GB2463912A - Anchor with a shank rigidly attached to diverging half flukes - Google Patents

Abstract

The invention relates to a new class of marine anchors of particularly high holding power, which are particularly applicable to the safe mooring of leisure craft from 1 to 100 tonnes displacement. The anchor comprises a shank 2 rigidly attached to two mirror image half-flukes 3A and 3B disposed symmetrically about the plane of the shank. The inner edges of said half flukes are separated by a slot diverging from the attachment of the half flukes to the shank towards the tips 5A and 5B of the half flukes. The shank contains a pulling eye 6 near the end farthest from the attachment of said half flukes to the shank. The half-flukes may be bolted or welded to the shank.

Description

DESCRIPTION

BACKGROUND OF THE INVENTION -TYPES OF ANCHORS

The following terms are commonly used to describe the different components of an anchor and are illustrated for the main types of anchor used by small boat owners in Figures 1, 2 and 3.

Anchors in general are disposed about a plane of symmetry (1). An anchor consists of a shank (2) which lies within the plane of symmetry (1) and a fluke (3) which is positioned symmetrically on either side of the plane of symmetry (1). The shank (2) is generally attached towards the heel (4) of the fluke (3) while the tip (5) is free to engage with the mooringbed surface when the anchor is laid on the mooringbed surface and pulled. The anchor cable or rode is attached to the anchor by a shackle which engages a ring or pulling eye (6). Some anchors have two half-flukes or palms (3A and 36) instead of a single one-piece fluke; some have a stock (7) mounted perpendicular to the plane of symmetry (1) which assists initial embedment of the anchor in the mooringbed; some contain an arm (8) which supports two half flukes or palms (3A and 3B); some incorporate a pivot box or crown assembly (11) to retain a pair of pivoting half-flukes (3A and 3B): the pivot box allows the shank (2) of such an anchor to swing to either side of the fluke and is held in position by the stock (7) as it passes through the pivot-box (9) of, if the anchor has no stock, by a pin.

The three main classes of anchors used by small-boat owners are now described, viz, the Fisherman's Anchor, the Rigid Shank-and-Fluke Anchor, and the Pivoting-Fluke Anchor.

(A) Fisherman Anchor Until the early twentieth century, the standard anchor for small craft was what is now termed the Fisherman's Anchor. As shown in Figure 1, the Fisherman's Anchor consists of a straight shank (2) attached to an arm (8) disposed symmetrically within the plane of symmetry (1) at one end of the shank (2). Attached to the ends of the arm (8) are two half-flukes or palms (3A and 3B).

These form the equivalent of the single fluke (3) in other anchors and, in use, one of the palms (3A or 3B) is responsible for generating the hold of the anchor. A pulling eye or ring (6) is attached to the other end of the shank (2) along with a stock (7) which, in use, is mounted perpendicular to the plane of symmetry (1) containing the shank (2) and the arm (8). The stock (7) assists in positioning the anchor on the mooringbed so that, when the anchor is pulled along the surface of the mooring bed, one of the palms (3A or 3B) digs into the mooringbed, and generates the hold of the anchor. The stock (7) is normally demountable, and, in use, is held in position by a pin. The Fisherman's Anchor has a poor holding power relative to its weight and is now more or less obsolete. It has been replaced by more efficient anchors, Types (B) and (C).

(B) Rigid Shank-and-Fluke Anchor In Rigid Shank-and-Fluke Anchors, as shown in Figure 2, the shank (2) is rigidly attached to an integral fluke (3). Normally, the shank (2) is welded or bolted towards the heel (4) of the fluke (3).

