Stolt Aspiration / Thorngarth

April 15th, 2006 by JCB
Posted in Articles, Features, Incidents & Investigations | No Comments »

MT STOLT ASPIRATION / TUG THORNGARTH

MAIB REPORT

Link to the original illustrated articlae (page 10):

A consequence of changes to traditional tug operations has introduced new challenges for both tug masters and pilots. The increasing popularity of Azimuth Stern Drive (ASD) tugs has introduced a particular handling change since most of these tugs are designed with a bow towing winch resulting in towage over the bow. When on the stern or operating in the push/pull mode this does not cause too many problems but if required to operate on a centre lead the operation has increased risks of which pilots should be fully aware. On page 13 there is a review of the a monograph on this mode of towage published by the Nautical Institute and I would recommend that all pilots operating with tugs in this mode read this book in order to be aware of the risks and if possible also hold liaison meetings with the tug masters. When things go wrong operating in this mode the tug can rapidly lose control and the following is an edited extract from an MAIB report into one such incident.

Stolt Aspiration, a 7901gt chemical tanker was bound for East Lewis Quay, Birkenhead. Entrance to the Birkenhead Docks is through the Alfred Lock The master and pilot had discussed the passage plan, and the pilot had signed the ship’s information sheet. Thorngarth, a Twin Azimuth Stern Drive (TASD) tug of 45t bollard pull, had been tasked with assisting Stolt Aspiration along with the tug Ashgarth. Both Thorngarth and Ashgarth were TASD tugs and towed over the bow. The two tug masters agreed that Thorngarth would act as the bow tug during the planned operation. Neither tug had any mechanical defects. As Stolt Aspiration approached Alfred Lock, the pilot began reducing speed steadily from 10 knots. The master of Thorngarth requested that Stolt Aspiration proceed at slow speed to allow the connection of the forward towline and, as this was normal practice, the pilot agreed. As the tugs approached, the pilot noted his speed through the water as 6.5 knots and slowing. Ashgarth reported that his line was being made fast and that he was happy with the speed. Thorngarth then began to make his approach. Because Thorngarth is designed to pass its towline from its bow, the tug had to approach Stolt Aspiration bow-to-bow, then manoeuvre stern-first to maintain the correct station off the larger vessel. The pilot was unhappy with the speed of Thorngarth’s approach, and warned the tug master. The tug slowed and the approach continued. Thereafter, Stolt Aspiration maintained a steady course, with the speed continuing to slowly reduce. Having received a heaving line from Stolt Aspiration, and having positioned close under the ship’s bow, Thorngarth backed away from her. The tug’s stern began to move to port, and this was corrected to maintain its position right ahead of the ship. However, the tug’s stern began to move to port again, which caused Thorngarth to move quickly across to the starboard side of Stolt Aspiration’s bow which, at this stage, was approximately 6 metres away from the tug. The tug master again attempted to position Thorngarth directly ahead of Stolt Aspiration’s bow, but this time, the corrective action caused the tug to move directly into the path of the vessel’s bulbous bow. Stolt Aspiration struck Thorngarth on its starboard side, causing the tug to heel heavily to port while being bodily displaced to port by the impact. On Stolt Aspiration, the pilot, noting the movement of Thorngarth’s masthead light, immediately ordered full astern, and used the bow thruster to counter the transverse thrust of the propellers and to maintain the vessel’s heading. Ashgarth also began to pull directly astern at full power to slow the ship. Thorngarth managed to pull clear and since she could no longer assist the ship was released and the Stolt Aspiration resumed the berthing operation without further incident.

