Engineers and managers at Tacoma Narrows Constructors were still puzzling Saturday over how they could have been so wrong about the height of the first shipload of deck sections for the new bridge.
The bridge builders expected the ocean transport vessel the Swan to slide under the side span of the existing Narrows bridge Friday with 36 feet to spare. Instead, the top of the load grazed the underside of the bridge deck, forcing the ship to turn around and return to Commencement Bay.
The problem and the solution are simple, said Erin Hunter, a TNC spokeswoman: The ship was riding too high in the water and ballast needs to be added to lower it.
What is not so simple, she said, is how engineers were so far off the first time.
“What we’re looking for is, where was the disconnect?” she said. “We’re evaluating the situation so it doesn’t happen again. We’re taking all the measurements and calculations and reassessing and recalculating them. We’re checking everything and then double-checking it and then checking it again.”
Hunter said no damage was done, either to the bridge or the new deck sections. And she said the mishap will not affect the lifting schedule, because the loaded ship was to stay under the existing bridge for several days before lifting began.
No date has yet been set for the next attempt to bring the ship into the Narrows, Hunter said.
The lifting operation is expected to begin within the first two weeks of July.