Water anchors

Abstract

Anchor apparatus (1) including an anchor (2) and a slideable anchor bridle (3), the anchor having a lower part or body portion with oppositely disposed anchoring formations (6a,6b) extending therefrom and an upper part including bridle attachment means in the form of at least two parallel bridle rails extending above and between the oppositely disposed anchoring formations (7,8), limbs (4,5) of the anchor bridle being slideably attached, in use, to respective bridle rails (7,8), the arrangement being such that when deployed, the anchor can be pulled in one direction whereby to permit one of the oppositely disposed anchoring formations to penetrate the sea bed and whereafter if and when the anchor is pulled in the opposite direction after the bridle limbs have slid along the bridle rails, the other of the oppositely disposed anchoring formations also penetrates the seabed, whereafter the anchor can continue to be pulled in successively alternate directions via the bridle to penetrate progressively further into the sea bed until firmly fixed therein.

Claims

1. Anchor apparatus including an anchor and a slideable anchor bridle, the anchor having a lower part or body portion with oppositely disposed anchoring formations extending therefrom and an upper part including bridle attachment means in the form of at least two parallel bridle rails extending above and between the oppositely disposed anchoring formations, bridle limbs of the anchor bridle being slideably attached, in use, to respective bridle rails, the arrangement being such that when deployed, the anchor can be pulled in one direction whereby to permit one of the oppositely disposed anchoring formations to penetrate the sea bed and whereafter if and when the anchor is pulled in the opposite direction after the bridle limbs have slid along the bridle rails, the other of the oppositely disposed anchoring formations also penetrates the seabed, whereafter the anchor can continue to be pulled in successively alternate directions via the bridle to penetrate progressively further into the sea bed until firmly fixed therein.

2. Anchor apparatus according to claim 1 wherein the oppositely disposed anchoring formations are fluted claws or spikes.

3. Anchor apparatus according to claim 2 wherein at each end of the anchor, and fixed above an open end of each set of said claws, are cross-struts for additional lateral and torsional stiffness.

4. Anchor apparatus according to claim 3 wherein each respective pair of cross-struts at each end of the anchor is “V”-shaped.

5. Anchor apparatus according to claim 1 wherein the anchoring formations protrude from either end thereof.

6. Anchor apparatus according to claim 1 wherein the at least two parallel bridle rails comprises three parallel bridle rails including a central bridle rail and an outer rails and the bridle limbs comprise a central limb and an outer limbs, the central bridle rail being slightly longer than the outer rails such that, in the event of the anchor being pulled by the outer limbs of the bridle tipping forward the central limb of the bridle comes momentarily into tension, allowing the outer limbs to slacken and, because of its forward, protruded, position at an end of the central bridle rail so imparts to the anchor a restoring moment countering any forward tipping effect until the anchor resumes its proper attitude and its drag load is once more transferred to the outer bridle limbs.

7. Anchor apparatus according to claim 1 wherein the body portion of the anchor is fabricated from metal or other structural sheet.

8. An anchor adapted for use with a slideable anchor bridle, the anchor comprising or including a body portion with oppositely disposed anchoring formations extending therefrom and bridle attachment means in the form of at least two parallel bridle rails extending above and between the oppositely disposed anchoring formations, the bridle rails being connectable to respective bridle limbs of an anchor bridle such that, in the use, when the anchor is deployed it can be pulled in one direction whereby to permit one of the oppositely disposed anchoring formations to penetrate the sea bed and whereafter if and when the anchor is pulled in the opposite direction after the bridle limbs have slid along the bridle rails, the other of the oppositely disposed anchoring formations also penetrate the sea bed, whereafter the anchor can continue to be pulled in successively alternate directions via the bridle to penetrate progressively further into the sea bed until firmly fixed therein.