The fluke (3) is often roughly triangular. In plough anchors the fluke (3) has a convex shape when viewed from the pulling eye (6). In scoop or spade anchors, the fluke (3) has a concave shape when viewed from the pulling eye (6). In a few anchors the fluke (3) is planar. In order to ensure that the anchor will embed itself when pulled along the mooringbed surface such anchors will either have a weight (9) attached near the tip (5) of the fluke, or a roll-bar (10) towards the heel (4) of the fluke (3). Anchors of this type include the convex Delta and Sarca anchors and the concave SPADE, Rocna, and Manson Supreme anchors. The original convex CQR anchor also falls into this class. It was invented by G. I. Taylor in 1923, and still widely used. It differs from other anchors in this class by having a hinge near the bend in the shank (2) whose axis points towards the tip of the fluke (5). This helps to avoid disengagement from the mooringbed when the anchor is veered, The unique concave Bruce Anchor, invented by Peter Bruce around 1950, has a shank (2) and fluke (3) forming a single forged unit. The part which may be identified as the fluke has two wings and a central palm. There are now many copies of the Bruce anchor including the Claw anchor marketed by Lewmar Ltd. (C) Pivoting-Fluke Anchor The Pivoting-Fluke Anchor was invented by R.S. Danforth in 1939, and has been widely copied.

A recent example is the very light aluminium Fortress anchor. As shown in Figure 3, Pivoting-Fluke Anchors have a shank (2) which can pivot on either side of the composite fluke (3). In order to allow this, the flat fluke (3) is divided equally into two parts (3A) and (3B) which are disposed on the two sides of the plane of symmetry (1). The anchor can then engage the mooringbed surface from either side, whichever happens to land on the surface of the mooringbed when the anchor is lowered. The space between the half-flukes widens towards the tips (5A) and (5B) of the half-flukes (3A) and (3B). The half-flukes (3A) and (3B) are generally welded or otherwise fixed into a pivot box or crown assembly (11). Most such anchors also include a stock (7) which projects sideways from the heels (4A) and (4B) of the fluke assembly to enhance the stability of the anchor with respect to rolling. The shank (2) is retained within the pivot-box (11) by means of the stock (7). The pivot-box (11) limits the angle through which the shank (2) can swing. In some versions this angle can be altered to enable the holding in different mooringbeds to be optimised. The Brittany anchor has no stock (7), and the shank (2) is retained by a pin, equivalent to a very short section of a stock (7), This anchor rolls out when forced to plough through the mooringbed: it then turns over and re-engages.

Each type of anchor has desirable and undesirable features. The advantages and disadvantages of the different types of anchors are summarised in Table 1. The most desirable features are highlighted in bold type. They are associated with the concave rigid Shank-and-Fluke type and the Pivoting-Fluke type.

Table I Advantages and Disadvantages of Types (A), (B) and (C) Anchors.

Anchor type Initial engagement Roll stability when Holding Veering stability ploughing power to ________________ ________________________ __________________ weight ratio _____________________ (A) Fisherman Excellent, the only anchor Excellent Very poor Excellent ________________ which will set in kelp. __________________ _____________ ____________________ (B) Rigid Shank-Good in soft to Excellent, except Moderate Very good, except for and-Fluke moderately hard for CQR which can COR which can roll mooringbeds; poor in roll out or plough out or plough on its Convex or hard mooringbeds on its side. side.

Plough type ________________________ __________________ _____________ ____________________ (B) Rigid Shank-Excellent due to chisel-Excellent Good Excellent and-Fluke like engagement profile Concave or Scoop type _______________________ _________________ ____________ ___________________ (C) Pivoting-Good in soft sand but Uncertain: likely to Excellent Poor, likely to roll out Fluke, with stock poor in hard mooringbeds roll out and turn when fully and turn over before due to small angle of over. Re-buried, re-engaging attack. engagement ________________ ________________________ uncertain. _____________ ____________________ (C) Pivoting-Good in soft sand but Dangerous, rolls Cannot be Rolls out consistently Fluke without poor in hard mooringbeds out and turns over: determined stock due to small angle of Re-engagement due to lack of ________________ attack. uncertain, roll stability. ____________________

ESSENTIAL TECHNICAL FEATURES OF THE INVENTION

The present invention, provides a new class of anchor, distinct from and in addition to the classes of anchor (A), (B) and (C) described above. The anchor of the invention is self-launching, roll-stable and has exceptional holding power: it combines the desirable features of the concave Rigid Shank-and-Fluke type (B) with the high hold to weight ratio of the Pivoting-Fluke type (C).

