ANCHORS

Abstract: In an anchor a shank having a tip and a base joined by an intermediate portion which are normally in alignment along a longitudinal axis extending from the tip to the base when the shank is at rest. The shank is inflexible in a first vertical plane and flexible in a second horizontal plane, the flank being flexible to an extent such that the tip can be moved in the second plane with respect to the base into a position where it is substantially perpendicular to the longitudinal axis without causing permanent deformation of the shank.

Description: DESCRIPTION TITLE: ANCHORS The present invention relates to anchors. An anchor generally comprises several elements including ground engaging means usually in the form of one or more planar or curvilinear flukes. Various fluke shapes are shown in U.S. Patent Nos. 709,914; 2,249,546; 2,674,968; 2,711,150; 2,840,029; 3,024,756; 3,777,695; 4,134,356; 3,015,299; 3,783,815; 3,902,446; 3,964,421; 4,089,288; 1,974,933 and 4,024,090. The fluke or flukes can be solid or hollow for example as shown in the POOL anchor of N.V. Koninklijke Nederlandsche Grofsmederij. Means, usually termed the crown, are provided to facilitate and maintain the proper engagement of the flukes with the bottom,-by initially lifting the rear of the anchor and forcing the flukes into bottom engagement. Extending forwardly from the crown and in advance of the flukes for attachment to a cable or chain is a so-called shank, in the form of a heavy, solid rectilinear bar. Various authors have pointed out that, particularly in a harder soil such as sand, penetration of an anchor into bottom is limited by the shank which slides over the bottom resisting penetration. It has long been recognized that deep penetration into the bottom is a prime factor in determining the efficiency of an anchor, since if the anchor does not penetrate sufficiently it merely slides across the bottom. One or more elements, usually referred to as stocks, extending laterally from the flukes are provided to stabilize the entire anchor structure, so that it does not rotate when subject to the pulling action applied to the shank by an attached warp, cable, chain or the like, hereinafter referred to as a "rode". According to the present inventin there is provided a shank for an anchor comprising a tip, an intermediate portion and a base end, which are aligned along a longitudinal axis extending from the base to the tip, the shank being substantially inflexible in a first plane and flexible in a second plane perpendicular to the first plane, the tip being able to be moved in the second plane with respect to the base end into a position in which it is substantially normal to the longitudinal axis without causing permanent deformation of the shank. With such a structure, the holding power of the anchor is greatly increased many fold over that of any anchor structure known heretofore. Since its resistance to penetration is greatly reduced, this enables the entire anchor structure to penetrate more deeply into any bottom to provide higher holding power and this promptly upon the anchor structure engaging the bottom. With the shank of the present invention, the tip can be pulled by the rode into a position in which the tip attempts to follow and may, in fact, follow the direction of pull of the rode. The entire shank, in plan view, will then be curved to a varying degree by (a) the pull of the rode and (b) the resistance of the anchor structure which is, at least momentarily, fixed in the bottom with which it is engaged. Depending upon the magnitude of the resistance by the bottom, the shank can be in any one of several curvilinear forms. Such curvilinear forms can vary from that (a) in which the shank, in response to the pull of the rode, has adopted a curved form like that of a flyrod under the stress imposed by a fish being played by the rod, (b) a position in which the forward portion of the shank corresponds to an arc of a circle, (c) any one of various arcuate configurations such as those of a parabolic character, and (d) the position imparted by burial in a very soft bottom such as a soft mud in which the shank is only bent to a slight extent. The shank of this invention is fully capable of movement to approximate any one of these postures by the pull exerted by the rode and the opposition to the pull which opposition is provided by the anchor structure in engagement with the bottom. Such flexible shank provides several advantages. For example, when the anchor