This case study is based on the accident report investigated by the MAIB with regard to the the grounding and recovery of the container feeder vessel Thea II and the tug Svitzer Josephine in the approaches to the Humber Estuary on 15 December 2018.
The sole objective of the investigation of an accident under the Merchant Shipping (Accident Reporting and Investigation) Regulations 2012 shall be the prevention of future accidents through the ascertainment of its causes and circumstances.
It shall not be the purpose of an investigation to determine liability nor, except so far as is necessary to achieve its objective, to apportion blame.
Summary of the accident
At approximately 1500 on 15 December 2018, the main engine of the Cyprus registered
container feeder vessel, Thea II, failed while approaching the Humber pilot station.
With no propulsion the master anchored the vessel in gale force weather conditions. While awaiting the arrival of tugs, the weather deteriorated further and Thea II dragged its anchor towards the Binks shoal.
At 1739, before Thea II could be towed clear, the container vessel and one of the tugs
attending, Svitzer Josephine, ran aground. Search and rescue assets were deployed, but
no personnel were evacuated from either vessel.
As the tide rose, both vessels refoated. Just before 2200, Svitzer Josephine was able to
get underway and return to harbour. However, Thea II’s tow was delayed while the vessel’s
managers attempted to agree contractual terms with another tug operator.
At about 0100 the following day, its managers signed Lloyd’s Open Form. The vessel was then towed to the deep water anchorage before being taken into harbour on 16 December 2018. There were no injuries and no pollution as a result of this accident.
The investigation found that Thea II had lost propulsion due to the failure of its main engine governor, which could not be repaired, and the master had no choice but to anchor the vessel and await the arrival of tugs.
However, as the weather deteriorated and the vessel began to drag towards the Binks shoal, the master did not deploy all his remaining chain or his vessel’s second anchor.
Had he done so, it would have slowed or arrested the vessel’s rate of drift and allowed more time for tugs to secure lines and tow the vessel clear.
The investigation also found that the tug Svitzer Josephine grounded because the master,
focused on passing the towline to the crew of Thea II, lost positional awareness and did not
appreciate the rate of drift of both vessels towards the Binks shoal.
Thea II refoated on the rising tide. However, despite the best eforts of the harbourmaster,
the Maritime and Coastguard Agency and local tugs, in difcult weather conditions, Thea
II’s managers only agreed salvage terms 2½ hours later, under the threat of formal direction from the Secretary of State’s Representative.
This delay almost led to Thea II re-grounding, risking damage to an environmentally sensitive area.
As a result of this accident, action has been taken by Associated British Ports Humber
and Svitzer Marine Ltd, to review their risk assessments and operating procedures.
The Secretary of State’s Representative has continued an industry wide engagement
programme to promote a greater understanding of his role.
A recommendation has been made to Thea II’s managers, TS-Shipping, to review their emergency response organisation and procedures.
Once Thea II’s cargo had been discharged at Hull, the vessel was towed to
Germany for repair. After the vessel had been dry docked it was found that:
The rudder and steering gear were damaged, but operational.
● The vessel’s hull was intact, but the hull bottom paintwork was damaged.
● There was minor damage to the propeller blades.
● Two quarter deck ventilation pipes had been broken by the tug’s towline.
Thea II was out of service for 6 weeks for repair. The vessel resumed its charter in
Tug Svitzer Josephine
Post-accident in-water survey of Svitzer Josephine revealed that the void space
containing the starboard engine room vent fan had fooded.
This had shorted the fan motor and probably triggered the fre alarm.
The starboard weather deck door had also vibrated open during the grounding, causing water damage to the tug’s accommodation and recreational spaces.
Initially it was thought that the tug’s hull and Voith Schneider propellers (VSP) were undamaged.
However, during the dry-docking of the vessel in June 2019, extensive cracking was identifed along the skeg and adjoining keel plating, which had not been detected during the in-water survey.
Yeoman’s hull was damaged when, during its approach to Thea II, it was pushed
onto the container vessel’s anchor cable.
