Quote:
Originally Posted by Sos
As a matter of interest, what were the weather conditions that caused it to fail. Would you consider it high a loading?
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The
wind was only about 15-20 knots, but there was a bit of wave action. The
boat concerned had no snubber. Notice a pattern: unmoused shackles, non-rated swivel, no snubber. Surprisingly, the
boat was otherwise immaculate and in beautiful condition.
This
wind strength would not normally be enough to
lift the chain, even in the gusts, but you can see the chain lifting in one of the photos so the wave action was having a significant effect (fans of the great benefit of catenary take note how quickly much of it disappears

).
One of the surprising things even with a broken swivel is how the forces managed to straighten out the
stainless steel loop. I didn't have my callipers down there

, but my guess is that the swivel was 18-20 mm SS rod. It takes a lot of force to bend something that thick even when it is an open loop only attached on one side. I sometimes think the theoretical calculations of wind loading on
anchoring gear seriously underestimates the forces involved when there are factors such as wave action and sheering forces, which is often present.
I agree with the comments about crevice
corrosion (or perhaps a bad weld, crack, and then crevice corrosion inside the crack) being the major factor, but the
photo in the second post does show how easy it can be for swivels and shackles to have a load that is well outside the straight pull they are rated for. A bit of overkill with this terminal
gear is good
insurance.