US2282566A - Twin fluke anchor - Google Patents

Description

May 12 1942- R. s. DANFoRTH 2,282,566 l TWIN FLUKE ANCHR original Filed March 12. w41- ATTORNEY Patented May 12, 1942 UNITED STATES PATENT OFFICE TWIN FLUKE ANCHOR Richard S. Danforth, Berkeley, Calif.- Original application March 12, 1941, Serial No.

382,943. 1941, Serial No.

Divided an d this application July 7, 401,323

1o claims.- '(01.114-208) .1941, and entitled Twin fluke anchors, now

Patent Number 2,249,546, of July 15, 1941. This case, as will presently hereinafter be set forth in detail, is concerned with an anchor wherein the fluke area, fore and aft of the pivot mounting the ukes on the shank, is approximately balanced.`

For general purposes of classification and to delineate clearly the present invention, anchors can be divided into two groups, the so-called kedge anchor and the stockless anchor. Briefly, the former includes a shank from one end of which projects two oppositely extending curved arms carrying ukes or palms. At the other end, a long bar, the so-called stock, is positioned in a plane transverse to that of the iiuke arms so that one arm and its palm engage the ground'. Such an anchor is typically shown in the British Patent No. 6,004, of 1830, anchor (also called the Admiralty anchor because of itspuse in the British Navy during the nineteenth century) was later modified by Porter so the nukes could pivot on the shank as in United States Patent 2,497, of March 18, 1842.

The latter type of anchor. the stockless anchor, is that commonly used today on most merchant ships and by many navies because'of the ease with which it can be drawn up into a. hawse pipe and held there ready for use. As commonly employed, it omits a stock; it includes a shank and twin uke arms, usually secured together as a unit, pivoted at one end of the shank whereby both flukes engage the ground together. This anchor has been variouslyconstructed but reference is made for a typical showing Ato the United States Patent No. 1,366,218, to Steele.

Many anchors of both typesphave been made and employed heretofore. In general, their hold? ing power, measured in pounds per pound of weight has been low, of the order of from two to ten pounds per pound of weight.

The holding power of an anchor is usually re-v ported together with a reference to the type'of only a poor. or at the best only a fair anchorage with reference to anchor drag resistance.

' I have determined that the .twin-fluke type of anchor, as compared to the kedge type anchor, is particularly susceptible to modifications which adapt it to continued penetration under continued pull to attainnally deep burial in the compact bottom offering the best anchorage. This is due in part to the ground plowed up by the flukes passing by the sides of the shank instead of against its lower surface and so its burial resistance is lessened; because the undisturbed ground encountered by the shank during burial may pass back between the two ukes, and because there is no nonfunctional iiuke to resist burial. In those instancesI when the hard underlying bottom is at such a depth that the anchor cannot reach it, nevertheless the anchor of this invention will penetrate so deeply that it 4will to Perlng. The Perin'g bottom on which the test was made; for exam- V ple, a blue mud, a mud andshale bottom, etc.

The anchor would only engage this surface layer. and its resistance would largely be merely that attendant upon pulling it through such material. Now .as a matter of fact, it has been observed that hard, relatively compact bottom will be foundunderneath almost any overlying layer offering given only insulcient reach a harder, more compact and more resistive material at a` substantial depth to ensure a materially higher holding power than any prior art anchor of similar weight under the same circumstances. In these respects the twin-fluke'an-l chor. is far superior to anchors of other types. and particularly to the kedge type of anchor in which the flukes are so arranged that only one of them can enter the ground at a time. Deep burial cannot be attained withany other type of anchor. For these and other presently explained reasons the present invention is restricted to improvements in twin fluke anchors wherein the flukes engage the ground more or less simultaneously and cooperate in providingholding power.

