Incorrect lineup leads to tug damaging bridge's fender system in Tacoma, Washington

The deteriorated fender system protecting the Hylebos Bridge in Tacoma, Washington, was damaged beyond repair last October after being struck by a tug assisting an articulated tug and barge (ATB).

The National Transportation Safety Board (NTSB) said in its recently released marine investigation report that the captain of the ATB did not line up the vessel correctly to safely transit underneath the bridge.

The tug Olympic Scout was assisting the ATB Montlake/Sodo as it transited outbound on the Hylebos Waterway in Tacoma, Washington on October 12, 2023. Montlake/Sodo’s captain requested the Hylebos Bridge operator open the bridge.

While waiting for the Hylebos Bridge to open, the ATB had to pause, and the bow drifted from the center of the channel and moved farther to port (the left side of the channel).

The captain steered to starboard, attempting to line up for the bridge, but due to the drag from the tug on the port bow, he was unable to move the ATB to starboard.

​The distance between the bow of Montlake/Sodo and the bridge was 1,276 feet (388.9 metres) when it began the transit of the waterway, and the channel width between the Hylebos Bridge fenders was 150 feet (46 metres).

The combined beam of the 78-foot (24-metre) Montlake/Sodo and the 26-foot (7.9-metre) Olympic Scout was 104 feet (31.7 metres), leaving a maximum clearance of 23 feet (seven metres) on either side of the combined unit.

“Because of the short distance to the bridge and the speed of the ATB, there was insufficient time to correct the lineup before Olympic Scout struck the fender,” investigators concluded. “Given the slim margin of error for making the bridge transit and the short distance to make the approach, slowing or fully stopping the ATB’s forward motion earlier would have provided the operators more time to correct the lineup and successfully transit through the opening between the bridge’s protective fendering.”

The Hylebos Bridge was undamaged following the contact, but the fender system had to be replaced. A marine surveying and consulting firm stated that the damage caused by the contact resulted in significantly more damage being sustained as would have been, had the fendering structure been of sufficient structural strength.

The bridge fender system’s deteriorated condition contributed to the severity of damage, the NTSB said.