GB2227988A - An omnidirectional burial anchor - Google Patents

Abstract

An anchor has an elongate body (1) of tubular or rolled section which is substantially symmetrical about both its vertical longitudinal and transverse planes and which will tend to bury itself when dragged from either end and incorporates the means by which the pulling cable may transfer its point of action from one end to the other such as by its attachment to the anchor via a sliding ring (4) which can move freely along a longitudinal bar (3) attached to the anchor at both ends. <IMAGE>

Description

AN OMNIDIRECTIONAL BURIAL ANCHOR This invention relates to an anchor for mooring a vessel or structure to a mooring bed; it is especially suited to mooring situations where the direction of pull may vary in direction anywhere within 3600 in azimuth such as occurs during the normal ebbing and flowing of a tidal stream or in response to a changing wind direction.

A universal drawback in existing designs of burial anchor is their limitation to a single direction only, in which they are effective, and that is in a line along the shank of the anchor; any change in pulling direction causes the anchor to reorientate in a different direction which is inevitably accompanied by a partial or total loss of effectiveness. Conventional burial anchors are thus known to be 'tripped' when the direction of pull is changed. In such instances the anchor may break out of the holding ground with attendant loss of function. It is subsequently required to re-bury itself in a new direction before it can re-establish its effect.

This common mode of failure of burial anchors is responsible for a large number of accidents and considerable loss of property.

Thus, in a typical situation where a vessel is moored in a tidal location the vessel would normally swing around the anchor as the direction of the tidal stream changed. In such a situation the pulling force on the anchor would normally be the highest when the tide was either at full ebb or full flow. Furthermore, in most cases, the direction of the ebb and flow are roughly on reciprocal headings in azimuth.

With reference to the above typical situation, the present invention offers, for the first time, a burial anchor which, once buried, will provide an efficient anchoring function regardless of any subsequent change in the direction of pull in azimuth and without any appreciable change in the anchor's orientation. The anchor is thus described as possessing omnidirectional, high holding power. Furthermore, it is a primary feature of this invention that, when pulled from the reciprocal direction in which it was first buried the anchor will maintain essentially the same burial characteristics in the opposite direction without any accompanying tripping or reorientation of the anchor itself.In consequence, the alternating changes in the pulling direction on the anchor, which is the subject of the present invention, will cause the anchor to tend to bury itself continuously without tripping in a vertical, zig-zagging downward course until it reached its maximum burial depth appropriate to the given mooring ground.

An object of the present invention is to provide anchors which, when pulled from opposite directions, will maintain their burial characteristics without tripping or re-orientation and thus provide uninterrupted high holding power independent of consequent changes in pulling direction.

According to the present invention, there is provided an anchor which is generally elongate and based on a tubular or rolled section structure which is substantially symmetrical about both its vertical longitudinal and transverse planes and having a facility whereby the point on the anchor at which the pulling cable functionally exerts its force may be transferred from one end of the anchor to the other. As a result of the anchor's symmetry about its transverse plane the anchor thus maintains substantially the same burial characteristics when dragged from either end.

To enable this to operate in practice, an example of this invention incorporates the facility for the pulling cable to move its point of attachment to the anchor from one end of the anchor to the other, as the direction of pull changes. This may be achieved, for example, by a sliding ring or similar device at the termination of the pulling cable which is free to move along a longitudinal bar, slot or similar arrargernent on the anchor.

The anchor ma > be constructed such that the centre of gravity is lower than the longitudinal axis by, for example, wadding weight to the base and/or removing a section of the upper half of the main body. By this means, the anchor is given a self-righting. stabilising tendency. Thus, whilst such an anchor is lying on or under the mooring ground, it will tend to rotate about its longitudinal axis towards its upright, burying configuration, that is, with the point of connection of the pulling cable and the longitudinal bar uppermost.

The required anchor-to-cable angle developed between the pulling cable and the longitudinal axis of the anchor during the burial phase is produced as a result of the drag resistance and geometric disposition of the forward facing surfaces with respect to the point of attachment of the pulling cable and which in turn are dependent upon the ratio of the length to the diameter of the main body of the anchor. Variations in this anchor-to-cable angle may be achieved, for example, to suit different types of holding ground, by restricting the length of travel of the pulling cable attachment along the anchor. This may, for example, be conveniently carried out by welding stops to the underside of the longitudinal bar at both ends.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figs 1-8 show perspective views of different embodiments of the present invention.

