On March 16th, 2010, three Super-Post Panamax cranes loaded on the Zhen Hua 15, a specially modified freighter, passed under San Francisco’s Bay Bridge with a clearance of approximately nine feet between the top of the cranes and the underside of the bridge’s middle span. The tops of the cranes were 217 feet above the Bay at time of passage, and are believed to be the tallest shipment to successfully pass under the Bay Bridge.
Port of Oakland Chief Surveyor Dave Murtha depended on Leica Geosystems’ SmartNet North America before and during the passage. SmartNet, launched on March 1st, 2010, is a subscription-based service that uses Leica Geosystems’ GNSS Spider software to offer GNSS Network RTK corrections throughout North America. In the weeks prior to the delivery, Murtha relied on SmartNet and static observations to verify local tidal datum benchmarks and relate them precisely to North American Vertical Datum 1988 (NAVD 88). He also established control points for additional receivers, to be used for real-time kinematic (RTK) surveying during the passage.
On March 16th, Murtha mounted two Leica GNSS receivers on top of the cranes. One used a cell phone modem to link directly to SmartNet and, for redundancy, the other used a spread-spectrum radio modem to link with a Leica Geosystems receiver used as an independent base station. During the passage, both systems worked perfectly and verified each other’s real-time data, providing much appreciated assurance as the Zhen Hua 15 approached the Bay Bridge.
“The elevation measured as we passed under the bridge matched what I had predicted,” said Murtha, “based on the measured crane height, the amount of freeboard, and the predicted tide. The system really came through for us, before and during the transit.”
“SmartNet was built to provide high-precision, high-availability network RTK corrections for any application,” says Wendy Watson, Leica Geosystems’ director of reference station operations, “With the SmartNet network, Leica Geosystems is providing the largest and only North American wide GNSS RTK Network available in the market today, and we’re proud that the Port of Oakland relied on our system for real-time information during a critical, high-pressure day.”
For additional information, please visit: smartnet.leica-geosystems.us/smartnet.html
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