`In developing an anchor which would bury itself consistently and be reliable in performance in other particulars, I found that merely altering one or two characteristics in various known anchors was insuiilcient for the anchor so achieved would, in some holding grounds, skid, furrow, rotate, or otherwise exhibit some failing making it unreliable in use. Some of the objectionable failings are as follows:

Floatlng" can occur mos't often on soft and muddy holding ground; the nukes lie at on theground surface or even inclined upward and do not fall into operating position even though the anchor is drawn over the bottom. An anchor of the twin iluke type may float on hard ground if lift at the fluke end. If grips are provided, as in some anchors, to ensure the anchor does not float, then the anchor generally will not bury because its resistance is too high. Skidding" occurs when the anchor falls on its side and opens but rideson the forward end of the sha the point or side of one nuke and; the end o the stock, without digging in. "Furrowing occurs in soft mud when the anchor rides along with one nuke superimposed, or nearly so, over the other end with one end of the stock and one nuke only engaged with the ground. Rotation can occur in ground of any type; at some point during the seating of the anchor but'before it has come to rest the downwardly acting forces applied to the two nukes become unbalanced, whereupon the anchor rotates about the shank axis and frees itself from ground engagement.

The anchor of my invention is sharply distinguished from prior art anchors,-and particularly those-of the twin fluke type, heretofore known and employed, by the possession of certain characteristics.

Some of the critical factors which I have found are set orth here by way of example. The order of the' appearance hereinafter does not necessarily fiect the order of their importance, for,

asa m tter of fact, an anchor, to'operate satisfactorily, must' possess several fof the characteristics as will be presently explained,

First, the anchor is of the twin nuke type in which the shank passes between the nukes and both fiukes e age the ground more or less simultaneously nd cooperate to provide holding power; to ensure proper fluke engagement and prevent rotation the-anchor is provided with atock or equivalent means.

econd, I have found that the nuke area must be proportioned relative to the resistance area, both areas being hereinafter further defined with particularity. When attention is given to this relation, in conjunction with the other characteristics, sufncient driving force is provided to cause the anchor to continue its downward penetration through soft holding ground for a relatively indefinite distance or until harder ground is reached. Generally stated, the nuke area should be as large as is practical andthe resistance areaas small as is feasible. I have found that certain minimum ratios should be observed between these areas to ensure reliable performance.

Third, the nukes in operating position adopt certain dennite angular positions. These are presently defined hereinafter in some detail. Taken as a measure of certain anchor operating characteristics, these angular relations have been determined by me to fall within certain values to the end that the fluke surfaces are most effective in their antagonistic functions of (l) producing initial burial with certainty, (2) thereafter urging the anchor downwardly until it is embedded in firm ground and (3) finally, holding the anchor stationary against the cable pull after it has been firmly embedded.

Fourth, rotation of the anchor is prevented by giving attention to two factors. First, the nuke areas are positioned with respect to each other and with res ct to the axis of the shank, as hereinafter fur her explained in detail, to minimize any tendency of the anchor to rotate under pull. Second, the length of the stock relative to the nuke center spacing is held above certain presently defined limits to overcome any residual rotational tendency. These two factors ensure absence from rotation.

In addition to the foregoing I have found that the reliability of initial engagement is affected by the relation of the stock length to shank length and that to ensure reliable initial engagement this relation must be held within certain limits. Also, the crown of the anchor is so constructed as to ensure engagement without offercreased holding powerper unit of weight- -the factor which, when coupled with stability and with dependability of engagement, provides the ultimate measure of value of anchors.

' Holding power is, by definition, resistance to further movement in the direction in which the anchor is being dragged, and is dependent both on the areas of the parts being moved through the ground, as projected to a plane normal to the direction of movementand to the intrinsic resistance of the ground per unit of area. Thus theholding power of any anchor at the surface of a soft mud bottom will be very small, by reason of the low unit resistance of such ground, and to increase the holding power the anchor must continue to penetrate downwardly until firmer ground is encountered.

An anchor as herein described under continued pull continues this downward movement until the entire anchor is buried in nrmer ground, no matter how much soft material may overlie it. It is this ability of my anchor to move downward to an indefinite distance in search of nrm holding ground which makes its holding power substantially independent of the nature of the bottomV on which the anchor is cast, there being always at some depth good holding ground beneath even the softest mud.

The exact manner in which holding .power of the highest order is secured without sacrificing certainty and stability will now be described, with reference to the attached drawing showing the presently preferred form of theranchor'of this invention. The preferred form of anchor of my invention herein disclosed is particularly suited to manufacture from high tensile strength steel. This permits small sections to be employed with -extremely low resistance to burial. l' In the drawmg Figure 1 is a side elevation of the anchor in operating position.

Figure 2 is a plan view of the anchor shown in operating position in Figure l, while Figure 3 is a front view thereof.