is first engaged with bottom, the flexible shank bends with respect to its longitudinal axis and allows the anchor to penetrate bottom even if it is not exactly following the direction of the pull exerted by the rode. Further, after the anchor has buried, if the anchor is pulled to one side as by the action of a shifting tide on a ship, the flexible shank curves in its attempt to follow the direction of the pull exerted by the rode. This is in contrast with prior art anchors having a stiff shank which, upon application of such a side thrust, upsets the anchor and dislodges the anchor from engagement with the bottom. Thus, the anchor of the present invention has an improved shank which greatly increases the holding power of the anchor since the flexible shank does not ride over the bottom but, instead, buries in the bottom and assists the anchor structure in penetrating bottom. Further, being very flexible, the shank of the present invention flexes so that a force from the side does not immediately dislodge the anchor from engagement with the bottom. In addition, the shank is much stronger than the conventional shank which usually breaks or permanently deforms if subjected to an excessive force from the side. In order that the present invention may be more readily understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which: Figure 1 is a plan view of one embodiment of anchor according to the present invention; Figure 2 is a side view of the anchor shown in Figure 1; Figure 3 is a view, partly in section, taken on the line 3-3 of Figure 2; Figure 4 is a plan view of a modified form of anchor according to the present invention; and Figure 5 is a diagrammatic view illustrating the various factors used in determining shank design. In Figures 1-3 an embodiment of an anchor is shown which includes flukes 10 and 11, a shank 12, a stock 13 and opposite crown plates 14 and 15. Intermediate portion 40 of the shank 12 tapers in side elevation (Figure 2) between the base end 26 of the shank and its tip end 24. The flukes are secured in a co-planar relationship on either side of the shank 12, the latter having an eye 16 at its forward end for attachment to a rode (not shown). The edges of the shank can be sharpened as at 28 and 29 to aid penetration and burial of the shank. The flukes 10 and 11 have reinforcing ribs 18 and 19 formed on the flange edge nearest the shank. Each rib is secured to one of spacer plates 20 and 21 provided on each side of the shank. These confine the shank to its position on the stock 13 and support the crown plates 14 and 15. Each crown plate may be relieved as at 22 to permit the desired swing of the flukes relative to the shank, this swing being termed the fluke angle. A favourable fluke angle for use in hard sand is about 33 , while that for use in soft mud is about 55 In that form of the invention shown in Figure 4 the shank tapers in thickness as at 30 from its tip end 24 to its base end 26. This is in contrast to the shank shown in Figures 1-3 which tapers only in its side elevation from its tip end 26 to its stock end 24. The dimensions and the material of the shank must be selected so that the flexibility is achieved without exceeding the limit of the elasticity of the shank, i.e., upon release of pressure, the shank must return to substantially its unstressed position at right angles to the stock. The shank can be regarded as a single leaf cantilever spring and can be made from any one of the various fine grain alloy steels, e.g. a spring steel having a yield strength of the order of 1.4 x 108 kg/sq.m, or a high carbon alloy steel. When it is desired to provide a shank manufactured by forging or by casting, a flexible material such as nodular graphite can be utilized. One can also use a fiber-reinforced plastic as produced by Union Carbide Corporation, 3M and Hexcel. A process for producing such material is set forth in U.S. Patent 3,462,289. One can also utilize KEVLAR, a product of E.I. du Pont de Nemours and Company, which is a solid resinous material containing an aromatic polyamide, a fluorocarbon polymer and a polyamide, see U.S. Patent 3,356,760. Two criteria of importance in design of the shank are "included angle" and the "linear deflection". As seen in Figure 5, the included angle a is that angle a between a line drawn through the tip of the shank, when deflected, at that point on the longitudinal axis of the shank at which curvature of the shank commences and the longitudinal axis A of the shank when the shank is