The key features of the invention are illustrated in Figure 4. According to the present invention, there is provided an anchor whose fluke is configured as two half-flukes (3A and 3B), such as those found in a Pivoting-Fluke Anchor, type (C). The two half-flukes, (3A) and (3B) are disposed symmetrically one on each side of the plane of symmetry (1), and are mirror images of one another. In use, the half-flukes (3A) and (3B) are attached rigidly to the shank (2) either by bolting or welding. They are separated by a slot which diverges towards the tips (4A) and (4B) of the half-flukes (3A) and (3B) from the attachment of the half-flukes (3A) and (3B) to the shank (2) The two half-flukes, (3A) and (3B) can be configured in a convex, concave or flat manner as viewed from the pulling eye (6). As for Rigid Shank-and Fluke anchors, illustrated in Figure 2, initial engagement with the mooringbed is ensured, either by placing weights (9) under the tips of the half-flukes (3A and 3B) or by fitting a roll-bar (10) towards the heels (4A and 4B) of the half-flukes (3A and 3B),.

EXAMPLE OF AN EMBODIMENT OF THE INVENTION

A specific embodiment of the invention is now described.

Figures 5 shows a view of a prototype embodiment of the anchor of this invention. The material of construction of this prototype is stainless steel. The weight of the prototype is 4.8 kg. In this embodiment of the invention, two half flukes (3A) and (3B) are bolted to the shank (2) and also to two flanges (12A) and (12B). The flanges (12A) and (12B) are bolted to a hoop or roIl-bar (10) which passes through a slot in the shank (2). The flanges (12A) and (12B) and hoop (10) are necessary to ensure that the anchor, when placed on the mooringbed surface, will roll into a position where the tip (5A) or (5B) of one of the half-flukes (3A) or (3B) can engage the surface with sufficient force that it immediately starts the process of embedment. Correct geometry of both the flanges (12A) and (12B) and the hoop (10) are critical to fulfil this function effectively.

The two half-flukes (3A) and (3B) at their inner edges are welded to vertical upstands (1 3A) and (13B). These vertical upstands are tapered towards the tips of the half-flukes (3A) and (3B) and perform the function of providing rigidity to the half flukes (3A) and (3B) towards downward bending when in use. The vertical upstands (13A) and (13B) also serve to carry the bolts which attach the half flukes (3A) and (3B) to the shank (2) in the prototype. The vertical upstands (1 3A) and (13B) can also be fabricated by bending the inner edges of preformed half-flukes. The shank (2) is relatively thin in the transverse direction, but sufficiently wide within the plane of symmetry (1) that it provides adequate resistance to bending perpendicular to the plane of symmetry (1) and to the normal force within the plane of symmetry (1)when the anchor is forced to plough as it embeds itself in the mooringbed. In the current embodiment, the two half flukes (3A) and (3B) are mounted at a dihedral angle of 20° in order to provide additional roll-stability to the anchor.

When tested for holding by the method described below, the embodiment of the Anchor of this Invention, shown in Figure 5, provides exceptional holding power, between two and five times that of conventional anchors of the Rigid Shank-and-Fluke type.

The Anchor of this Invention provides all the desirable features of anchors highlighted in Table 1.

The components of the Anchor of this Invention can either be welded together or bolted together to provide an anchor which, in use, is rigid with no moving parts.

The invention includes anchors with a plough or concave configuration or with half-flukes (3A) and (3B) which are essentially flat apart from the vertical upstands at their inner edges.

The invention does not restrict the dihedral angle of the two half-flukes to 20°. Both positive and negative dihedral angles are envisaged including zero corresponding to flat half-flukes.

The invention includes anchors with half flukes (3A) and (3B) which have vertical upstands (13A) and (1 3B) at their outer edges, anchors with upstands at both their inner and outer edges, and anchors whose half-flukes (3A) and (3B) are without upstands. The said upstands (13A) and (13B) may be on either the upper or lower sides of the half-flukes (3A) and (3B), or on both sides.

The shape of the shank (2) of the Anchor of this Invention can take many different forms including those typical of conventional Rigid Shank-and-Fluke Anchors, type (B), and the straight form present in typical Pivoting-Fluke Anchors, type (C), although, according to this invention, the shank (2), in use, is always rigidly attached to the two half-flukes (3A) and (3B) and cannot swing relative to the half-flukes (3A) and (3B).

