigid throughout its entire length, these lateral loadings upon the buoy would produce a sizable bending moment in the buoy. Mooring loads also contribute to the bending moment imposed on the buoy. Because the buoy has a relatively small diameter, the fiber stresses in the pipe lengths used in the construction of a rigid buoy could readily possibly exceed the yield strength of the materials used in constructing the buoy unless the pipe sections were made of special steel or provided with substantial wall thickness. The use of special alloys in the construction of the buoy is to be avoided, however, in order that the cost of the buoy may be held as low as possible. The use of pipe sections having thick wall sections is incompatible with large buoy payload capacity. Moreover, assuming that the buoy is rigid along its length, the buoy is free to rotate within the sea unless complex and costly mooring systems are used to prevent rotation. If the buoy is free to rotate while being subjected to a given bending load, the fiber stresses in the buoy body vary cyclically. Cyclic loads and the stresses associated therewith, even of relatively small orders of magnitude, particularly when superimposed on large static loads, are to be avoided to the greatest extent possible. Cyclic stresses at levels below the yield stress of the material are known to cause metals and other materials to fracture from fatigue. Superimposed upon the static and dynamic bending stresses are the fiber stresses which are produced by the hydrostatic crushing loads imposed upon the buoy; these stresses increase with water depth.

The pivotal interconnection of buoy sections 15, 17 and 19 by moment-free connectors 18 prevents the buoy from being subjected to large bending moments over its length. As a result, the maximum stress present in the pipe lengths from which the buoy is made is maintained wellbelow the stress corresponding to the yield point of the pipe metal. Furthermore, any bending moments which may be imposed upon any given section of the buoy between a pair of universal joints is maintained at a low level and cyclic variations in these moments are likewise held to inconsequential levels. As a result, the useful life of the buoy is extended since fatigue is minimized.

The use of moment-free connectors in buoy 10 also substantially eliminates electrolytic corrosion related to stress. It is known that steel, when disposed in an electrolyte such that it forms one electrode of a galvanic cell, corrodes fastest where the stress in the steel is greatest. By minimizing the stress levels in the buoy by use of the moment-free connections between adjacent buoy sections, deterioration of the buoy by corrosion is less than in an equivalent rigid buoy.

The use of the moment-free universal joint couplings in buoy at selected locations along its length permits the buoy to be fabricated and erected easily and economically by the procedure illustrated in FIGS. 36. Each buoy section 15, 17 or 19 is assembled on a slightly inclined way structure located on shore immediately adjacent body of water 11. The body sections are made up as previously described to the desired length from pipe lengths 14 of the desired diameter and wall thickness. Each body section is fitted with a conical end fitting 20. Instrument transducers are mounted to each section as required and each body section is assembled free of ballast. As each pipe length is added, the body section is moved down the way structure toward water 11. No given body section is launched from the way structure until it has been connected via a moment-free coupling 18 to the adjacent end of the next body section. Thus the construction of the buoy progresses from one end of the buoy to the other.

After the fabrication of the buoy body is complete, the buoy, with the platform structure in place, is towed by a tow vessel 36 to the site where the buoy is to be moored, as shown in FIG. 4. If desired, auxiliary flotation or buoyancy chambers 37 are strapped to the unballasted buoy so the buoy floats on water surface 12 during the towing process. At the location where the buoy is to be moored, a cable 38 is connected from the buoy mooring ring to the tow vessel via a winch 39 mounted on the vessel; this cable may be the same cable used to tow the buoy to the mooring location from the initial fabrication site. Also, as shown in FIG. 5, mooring cable 32 is connected to the mooring ring and extends from the floating unballasted buoy to an anchor disposed on the bottom of body of water 11.

The buoy body sections at and adjacent the intended lower end of the buoy are then filled with ballast as required. The buoy may be ballasted by flooding selected pipe lengths with water or by filling selected pipe lengths with concrete, sand, steel shot or the like; the use of concrete, sand or steel shot as ballast is preferred since such ballast material, as opposed to water, produces a more effective regulation of buoy center of gravity because of its greater density. The auxiliary buoyancy tanks, if fitted, are then removed before cable 38 is payed out from the tow vessel. The ballasted buoy then assumes a configuration resembling a catenary between the end of cable 38 and the positively buoyant buoy sections at and adjacent the upper end of the buoy, as shown in FIG. 5. Such a catenary configuration of the buoy causes no harm to the buoy, however, since the articulated construction of the buoy prevents appreciable bending moments from developing along the length of the buoy; the same stress-free conditions within the buoy are also obtained as the buoy is being towed from the on-shore construction site to the location where the buoy is to be used, even though the buoy may be towed through heavy seas.

The next step in the process of erecting the fabricated buoy is shown in FIG. 6, i.e., paying out cable 38 from tow vessel 36 to lower the ballasted end of the buoy downwardly of the vessel through water 11. This procedure is carried out gradually so that the descent of the lower end of the buoy is controlled at all times. If the buoy were merely cast oif from the tow vessel, the buoy would plummet downwardly and become totally sub-' merged before it assumed a stable position after bobbing vertically for some time. Such motion of the buoy, especially where the length of the buoy is great, would impose severe dynamic loads upon the buoy, and particularly upon the moment-free connections, such that the moment-free connections may part or become permanently damaged. Moreover, the upper sections of the buoy would tend to whip through the Water so fast that the transducers carried by the buoy would be severely damaged. Impact between the upper section of the buoy and the tow vessel would also be likely.