Later during the tow, the tug lost the use of both engines. Yeoman was towing Thea II bow to bow, and its master initially assumed that its propellers had been fouled by fshing gear.
However, when Yeoman was in dry dock it was discovered that the port and starboard azimuth units had been fouled by a towline.
The following damage was also discovered:
● The internal engine room mountings were out of tolerance.
● The starboard bilge keel and starboard side of the hull were damaged.
The vessel was in dry dock for 10 weeks and returned to service in February 2019.
Post-accident inspection of the rope recovered from Yeoman’s azimuth units
suggests that it was an 80mm, 3-strand ‘Strongline’ polyester, Langhorst towing
hawser, attached to a 15m yellow/orange towing pennant.
This was similar to Svitzer Josephine’s towline, which had been discarded by Thea II’s crew.
The purpose of the analysis is to determine the contributory causes and circumstances of the accident as a basis for making recommendations to prevent similar accidents occurring in the future.
While approaching the Humber pilot station, the container feeder vessel Thea II
sufered an engine failure that could not be immediately repaired and which meant
that the vessel had to anchor in gale force conditions.
The master had no choice but to ask for tug assistance to enter port. While at anchor the winds increased to storm force, leading to Thea II dragging its anchor as insufcient chain and no second anchor were deployed.
Subsequently, while trying to establish a tow, both Svitzer Josephine and Thea II
grounded on the Binks shoal.
The tug grounded because its master, focused on securing a towline, lost positional awareness and did not fully appreciate the drift rate of the two vessels.
The delays in Thea II securing a tow after refoating were due to the managers’ lack
of awareness of the vessel’s situation.
Despite numerous emailed requests by Thea II’s master, and a special direction issued by the Humber harbourmaster instructing him to secure tug towlines.
It was only the threat of intervention by SOSREP that persuaded the managers to take action to prevent their vessel re-grounding in an environmentally sensitive area.
Thea II – Grounding
Main engine failure
Thea II, which was 23 years old, was a well-maintained vessel with a reputation
for being mechanically reliable. Its C/E, with over 13 years’ experience on board,
was able to quickly identify the engine defect.
This revealed that Thea II had lost propulsion due to the failure of its main engine governor circuit board. Without a replacement component, the engine could not be repaired.
Thea II did not carry a spare circuit board, as such a repair would normally be
carried out by service engineers. Consequently the master had no option but to
anchor his vessel and summon assistance.
Thea II dragging anchor
Thea II maintained its position for almost 90 minutes, lying to its port anchor with
5 shackles of cable in the water.
The master believed that his vessel would be at anchor for only a short period awaiting the arrival of tugs; the amount of cable he had deployed refected this.
However, as the wind increased to storm force 10, the vessel started to yaw, and shortly afterwards began to drag its anchor. The master’s response was to deploy a further shackle of cable.
This was unsuccessful in stopping the anchor dragging, and Thea II continued to
drift towards the Binks shoal at 1.7kts.
The frst option was to deploy all remaining cable on the port anchor.
Thereafter the master could also, as the vessel’s SMS advised, have deployed the starboard
anchor, either ‘underfoot’, or as a second anchor.
Had the master taken any of these actions they might have stopped, or at least reduced Thea II’s rate of drift towards the Binks shoal.
Had the vessel’s rate of drift been reduced by 0.5kt, it would have allowed the tugs a further 25 minutes to secure lines and tow Thea II to safety.
The master was reluctant to drop a second anchor because, like many mariners, he
was concerned that the two anchor cables would become entangled.
In addition, at 1505 the VTSO had advised Thea II not to drop a second anchor because it might have hampered or prevented the vessel from securing tugs.
The tow to the anchorage
At approximately 2200, Svitzer Josephine jettisoned its tow and got underway. This
left Thea II with 130m of heavy, 80mm towline attached to its forecastle, which
needed to be cleared before Yeoman’s line could be made fast.