Throughout this description and in the claims, the end of the anchor to which the cable is attached will be referred to as the forward end, the end at which the fluke unit is pivoted will be referred to as the after end.

In the form of anchor shown in Figures 1 and 2, a shank 5| is provided. This is pivotally mounted as at 52 on the nuke structure generally indicated at 53 and which comprises the two generally triangularly shaped nukes 54 and 55. Fluke structure 53 can be made up in any suitable manner to provide a one piece nuke structure, as by bolting substantially identical halves together, with the shank pivoted therebetween in a suitable manner. At the rear end of the nukes and adjacent the rear edge thereof crown portion 56 is provided. .This includes rearwardly sloping faces 51 which engage the ground, as

sistance to burial.` An extension 58 is provided on each fluke andintegraltherewith, the extension serving as a stock. The extension Vas well as the rear edge portion which it continues is preferably though not necessarily of arcuate contour, so that a minimum resistance area is provided; the nukes can extend to each side along their rearward edges to provide the functional equivalent of a stock.

The flukes 54 and 55 are preferably triangular in outline with the forward edges thereof at approximately an angle of 24. The inner edge of each 'fluke is formed with a rib 59 which slopes outwardly away from the adjacent shank at an angle of about 6 to prevent furrowing.

I shall now consider the various angular and dimensional relations which I have found to be essential to or desirable for the production of high holding power coupled with reliability, first defining the terms used.

A is the pointof the cable attachment; B is the axis of the pivot, in this-case the stock. The line B-'B is the axis of the stock; the line C-D is the axis of the shank. f

The line E-F lies in a plane coinciding with the rforward or advancing faces of the flukes. The points G-G are the respective centers of area of the entire forward faces of the flukes. The points H-H are the points or forward ends of the flukes.

The effective shank length is the distance A-B from the point A of cable attachment to theaxis of the pivot; it is indicated by the dimension K and is referred to herein as the shank length. The measurement Mis the distance between the pivot axis B-B and the fluke. points'H-H and is referred to herein as the overall fluke length.

The measurement P between the centers of area G--Gv of the .flukes is termed the fluke center spacing. The measurement R is the overall length of the stock.

The angle S between the plane of the fluke forward faces and a plane passed through. the point of cable attachment A and the centers of areas G-G of the forward faces oi the flukes,ris termed the. attack angle.

TheY angleT between the plane of the fluke forward. faces and the axis of the shank is termed the nuke angle.

'I'he angle U betweenthe plane of the fluke forward faces and a planeV passed through cablel attachment point, A and the points or forward ends H-H of the flukes is termed thev point angle.

The fluke directional angle is measured between the inner. edge. of the iiuke and the axis of the shank when both are in substantially the same plane.

The angle Y is the crown angle taken between the crown face and the fluke axis.

The angle X isfthe-uke point angle, between the inner; and outer forward edges of the fluke.

The resistance area is the total sectional area ofthe anchor projected parallel to the fluke axis with the nukes open, the projection being made onto a plane normal to this axis. It can be visualized as the shadow `cast on vlevel ground by the sun' in zenith when the anchor in operating position (the flukes open) is held with the flukes pointing directly toward.v the sumand is' represented by the entire area in Figure 3.

The ilukearea is-thevsum of the areas'of the totali forward faces of the two flukes.

The several factors primarily characterizingran anchor of my invention will now be discussed, not in the order of'their importance, but rather as I believe them logically related.

. Relation of fluke area to resistance area In the development of the anchor of the present invention I lfound that the fluke area should be relatively large as compared to the resistance area and that; in fact, the flukel area, in this form of anchor, should be at least 40% of the resistance Aarea Vand preferably 60% and as much as Aand more of the resistance area.

In those forms of anchors shown in Figures 1 and2, due to the relatively large fluke area and the thin sections employed, the iiuke area is over 1.5 times as much as the resistance area.

When the importance of this relation is considered, it should be apparent that the fluke area must be so proportioned relative to the resistance area as to provide the burial force necessary to overcome the resistance provided by the purely functional portions of the anchor as well as those Relation of resistance area to shank length Deep burial and its attendant high holdingV power are favored, I have found, by providing a maximum downward driving force acting against av minimum of resistance. From this it follows that the resistance area should be minimized to the greatest extent consistent with the strength required to avoid bending. or breakage. This is quite feasible with structures embodying this invention for high tensile strength steels can be employed.

