200827 Podded propulsion failure
Official report: Edited from MAIB report, 2007; /www.maib.gov.uk
In view of the recent two-part feature on podded propulsion (Seaways December 2007 and January 2008), this report is of particular import and relevance.
A product tanker was making the final approach to come alongside a jetty when suddenly, and without warning, control of the vessel's podded propulsion system was lost. This resulted in the vessel making multiple contacts with the jetty's infrastructure, resulting in material damage to both the jetty and the vessel before control was regained.
At the time of the accident, the master and a pilot were on the bridge, but no tugs had been engaged due to the excellent, slow-speed manoeuvring capabilities of the ship's podded propulsion systems and an effective bow thruster unit. As the vessel approached the jetty, the master transferred the conning position from the centre to the port control console in preparation for berthing the vessel port side alongside.
When the vessel was about 100 metres off the jetty, at a speed of 1.2 knots, the control lever inexplicably moved on its own to approximately 70 per cent of full power. The pod had been angled to thrust the vessel's stern away from the jetty and as the tanker suddenly increased speed, her bow swung rapidly to port. The master attempted to pull the control lever back to zero but the power remained at 70 per cent and the vessel rammed the concrete apron of the jetty, shortly after which the flare of the bow made contact with the steel gantry support of the jetty's oil loading arms.
While he was unable to control the pod's power, the master still had control of its direction. He rotated the unit to move the vessel's head to starboard and also operated the bow thruster to push the vessel's bow off the jetty. This brought the vessel parallel with the jetty, but with the pod's power still at 70 per cent. The master attempted to regain control by transferring control back to the central console and selecting the push button power control function but this was not successful. The master then ordered the vessel's anchor to be let go and rotated the pod to astern mode to reduce the vessel's headway.
Shortly after this, and for no apparent reason, the power returned to zero. However, while the master was still evaluating the situation, the pod's power again increased to 70 per cent and the vessel accelerated astern towards the jetty. The master was again unable to regain control. The pilot warned the personnel on the jetty to vacate the area, shortly after which the vessel's port quarter made heavy contact with the first of the mooring dolphins. She then continued astern, making contact with the second dolphin. This resulted in material damage to both the vessel and the mooring dolphins.
By transferring pod control to the engine room and back to the wheelhouse, the master was able to regain control of the pod and stabilise his vessel until tug assistance arrived and the vessel was moved to a nearby jetty.
When the vessel's primary propulsion control system failed, the master was not alerted to the failure. He also did not obtain any warning before the pod began to change power on its own...
Root cause/contributory factors
Innovative and untested technology was designed and fitted, for which no dedicated technical standards existed at the time;
The company depended heavily on the manufacturers for all aspects of product support;
Lack of in-house maintenance procedures;
Inadequate knowledge of the system by ship's officers and shore staff;
Weak SMS and onboard system documentation, which reduced resilience to defects and emergencies;
Previous incidents of control system failure on this vessel and her sister vessel had not been investigated in detail and no corrective action had been taken.
Corrective actions
To provide training to the vessel's deck and engineering staff on the operation and maintenance of the pod propulsion system;
To put in place a service and maintenance regime for the company's pod propulsion fitted vessels;
To improve onboard documentation;
To cooperate with the manufacturers and classification society to complete a failure modes effect analysis (FMEA), and to retrospectively assess the ship's pod propulsion system against the current criteria for podded vessels.
Editor's note: Mariners must activate the 'Emergency Stop' immediately when it is clear that loss of control over machinery or equipment is leading the vessel into danger.