The shape of the individual half-flukes (3A) and (36) of the Anchor of this Invention can take many different forms including concave, convex or flat shapes.

The invention includes the possibility of a demountable version in which the angle of attack of the half-flukes (3A) and (3B) can be altered by dismantling the bolts attaching the half flukes (3A) and (3B) to the shank (2) and repositioning them to provide a different angle of attack.

The invention includes versions in which the roll-bar (10) is absent, and weights (9) are added to the tips of the half flukes (3A) and (3B) to ensure that the anchor when placed on the mooringbed surface will roll into a position where the tip (5A) or (5B) of one of the half-flukes (3A) or (3B) can engage the surface with sufficient force to immediately start the process of embedment.

The invention envisages versions in which both a roll-bar (10) and weights (9) at the tips (5A) and (5B) of the half flukes (3A) and (3B) are present to ensure initial engagement of the anchor.

The invention makes no stipulation as to the material of construction of the anchor. Preferred materials are galvanised steel, stainless steel and aluminium alloy, of combinations thereof.

TESTING ANCHOR HOLDING

The testing of the holding power of anchors is an essential part of their design process, and is necessary for comparing the performances of different anchors.

A statement in early literature from Bruce Anchors Ltd. clarifies the behaviour of an anchor when it is pulled through a mooringbed: lithe Bruce Anchor is loaded in excess of its maximum holding power, it will drag. The dragging pull exceeds the maximum holding pull and increases progressively with speed of dragging. Owing to its absolute roll stability, the Bruce anchor will not roll out of the seabed as other anchors do when dragging". In what follows, the "maximum holding pull" before an anchor drags will be called the Static Holding Force or SHF: while "The dragging pull" required to force the anchor to drag or plough through the mooring bed will be termed the Dynamic Holding Force or DHF. The DHF depends strongly upon the speed at which an anchor is forced to drag or plough and will always exceed the SHF.

Published methods for testing anchor holding are generally crude and unsatisfactory. One method of testing anchors involves pulling the anchor by means of a tug. The hold is measured as a function of time and the maximum hold which the anchor will withstand before pulling out of the mooringbed is regarded as its holding power. This maximum hold which an anchor will provide before disengaging from the mooring bed is termed the Ultimate Holding Capacity, or UHC, of the anchor. According to another method, the anchor is pulled by a fixed mechanical installation such as a winch. The maximum pulling force applied to the anchor is recorded, but generally not the speed at which the anchor is pulled. In some tests the force is recorded as a function of the distance ploughed or time. In this method, the hold of the anchor is determined while the anchor is moving through the mooring bed, and is therefore a measure of its DHF. In none of these tests has the SHF been measured nor has it been recognised as an important measure of anchor holding.

These types of measurement can at best provide only comparative data on the holding power of different anchors which enables them to be ranked in order of holding power. The values obtained in the above types of test are not directly relevant to small boat owners. In practice, a boat owner needs to know the maximum hold which his anchor will provide when it is NOT moving or ploughing through the mooringbed, that is, its SHF. It is also useful for him to know what will happen to his anchor when the pull exceeds this value, that is its hold when ploughing, namely its DHF, and how this DHF depends upon ploughing speed..

Experiments which address this issue have been carried out by the inventor, and published in Practical Boat Owner, in Issue No 427 July 2002 pp. 78-81 and in Issue No 428, August 2002 pp. 99-104. The inventor's experiments have provided data on the performance of a number of commercial anchors, for which both the SHF and DHF have been measured. An example of how the SHE and DHF are related is shown in Figure 6 for a 2 kg stainless steel Claw anchor originally manufactured by Simpson Lawrence, Ltd., UK, now taken over by Lewmar Ltd., UK. This anchor is similar in design to the original Bruce anchor. The experiment which provided the data shown in Figure 6 was carried out in a shallow tidal pooi at Longniddry Bay, East Lothian, UK, where the mooringbed consists of medium-hard sand. A simple manual 5-part pulling tackle was used to pull the anchor.