Takingshank length as an approximately xed quantity for an anchor of any given size, and thereforefa basis to whichv other dimensions may be referred, the resistance area as hereinbefore defined permlssible'in an anchor of any given size can be expressed as a function of shank length. To avoid comparison of an area with a lineal iigureV this relation is expressed by comparing the resistance area with the square of the shank length, in similar dimensional units.

Using this manner .of comparison I find that generally satisfactory performance can be expected when the resistance areaiI is not greater than 25% of the square Vof the shank length, and that the optimum performance is obtained by holding the resistance area to a value less than 13%, and even more preferably 10%, of the square of the shank length. f

Angular relations Possibly the simplest approach is to consider what occurs when an anchor is cast over the side to fall upon and engage the bottom under continued cable pull. Under any consideration the anchor must first engage the ground and then dig into the ground. It should not scratch the ground and drag along with the points of the nukes acting like rakek teeth. To provide for reliable initial engagement I have, found that the point angle U should be taken into consideration and my experience indicates that a point angle larger than 75 should be avoided for beyond this, while occasional engagement may occur, dependability is not present; preferably this should be below 70. Since the point angle, according to definition, includes a consideration of shank length and other characteristics, in some instances the point angle can be taken, together with other values indicated herein, asdenitive of the present invention.

Attack angle As a result of my investigations I have determined that the attack angle, angle S, between the plane of the fluke forward faces and a plane passed through cable attachment point A of the shank and the centers of area G-G offthe nuke forward faces, represents the effective angle of opposition of the fluke faces to the pull of the cable as transmitted through the pointpfcable attachment A.

In the lighter weight designs having a very low resistance to ground engagement and to which the anchor of this invention is particularly suited, I have found that a considerable portion of the fluke area may be located behind the pivot and the resistance to bun'al further reduced. In this instance, I have found the governing limitation is usually the point angle rather than the attack angle. For this reason the attack angle for this form should be kept in the range of 30-50. Because of the necessity of having a point angle of less than 75 it will ge found that generally the attack angle will run below 45. This modifled form of anchor, wherein at least 35% of the area of the ukes is aft of the pivot axis about which the flukes are pivoted on the'shank, possesses the advantage that because the fluke area is approximately balanced fore and aft of the pivot axis. the vertical bending stress placed on the shank is less permitting a lighter shank to be used with less burial resistance. approximately balanced fore and aft of the pivot, as employed herein and in the claims I mean that a material portion of the moment of the fluke area forward of the pivot is balanced by the opposite moment of the fluke' area aft of the pivot. Obviously, the moment of the fluke area aft of the pivot cannot exceed the moment of the fluke area forward of the pivot; otherwise the tlukes rotate and tend/to assume an ineffective position parallel to the shank.

Fluke angle The value of this angie (angle T) is related to attack angle and shank length: i. e., the attack angle may be varied by changing either the shank length or the fluke angle. If the fluke angle be too wide a desired attack angle is liable to require an excessively long shank, which has an advantage in'breaking out the anchor by By the term.

angle is too large for dependable initial engagement. While I consider the uke angle of secondary importance, I prefer to keep it within the limits 27 to 42.-

Relation of flake center spacing to shank length and to stock length spaced. I preferably keep this spacing to the minimum by the use of a relatively long and than 13%, and more preferably less than 10%,

reason of the greater leverage thus applied but-is narrow fluke and by placing the inner edge of the fluke as close to the face of the shank as will avoid undue danger of obstruction to the passage of the fluke past the shank. However, it is sometimes desirable to cause the flukes to diverge somewhat forwardly in order to overcome any tendency ofthe anchor to furrow on its side in soft mud.

Shank length being taken as an approximate function of anchor size, the center s acing can be described as related to shank leng h. Il have found by experiment that if this spacing (dimension P) exceeds 44% of the shank length (dimension K) the anchor will be unduly unstable and throw an excessive corrective burden on the stock, which in turn increases resistance area by necessitating a longer stock. I prefer to keep ths'spacing below a third of the shank summation of important characteristics By way of summaryand to further define the anchor of this invention, both with regard to its essential features and certain other features which, while not essential, are nevertheless important, I have indicated heretofore that the following are among the characteristics that should be observed A. The fluke area should not be less than 0.4 the resistance area. Preferably it should be not less thanY 0.6 and even more preferably it should be greater than the resistance area and as much as 1.5 times vas much as the resistance area.

