Bank effect eyed in $29.5 million tanker strike on pier

Bow Triumph at the Odfjell Terminal in Charleston on September 8, 2022, showing damage to the vessel’s starboard side.[Photograph: U.S] Coast Guard]

The “bank effect” was in play when the 49,662 dwt tanker Bow Triumph, operated by Odfjell Management, struck a 300-foot section of pier at Joint Base Charleston’s Naval Weapons Station in South Carolina, on September 5, 2022, the National Transportation Safety Board reports. The contact resulted in $29.5 million in damages. No pollution or injuries were reported.

Damage to the 600-foot Bow Triumph included a punctured bulbous bow and damage to side shell, frames, and stringers in way of the forepeak ballast tank and the no.1 starboard ballast tank, which compromised the watertight integrity of the hull. A September 7, 2022, diver survey report noted small areas on the keel, port of the centerline, where there was no marine growth and the hull plate coating (paint) was missing. The total cost of repairs was estimated at $2,459,570. The cost to demolish and reconstruct the damaged portion of the pier was estimated at more than $27 million.

“On September 5, 2022, after having finished discharging cargo at the INEOS Aromatics Terminal in Wando, South Carolina, the Bow Triumph prepared to depart,” says the NTSB report. “A Charleston Branch Pilots Association (CBPA) pilot came aboard the vessel at 1518, and the CBPA pilot and master conducted their exchange at 1520. During the exchange, the master informed the CBPA pilot that there were no deficiencies with the vessel’s propulsion, machinery, steering, or navigation systems.

“About 1528, the Bow Triumph got underway on the Cooper River with the CBPA pilot, a docking pilot, and a crew of 24, en route to the Odfjell Terminal, 6.7 miles down the Cooper River, to discharge additional cargo. The docking pilot and the tugs Jeffrey McAllister and Capt. Jim McAllister assisted in the undocking, and then the docking pilot released the tugs. The vessel’s deepest draft was 27.6 feet at the stern.

“​After making a right turn onto Range D of the channel, the pilot maneuvered the vessel closer to the left bank as he approached the next turn, a left turn around a bend. The maneuver caused the vessel to experience bank effect—when a ship’s bow is pushed away from the bank and the stern is pulled toward the bank while transiting in confined waters. The pilot’s subsequent rudder and engine orders could not overcome the bank effect, and the tanker struck the pier, which was on the opposite side of the river.”

BANK EFFECT

In its analysis of the incident, the full NTSB report notes:

“When the pilot maneuvered the Bow Triumph closer to the left bank while approaching the turn, the vessel was susceptible to bank effect. Bank effect is experienced by ships maneuvering in confined waters (e.g., close to a canal bank, riverbank, or shoal). While making headway, water flow down the side of a ship creates positive pressure forward of the pivot point and negative pressure aft. In a channel, the resultant forces can attract a ship’s stern toward the bank (bank suction) and yaw the bow away from the bank (bank cushion). Though bank effect is often experienced in waterways with steeply sided banks, The Shiphandler’s Guide explains: ‘To a ship running in shallow water, with adjacent but gently shelving mud or sand banks, such as low-lying estuarial areas … the effect can be far more insidious and violent.’ Generally, the faster the ship sails, the greater the suction at the stern.

“Hydrodynamic forces reduce rudder effectiv​eness (squat and shallow water effect) and yaw the bow away from the closest bank and pull the stern in (bank effect),” the report said. “When maneuvering in shallow waters such as channels, shoaling can reduce the water depth below charted or expected, and therefore exacerbate the forces on a vessel. Bank effect can have an undesired effect on vessels, even for the most experienced shiphandlers. Pilots, masters, and other vessel operators should consider the risks in areas known for shoaling when planning transits.”

The NTSB also is investigating a Jan. 14 contact between the tanker Hafnia Amessi and Pier B after the tanker attempted the same turn at the bend. That investigation is ongoing.

PROBABLE CAUSE

The National Transportation Safety Board determines that the probable cause of the contact of the Bow Triumph with Naval Weapons Station Pier B 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.

LESSONS LEARNED

Planning for hydrodynamic forces in areas subject to shoaling: Hydrodynamic forces reduce rudder effectiveness (squat and shallow water effect) and yaw the bow away from the closest bank and pull the stern in (bank effect). Shoaling can reduce the water depth in shallow waters, such as channels, below the charted or expected depth, and therefore exacerbate the forces on a vessel. Bank effect can have an undesired effect on vessels, even for the most experienced shiphandlers. Pilots, masters, and other vessel operators should consider the risks in areas known for shoaling when planning transits.

• Download the full NTSB report HERE