Having examined the 43m of towline recovered from Yeoman’s propellers, it appears
that Thea II’s crew attempted to recover Svitzer Josephine’s hawser.
However, having brought the frst 43m on board, the crew made the decision to cut and
jettison the remaining 87m.
Subsequently, as conditions moderated once Thea II was clear of the Binks, the crew made the decision to dispose of the remaining 43m of towline.
Tug to lose the use of both its ASDs
This remnant of the towline was probably thrown overboard just before 0200.
While the 80mm hawser sank, the buoyant 15m messenger did not, and it was drawn
into Yeoman’s propellers.
This caused the tug to lose the use of both its ASDs. Fortunately, Irishman was able to control the tow until the tug Pullman arrived on scene and took over the tow from the disabled Yeoman.
Emergencies require rapid decisions to be taken, the consequences of which are
often not fully understood at the time.
In this case, Svitzer Josephine’s towline being jettisoned by Thea II’s crew disabled Yeoman and almost undermined the integrity of the towing operation to salvage the vessel.
Had Thea II’s crew made a proactive decision to recover the towline on board, instead of simply jettisoning it, the disabling of Yeoman could have been avoided.
Safety issues directly contributing to the accident that have been addressed or resulted in recommendations.
Thea II lost propulsion due to the failure of its main engine governor central processing unit.
Thea II’s crew could not repair the main engine. As a result, Thea II’s master had no
choice but to anchor and request tug assistance.
It was unsurprising that Thea II dragged its anchor in the severe weather conditions.
However, had Thea II’s master deployed a second anchor and/or increased the scope of the anchor already deployed, it would have slowed, and might have arrested the vessel’s rate of drift towards the Binks shoal, allowing more time for a tug to secure a towline.
While VTS Humber had earlier advised Thea II not to deploy a second anchor, it
was the master’s concern – that a second anchor would become entangled with the
frst – that resulted in his decision not to deploy the starboard anchor.
Svitzer Josephine’s master
Svitzer Josephine’s master did not fully appreciate the level of risk he was exposing
his vessel to when he took the tug out of the main channel to attend Thea II.
Svitzer Josephine grounded because the master, focused on passing the towline to
Thea II, lost navigational positional awareness and did not appreciate the rate of drift
of both vessels towards the Binks shoal.
The assistant harbourmaster and his VTS team
The assistant harbourmaster and his VTS team had the tools necessary to estimate
the time of Thea II grounding. Had they done so, this would have allowed the time
available to secure Svitzer Josephine to be calculated, enabling a more informed
decision or additional precautions to be taken.
While responsibility for the safety of the tug rested with its master, timely advice from
VTS Humber might have prompted him to take action to prevent Svitzer Josephine
The harbourmaster correctly assessed that if not towed clear during this tidal cycle,
it is likely Thea II would have been blown on to the Spurn peninsula, risking potential
damage to several environmentally sensitive sites.
The harbourmaster used his powers of special directions appropriately and, when
Thea II did not take the tugs’ lines, successfully engaged the Secretary of State’s
Representative to ensure Thea II was towed into safe water.
Significance of the direction
Transmitting the harbourmaster’s special direction by email, as well as by radio,
to Thea II’s master, agent and managers would have ensured that all of the key
decision makers understood the signifcance of the direction, the gravity of the
situation and the need to take urgent action.
The vessel’s managers’ instruction to Thea II’s master, not to take tugs’ lines without
their prior approval, undermined his authority to act in the best interest of his ship
A tow under Lloyd’s Open Form
It is estimated that Thea II was only 20 minutes from re-grounding on a falling tide
when the vessel’s managers agreed that the master could accept a tow under
Lloyd’s Open Form.
Thea II’s managers, operating remotely from home, did not fully appreciate the
seriousness of the situation, the need for urgent action, or the environmental risk
posed by their vessel.
The duty counter-pollution and salvage officer’s threat of action by the Secretary of
State’s Representative worked, and ultimately ensured that Thea II was towed clear
into safe water.
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Source: MAIB INV Report