B. lThe' resistance area should be less than 25% of, the square of the shank length, preferably less of the square of the shank length.

C. The point angle should be less than and preferably less than 70.

D. With the fluke area. approximately balanced about the pivot point, the attack angle should be in the range of 3050.

E. The stock vlength should be at least twice the distance between the respective centers of area ofthe nukes and preferably two and onehalf or three times this distance.

Other characteristics Several other characteristics 'will now be con- Relation of stock length to shank length A minimum relation of stock length to shank length is important to prevent skidding. If the 'stock be too short the anchor may open on its side and rest on a three point support consisting of one end of the shank, the end of the stock and the point or outer edge of the fluke. Length- Vening the stock tends to move the center of gravity outside the base and to cause the anchor to fall flat, in which position initial engagement can take place. The measurement R (stock length) should not be less than about eight-tenths of the shank length (measurement K) to prevent skidding with certainty under adverse conditions.

The flukes are preferably approximately triangular in shape because this provides a maximum area consistent with a uniformly low resistance to burial. The angle X between the inner and the outer forward edges of the fluke is preferably about 21 to 27, this being the range within which sufficient fluke area can be provided without too greatly increasing the burial resistance. Also, the inner edge of each fluke diverges outwardly at an angle of between and 15 because this has a beneficial effect in reducing skidding.

The fiukes are as thin as the material of which they are made will permit. Preferably, they are substantially uniform in thicknesson any line parallel to the shank axis, and are gently tapered in cross section.

Fluke clearance The clearance between the fluke and the side of the shank cannot be too small without incurring serious risk of the flukes being held up in a position above the shank by an accumulation of stiif mud or sticky gravel on the shank, which would render the ukesinoperative. I

prefer to keep the average clearance between the inner edge of the fluke and the side of the shank at more than two percent of the shank length, and in no case should it be less than one percent of the shank length.

Design of crown The structure of the crown is important. It is preferable that the faces arranged to produce lift be sloped upwardly opposite to the direction of dragging. If the angle of the faces is too steep, they act as grips and prevent burial. They are preferably sloped at about 35 and between 25 and 45 is a good range. It is also desirable that they be centrally located, i. e., on or close to the crown. If such faces be spaced any material distance from the crown, even if the disposition is completely symmetrical, they are almost certain'to set up a tendency toward rotation under certain conditions. On the other hand, any portions of these faces lying directly under or back of the shank are liable to be rendered ineffective by the trenching effect of the forward end of the shank, lift being required solely in advance of engagement and therefore at a time when there is no resistance to cause the forward end of the shank to lift away from the ground.k Consequently, the faces producing lift should be symmetrically located as regards the shank axis and as close thereto as is conof the shank.

Contour and location of stock To provide means for preventing the anchor from riding on its side, for positioning the fiukes to engage and enter the ground and for stabiliz` ing the anchor when 'engaged and preventing rotation, I provide extensions laterally on each side of the shank. In the forms of anchors shown in Figures 1, 2 and 3 the lateral extensions are provided as portions ofthe flukes. In either case, the terms "stock or stabilizing bar are applied herein and in the. claims-to such A stock of circular section or one in which the faces are arcuate in form is preferred as combining strength with minimum resistance. However, any form can be used which will not give undue resistance or introduce an unbalancing effect sufficient to cause rotation.k

It is also preferable to project the stabilizing bar from the after end of the anchor, as illustrated, though the more common practice of projecting it from the forward end of the shank may be followed if desired. In such location the advantage of being able to stow the anchor by drawing it into a hawse-pipe is lost. A stock forward also increases the resistance to burial of the forward end.

An anchor constructed in-accordance with the` above specification and within the limits defined by the appended claims will also bk found desirable in the following respects, to wit: freedom from danger of fouling the cable when the boat is ranging with wind or tide; ability to stow the anchor by hauling it into a hawse-pipe; ability to stow the anchor vflat on deck without the necessity for folding of nukes or stock; immediate readiness for use at all times; freedom from risk of damaging the hull when bringing the anchor on deck; great rapidity' and entire certainty of engagement in any type of holding ground; ready disengagement when it is desired to weigh the anchor, and a holding power per unit of weight far higher than any heretofore known. 'I'he anchor shown and described herein has been set forth correctly with respect to the size, shape and relative relation of the various elements thereof, particularly the showing of the drawing.