9. An anchor according to claim 8 comprising or including a central bridle rail and two oppositely disposed side rails.

10. An anchor according to claim 9 wherein the side rails have curved ends.

11. An anchor according to claim 10 wherein the curved ends are fixed to the oppositely disposed anchor formations.

12. An anchor according to claim 8 wherein the anchor formations are in the form of fluted claws or spikes.

Description

(1) The invention will now be described, with reference to the accompanying drawings in which:

(2) FIG. 1 is a perspective view of an anchor and a bridle assembly according to the invention,

(3) FIG. 2 is a perspective view of the anchor apparatus of FIG. 1 being dragged along the sea bed,

(4) FIG. 3 is a view corresponding to that of FIG. 2 but in which the anchor has become snagged on the sea bed at its leading end and has begun to tilt with its trailing end rising upwards, and

(5) FIG. 4 is a perspective view of a preferred embodiment of the invention.

(6) Referring firstly to FIG. 1 anchor apparatus shown generally at 1 comprises a generally long, flat anchor 2 and associated 3-limb bridle 3 having a central bridle 4 and respectively opposite outer bridles 5. When deployed, the anchor body is designed to remain at an approximately horizontal attitude during and after setting, hanging vertically from the anchor line bridle only during dropping and recovery.

(7) The body of the anchor 2 is fabricated from metal or other structural sheet and includes at each end one or more downwardly pointing fluted open spikes or claws 6a and 6b with which to dig into and funnel e.g. sand or mud from the sea bed (not shown).

(8) The claws are permanently and rigidly attached to the horizontal back-plate of the anchor, and thus act as an integral structural element imparting a longitudinal flexural stiffness to the anchor body. At each end of the anchor 2, and fixed above the open end of each set of claws 6a, 6b is a plate (“V”-shaped in the example as illustrated) for additional lateral and torsional stiffness and affording suitable locations onto which are welded or otherwise secured the three parallel bridle rails; a central rail 7 and a pair of slightly shorter outer rails 8.

(9) Other than the bridle and its sliding attachment described below, the anchor has no moving parts. Manufacture is based on simple fabrication techniques and involves no custom forgings or castings. Maintenance requirements are likewise minimal and simple.

(10) The design is readily scalable according to required duty, and the basic anchor could also be incorporated into more complex configurations for specialist application. Conversely, several of the design's advantages could still be realised in a simplified, uni-directional variant, in applications requiring minimal size and weight.

(11) The central bridle limb 4 and outer bridle limbs 5 are each connected to respective bridle rails 7, 8 via bridle rings 9 free to slide along the bridle rails 7, 8 so that the bridle 3 can re-orientate and move from the position shown at one end of the anchor 2 to the opposite end. The three bridle limbs 4, 5 are connected at their respective other ends to a single pulling ring 10 for pulling the anchor 2 in the manner as shown in FIGS. 2 and 3 via an anchor chain or cable (not shown).

(12) The central bridle rail 7 is supported above the anchor 2 by leading and trailing bridle rail support plates 11a, 11b connected at their lower ends to the central ones of claws 6a, 6b and are supported centrally by cross-struts 12 which connect with the ends of the side rails 8.

(13) In FIG. 2 the anchor 2 is shown resting on the sea bed with the bridle 3 being pulled via the pulling ring 10, itself connected to a cable or chain (not shown) of e.g. a boat or navigation buoy. In this condition the direction of travel of the anchor 2 along the sea bed is as shown arrowed in which the leading claws 6a are therefore able to dig into the sea bed as they are dragged along it, whereas the trailing claws 6b offer comparatively very little resistance to the drag over the sea bed. Upon reversal of the direction of the pull on the ring 10, such as could be caused by the ebb and flow of the tide it will be apparent that the ring 10 and hence bridle 3 will assume the opposite configuration whereby the formerly trailing claws 6b become leading claws. At each such reversal, because of the fluted shape of the claws 6a, 6b, which serve to act as scoops, it will be apparent that the anchor 2 becomes progressively embedded deeper in the sea bed, until an equilibrium is reached between the developing resistance of the bed material and the maximum load on the anchor line. The anchor 2, therefore, by this oscillatory motion buries itself into the sea bed at each change of direction of the tide, this being a particularly suitable feature where the anchor is used to secure vessels such as marker buoys.

