Lost anchor chain
A vessel losing one anchor and four lengths of chain cable during anchor handling. During the vessel’s previous dry docking, a number of chain cable lengths had been renewed on both port and starboard sides, including a number of Kenter shackles (joining shackles) as found necessary, due to wastage in excess of allowable limits. The remaining part of the anchor chain cable lengths and Kenter shackles were at that time found to be in satisfactory condition.
It was discovered on investigation that the probable cause of the damage was the fracture of a Kenter shackle that had not been renewed in the previous dry dock.
Note that the intricate shape of the various parts of a Kenter shackle means that large forces are transferred through relatively small contact areas. Proper design and well machined faces and corners are very important for the durability of such shackles.
In the above case the failure may be attributed to mishandling of the Kenter shackle during the opening/ fitting operation. Since in most cases Kenter shackles on old anchor chains are rusty/frozen, and opening up and reassembly requires the use of heating or mechanical force, cracks are likely to develop and should result in replacement rather than re-use.
The lesson to be learnt from this incident is, when a chain cable length is replaced due to wear and tear, the Kenter shackle(s) are normally worn as well and should generally be replaced.