Human Error Caused Ramming of Lock Gate
The German Federal Bureau of Maritime Casualty Investigation (BSU) has released a report into the allision of the special purpose dive support vessel Red7 Alliance with a lock in Germany, noting both human error and a potential lack of control system functionality.
On the morning of January 17, 2015, the Red7 Alliance, sailing under the flag of the Bahamas, arrived at the locks in Brunsbüttel to transit the Kiel Canal during her voyage from Great Yarmouth to Mukran. Apart from the pilot, the master and the second officer were on the bridge for the approach maneuver when Neue Südschleuse (new south lock) became available. Just after the fore spring and stern line had been placed over the quayside bollards, Red7 Alliance continuously accelerated and rammed the closed lock gate with such velocity that exiting again under her own steam was impossible.
Assisted by the tug Bugsier 21, she was finally hauled out of the lock sternwards and, supported by a second tug, the Wal, towed away. There was extensive damage to both her bow and the lock gate, but no one was hurt.
ANALYSIS
Red7 Alliance is equipped with two rudder propellers for forward thrust and four thrusters for traversing.
To improve his angle of visibility, the pilot had handed over control of the tiller to the second officer and moved to the starboard wing. The master initiated the sternward maneuver on the recommendation of the pilot. In the process, he must have assumed that he operated the control levers on both control consoles in manual mode and switched both control levers by 180°. He thus failed to switch the starboard propulsion, so far working in automatic pilot mode, to manual mode.
The outcome of the master’s assumption that both propulsion units worked in manual mode was that the port gondola rotated 180°, as required, but the starboard gondola held its position (0°) and pushed the ship further forward. This unintended forward thrust of the starboard propeller took effect immediately, but the required sternward thrust of the port propeller could have only taken effect after the gondola turned completely by 180°.
If the master was aware of the starboard propulsion operating in automatic pilot mode he could have just set the controllable pitch propeller to astern; the port azipod should have been turned by 180°.
The recording of the conversations on the bridge indicate that immediately after the collision the master apparently assumed there had been a technical failure in the propulsion units, because the systems had not responded as he had expected. That the systems were forced to respond in the manner they did because of the failure to switch the starboard propulsion unit to manual mode had not yet been recognized.
The erroneous assumption that in the absence of alarm signals it concerned a short-term fault and both propulsion units were operating in a sternward direction, an attempt to release the ship from the gate under her own steam was apparently made after the collision.
In the process, the aft thruster was also used to swing the hull. This maneuver was destined to fail, because the port propulsion unit had turned 180° in the meantime and the pitch of the propeller blades on both the propulsion units had now reached its limit (100 percent ahead). The propeller thrusts cancelled each other out due to the misalignment of the two propulsion units.
After the failed attempt, further use of the propulsion units was dispensed with and the propulsion motors for the propellers switched off on the recommendation of the pilot.
CONCLUSIONS
BSU stated that a technical failure in the control system can be ruled out with certainty. Consequently, the accident was caused by an error in operating the starboard propulsion since the master assumed that this azipod already operated in manual mode. If he had been aware that this unit operated in the automatic pilot mode he should not have turned the gondola but instead only switched the pitch on “astern” to achieve a stop effect.
The accident would not have happened if the propulsion unit controls were operated, having regard to the different operating modes (auto mode and manual mode). Moreover, it would have been helpful if the technical equipment had indicated the operator error or possibly even prevented it. The manufacturer was requested to check whether the avoidance of such operator errors is technically feasible.
The full report is available here.