Findings

The master of the Thorngarth had been appointed to the tug 10 days before the accident and had never carried out this manoeuvre on this tug and, although as mate he had seen it done on tugs of similar configuration, he was not fully familiar with the manoeuvring characteristics of Thorngarth. The collision occurred when the tug

master was re-positioning his tug ahead of the ship In backing away from the ship’s bow, the stern of the tug began to move to port. To correct this, he pushed the port ahead-astern handle forward, which swung the stern back to starboard. However, this slowed the tug and it closed the ship. Engine speed was increased to regain position ahead of

the ship. Once ahead of the ship, the stern again moved to port and again the port ahead/astern control handle was pushed forward to correct the swing. Because Thorngarth was now to starboard of Stolt Aspiration’s bow, as speed reduced due to

the change in astern power, she ended up on the starboard bow of Stolt Aspiration.

In attempting to recover from this position, the tug master caused Thorngarth to move across the closing bow of Stolt Aspiration where he was hit on the starboard side.

Tug manoeuvring controls and their propulsion systems cover a wide spectrum and, even among tugs of the same type, the speed of reaction of the propulsion gear to a control input will vary. As a consequence, any tug master will need to spend time familiarising himself with the controls of a new tug, even if he is familiar with the propulsion type and control system. Although the change of personnel between different types of tug is a necessary part of the flexible operation of a tug fleet, doing so without extensive initial or ongoing familiarisation training, where the complexities and nuances of control of different tug types can be properly understood and practised by the personnel concerned, will inevitably increase the risk of mistakes being made during operational situations. It was assumed that by the time an individual qualified as master, he would have experienced every type of tug manoeuvre, and that this experience would have been overseen by at least one other experienced master. No records were kept to monitor the training and experience gained.

OTHER INCIDENTS

Two similar accidents occurred elsewhere within the UK, within 4 months of the

collision between Thorngarth and Stolt Aspiration. In the first, a tug was operating

as the stern tug in moving a ship astern. After being asked to pull the ship’s stern to

one side, the tug found it could not regain its original position, and collided with the

ship’s stern. The second incident occurred when a tug, acting as the bow tug in a

berthing operation, was manoeuvring to pass its towline to the ship. Once the line

had been passed to the ship, the tug intended to move ahead of the ship, but collided with her bulbous bow. In neither case were there any injuries or pollution caused. In both cases, the tug masters had a wealth of experience in tug operations within their respective ports. However, both were operating tugs with unfamiliar propulsion systems and manoeuvring controls, and attempting manoeuvres with

which they were not entirely familiar. Safety issues identified as a result of the investigation.

1. Fatigue was not an issue in this accident.

2. There were no mechanical failures on either vessel that could have led to the collision.

3. The accident occurred when the tug master of Thorngarth was adjusting his position ahead of the ship and, due to his unfamiliarity with the tug, misjudged the amount of control movement required.

4. There was little that Stolt Aspiration’s crew could have done to prevent the collision.

5. Although the change of personnel from tug type to tug type is a necessary part of the flexible operation of a tug fleet, doing so without extensive initial or ongoing familiarisation training, where the complexities and nuances of control of different tug types can be properly understood and practised by the personnel concerned, will

inevitably increase the risk of mistakes being made during operational situations.

6. The bow-to-bow approach is conducted many times a day by tugs throughout the world.

7. No formal guidance was given to pilots concerning the capabilities and limitations of tugs in the port.

8. The introduction of new qualifications for Inshore Tug Operators has standardised the training requirements. The previous system was not satisfactory in that it relied on

personnel gaining the relevant experience over time but no records of experience gained were maintained.

9. The pilot and master of a ship would not know which type of tug has been allocated to the vessel until just before the planned operation. However, they could be confident that the tug would make the bollard pull requirement and would be capable of carrying out the designated task, despite not necessarily being the optimum choice of tug for the task.

10.There was no forum for the tug operators, pilots and port authority to raise matters of mutual concern.

11.By not informing the VTS operators of the accident, the VTS operators were unable to co-ordinate the response from the rescue services.

12.Two other accidents occurred elsewhere in the UK in a short period of time, both also caused when tug masters were operating tugs with unfamiliar propulsion systems and

manoeuvring controls, and attempting manoeuvres with which they were not entirely familiar.