1. An anchor of the twin` fluke type comprise ing a shank having a forward and an after end with a point of cable attachment at said forward end, a pair of ukes joined together to form a one piece structure with each fluke fixed relative to the other, a pivot mounting said flukes on said shank at said after end with said ukes extend-r at an angle thereto of between 25 and 45 and terminating at a point raised above the fluke faces to slide along the ground and rotate the nukes when the anchor is on the ground with the flukes and shank in substantially the same plane, saidshank and ukes being so proportioneol and positioned relative to each other when` I in operative position that the area of said flukes is approximately balanced about said pivot with at least 35% of the area of the fiukes aft of said pivot, and a plane, passed through said point of cable attachment and through the centers of area of the uke forward faces makes an angle with the plane of said forward fluke faces in the range of substantially 30 to 50, said stock having an overall length at least twice the distance between the respective centers of area of the entire fluke forward faces, the area `of said entire fluke forward faces being at least 60% of the resistance area of said anchor, as herein defined. f Y v I 2. An anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forwardend, a pair of fiukes joined together to form a one piece structure with each fluke fixed relative to the other, a pivot mounting said ilukes on said shank at said after end with said flukes extending toward said forward end and with said shank between said fiukes, and a stock adjacent the after end of said flukes, said flukes substantially simultaneously engaging the ground when in operative position, each fluke having a major forward portion approximately triangular in outline with the two forwardedges approaching each other at an angle approximately between 21 and 27, said shank and fiukes being so proportioned and positioned relative to each other when in operative position that the area of saidiiukes is approximately balanced about said pivot with at least 35% of said area. aft of said pivot, and a plane, passed through said point of cable attachment and through the centers of area of the uke forward faces makes an angle with the plane of said forward fluke faces in the range of substantially 30 to 50, said stock having an overall length at least twice the 1 distance between the respective centers of area of the entire uke forward faces, the area of said entire fluke forward faces being at least 60% of the resistance area of said anchor, as herein defined.

3. An anchor of the twin iiuke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a pair of flukes joined together to form a one piece structure with each fluke xed relative to the other, a pivot mounting said flukes on said shank at said after end with said flukes extending toward said forward end and with said shank between said fiukes, and a stock adjacent the after end of said flukes, said flukes substantially simultaneously engaging the ground when in operative position, said shank and ukes being so proportioned and positioned relative to each other when in operative position that the area of said fiukes is .approximately balanced about said pivot with at least 35% thereof aft of said pivot, and a plane, passed through said point of cable attachment and through the forward ends of the flukes in operative position makes an angle with the plane of said forward fluke faces of less than 75, said stock having an overall length at least twice the distance between the respective centers of area of the entire fluke forward faces, the resistance area of said anchor, as herein defined, being less than 25% of the square of the shank length.

4. An anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a pair of fiukes joined together to form a one piece structure with each fiuke fixed relative to the other, a stock integral with said flukes and adjacent the' afterend thereof, and a pivot mounting said flukes on said shank at said after end with said flukes extending toward said forward end and with said shank between said iiukes, said iiukes substantially simultaneously engaging the ground when in operative position; said shank and fiukes being so proportioned and positioned relative to each other when in operative position that the area of said flukes is approximately balanced about said pivot with at least 35% of said area aft of said pivot, a plane, passed through said point of cable attachment and through the centers of area of the entire fluke forward faces makes an angle with the plane of said forward fluke faces in the range of substantially 30 to 50, and the total area of said fluke forward faces is at least 60% ofthe resistance area, as herein defined; said stock having an overall length at least twice the distance between the respective centers of area of the entire forward faces of said flukes.

5. An anchor of the twin iiuke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a pair of fiukes joined together to form a one piece structure with each fluke fixed relative to the other, a pivot mounting for said fiukes on said shank at said after end with said iiukes extending toward said forward end and with said shank moving between said iiukes, said flukes substantially simultaneously engaging the ground when in operative position, and a stock adjacent the after end of said fiukes; said shank and fiukes being so proportioned and positioned relative to each other when in operative position that the area of said flukes is substantially balanced about said pivot mounting with at least 35% of the area of said fukes aft of said pivot, and a plane, passed through said point of cable attachment and through the centers of area of the entire fluke forward faces makes an angle with the plane of said forward fluke faces in the range of substantially 30 to 50, and the total area of said fluke forward faces is at least 60% of the resistance area, as herein defined, said stock having an overall length at least two and a half times the distance between the respective centers of area of the entire forward faces of said flukes.

