Design of a Steel Stop Log Gate and Basin Operations

In February 2011, construction began on the first dry dock to be built in Washington State since 1962. Eight months later, the final piece, a three-part steel stop log gate, was lowered into place, sealing off the 4-acre basin from the waters of Grays Harbor in Aberdeen, Washington. This massive, stop log gate spans 33.5 meters (110 feet), is 9.1 meters (30 feet) tall and weighs 130 tonnes (300 kips). Most dry docks utilize floating gates to seal the basins, but these large structures take hours to remove and require the use of tug boats and a local mooring site when not in use. They also need a ballast management and transfer system to raise and lower them as needed. In contrast, the three-piece steel stop log gate can be removed or installed in under two hours. The steel gate was designed in separate sections to allow a 300-ton crane on shore to install and remove the segments. This paper will focus on the specific design and construction challenges encountered with the steel gate.