Figs 9 and 10 show end views of two optional embodiments of adding a heavy plate to the base of the main body of the anchor.

Figs 11-13 show perspective views of optional embodiments of the bar configurations.

With reference to Figure 1 in one embodiment of the present invention, an anchor (1) consists of a length of tube of circular cross-section the upper portion of which is an open void (2) and along the top of which is fitted a longitudinal bar (3) connected to the anchor at its extreme ends. A ring (4) forms the termination of the pulling cable on the anchor and is free to slide to and fro along the length of the anchor and when coming to rest at either end may pull the anchor in either direction along its longitudinal axis (AT. The leading edges at both ends of the anchor are bevelled to provide sharper edges in order to assist the anchor's penetration of the mooring bed.

The ratio of the overall length of the anchor (L) to its diameter (D) is greater than 1:1 in order to achieve an elongate structure.

In normal operation the anchor is connected to a vessel by a pulling cable of suitable length and construction. One or more swivel connections may be placed at some point(s) along this cable to allow the cable to rotate with respect to the fixed anchor whilst the moored object swings around the mooring position.

Alternatively, a swivel may be incorporated on the sliding ring permanently attached to the longitudinal bar. Once lowered to the mooring bed the anchor will adopt a position with its longitudinal axis (A) substantially parallel with the mooring bed and in line with the direction of pull. The pulling cable connection and bar will be located at a level somewhere between the mooring bed level and the uppermost level of the anchor. Due to its low centre of gravity, the anchor will tend to rotate around its longitudinal axis (A) to bring the bar and pulling cable connection towards the uppermost point. When a pulling force is exerted, the anchor will tend to adopt an acute, vertical angle with the mooring bed due to a combination of the weight of pulling cable supported off the mooring bed at the forward end of the anchor and the asymmetric drag of the lower surfaces of the anchor against the mooring bed.

Figures 2 to 15 refer to embodiments of the present invention. Figure 2 illustrates a tubular anchor of circular cross-section where the main body consists of two tubes of equal diameter joined at the centre by a mitre joint giving each section an acute angle with the main longitudinal axis of the anchor body. An additional longitudinal plate (5) is fixed at the bottom of the anchor to lower the centre of gravity and provide additional structural strength.

Figure 3 illustrates an embodiment similar to Figure 2 but provides for two opposed, conical tubular sections joined at the centre at their smaller diameters and sharing a common longitudinal axis.

Figure 4 illustrates an embodiment similar to Figure 1 but where the tubular body is formed from a section of a bend or toroid.

Figure 5 illustrates an embodiment similar to Figure 1 but where the tubular body consists of a hexagonal section.

Figure 6 illustrates a further embodiment similar to Figure 1 but where the tubular body consists of a pentagonal section.

Figure 7 illustrates an embodiment where the main anchor body is * rmed from a rolled 'T' section or cast in a similar shape. The sliding termination of the pulling cable may be provided with a slot (6) in the vertical component of the anchor body or a bar attached to the extreme ends of the anchor.

Figure 8 illustrates an embodiment similar to Figure 7 but where the main anchor body is formed from a rolled 'I' section or cast in a similar shape.

Figures 9, 10, 11 and 12 illustrate embodiments where the centres of gravity of the anchors may be lowered by the incorporation of heavier components (7) at the bases of the anchors.

Figures 13 and 14 illustrate embodiments where the longitudinal bar may be curved as in Figure 13 or include one or more angle bends as in Figure 14.

Claims (3)

CLATM S

1. An anchor which is generally elongate and based on a tubular or rolled section structure which is substantially symmetrical about both its vertical longitudinal and transverse planes and having a facility whereby the point on the anchor at which the pulling cable functionally exerts its force may be transferred from one end of the anchor to the other. As a result of the anchor's symmetry about its transverse plane, the anchor maintains the same burial characteristics when dragged from either end.

2. An anchor as claimed in Claim 1 wherein the base is given additional weight by the incorporation of heavy structural components to lower the centre of gravity of the anchor below its longitudinal axis (see Ouery f

3. An anchor substantially as herein described with reference to and as shown in the accompanying drawings.