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?
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.
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