Know your vessel capabilities and when to stop!

With all engines and thrusters engaged, a DP equipment class 2 pipe supply vessel (PSV) was operating in open bus configuration. The vessel was engaged in cargo operations with a larger DP pipelay vessel (PLV) during adverse weather conditions.

The supply vessel had been engaged in cargo transfer operations for 25 minutes prior to the DP incident occurring. The weather at the time of the cargo operations was described as adverse with wind gusts of approximately 40knots and a swell of 2m.

Upon arrival alongside the pipelay vessel, on the leeside, the Master of the supply vessel confirmed that they were in position but also made comment that the thrust wash from the pipelay vessel was strong and requested the bridge of the pipelay vessel to reduce the wash in some way. The pipelay Bridge acknowledged the request and cargo operations commenced.

10 minutes later, the supply vessel’s Master informed the pipelay Bridge that they were using too much thrust to stay in position and were up to 70% power capacity with the thrusters at 77% capacity. The pipelay Bridge acknowledged and said they would try to reduce thruster wash.

A further 15 minutes later, the supply vessel suffered a loss of one thruster, and due to the vessel operating outside of the DP equipment class 2 station keeping capabilities, was forced off position by the high thrust wash of the pipelay vessel.

The Master of the supply vessel immediately informed the pipelay vessel Bridge however there was not enough time to disconnect the load on the hook and a container was dragged from the deck of the supply vessel and into the water, as the supply vessel was forced off position. Fortunately, there was no damage to equipment, and no-one was harmed.

Following investigation, the following was found:

• Sudden gusts of wind of around 40 knots created an increased wind load on the pipe layer, causing an increased thruster wash towards the PSV which caused the PSV to lose position.
• The failure of the PSV’s azimuth thruster contributed to the loss of position.
• The operational limits of PSVs operating alongside other vessels were not considered in the Activity Specific Operating Guidelines (ASOG).
• No-one stopped the job: the operation was not stopped despite alarms indicating the PSV was outside defined operational limits.