UK MAIB published its investigation report into the immobilisation of the dredger Shearwater, after its propeller shafts were fouled by its own towline while towing the barge Agem One on 9 April 2020.
The incident
On 9 April 2020, Shearwater departed from Stoerhead for passage to Loch Eriboll. Shearwater was towing Agem One alongside (on the dredger’s port side) and was proceeding at a speed of between 3 and 5.2 knots (kts). The master was on the bridge and in control of the vessel, and Shearwater’s owner was overseeing towing operations.
Shearwater passed Cape Wrath at about 1030 and started to encounter a long swell with a height of approximately 2.5 metres (m), causing Agem One to move heavily against the dredger’s side. The alongside towing confguration was judged untenable by Shearwater’s owner who ordered that Agem One be moved to an astern tow.
The AB and the excavator driver stepped across to Agem One from Shearwater’s deck and prepared for an astern tow by connecting the shackle on the barge’s bridle to the towline’s hard thimble eye. Both crewmen then returned to Shearwater, Agem One was cast of and the 80 metre (m) towline payed out. After Shearwater had towed Agem One a short distance, the towline broke and the barge drifted free.
Shearwater’s master then manoeuvred to retrieve Agem One and the two crewmen once again stepped across to the barge to reattach the tow. The towline had failed at the point of connection to the barge’s bridle and the hard eye was observed to be distorted, so the crewmen tied a bowline knot in the towline as an alternative connection. The passage towards Loch Eriboll continued but the towline failed again with Agem One needing to be retrieved and the tow reattached once more.
At about 1200, following the repeated failures of the towline, the owner and master decided to abort the passage and head back towards shelter in Kinlochbervie.
At about 1900, Shearwater was just over 3 nautical miles (nm) west of Kinlochbervie with Agem One back in an alongside towing arrangement. In this area, there was a moderate breeze, a short, choppy sea and good visibility. A decision was then taken to revert to an astern tow due to the narrow width of navigable water
available in the approaches to Kinlochbervie.
Agem One was cast of with the excavator driver on board and the owner and the AB passed the towline from Shearwater’s aft deck down to him to connect up. Once connected, the master needed to go astern to close the gap between the dredger and the barge so that the excavator driver could be retrieved back on board.
Prior to applying astern propulsion, the owner, who was on the bridge, asked the AB to confrm that the towline was clear of the water. The AB shouted back that it was, so the master applied astern power on both shafts. When Shearwater was adjacent to the barge, the excavator driver scrambled back across on to the dredger’s side deck; at the same time, both engines stopped. The master restarted the engines and attempted to engage propulsion but neither engine would clutch in.
The excavator driver then went to the engine room to assess the situation and found that the port shaft was dislodged from the gearbox and the gearbox’s casing was damaged. He went to the bridge and briefed the master and the owner about the damaged propulsion. By this time, the owner and master had seen from the aft deck that the shafts were fouled by the towline
The master was aware that both vessels were then drifting north with the tidal stream at about 1kt and the only safe course of action was to drop the anchor. The port anchor was let go and, as it started to hold, Shearwater swung round into the tidal stream; at this point, Agem One, which was not under control, made several heavy, damaging collisions with Shearwater’s port side.
The crew tried to regain control of Agem One by securing it alongside Shearwater but were unable to do so. Agem One was then held briefy astern of the dredger by the fouled towline before drifting free when the towline broke.
When the crew checked Shearwater for damage, water was found entering the port side buoyancy space through damage holes in the shell plating.
Probable cause
According to the UK MAIB:
- Shearwater was not a suitable vessel to conduct a lengthy coastal tow, and there was insufficient planning or safety procedures for the voyage;
- Shearwater’s crew did not have the necessary competence for the towing voyage, and there was no tow master;
- Safety certification by the flag state did not provide sufficient assurance for safe operation of the vessel.
Recommendations
Recommendations have been made to Shearwater’s owner to assess all on board hazards and provide safe systems of work to mitigate the foreseeable risks, and to ensure the vessel is safely manned.
The report also makes a recommendation to the Maritime and Coastguard Agency to ensure that certification of vessels such as Shearwater includes the application of all appropriate regulatory conditions relevant to the vessel’s intended function and area of operations.
EXPLORE MORE ON UK MAIB’S REPORT