Figure 6 shows that an approximately linear relationship exists between the hold of this anchor and the speed at which it is forced to plough through the mooringbed. Other anchors behave similarly. The SHE is identified as the maximum hold of an anchor when it is stationary in the mooringbed, that is when the ploughing speed is zero. The DHF is the hold when the anchor is ploughing (or dragging) at a particular speed. The SHE for this anchor is represented by the intercept of the line at zero ploughing speed, and has a value of around 28 kgf (lkgf = 9.8 Newtons). The DHF is seen to be as high as 200 kgf, or seven times the SHF, when ploughing at cm/sec or 0.2 knots. At still higher ploughing speeds the DHF would be expected to be higher still, although there must be a ploughing speed at which the anchor eventually pulls out completely, having reached its Ultimate Holding Power or UHC. The best straight line through the data points shown in Figure 6 has the equation: (DHF/kgf) = 28 + 19 x {Ploughing Speed/(cm/sec)} 28{1 + 0.68 (ploughing speed)/(cm/sec)} The general relationship between DHE and ploughing speed can be written: DHF = SHF{1 + a (Ploughing Speed)} When the ploughing speed is measured in cm/sec, experiments by the inventor cited above have shown that, for the medium-hard sand at Longniddry Bay, East Lothian, UK, a is generally between 0.5 and 0.8. However, for a given anchor, both the SHE and a are expected to be different for different mooringbeds.

To be meaningful, any statement of the hold of a ploughing anchor requires a statement of the speed of ploughing. Comparisons of holding power of different anchors as they are being pulled are valid only when the speed of ploughing is the same for all anchors tested. By contrast, the SHF of an anchor is unique for a given mooringbed in that the ploughing speed is zero. The SHE provides the simplest measure for comparing the holding powers of different anchors. It is also the most useful measure of the hold of an anchor from the point of view of the practicing yachtsman.

Experimental data, such as that shown in Figure 6, for small anchors can be acquired by relatively simple equipment employing a manual pulling system with the test anchor at one end of the pulling system and one or more larger fixed anchors at the other end. A load cell is incorporated in the pulling train to measure the tension on the anchor cable. Normally the anchor under test will be submerged while the pulling train will be on a beach or dry land. Such a system was used to obtain the data shown in Figure 6 and for related experiments detailed in the articles cited above.

IMPROVED EQUIPMENT FOR ANCHOR TESTING

Improved equipment for testing anchors has been developed by the inventor to facilitate an improved Method of Anchor Testing.

The improved equipment uses a battery-operated winch as motivator is shown in Figure 7.

The anchor under test (14)is pulled by an essentially inelastic cable or rode (15) which leads via a load cell (16) to a sheave (17). The sheave (17) is pulled by a polyester rope cable (18), which has a small degree of elasticity. The motivating power is a winch (19) powered by a battery (20).

The land-side of the assembly is anchored by means of two land anchors (21) which are sufficiently large that they do not move when fully buried under the maximum load created by pulling the test anchor (14) It should be understood that the two-fold purchase shown in Figure 7 is illustrative only. The test anchor can be pulled directly by the winch or by a multi-part purchase as desirable to meet experimental requirements. It is also understood that the pulling cable can be raised over a frame carrying a pulley at a position indicated by the arrow (22) so that the scope of the pulling cable can be adjusted. The scope, in this instance, is defined as the length of the cable (15) from the test anchor (14) to the pulley divided by the height of the pulley above the mooringbed surface.

IMPROVED METHOD OF TESTING ANCHORS

An improved method of testing the holding power of anchors, is now described. The improved method comprises laying the test-anchor (14) on the mooringbed surface under water, gently tensioning the pulling train, marking the initial position of the test-anchor (14), pul'ing the test-anchor (14) in a series of stages, in each said stage recording the cable loading at frequent intervals, measuring the distance ploughed by the test-anchor (14) during each stage along with the time taken for the stage, locking the winch at the end of each pulling stage, allowing the pulling system to relax until the test-anchor (14) becomes stationary, and measuring the load when said load reaches a steady value.

