US3902446A

US3902446A - Anchor

Info

Publication number: US3902446A
Application number: US487538A
Authority: US
Inventors: Den Haak Rob Van
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-04-10
Filing date: 1974-07-11
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02

Abstract

An anchor comprising flukes, a shank hinged to the flukes and transversely extending stabilizing arms, wherein the hinge point of the shank substantially coincides with the geometric centre of the fluke surface area and head faces are provided on either side of the hinge point, which head faces are formed by head plates spaced from the geometric centre of the fluke surface area, which head plates converge towards the front of the flukes both in vertical and in horizontal direction, delimit the slewing angle of the shank and are connected to the flukes by means of support plates parallel to the shank. The hollow flukes are joined behind the hinge point of the shank to form one fluke surface and converge towards their sharp front, side and rear edges along flowing lines.

Description

United. States Patent 1191 van den Haak [4 1 Sept. 2, 1975 ANCHOR [76] Inventor: Rob van den Haak, Codijn van Dormaalstraat 150, Rotterdam, Netherlands 22 Filed: July 11, 1974 21 Appl. No.: 487,538

abandoned.

[30] Foreign Application Priority Data Apr. 10, 1972 Netherlands 7204763 [52] US. Cl 114/208 R [51] Int. Cl B63b 21/38 [58] Field of Search 114/207, 206 R, 208 R,

[56] References Cited UNITED STATES PATENTS 2,282,566 5/1942 Danforth 114/208 R 2,641,215 6/1953 Danforth... 114/208 R 2,743,695 5/1956 Bowman... 114/207 2,981,219 4/1961 Wins1ow.... 114/208 R 3,274,969 9/1966 Boas 114/208 R 3,306,248 1/1967 Austin 114/208 R 3,373,712 3/1968 Stokes 114/208 R 3,822,664 7/1974 Hedman 114/208 R FOREIGN PATENTS OR APPLICATIONS 143,111 12/1950 Sweden 114/208 R 809,949 4/1969 Canada 114/208 R Primary Examiner-Trygve M. lBlix Assistant Examiner-Sherman D. Basinger Attorney, Agent, or Firm-Marn & Jangarathis [57] ABSTRACT An anchor comprising flukes, a shank hinged to the flukes and transversely extending stabilizing arms, wherein the hinge point of the shank substantially coincides with the geometric centre of the fluke surface area and head faces are provided on either side of the hinge point, which head faces: are formed by head plates spaced from the geometric centre of the fluke surface area, which head plates converge towards the front of the flukes both in vertical and in horizontal direction, delimit the slewing angle of the shank and are connected to the flukes by means of support plates parallel to the shank. The hollow flukes are joined behind the hinge point of the shank to form one fluke surface and converge towards their sharp front, side and rear edges along flowing lines.

7 Claims, 1 Drawing Figure ANCHOR This is a continuation of application Ser. No. 348,164, filed Apr. 5, 1973, and now abandoned.

The invention relates to an anchor comprising at least two flukes, a shank hinged to the flukes and transversely extending stabilizing arms.

In addition to the long-known stock anchors and more recent stockless anchors, during the last 30 years many new types of anchors have been tested and adopted for use. The best-known new types are the US. Navy type LWT anchor, the Pool anchor, the Danforth anchor, the Stato anchor and the Delta anchor. Except for the Delta anchor, which has a fluke with a fixed shank, these anchors comprise shanks hinged between the rear ends of the flukes. To avoid tilting of the anchor, the LWT anchor, the Danforth anchor and the State anchor comprise a stock mounted in the flukes in or near the hinge point of the shank transverse to the direction of pull.

Due to the improved anchor types, the anchorage ground has come to play a more important part than this was hitherto the case with the old-fashioned stock anchors. Present day anchors will less easily bury themselves in weak ground. However, the shoulders will find less grip on hard ground, so that the flukes need more time to dig in.

Good anchorage grounds are, for example: normal sea clay, hard sand and soft lime.

Bad anchorage ground is, for example: gravel (i.e. fine pebbles with coarse sand).

Extremely bad anchorage grounds are:

coarse pebbles with hard clay and rock;

shells with hard clay;

soft sand on a rocky bottom.

Mud constitutes good anchorage ground for the oldfashioned anchors and heavy conventional types, whereas it constitutes definitely bad anchorage ground for the modern types, such as the Danforth anchor.

Clay and soft lime tend to stick to the flukes of the Danforth anchor, thereby forming a lump of material which obstructs and even prevents digging-in of the flukes after the anchor has broken out or has been toppled over due to swaying of the ship.

The behavior of different types of self-burying anchors 1. In the case of a certain type of anchor the maximal holding power is achieved only at a specific fluke angle (the angle between the fluke surface and the shaft).

2. Long flukes produce great resistance against toppling over of the anchor due to swaying of the ship, which often results in bent anchor shanks (Danforth and LWT anchor).

