Marinetek North America completed the construction and installation of its floating breakwater for San Francisco's West Harbor Marina project.
The breakwater is at the entrance of the marina basin in San Francisco Harbor and will serve to protect the basin from the heavy seas that commonly roll in from the large fetch of San Francisco Bay.
“The floating breakwater design included some strict wave attenuation and performance specifications,” Marinetek sales director Richard Murray said in a statement. “The Marinetek system must withstand the forces of sustained winds of 85 mph with waves up to 6.7 feet high with a period of 4 seconds.”
The 225-foot-long breakwater is composed of five sections; each measuring 45 feet long, 15 feet wide and 9 feet high overall. The system has a freeboard of 3 feet and a draft of 6 feet. Each section weighs more than 100 tons. Anchoring is accomplished using 1-3/4-inch galvanized steel chains secured to 20 30-inch diameter by 75-foot long submerged steel piles that are driven 72 feet into the seabed.
Using 1,200-pound concrete weights secured to each chain, safely below the waterline and yet remaining above the seabed, helps dampen the loading on the system by creating a catenary in the mooring rode. This also helps maintain accurate positioning of the breakwater and allows for adjustment of the freeboard, which the city required.
Along with the high freeboard, a raised wooden bull-rail was installed around the top perimeter of the floats to inhibit seals from occupying the breakwater. The large pontoons were fabricated in a casting yard 50 miles away in Antioch, Calif., by Marinetek’s mobile production team. Once the floats were adequately cured, they were launched, towed to the site and anchored in place.