Typically during each stage, the cable loading is recorded manually at intervals of say 2 to 5 seconds while the test-anchor (14) is pulled for a distance of 30 to 120 cm. From the time taken for the stage and the distance ploughed by the test-anchor (14) during the stage, the average speed of ploughing during the stage can be evaluated. Typical ploughing speeds are in the range of 0.5 to 3 cm/sec. At the end of the stage, when the winch is locked, the tension on the cable will relax over a period of 1-3 minutes depending upon the elasticity of the pulling rope (18).

After this relaxation period, the tension on the cable will normally have settled to a constant value, which can then be maintained for at least 20 minutes if the anchor is not disturbed. The value of the tension when it reaches this steady value is the SHE of the test-anchor (14) at that point in the experiment. The instantaneous value of the tension when the test-anchor (14) is plough ing is its DHF for the specific plough ing speed at that moment. Normally the DHF values will be averaged over a stage and taken as the DHF of the anchor for the average ploughing speed over the stage.

The procedure for a stage is repeated a number of times until the test-anchor (14) has ploughed at least ten times the length of its shank (2). A plot of cable tension against distance ploughed is then constructed which shows how the DHF and SHF of the test-anchor (14) change during the experiment. The experiment is continued until both the DHF and SHE values have reached near-plateau values, or until the anchor has ploughed a distance of at least ten times the length of its shank (2).

It is also envisaged that continuous monitoring the cable load can be carried out by means of a data acquisition system whose output can be fed to a computer to give an effectively continuous record of load against time and, by additionally incorporating a distance transducer in the pulling train, to provide an effectively continuous record of load against distance ploughed by the test anchor (14).

When comparing the performance of different anchors, which may be done over several experimental sessions, it is important to calibrate using a standard test-anchor. This should desirably be done in each experimental session, or whenever the properties of the mooringbed are likely to have changed due, say, to relocation of the pulling equipment. In the current round of testing a 5.1 kg SPADE anchor has been used as the standard test-anchor..

A typical plot of the cable tension against distance ploughed is shown in Figure 8 for the standard 5.1 kg SPADE anchor. For this test, the rode (15) consisted of 3 metres of 1/4 chain directly shackled to the anchor and then to a further 10 metres of 7 mm plastic covered wire. This rode was virtually inelastic, and was therefore suitable for measuring the distance ploughed by the anchor at the point where it was connected to the load cell (16). The slightly elastic pulling rope (18) consisted of 15 m of 12 mm diameter polyester rope. The experiment represented in Figure 8 was carried out in a shallow tidal pool at Longniddry Bay, East Lothian, UK, where the mooringbed consists of medium-hard sand. The anchor was pulled directly by the winch (19) and the speed of plough ing was approximately 1.5 cm/sec.

In the plot shown in Figure 8, the ordinate shows the cable loading in kilograms force, kgf, (1 kgf = 9.8 Newtons), while the abscissa shows the distance ploughed by the anchor in metres. It is seen that the DHF measured along the ordinate, and indicated by the filled diamonds, increases continuously as the anchor ploughs, and appears to approach a plateau value. The SHF, indicated by the open squares, also increases towards a plateau value of around 110 kgf. The final plateau values of the SHE and DHF have probably not been reached even after nearly 6 m of ploughing. The final depth of burial of the heel of the anchor in this test was 32 cm.

The SHF and DHF of any anchor are specific to the conditions of the test. For example they depend upon the nature of the rode (15): if the chain part of the rode (15), which is directly attached to the anchor, is replaced by a length of thin wire, substantially higher values of both the SHE and DHF are obtained, since the thinner wire provides less resistance to burial than chain.

In addition, both SHF and DHF depend on the nature of the mooringbed. A relevant property of the mooringbed may be determined using a penetrometer, an instrument well known in the discipline of soil science.

TEST OF A PROTOTYPE ANCHOR OF THIS INVENTION

The prototype anchor of this invention, shown in Figure 5, has been tested according to the improved method of testing anchors. The anchor was pulled using a double purchase as shown in Figure 7. The rode (15) was identical to that used for the test of the SPADE anchor. The speed of ploughing was around 0.9 cm/sec. The location of the test was the said Longniddry Bay, East Lothian, UK. The weight of the prototype anchor was 4.8 kg. The plot of load against ploughing distance is shown in Figure 9.