(14) The use of a bridle as opposed to a single-point attachment for the anchor line confers a further design advantage, in that the anchor 2 when being set is dragged along the sea bed primarily by the outer bridle limbs 5, which are physically separated at their respective attachment points to the outer bridle rails 8, close to the outboard extents of the anchor 2. This results in a more orderly passage as the anchor is dragged across the sea bed, minimising any yawing and transverse rolling due to unevenness and non-uniformity of the sea bed, and ensuring a good final alignment with the direction of pull.

(15) The central bridle limb 4 and the central rail 7 to which it is attached, which extends slightly further at each end of the anchor 2 than the side rails 8. are not necessary to the basic setting operation of the anchor as described above, but serve to realise an important additional feature as can be seen with reference to FIGS. 2 and 3. In FIG. 2 it will be seen that the anchor 2 lays flat on the sea bed and is being pulled by the outer bridle limbs 5 with the central bridle limb 4 being slack. By contrast, in the position shown in FIG. 3 the anchor 2 has started to tilt—such as might result from encountering a hard spot in the sub-water substrate—with the trailing end beginning to lift (arrowed). This slight forward rotation of the anchor 2 results in the central bridle limb 4 becoming taut and the outer bridle limbs 5 correspondingly slack, thus lowering the point of action of the pulling line load on the anchor. This relatively sudden shift, acting in combination with the anchor's own weight, causes a temporary restoring moment about the anchor's leading end, bringing it back towards its desired near-horizontal attitude, until the corrected geometry re-tensions and transfers the pulling load back to the outer bridle limbs. In combination with the generally greater directional control effected by the bridle and as previously described, this self-correcting feature substantially reduces any propensity for the anchor to skip or overturn during setting. In comparison with a conventional anchor under similar sea bed conditions, the reliability of the setting operation is improved, and the drag distance required to achieve a secure set is substantially reduced.

(16) Once set, the anchor offers several advantageous performance characteristics and operational features:

(17) Holding capacity is very high in relation to the anchor's weight. Compared to a conventional anchor, a greater proportion of the device is ultimately “usefully” embedded, so maximising the shear and displacement resistance of the holding ground. Similarly, the efficiency of the claw design means less reliance on the weight of the anchor to achieve a secure initial embedment.

(18) The reversibility of operation, as described above, affords secure holding under tidal or otherwise varying current and wind conditions.

(19) The anchor, having no conventional shank, has a minimal above bed profile, thereby reducing hazard to other vessels operating in the vicinity in the case where navigable depths may be limited.

(20) The anchor remains secure at comparatively steep mooring line angles—prototype trials have suggested safe working angles of the order of 45 degrees, nearly twice that at which conventional anchors may lift. This enables swinging circle radii to be substantially reduced. This does not however affect the ease of recovery by simple vertical haul, with no chaser system required.

(21) In FIG. 4 there is shown a preferred embodiment of the invention which essentially differs from the embodiment shown with reference to FIGS. 1 to 3 by the removal of the cross-struts 12 in favour of an arrangement in which the central bridle rail 7 is supported above the main body of the anchor 2 solely by the leading support plate 11a and at its trailing end by a trailing support plate 11b, between each of which is slideably disposed on the central bridle rail 7 an elongate anchor shank 14 having three bridle rail capture sleeves 15 by which it is slideably secured on the central bridle rail 7, which itself is preferably made of high tensile steel. The use of a slideable anchor shank 14 instead of a single bridle ring 9 provides improved strength for the entire arrangement, it being understood that when the anchor 2 is being set the greatest load is borne by the central bridle rail 7 and its attachment to the central bridle limb 4.

(22) In the preferred embodiment shown with reference to FIG. 4 it will also be seen that the side rails 8 are secured to but spaced from respectively opposite sides of respective leading and trailing claws 6a, 6b of the anchor 2, with each respective end 16a, 16b, being curved to provide a smooth transition for the bridle limb from the linear to the radial direction when anchor is pulled by the two outer bridle limbs 5.