Shanghai Zhenhua Port Machinery Co Ltd (ZPMC) has delivered four super-sized quayside container cranes to the Port of Oakland, California.

Each crane costs USD7 million, including delivery, and can handle new-generation ships with cargo berths 22 containers wide. For example, ships traversing the Panama Canal can only carry cargo up to 13 containers wide.

One of ZPMC's five specially-converted cargo ships, the Zhen Hua 4, left on May 20 from Shanghai, China, to deliver the cranes. On June 14, it proceeded at low tide under the Golden Gate Bridge with 10 feet (3.3 metres) to spare and the San Francisco-Oakland Bay Bridge with a margin of three feet (one metre).

The cranes' booms were lowered to 220 feet (66 metres) to fit under the bridges. The booms usually measure 365 feet (109.5 metres) high during cargo operations and during the trans-Pacific journey.

Each crane weighs about 1,200 tonnes, can lift 145,600 pounds (66 tonnes) at a time and can load or unload more than 30 containers an hour. Hoisting speed is 230 feet per minute.

Over the past week, the super-Panamax cranes were offloaded at the new Stevedoring Services of America terminal at Oakland. ZPMC will complete installation by mid-July.

In May, ZPMC delivered four large cranes to Oakland, two for Stevedoring Services and two for Transbay Container terminal. Last October, four others were delivered to the Hanjin terminal.

Shares in ZPMC, which has net assets of about USD220 million, trade on the Shanghai Stock Exchange. ZPMC makes rubber-tyred gantry cranes, bulk-material ship loaders and specialised stackers, reclaimers, vessels and steel bridges, in addition to quayside container cranes.

The Port of Oakland, established in 1927, operates as an independent department of the City of Oakland. The port employs 600 people, has responsibility for 19 miles (30 kilometres) of shoreline, and is the fourth-largest container port in the USA.

"We're creating the infrastructure needed to accommodate increased cargo shipping demands anticipated regionally and globally," Port of Oakland executive director Tay Yoshitani said.

The port installed its first container crane in the 1960s.

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