3. Vertical stiffenings on the inside of the flukes compress the ground, as a result whereof the anchor will form a lump and break out (Danforth and LWT anchor).

4. The holding power increases as the anchor buries itself deeper in the ground.

5. Preferably, in front view an anchor should have an optimally small surface area so as to be able to dig in easily.

6. Shoulders disposed transversely to the flukes highly reduce the burying capacity.

7. Usually, the rear end of an anchor is provided with a head serving to dispose the fluke in a downwardly slanting position when the anchor rests on the sea bottom, which is particularly important in hard ground, where there is a greater chance that the front of the fluke will not dig in but will drag over the ground (socalled scratching).

8. Short shanks, short stocks and large fluke angles each individually and, to a greater extent, in combination promote lifting of the head when a pulling force is applied to the anchor, which causes the anchor to tilt so that one side of the fluke will be dragged over the ground.

9. Anchors the stock and flukes of which have a fixed position relative to each other (e.g. the Delta anchor) are possible, privided it is ensured that the stock and the shank are long enough and the fluke angle is small. When the anchor is placed on the end of the stock, the end of the shank and the tip of the fluke, it should automatically assume the proper burying position.

10. Anchors the fluke tips of which are wide apart are liable to rotate, as when the anchoris dropped on the bottom in a slanting position and, consequently, one fluke is lower than the other, the lower fluke will bury itself deeper than the other fluke and the resultant torque results in rotation and breaking out of the anchor.

The breaking out of anchors consequently, only a The break-out force depends upon the anchorage ground, duration of the anchorage period and, particularly, the holding power required. An anchor whereto only a slight pulling force has been applied will have hardly buried itself and, consequently, only slight break-out force is required for lifting the anchor. However, when the anchor had to supply the maximal holding power, it will have buried itself deeply to produce this holding power and it will be self-evident that a large break-out force is required for lifting the anchor.

Practical experiments show that when a catting eye is provided at the foot of the head of the anchor for lifting purposes, the breakout force is 40% and more of the available holding power. This applies to practically any type of anchor. However, when the catting eye is provided at the upper end of the shank, the break-out force will be considerably reduced as the shank will function as a proper lever.

The break-out force is proportional to the length of the flukes before the hinge point of the shank, i.e., the longer the flukes the higher the required break-out force.

It is an object of the invention to provide an anchor having high self-burying capacity in any kind of anchorage ground, a high stability, i.e. resistance to lateral turning and, consequently, dragging of the anchor, a high holding power but a low break-out force.

To this end the anchor in accordance with the invention is formed such that the hinge point of the shank substantially coincides with the geometric centre of the fluke surface area with head faces being provided on either side of the hinge point.

In accordance with the invention the head faces may be formed by plates spaced from the fluke surface and connected to the flukes by means of support plates parallel to the shank. In accordance with a preferred embodiment of the invention the head plates are provided such that they converge towards the front of the flukes. Furthermore, in accordance with the invention the head plates may be provided such that they delimit the slewing angle of the shank. Furthermore, in accordance with the invention the head plates may have the form of an isosceles trapezium converging towards the front. The head plates have such a width that, when the anchor is dropped on the anchor chain with the shank in the wrong direction, the anchor will rotate about its centre of gravity without tilting when the anchor chain is pulled. When the anchor chain is caught between the fluke and the shank, upon pulling the fluke tips will be raised so that the chain is released. This is contrary to anchors having head plates mounted at the back, as in these cases the weight distribution of the flukes is such that it is practically impossible to tilt the fluke tips over the chain.

In order to obtain a rigid structure, in a preferred embodiment of the invention the flukes are joined behind the hinge point of the shank to form one fluke surface.

For considerations of rigidity and reduction of weight of the anchor, in accordance with the invention the flukes are hollow and converge along flowing lines towards their sharp front, side and rear edges.

Instead of the stock present in most anchors, the anchor in accordance with the invention comprises stabilizing pins provided on either side of the flukes at about one-third of the fluke length from the rear edge. This is contrary to conventional anchors having the stockes mounted at the rear edge of the flukes. These stabilizing pins are directed slightly backwardly to easily pass obstacles that may be prevent on the bottom. The new anchor has sharp, smooth flukes to obtain good dig-in and burying properties.

The head plates, the shape and position of which provide minimal resistance to burying, automatically place the flukes in the proper dig-in position.

In a thin layer of sand on a hard subsoil the short fluke length before the hinge point of the anchor and the fluke portion therebehind provide a (to 50%) higher holding power than, for example, a Danforth anchor of the same weight but having a far longer fluke length before the hinge point of the shank.

The large surface area behind the hinge point will grip the moved ground for a larger period of time, which results in a large holding power. Due to the short fluke length before the shank, this shank may be far shorter than that of the Danforth anchor or other known anchors, provides an important weight reduction.