6. An, anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a pair of ukes joined together to form a one piece structure with each fluke fixed relative to the other, a pivot mounting said fiukes on said shank at said after end with said fiukes extending toward said forward end and with said shank between said flukes, and a stock adjacent the after end of said fiukes, said flukes substantially simultaneously engaging the ground when in operative position; said shank and ilukes being so proportioned and positioned that the area of said ukes is approximately balancedthat the area of balanced about said pivot 'and at least 35% is 7. An anchor o! the twin nuke type comprising a shank having a forward and an after end with a point vof cable attachment at said forward end, a pair voi' nukes joined together to form a one piece structure with each nuke nxed relative vto the other, a pivot mounting said nukes on said shank at said after end with said nukes lextending toward said forward end and with said shank between said nukes, and a stock adjacent the after end of said nukes, said nukes substantially simultaneously engaging the ground when in operative position, said shank and nukes being so proportioned and positioned relative to each other when in operative position said nukes is approximately aft of said pivot and a plane, passed through said point of cable attachment and through the centers of area of the entire nukeforward faces makes an angle with the plane of said forward nuke faces inthe range of substantially 30 to 50, the area of said entire nuke forward faces being at least equal to the resistance area of said anchor, as herein denned, and the distance between the entire nuke forward faces is less than 44% of the length oi' said shank.

8. An anchor of the Itwin nuke type, comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock, a pair of nukes joined together to form a one piece structure with each nuke nxed respective centers of area of the f end with a relative to the other, and a pivot mounting said nukes on said `shank at said afterend with said nukes extending toward said forward end and with said shank between said nukes, said` nukes substantially simultaneously engaging the ground when in operative position, said shank and nukesl being so proportioned and positioned relative to each other when in operative position that the area of said nukes is substantially balanced about said pivot with atleast oi' the area thereof aft of said pivot, a. plane, passed through said point of 'cable attachment and through the centers of area of the entire nuke forward faces makes an angle with the plane of said forward nuke faces in the range of substantially 30 to said stock having an overall length at least two and a half times the distance between the Vrespective centers of area of the entire forward faces of said nukes, the resistance area of said anchor, as herein dennedbeing less than 25% of the square of the shank length.

'an overall length v between the respective centers of area of-the 9. An anchor of the twin nuke type oo prising a shank having a forward and an after point of cable attachment at said forward end, a pair oi' nukes Joined together to form a one piece structure with each nuke fixed relative to the other, a pivot mounting for said nukes on said shank at said aiter end with said nukes extending toward said forward end and with said shank between said nukes, and a stock at the after end of said nukes, said nukes substantially simultaneously engaging the ground when in operative position; said, shank and nukes being so proportioned vand positioned that the area of said nukes is approximately balanced about said pivot with at least 35% of saidv area aft of said pivot, the total` area of the entire nuke forward faces is at least equal tothe resistance area, as herein denned, said stock having atleast twice the distance entire forward faces of said. nukes, anda plane passed through said cable attachment point and thefforward ends of said nukes in operative position makes an angle with the projected nukefforward faces of less than 10. An anchor of prising a shank `having a forward and an after end with a point of cable attachment at said forward end, a stock, a pair of nukes joined together to form a one piece structure` with veach nuke nxed relative to the other, and a pivot mounting said nukes on said shank at said after end with said nukes extending toward said forward end and with said shank between said nukes, said nukes substantially simultaneously engaging the ground when in operative position, said shank and nukes being so proportioned and positioned relative to each other when in operative position that the area of said nukes is substantially balanced about said pivot with at least 35% of the area thereof aft of said pivot, a plane, passed through saidpoint of cable attachment and through the centers of area of the entire nuke forward faces makes an angle with the plane of said forward nuke .faces in the range of substantially 30 to 50, said stock l having an overall length at least twice the distance between the respective centers oi area of the entire forward faces of said nukes, vthe area oi' said nukes being at least 60% area of said anchor, as herein defined.

RICHARD S. DANFOR'I'H.

the twin nuke type, comof the resistance

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