Two container cranes tower over the marshes and estuaries of the northern Bay area in California. The bright white structures have now dominated the little shipyards and townships along the picturesque coast for 14 months.

“So much so,” says Phil Reed, California manager for Spantec Constructors, which has been assembling them, “that the first site we found for erecting them was refused us. Local town ordinances forbade high structures, even temporary ones.” The two 61m-high cranes are temporary enough, being due for transport this month about 10km downstream to the US navy base, Concord. There they will have the rather special function of loading and unloading ammunition into hillside bunkers. The 45m-long booms carry interchangeable lifting carriages for the purpose.

“Clearly we could not have built the cranes in situ,” says Reed, “because of safety and security problems.” Quite apart from obtaining security clearances for the steelworkers there would have been endless pauses in the work whenever high explosives had to be moved around.

Fortunately at Antioch on the San Joaquim river estuary, alongside the Sacramento river, Spantec was able to find an unused boatyard big enough for the work and, crucially, far enough down river for there to be no bridges in between the yard and the naval facility. The Fulton yard was big enough to stack the various components of the cranes as they arrived in bargeloads from IMPSA’s factory in Mendoza, Argentina.

“The US Navy tenders worldwide for products and IMPSA International won the design and manufacture contract,” says Reed. The order was for three 1,500kW cranes in total, though the third crane was for another location.

The assembly contract for the Concord pair was let to Spantec, which is a wholly owned subsidiary of the Canadian consultancy and project management group UMA. Assembly was carried out with a team of 32 steelfixers (or ironworkers, as they are called in the USA) and 10 electricians. Site superintendent Paul Becom said hanging on to men for the work was difficult as there are a number of major steel contracts going on in the area, not least the retrofitting of the Golden Gate bridge to protect it against earthquakes.

Manitwoc M250 lattice boom crawler cranes were used for the bigger lifts which were up to 150t for the back boom. “In fact we strand-jacked the back reach girder at one end and tailed it with the cranes,” says Becom.

Main boom elements weighed up to 90t. Components were bolted, though smaller items like guard railing were welded on. One complication for assembly and later delivery was in the uneven leg lengths for the cranes which run on rail tracks with a 1m difference on the hillside within the base.

The two complete cranes will now be skidded sideways on the rails across the hardwood Ekki timber flooring used as a working platform, and onto barges manufactured by transport subcontractor ETALCO. The firm will roll the cranes forwards by winching at the Concord base.

The upright, fully assembled, travel status of the cranes accounts for the need to find a yard downstream of any bridges. A high trestle crosses the Joaquim just 1km upstream, so that had ruled out any yards in that direction.

Delivery was initially due in February after proving tests on the cranes but had been delayed until the end of March as Cranes Today went to press, because of control modifications requested by the Navy.