Although the burying capacity is very large, the break-out force is relatively slight as the catting eye is built-in in the rear side of one fluke (about 24% of the holding power). The breaking-out of the anchor over the head also requires relatively slight force (about 13% of the holding power) as the fluke portion before the hinge point of the shank is relatively short and the fluke portion behind the hinge point acts as a lever, while, moreover, the fluke rotates about the lower head plate.

Comparative anchor tests have been performed by the Dutch Department of Ways and Waterworks in March 1973 in the Oosterschelde. These tests showed that in tidal stream, in firmly compacted sand and at about 4.5 m depth, a so-called Stevin anchor in accordance with the invention having a weight of 950 kg can supply a maximal holding power of 32 tons, i.e, a holding power efficiency of 33.6. A Danforth anchor of 900 kg tested at the same location under identical conditions supplied a maximal holding power of 13.2 tons, i.e., a holding power efficiency of 14.7. Consequently, the holding power of the Stevin anchor is 2.29 times as large as that of the Danforth anchor.

The invention will be elucidated hereinafter with reference to the drawing showing and embodiment of the anchor.

In the drawing the anchor comprises two relatively thick flukes 1 and 2 separated by a slot 3, the surfaces of the flukes sharply converging towards the outer edges. At 4 the rear edges of the flukes are joined to form one fluke surface. The relatively large flukes are hollow to reduce the weight of the anchor. A shank 6 disposed in the slot 3 is hinged to the flukes 1 and 2 in the geometric centre 5 of the common fluke surface area.

Between the shank 6 and the parallel vertical inner faces 7 and 8 of the flukes l and 2 two support plates 9 and 10 are secured to the flukes normal to the fluke surface, which support plates extend above and below the flukes.

Isosceles

trapezoidal head plates

11 and 12 are welded to the support plates behind the geometric centre 5 on either side of the flukes, the sides of the trapezium converging towards the shank 6. The support plates are formed such that the headplates l1 and 12 converge towards the front of the anchor flukes and are preferably directed to the tips of the flukes.

With their bevelled front edges 13 and 14, respectively, the head plates delimit the slewing angle of the shank relative to the flukes and further serve to dispose the flukes at the correct angle relative to the sea bottom as soon as the anchor hits the bottom, so that the flukes can easily dig in.

As the head plates are only at a small angle relative to the plane of the flukes, their resistance to digging-in only slightly affects the burying properties of the anchor, whereto the sharp fluke edges contribute in a favourable manner.

Instead of the stock present in most anchors, the anchor in accordance with the invention comprises stabilizing

pins

15 and 16 provided on either side of the flukes at about one-third of the fluke length from the rear edge, which stabilizing pins may be hollow to reduce the weight and may be directed slightly backwardly relative to the transversely directed hinge axis. In this manner cables or hawsers present on the sea bottom will easily slip off the stabilizing pins.

I claim:

1. An anchor comprising:

an anchor base comprised of upper wall means, lower wall means spaced apart from said upper wall means and inner wall means defining an enclosure within said wall means, said upper and lower wall means converging towards each other to form sharp leading and side edges, said inner wall means extending from said leading edge to a point intermediate said leading edge and a trailing portion of said anchor base thereby forming fluke means,

a shank means hingedly mounted between said fluke means at a point substantially coincident with the geometric center of said anchor base; and

head face means mounted to said anchor base about either side of said point.

2. The anchor as defined in claim 1 wherein said head face means includes head plate means spaced apart from said front and back wall means, said head plate means converging towards the leading edge of said fluke means and extending forward and rearward of said point.

the length of said fluke means.

6. The anchor as defined in claim 1 wherein said fluke means include a large surface area on a side of the anchor base opposite to said shank means.

7. The anchor as defined in claim 1 wherein said trailing portion of said anchor base is a sharp rear edge formed by said upper and lower wall means converging towards each other at the trailing edges thereof.

Claims

1. An anchor comprising: an anchor base comprised of upper wall means, lower wall means spaced apart from said upper wall means and inner wall means defining an enclosure within said wall means, said upper and lower wall means converging towards each other to form sharp leading and side edges, said inner wall means extending from said leading edge to a point intermediate said leading edge and a trailing portion of said anchor base thereby forming fluke means, a shank means hingedly mounted between said fluke means at a point substantially coincident with the geometric center of said anchor base; and head face means mounted to said anchor base about either side of said point.

3. The anchor as defined in claim 2 wherein said face means are in the form of isosceles trapeziums.

4. The anchor as defined in claim 1 wherein said plate means are mounted on support plate means affixed to said anchor base means and parallel to said shank means.

5. The anchor as defined in claim 1 and additionally comprising stabilizing pin means positioned on said side edges of said anchor base at a point from said trailing portion of said anchor base of about one-third of the length of said fluke means.