By comparison of the plot shown in Figure 9 with that for the 5.1 kg SPADE anchor shown in Figure 8, that the rise in the hold with distance ploughed over the first metre ploughed is significantly steeper for the prototype of the invention. It is particularly noted that the SHE, indicated by the open squares reaches around 350 kgf compared to around 110 kgf for the SPADE anchor. The final plateau values for both the SHE and DHF of the prototype have not been reached after the anchor has ploughed 4.2 metres, so still higher values of the SHE can be anticipated for a greater ploughing distance. The final depth of burial of the heel of the anchor was 55 cm. The greater depth of burial of the prototype compared to the SPADE anchor is largely responsible for the much greater SHF of the prototype rather than its weight or fluke area.

The test of the prototype of an anchor according to this invention has provided an SHF value which is three times that of a SPADE anchor of approximately the same weight and fluke area.

The SPADE anchor is itself the best Rigid Shank-and-Fluke anchor currently available which the inventor has personally tested.

Claims (12)

1. CLAIMS1 A roll-stable self-launching rigid marine anchor of the stockless type, having exceptional holding power relative to weight, comprising a shank rigidly attached to two mirror image half-flukes disposed symmetrically about the plane of the shank, the inner edges of said half-flukes being separated by a slot diverging towards the tips of the half-flukes from the attachment of the half-flukes to the shank, said shank containing a pulling eye near the end farthest from the attachment of said half-flukes to the shank.
2. 2. An anchor as in claim 1 where the half flukes are welded to the shank
3. 3. An anchor as in Claim 1 where the half flukes are bolted to the shank
4. 4. An anchor as in Claims 1, 2 or 3 where the half-flukes are angled so as to form a positive dihedral angle with respect to one another, thereby providing a concave fluke configuration when viewed from the pulling eye, often referred to as a scoop-type anchor.
5. 5. An anchor as in Claims 1, 2 or 3 where the half-flukes are angled so as to form a negative dihedral angle with respect to one another thereby providing a convex fluke configuration when viewed from the pulling eye, often referred to as a plough anchor.
6. 6. An anchor as in Claims 1, 2 or 3 where the half-flukes are in the same plane so as to provide a planar fluke configuration.
7. 7. An anchor as in claim 4 where the preferred dihedral angle is between 15° and 25°
8. 8. An anchor as in claim 5 where the preferred negative dihedral angle is between 150 and 25°.
9. 9. An anchor as in any of claims 1 to 8 where the half-flukes have upstands at their inner edges running to the tips of the half-flukes from the attachment of the half-flukes to the shank.
10. 10. An anchor as in any of claims 1 to 8 where the half-flukes have upstarids at their outer edges running from the attachment of the half-flukes to the shank to the tips of the half-flukes.
11. 11. An anchor as in any of claims 1 to 10 where the half-flukes have flanges attached to the rear of their outer edges, said flanges being bent upwards to impart additional roll-stability to the anchor.
12. 12. An anchor as in any of claims ito 10 where a roll-bar is attached to the outer edges of the half-flukes to assist in initial engagement of the anchor with the mooring bed when initially placed on the mooring bed.13 An anchor as in claim ii where a roll-bar is attached to the tips of the flanges to assist in initial engagement of the anchor with the mooring bed when initially placed on the mooringbed.14. An anchor as in any of claims 1 to 13 where weights are rigidly attached to the tips of the half-flukes to assist in initial engagement of the anchor with the mooring bed when initially placed on the mooringbed.An anchor as in any of claims ito 14 where the individual half flukes have a concave shape when viewed from the pulling eye.16. An anchor as in any of claims 1 to 14 where the individual half flukes have a cpnvex shape when viewed from the pulling eye.17. An anchor as in any of claims ito 16 in which the shank has an upward arched form as in a conventional rigid shank-and-fluke anchor.18. An anchor as in any of claims ito 16 in which the shank has a straight form as in a conventional pivoting fluke anchor.