Rethinking Anchor Shank Strength

Posted by at 11:48AM - Comments: (3)

JL Robertson
JL Robertson

Anchor proof tests do not account for significant side loading on the shank.
One topic often overlooked in any anchor discussion is shank strength. Yet bent anchor shanks are hardly rare, especially among low budget varieties. We accept that sometimes an anchor gets wedged into a crevice where bending is unavoidable, but it seems increasingly more common that anchors are bending during what would be considered normal use.

In the April 2013 issue of Practical Sailor, contributor Jonathan Neeves explores this topic in great detail. In his view, the reasons behind bent shanks are many.

  1. Industry tests used to rate and certify anchors do not test the shank's ability to resist bending when subjected to side loads. In fact, these certifications often have little bearing on how a recreational anchor might perform in the real world.
  2. Manufacturers are using thinner plate steel, or lower grade, lower-tensile steel than is specified in the original design. 
  3. Newer anchors tend to set deeper, remaining immobile when the wind shifts and the load changes direction, causing side-loading on the shank that can cause it to bend. We examine the mechanics behind the ability to deep set in the article, "An Inquiry into Anchor Angles," in the February 2017 issue of Practical Sailor. 
  4. Anchor makers are using the same design to make anchors of metals with different tensile strength—aluminum, stainless steel, galvanized steel, etc.—which is the same as building below spec.
  5. Plate stock used to make anchor shanks are sold in specific thicknesses. In order to cut costs, some off-brand anchor makers are using poorly laminated thinner stock to achieve the required shank thickness.

At the heart of our study is a critique of the existing test protocols used to certify these anchors. Neeves points out that these tests were principally designed for anchors used on commercial ships. As he describes, commercial ship anchors have radically different shanks than we find on recreational anchors—shanks that are equally strong no matter what direction they are loaded—and the anchors are used differently. Most ship anchors are, in effect, lunch hooks—not something you try to ride out a storm in.

Accompanying the April 2013 article are photographs of a pretty impressive collection of bent anchors from some of the biggest names in anchor manufacturing. If you have a bent anchor photo you’d like to add to our rogues' gallery, send it by email to practicalsailor@belvoirpubs.com, and tell us how it happened. 

Practical Sailor offers a four volume E-book Anchors at our online bookstore. The book delves into all the facets of anchoring, comparing the performance of the most popular anchors on the market in various bottoms and discussing the pros and cons of current trends in anchor design. The series also examines other important details such as selecting the right anchor rode, sizing and rigging a storm-ready anchor snubber, selecting the strongest anchor shackles, regalvanizing chain rode, and more. 

 

Comments (3)

Bending due to side loading is not a "failure" in that you are still hooked and the shank can usually be straightened to a usable configuration. For most non-cast materials used in anchor shanks the material is actually stronger after straightening.
If there were a Standard to which anchor manufactures could be certified, this subject would be a lot clearer. The materials and configuration would be as required to meet the standard.
The selection of an anchor and rode is always a best guess and considering what others have used successfully - there is always a stronger wind and a bigger sea or a poor holding spot.

Posted by: Captain Ed-79 | June 25, 2018 1:25 PM    Report this comment

After 200,000 miles there's only one golden rule for anchoring - its the chain, not the anchor. Two long lengths of chain do nicely. Even a 50 to 60' boat will weather major storms with 2 400' hi-test rodes. Worth remembering that Bering Sea fish boats routinely anchor in shallow waters with heavy storms using 125 lb anchors attached to upwards of a 1000 feet of 1/2" high test chain.

I've never seen/known a Bruce or CQR or a Paul Luke cast Hershoff Fisherman style anchor to suffer a major bend. Nor a WWII cast iron Danforth type used by Pacific Landing Craft. But lightweight aluminum Danforth designs are a different matter.

Old fashioned iron anchors were invented centuries ago and still work. Last forever. No other sailing gear is as durable and long lasting as proper iron anchors and US made hi-test chain and shackles.

Posted by: Piberman | June 21, 2018 10:17 AM    Report this comment

Under paragraph (4) you'd certainly have to include cast vs drop-forged construction and the difference in performance between the two under bending loads. The original CQR by Simpson-Lawrence was drop-forged, but they did make (maybe Lewmar still does) a cast version, identical in appearance, that they marketed only as a "galvanized plow." I have one - it was much less costly and performs as well as the "real" CQR - but I do ponder the difference in construction. Of course, there are other cast anchors out there too. A "real CQR" is on my wish list, but for now I've convinced myself that, in the mud of the Chesapeake, sudden loading of the shaft in bending is not a big concern.

Bruce Barber

Posted by: bruceb38@verizon.net | March 6, 2013 11:55 AM    Report this comment

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