Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation.
On 15 October 2019 at 2100 Eastern Daylight-saving Time, an anchor handling tug supply vessel was engaged in anchor handling operations with an offshore drilling rig. The operation involved deploying one of the rig’s anchor cables onto the vessel’s deck and disconnecting it from the rig. The vessel utilised a ‘J-lock’ to acquire and recover the chain. While in position approximately 45 m from the rig, the anchor handler believed they had J-locked onto the links of the anchor chain, close to where the cable transitions from chain to steel wire.
Once the anchor handler had locked onto the anchor chain, the rig paid out approximately 200 m of wire to allow the anchor handler to move to a safer spot to bring the chain onto the vessel’s deck. As the anchor handler began recovering the chain onto the deck (through a winching system), it became evident that the J-lock was not securely locked onto the anchor chain.
As the J-lock was deploying over the stern roller, the hook jumped from the anchor chain to the anchor wire. The abrupt change in weight and tension on the anchor handler’s winch wire resulted in the vessel being rapidly set stern-first towards the rig. Two of the vessel’s engines were set at maximum power ahead and the work wire was paid out, however neither of these actions could arrest the vessel’s sternway. At about 2118, the anchor handler made contact with the drilling rig. The anchor handler sustained structural damage to the rig leg.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
- A J-lock is a large hook in the shape of the letter ‘J’. The hook is used to snag and lock onto the chain links of an anchor cable.
- To retrieve the anchor, the anchor handler deploys a j-lock on a wire that sweeps the ocean floor and acquires the anchor chain. Once securely j-locked, the anchor handler is able to begin reeling in the wire and anchor chain.