After the buoy has been lowered to the point where it floats vertically in a stable manner and does not bob, cable 38 is disconnected from the buoy. The radio antenna and the radio transmitter may then be installed in the erected buoy to complete the buoy fabrication and installation procedure. If desired, the removal of cable 38 from the buoy may be delayed until after the antenna and transmitter have been installed. The buoy is then ready for use as an exceptionally stable, rugged and inexpensive oceanographic and meteorological instrumentation station.

Once the buoy has reached its intended location of use, the buoy can be erected and rendered operational within one working day.

The above-described method of fabricating and erecting a long spar buoy having the length contemplated by this invention is possible only where the buoy is articulated at several locations spaced along the length of the buoy. If the buoy were substantially rigid along its length, buoy construction would have to be carried out at the site where the buoy is to be moored. Such construction would require the use of a specially equipped vessel, such as a workboat fitted with a crane, similar to vessels now in use for drilling oil wells and the like at sea. A rigid buoy would have to be assembled in a vertical attitude. Once construction of a rigid buoy is commenced, it should proceed without interruption until the buoy body is completely assembled. Where the buoy is of great length and the construction time is long, the probability of a change in the weather at the construction site is increased. If the vessel is subjected to adverse weather, it must either ride out the storm with all its hazards, or alternatively, the partially completed buoy could be left in place, supported by auxiliary buoyancy members, while the construction vessel retreats to a safe place to wait out the storm. In either case, valuable time is lost. Further, specially trained personnel are required for on-site construction of a rigid long spar buoy. The above-described articulated long spar buoy structure and construction method inherently avoids many if not all of these handicaps attendant to rigid buoys. Economic construction and installation of the articulated long spar buoy is not dependent upon the existence of relatively long periods of fair Weather and smooth seas at the intended location of the buoy.

Certain structural arrangements and procedural sequences relating to this invention have been described above merely by way of example in furtherance of a complete and comprehensive explanation of the invention. It will be realized that these examples do not encompass all forms which this invention may take, although they do suggest and teach that the structures and procedures described may -be altered or modified Without departing from the scope of the invention. Accordingly, the foregoing description is not to be regarded as limiting the scope of this invention.

What is claimed is:

1. A long spar buoy comprising an elongate positively buoyant body having a length many times greater than its maximum transverse dimension, the body being comprised of a plurality of tubular members arranged in end-to-end relation to define a lesser plurality of serially arranged buoy body sections, and moment-free connector means connecting adjacent body sections for isolating bending moments developed in one section from the adjacent sections, the body sections being cooperatively configured and arranged in structure and buoyancy so that the body floats freely with the body sections disposed vertically of each other.

2. A long spar buoy according to claim 1 wherein each moment-free connector means includes a universal joint connected between the proximate ends of each two adjacent body sections.

3. A long spar buoy according to claim 2 wherein each universal joint is a double universal joint.

4. A long spar buoy according to claim 2 wherein the relatively movable parts of each universal joint are sealed Within a flexible watertight sheath.

5. A long spar buoy according to claim 2 wherein each body section adjacent a universal joint carries a conical end fitting to which one end of the adjacent universal joint is mounted.

6. The method of fabricating and erecting a long spar buoy comprising the steps of fabricating on shore an unballasted buoyant buoy body having a slenderness ratio of at least about fifty-to-one and including the installation at selected locations along the length of the buoy of articulation means between adjacent sections of the body of the buoy each of which has a length substantially greater than its diameter so that bending moments developed in one section are isolated from the sections adjacent to the one section, towing the unballasted buoyant buoy body to a desired location at sea by a tow vessel, at least partially filling at least a selected one of the buoy body sections adjacent the intended lower end of the buoy with ballast, and sinking the lower end of the buoy downwardly of the tow vessel until the buoy is submerged to the desired eXtent and the body sections are substantially aligned with each other in a substantially vertical relation.

7. The method according to claim 6 including the step, performed at the desired location at sea, of connecting to b the lower end of the buoy a mooring cable prior to sinking the lower end of the buoy.

8. The method according to claim 6 including the step, performed at the desired location at sea, of securing a cable from the tow vessel to the intended lower end of the buoy before ballasting the buoy, the sinking procedure being accomplished by paying the cable out from the tow vessel to lower the lower end of the buoy.

9. The method according to claim 8 wherein the lower end of the buoy is lowered at a rate substantially slower than the rate at which the lower end of the buoy would descend it free from restraint to the tow vessel.

10. The method according to claim 6 including the step of removably connecting to at least one of the body sections at least one flotation tank prior to commencement of the towing step, and of removing the flotation tank prior to commencement of the sinking step.

References Cited UNITED STATES PATENTS 52,522 2/1866 Bowlsby 98 612,109 10/1898 Hutchins 9-8 663,941 12/1900 Smith 9-8 2,473,618 6/ 1949 Stillwagon 64-32 3,092,852 6/1963 Devereux 98 3,256,537 6/1966 Clark 114-5 X FERGUS S. MIDDLETON, Primary Examiner. MILTON BUCHLER, Examiner.

T. MAJOR, Assistant Examiner.

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