In the latest Safety Digest by UK MAIB, a passenger/ro-ro cargo ferry arrived in port and berthed without incident. Its vehicle ramp was then landed and a shore ramp was lowered from an upper linkspan. Shortly afterwards, the upper linkspan shore ramp fingers dropped off the ferry and one mooring rope parted, before the ahead momentum stopped and the ferry came to rest 15m forward of its original position.
The incident
The ferry’s manoeuvring controls had been set to a bridge wing for arrival and, after completing the berthing, the master transferred control back to the bridge centre console. He then shut down the bow and stern thrusters, informed the duty engineer in the engine control room (ECR) that he had finished with engines (FWE), and placed both backup telegraphs to FWE. The engine room team started to reduce the speed of the engines in preparation to declutch them. The standard operating procedure (SOP) required that, once both engines had been declutched, control was to be transferred to the ECR as a prerequisite to initiating cargo discharge.
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With propeller pitch still in bridge manual control, the master and second officer went to the chart room to complete end of passage paperwork and to begin preparations for the next voyage. Shortly after, the cargo officer reported weight coming onto the stern mooring lines and the vessel moving ahead. The master applied astern pitch to both propellers, and the cargo officer lifted the vehicle ramp. However, the upper linkspan shore ramp fingers dropped off the ferry and one mooring rope parted under tension, before the ahead momentum was arrested and the ferry came to rest approximately 15m forward of its original position.
Probable cause
The SOP indicated to set both manual pitch controls to zero before placing both backup telegraphs to FWE. On this occasion, he had left the port propeller pitch control set at +2 and the starboard one set at -2. These settings were commonly used to hold the ferry in a neutral position until the mooring ropes were made fast. The duty engineer did not notice that the pitch controls were not set at zero before the engine room team started to reduce the speed of the engines in preparation to declutch them. As the port engine slowed, the engine management system automatically tried to balance the reduced engine speed by applying more ahead pitch to the port propeller, increasing it to 50% at one point, causing the ferry to move ahead.
- This was a routine port arrival operation that had been carried out on numerous occasions over a period of several years. However, with all routine actions there is a risk that familiarity can compromise safety. The SOP required both manual pitch controls to be set to zero before engine speed was reduced. While the master was familiar with the routine of setting the manual pitch controls to zero before placing both backup telegraphs to FWE, he was equally familiar with the neutral, and hence apparently safe, position adopted by the ferry in setting the port propeller pitch at +2 and the starboard one at -2 during the final stage of mooring. He had not expected the consequences of reducing engine speed with the manual pitch controls not set at zero and, hence, had undervalued the SOP.
- Operators must be familiar with the functionality of the equipment and systems that they are required to use. On this occasion, neither the master nor the chief engineer was aware of the full functionality of the engine management system. This lack of knowledge contributed to the SOP not being followed on this occasion. Machinery trials and operating procedures should identify the extent of the engine management functions, and suitable instructions and guidance should be available to operators. Following the accident, the ferry’s deck officers were informed of the importance of setting the manual pitch controls to zero before reducing engine speed. The importance was also recognised in the form of an additional bridge checklist item and a requirement for the duty engineer to double-check the status of the manual pitch controls before reducing engine speed.