at rest. The linear deflection is the distance D between the shank tip, when deflected, and the longitudinal axis of the shank at rest, the distance being measured along a line normal to the shank. With the shank at an included angle of 450, when it is made of the materials mentioned above, it is capable of a linear deflection of about 60% of the shank length without any adverse effect such as breaking or the imparting of a permanent set. The shanks used heretofore were incapable of a linear deflection of more than a few percent, at the most 5%, i.e. with an included angle of only a few degrees, usually less than O Any deflection of a prior art shank beyond either of the foregoing limits resulted in a failure by breakage or imparting of a permanent set. U.S. Patent 2,254,546 contains a comparison of the resistance to continued burial of several anchors then available on the commercial market (1940) with the anchor which was the subject of that patent. The resistance was given under a heading "holding power per pound weight". That value ranged from 2.0 to 206.9. Mention was also made of a 29 pound (13 kg) anchor whose resistance was such that a 3/8" (9.5 mm) chain, rated at 8,000 pounds (3629 kg) tensile strength, failed under continued pull. Under these conditions, the resistance was of the order of 275 kgs per kg of anchor weight. The tests reported in that patent were made in certain areas of San Francisco Bay. In tests made in the same areas utilized in the earlier reported tests and under like conditions, an anchor made in accordance with this invention provided a resistance to burial of 1,500 kgs and more per kg of anchor weight. The significance of that unexpected increase in burial resistance per unit of anchor weight is believed to be of great importance to every anchor user. In the small boat field, it enables a boat user to anchor safely with greater ease and convenience in the handling of the anchor before and after mooring. At the other extreme, for example, in the offshore drilling field where the weight of the anchor is measured in tonnes rather than in kgs, the difficulties in the placement of such immense anchors are materially reduced. Anchors were constructed as taught in U.S. Patent 2,249,546 with the exception of the shank, which was constructed to embody this invention, being made of a suitable thin, flexible and resilient high tensile steel which was heat treated, after being formed to the desired tapered configuration, to provide shanks having the dimensions indicated in the first four columns of Table A. Each shank was quite resilient and flexible and was easily moved into a position wherein the shank tip had the linear deflection shown in the last three columns of Table A. To effect this movement, the base of each shank was firmly hend as if attached to an anchor. A pull was then applied to the shank tip to bend the shank to a desired extent. Upon release of the applied pull, each shank returned to its normal straight-line position. No breakage or permanent set occurred. TABLE A EMI8.1 <tb> Shank <SEP> Shank <SEP> Shank <SEP> Shank <SEP> Shank <SEP> Linear <SEP> Percen- <SEP> Included <tb> <SEP> No. <SEP> Thick- <SEP> Length <SEP> Height <SEP> Height <SEP> Deflec- <SEP> tage <SEP> Angle <tb> <SEP> ness <SEP> (c) <SEP> mm <SEP> at <SEP> Tip <SEP> at <SEP> tion <SEP> Linear <tb> <SEP> mm <SEP> End <SEP> Base <SEP> De <SEP> flec <tb> <SEP> (a) <SEP> mm <SEP> End <SEP> tion <SEP> to <tb> <SEP> (b) <SEP> mm <SEP> Shank <tb> <SEP> Length <tb> <SEP> 1 <SEP> 4 <SEP> 483 <SEP> 4.8 <SEP> 63.5 <SEP> <SEP> 317.5 <SEP> 65.8 <SEP> 42 <SEP> <tb> <SEP> 2 <SEP> 6.3 <SEP> 787 <SEP> 7.1 <SEP> 101.6 <SEP> 558.8 <SEP> 71.5 <SEP> 460 <tb> <SEP> 3 <SEP> 10.3 <SEP> 1225 <SEP> 11.1 <SEP> 138.1 <SEP> 882.6 <SEP> 53.3 <SEP> 450 <tb> After performing the foregoing manipulation of each shank, each was then placed in position and secured in those elements necessary to provide a complete anchor, namely, the flukes, a crown and a stock. The three anchors thus provided were of the following weights indicated in the first column of Table B. Each assembled anchor was then attached to a rode so that the anchor could be engaged with the bottom and then pulled by the force provided by a landing craft; the actual craft was a Navy LCM, capable of exerting a force sufficient to drag the anchor under test, at least 11340 kgs. A strain gauge was positioned in engagement with the rode to determine the magnitude of the pull required to force the anchor to pass through