The Offshore Voyaging Reference Site

Spade Anchor Failure, Update and Summary

spade failure.jpg


A couple of weeks ago, I wrote an article looking at the possible causes of a Spade anchor bending spectacularly in use and then dragging.

Luckily, the boat was not damaged and no one was hurt, but a failure like this could have nasty outcomes, so it was worth digging into and writing about.

The article also spawned one of the most interesting and useful comment streams we have ever hosted here at AAC.

To refresh our memories, my original ranking on probable causes, most likely at the top, was [edited for brevity]:

  1. The anchor got jammed in a hidden seabed feature and so the stock was subjected to off-axis forces that no modern anchor could have withstood. This was exacerbated by:
    • The very short rode.
    • The snubber issues [see original article], particularly if it was polyester (Dacron), as seems likely, rather than nylon.
  2. The anchor was either previously damaged or deteriorated in use and that combined with #1 (above) to cause the failure.
  3. The anchor had a manufacturing defect that did not show up until an off-axis load was put on it.

I have now changed my ranking and some of the details of each possible cause, primarily based on some of the excellent comments to the last article, and I will also share my thinking on continuing to use Spade anchors.

But first, let’s look at why I changed my thinking—conclusions without process are useless.

This is not the Part 2 article I promised on general anchoring lessons I have learned from this incident. That will come later.