CA2117444C - Lightweight anchor - Google Patents

Abstract

The lightweight or twin-fluke anchor is the most frequently used type of anchor in service on commercial and pleasure boats today. The weakest part of this anchor is the crown assembly. When a force is applied to the shank, the shank bears against the crown plate of the crown assembly at a single point. The embodiment of prior art anchors causes a can-opener like shear stress at the joint between the crown plates and the spacer plates that can cause the anchor to fail. In this invention the problem is eliminated by adding a pair of stop plates to the crown assembly to limit the rotation of the shank. These stop plates engage the shank over a length and greatly strengthen the anchor, eliminating the above type of failure.

Description

SPECIFICATIONS:
This invention relates to an improved design of the lightweight or twin-fluked pivoting anchor. A common embodiment is described in Danforth's Patent No. 515,818.
The anchor consists of a shank which pivots on a stock, and is located between two flukes. At the pivoting end of the shank is a crown assembly which limits the angle the shank can rotate through and elevates the rear of the anchor so that the flukes slope downward to penetrate the bottom.
When the anchor is lowered to the bottom, the long stock ensures that the anchor rests flat and both flukes engage the ground simultaneously. The crown assembly ensures that the flukes are angled so as to engage the bottom quickly. The high holding 10 power of this type of anchor is achieved by the relatively large flat flukes that bury in different ground types.
When a pull is applied to the shank, the shank is drawn tight against the crown plate, preventing further rotation of the shank relative to the flukes. The holding load is transferred from the flukes to the shank through the crown assembly. Similar, or higher, loadings can occur when the anchor is weighed, and an upward load is applied to the shank to extract the flukes from the bottom.
The shank engages the crown plate at a single point, resulting in a high stress concentration at the joint between the crown plate and the spacer plates, and tends to act as a can-opener tearing the crown plate from the spacer plates. This phenomenon has 20 been reported by a number of authorities and is a major weakness of this style of anchor.
One embodiment to correct this weakness is Wilkinson's Patent No. 2,066,275 which incorporates a shank that is shaped so the rear end of the shank engages the opposite crown plate over a greater area.
This invention is an alternate embodiment which incorporates stops on each side of the shank, between the spacer plates to engage the shank before the shank can contact the crown plate. The stops are angled so as to engage the shank over a length, resulting in a CA2i 1 7444 uniform shear stress between the stops and the spacer plates, when a load is applied. This results in a much stronger assembly.
An embodiment of my invention which illustrates the above and other features of my invention is illustrated in the accol~lpallyillg drawings in which:
Figure 1 is a plan view of the improved lightweight anchor of the invention.
Figure 2 is a side elevation of the improved anchor of Figure 1 showing details of the stop plates in the crown assembly.
Figure 3 is an enlarged side elevation of the crown assembly of the improved anchor.
The improved anchor 1 of the invention includes a shank 2 with twin flukes 3,4 mounted on a stock 5 for pivoting movement about the stock at the pivot end of the shank 21. A crown assembly 6 is formed of two spacer plates 7, 8 each with a hole 20 for the stock and mounted on each side of the shank perpendicular to the surface 9, 10 of the flukes. The ouLward edges 11, 12 of the said spacer plates are at an acute angle of approximately 14 degrees to the surface of the flukes. Stops 13,14, are attached between the spacer plates at an angle of approximately 30 degrees to the surface of the flukes to engage the shank evenly and limit its rotation. The stops are attached to the spacer plates by welds 15,16 along the outer intersection between the stop, and the spacer. Two crown plates 17,18 are mounted centrally on the outer edge of the two spacer plates, even with 20 the forward edge 19 of the spacer plates and extending to the rear of the assembly. This relationship elimin~tes any loading on the crown plates due to contact with the shank.
Load on the shank is transferred through the stops by a shear force onto the spacer plates and from there to the flukes. This results in a construction which is simpler and much stronger than that of prior art anchors.
In a typical embodiment such as the Kingston Anchors' H-20 lightweight anchor, the spacer plates and crown plates are fabricated from 3/16 inch plate, the shank is 1/2 inch by 1 1/2 inch bar and the flukes are formed from 3/16 inch high tensile steel such as (~A ~ 1 i 7~ 44 ASTM A-242. The stops are fabricated from 3/16 inch bar and are 1 inch in length. A
heavy 3/8 inch filled weld is used to attach the stops to the spacer plates. (Dimensions and materials for the Model H-20 anchor are provided here and below for the purpose of example only; the requirements for anchors of other sizes will be apparent to those skilled in the art.) It is understood that the present invention is not limited to the structure precisely as described and illustrated. For example, the stops could be fabricated as a channel that is inserted between the spacer plates.

Claims (3)

1. A lightweight or twin-fluked anchor assembly comprising;
a shank with a pivoting end a stock a pair of flukes comprising a flat surface mounted upon the said stock in a manner to pivot as a unit at the pivoting end of the shank, with the shank disposed between the fluke elements, a pair of spacer plates mounted on the stock, each disposed between the shank and the fluke element, and firmly attached to the fluke element, a pair of stop plates mounted to each said spacer plate at an acute angle to the surface of the said flukes, limiting the rotation of the said shank, a pair of crown plates supported centrally on the said pair of spacer plates.

2. An assembly as defined in claim 1, wherein the length of the said stop plates are 2/3 to 1 times the depth of the shank at the pivot end.

3. An assembly as defined in claim 1 and 2 wherein the said stop plates are at an angle to engage the shank over the entire length of the stop plate.