A pilot’s navigation error and an unexpected “bank effect” caused a 600-foot-long tanker to hit a pier in South Carolina last September, sending a 300-foot section of the pier crashing into the water and cutting deep gashes in the tanker’s bow, according to a new report from the National Transportation Safety Board.
The accident occurred on the Cooper River, north of Charleston, just after 4 in the afternoon, when the tanker Bow Triumph was heading outbound on the Joint Base Charleston Channel. The tanker had a beam of 105 feet and a draft of 26 feet. The channel was 600 feet wide, and weather was not an issue.
A local pilot made a right turn in the channel and then moved the ship closer to the left bank, preparing for the next turn. But at that point, the bank effect took over, causing the ship’s bow to push away from the bank while drawing the stern toward it.
The pilot tried to use the ship’s 14,521-hp MAN diesel engine to gain control of the ship, but a one-knot current from the flood tide, combined with the bank effect, was more powerful. As he lost control, the pilot ordered the crew to drop the anchor, but it was too late. Less than a minute later, the tanker’s starboard bow hit the pier at a 90-degree angle. The crash caused $27 million worth of damage to the pier, and $2.5 million to the ship.
The NTSB explained that hydrodynamic forces in shallow water can reduce rudder and engine effectiveness, even for experienced captains. The bank effect is when the water flow down the side of the ship creates a positive pressure forward of the pivot point and negative pressure aft; in a channel, it moves the ship’s bow away from the bank and the stern toward it.
For recreational cruising boats, the bank effect can cause problems in narrow portions of the ICW in South Carolina, Georgia and Florida, among other places.
The NTSB says the probable cause of the accident “was the pilot’s decision to maneuver the vessel close to the left bank while approaching the turn immediately before the pier, exposing the tanker to bank effect, which the pilot’s subsequent rudder and engine orders could not overcome.”
Read more: https://www.ntsb.gov/investigations/AccidentReports/Reports/MIR2409.pdf