the layers of solids making up the bottom. With the passage of time, these layers became more compact as the water in which the solids were once suspended is forced from between the solids until they provide a very solid and dense mass. The anchor penetrated the bottom until it reached a level at which the resistance to further anchor penetration exceeds the applied pulling force. Because of a desire to examine each anchor after it had been pulled by the landing craft, none was pulled to the point where it was dragged. The maximum force exerted upon each anchor while it was still stationary in the bottom is shown in the second column of Table B, the third column shows the resistance measured in kilograms per kilogram of weight of the anchor. TABLE B EMI10.1 <tb> Anchor <SEP> eight <SEP> Maximum <SEP> kg <SEP> c <SEP> c <SEP> b <tb> No. <SEP> kg <SEP> Exerted <SEP> Resis <tb> <SEP> Force <SEP> kg <SEP> tance <SEP> a <SEP> b <SEP> a <tb> <SEP> per <SEP> kg <tb> <SEP> weight <tb> <SEP> 1 <SEP> 1.81 <SEP> 2721.6 <SEP> 1500 <SEP> 101 <SEP> 7.6 <SEP> 13.3 <tb> <SEP> 2 <SEP> 7.26 <SEP> 7257.6 <SEP> 1000 <SEP> 110 <SEP> 7.8 <SEP> 14 <tb> <SEP> 3 <SEP> 29.48 <SEP> 1814.4 <SEP> 615 <SEP> 112 <SEP> 9.2 <SEP> 12 <tb> While the three anchors tested were of a nominal weight, the test results are truly indicative of what can be expected in anchors of a greater size and weight. Those skilled in the art can readily determine the dimensions required for larger size anchors. This has proven to be true in the anchors made under U.S. Patent 2,249,546 in sizes of 10 to 50 and more tonnes. The relation of the height of the tip to the height of the base and to the length of the shank are shown in the last three columns of Table B in which (a) is the height of the tip; (b) is the height of the base end; and (c) is the length of the shank for the three discussed above. The above ratios can vary between 80 to 130 for the length of the shank to the height of the tip end, from 5 to 10 times for the ratio of the shank length to the height of the base end and from 10 to 15 times for the ratio of the height of the base end to the height of the tip end. The taper of the shank is preferably within these limits. While the improved shank has been disclosed with some specific references to the anchors disclosed in U.S. Patent 2,249,546, such reference is without any limitation of the disclosure because the novel shank can be employed with any structure useful to secure in place any water borne object attached by a rode to a device engaged with a bottom and which device restrains or limits the movement of the object with respect to the water supporting the object.

Claims: CLAIMS 1. A shank (12) for an anchor comprising a tip (24), an intermediate portion (40) and a base end (26), which are aligned along a longitudinal axis extending from the base to the tip, characterised in that the shank (12) is substantially inflexible in a first plane and is flexible in a second plane perpendicular to the first plane, and in that the tip (24) can be moved in the second plane with respect to the base end (26) into a position in which it is substantially normal to the longitudinal axis without causing permanent deformation of the shank. 2. A shank according to claim 1, characterised in that it is formed of a thin, flexible and resilient fibre-reinforced plastics material. 3. A shank according to claim 2, characterised in that the plastics material comprises aromatic polyamide, a fluorocarbon polymer and a polyamide. 4. A shank according to claim 1, characterised in that it is formed from a thin sheet of spring steel. 5. A shank according to any preceding claim, characterised in that the length (c) of the shank (12) between the tip (24) and the base end (26) is from 80 to 130 times the height (a) of the tip and from 5 to 10 times the height (b) of the base and in that the height (b) of the base end is from 10 to 15 times the height (a) of the tip. 6. An anchor comprising a shank (12) and flukes (10,11) connected to the shank, characterised in that the shank is one constructed according to any preceding claim with the flukes (10,11) extending in a plane substantially perpendicular to said first plane and angled with respect to said second plane. 7. An anchor according to claim 6 characterised in that the flukes (10,11) are pivotally mounted relative to said shank (12).

Inventors: OGG, ROBERT DANFORTH
Applicants: ALPHA OCEAN SYSTEMS, INC.
Application year: 1983
Main classification: B63B21
IPC codes: B63B21