MAIB: Shallow Water Effects Contributed to Ro/Ro's Grounding
The UK Marine Accident Investigation Branch (MAIB) has published its final report on the grounding of the ro/ro freight ferry Seatruck Performance last year, and it determined that shallow water effects - squat and bow cushion - were a contributing factor.
At 2243 hours on May 8, 2019, the ro/ro freight vessel Seatruck Performance grounded while transiting the Greenore Channel in Carlingford Lough, Northern Ireland. The casualty occured shortly after departing Warrenpoint on a voyage to Heysham, England.
The vessel departed the dock at 2205 hours with a newly-promoted master on the bridge. At 2241, as the ship transited outbound through the narrow and shallow Greenore Channel, the master took the vessel in hand steering. During a series of manual course corrections near the No. 21 buoy, the master initiated a turn to starboard too late, and the vessel strayed towards the north side of the channel and struck an underwater rock outcropping.
After the grounding, the ferry quickly developed a seven degree list, but steering and propulsion were not affected. she was able to return to Warrenpoint without assistance. There were no injuries to the 11 passengers and 22 crew aboard, and there was no pollution reported.
The grounding caused damage to plating on the bottom of the hull, including a 30-foot-long tear along the port side. A subsequent survey and dry docking found that a tank and a void space had been breached. Broken pieces of granite were found inside of the tanks. The vessel was out of service for three weeks for repairs.
An investigation by MAIB found that the crew was not in the habit of taking squat into account when calculating under-keel clearance (UKC) for departure from Greenock. Prior to the casualty, Seatruck Performance was making 14.5 knots, a speed that would add about 1.4 meters to her 5.5 meters of static draft. This left an insufficient UKC of just 0.1 meters. In addition, the vessel likely experienced bow cushion effect near the channel's edge, which would have contributed to uncertain handling characteristics in the maneuvers leading up to the grounding.
The MAIB concluded that the ferry grounded as a result of its heading being altered later than intended. In addition, the investigation found that:
- Bow-cushion and other shallow water effects were experienced as the ferry approached the intended turn, which affected heading and speed;
- The potential for squat was not considered when calculating the ferry’s under keel clearance before departure;
- The late initiation of the turn resulted from the newly promoted master’s nervousness and/or lack of confidence; and
- The master was steering by hand, which reduced his ability to maintain an overview of the situation, and a lack of support from the bridge team made him a single point of failure.