Rethinking Anchor Shaft Strength
Posted by at 11:48AM - Comments: (1)
March 5, 2013
In the upcoming April issue of Practical Sailor, contributor Jonathan Neeves explores this topic in great detail. In his view, the reasons behind bent shafts are many.
- Industry tests used to rate and certify anchors do not test the shaft’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.
- Manufacturers are using thinner plate steel, or lower grade, lower-tensile steel than is specified in the original design.
- Newer anchors tend to set deeper, remaining immobile when the wind shifts and the load changes direction, causing side-loading on the shaft that can cause it to bend.
- 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.
- Plate stock used to make anchor shafts 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 shaft 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 shafts than we find on recreational anchors—shafts 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 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 firstname.lastname@example.org, and tell us how it happened.