INCIDENT – Whilst manoeuvring from a lay-berth to the cargo wharf a 10,,000 dwt vessel made contact with a larger vessel, a tanker, moored on an adjacent berth. The smaller vessel sustained damage to her starboard side bulwark. The larger vessel sustained a minor indentation on her port bow.
IMMEDIATE CORRECTIVE ACTION – The smaller vessel safely berthed as planned starboard side to its intended berth. The duty superintendent, casualty coordinator, Flag State, P&I club, Classification society, owner and charterer were advised. P&I representative and a class surveyor attended the vessel and certified it as seaworthy.
INVESTIGATION BY THE OPERATOR – The vessel is fitted with a single medium speed diesel driving a controllable pitch propeller (CPP) and a shaft generator. The vessel is fitted with a 400kw bow thruster powered by either 3 generators or the shaft generator.
The engine is fixed speed (600 rpm) but has a low constant speed (400rpm) for clutching in the propeller and the shaft generator.
At the previous port, 2 mooring lines had fouled the propeller so upon arriving at the subsequent port the vessel had berthed at a lay by berth to allow divers to inspect the rudder and propeller and remove any rope remaining on the propeller. Prior to berthing the vessel had anchored and there had been some doubts over the performance of the CPP, resulting in the propeller being clutched in and out a number of times during the anchoring operation. Following the rope fouling incident the managing office advised that the bow thruster must be powered by 3 generators in parallel rather then the shaft generator. This would then allow the thruster to be available independently of having the propeller clutched in.
On the morning of the incident, the vessel was to be shifted from the lay-by berth to the cargo berth, a distance was around 1.0nm. Upon boarding, the Pilot advised the master that a single tug would be made fast aft and would tow the vessel to the loading berth. It was advised that the vessels engine would probably not be used. This information was passed on to the Engine Control Room. The duty engineer after clutching in the propeller at low constant speed did not increase to high constant speed because
1) the bridge had advised the engine would probably not be needed,
2) there was a recent history of having to clutch the propeller in and out at short notice and
3) the shaft generator was no longer required to power the thruster.
The fact that the M/E was not at high constant speed and therefore not in full standby condition was not passed on to the C/E or the bridge team.
Upon letting go the vessel was towed astern by a large tug with a 70mt bollard pull. The speed of the tow steadily increased to 7.5 kts at which point steps were taken to slow the vessel down by reducing the tug pull and using slow ahead on the main engine. The speed of the vessel did not slow fast enough and the main engine was put to full ahead pitch as she approached the cargo wharf. In order to avoid a collision with the larger vessel moored on an adjacent berth, the pilot requested the tug tow the stern to port. The bow-thruster was also put 100% to port but the resultant shear caused the bow to make contact with the moored tanker.
It was later proved that the operation of the CPP had not been affected by the fouled mooring ropes.
Root Causes of the incident
- The Master and pilot did not take action soon enough to slow down the movement of the vessel astern, possibly due to lack of experience handling a vessel of that size.
- The Tug involved was large and powerful relative to the tanker involved. The towing power used by the tug was excessive and resulted in excessive tow speed (7.5 kts).
- The vessels main engine was not in its full standby condition (high constant rpm) and was therefore unable to respond as required to arrest the vessel sternway.
- The Bridge team were unaware of any limitation imposed on the M/E performance.
- Towing a vessel astern with a single tug is not considered ‘best practice’. The tug should be in a position to stop a vessel should propulsion be lost. In this case the vessel should have been manoeuvred ahead under her own power, turning around as necessary and the tug should be in a position to stop her movement if necessary. Towing astern also reduces the effectiveness of the rudder.
CLOSE OUT ACTION TAKEN BY THE OPERATOR
- Masters who are proposed for appointment to small ships to be assessed on their experience of small ship handling
- A notice will be placed on the main engine (M/E) tachometer on the bridge of the vessel and sister vessels to warn that M/E is not in standby until the M/E is at high constant speed (600 rpm)
- Duty engineer to be advised that failure to follow documented and familiar safety procedures is not acceptable
- Revised procedure to be instigated on the vessel and her sister vessel such that bow-thruster is always powered by 3 x generators rather than shaft generator
- The guidance within the Safety Management System relating to the use of tugs shall be reviewed and updated.
This report has been kindly provided to CHIRP by the manager of the vessel so that the learning can be shared more widely in the industry. It is a useful case study that highlights a number of generic issues that frequently arise:
- It is vital that the plan for the passage to and from the berth is fully discussed with the pilot – a “one team” approach. In this case, the plan should have included the expected speed of towing.
- The Bridge Team must closely monitor that passage is being executed in accordance with the plan. If it is not, the Master should express concern to the pilot and intervene if necessary.
- Key points of the plan must be communicated to all involved, including the engine room and the tugs.
CHIRP fully endorses the learning point that during manoeuvring the thrusters should be powered by the independent generators rather than the shaft generator. (If this is not the practice on your ship, do raise the issue on board, or with your DPA or let CHIRP know.)
The decision on whether to tow a ship astern has to take into account the physical constraints of the port. At some ports this is a standard practice and can be exercised safely provided of course that the operation is properly planned and the pilot has the appropriate training and expertise.
Although the damage was minor, the consequences could potentially have been more serious. A thorough investigation was carried out, the root causes were identified and preventative action was implemented on the specific ship and sister vessels and generally across the whole fleet.