Stunning acrobatic engineering wowed Auckland

An anxious moment in December, 1958, as the 'Pick-a-Back' span is added to the bridge. Photo / Herald file

As Aucklanders were wowed by a feat of stunning engineering acrobatics on Waitemata Harbour towards Christmas 1958, block newspaper advertising was soliciting their cash.

"Red letter day for Auckland - 100-year-old dream comes true," declared the Auckland Harbour Bridge Authority in a call for subscribers to its latest issue of bonds to pay for the region's boldest infrastructure project.

"Here is your opportunity to invest in one of the world's great engineering projects and to see it come to completion before your eyes."

It was December 1, less than five months before opening day for the 1020m steel arc sprawling across the harbour that would change the face - and pace - of Auckland.

The half-page Monday morning Herald ad was timed to mark the end of the trickiest part of the four-year construction, throughout which tides and weather tested the endurance of the more than 1000 bridge builders.

But out on the Waitemata, high drama had unfolded throughout Sunday, when 30-knot (55km/h) winds blew up in the midst of a marathon operation using rising and falling tides to "float-in" the largest span of the bridge, on the back of a smaller span perched in turn on four large pontoons.

The so-called "Pick-a-Back" span, 177m long and weighing 1220 tonnes, had been built astride three others, which British engineers Cleveland Bridge and Dorman Long had already fixed to their permanent piers by cantilevering them out from Westhaven on giant trestles.

Deepening water towards the harbour's northern navigation channel called for fewer and larger piers, requiring a span too long to cantilever, which would therefore have to be manoeuvred into place after being assembled like a giant Meccano set from steel members prefabricated in Britain.

There was nothing new about the technique in principle, and project manager Wilf Cardno had been in a similar operation in Portugal.

But using the central smaller span of 61m to carry the Pick-a-Back to its permanent position was a breathtaking improvisation.

Although the precarious-looking assemblage was carried out to a temporary mooring on the Saturday, seven tugs were needed to hold the pontoons secure against the gale-force winds the next day, and completion of the final move had to be delayed until after the bridge authority's pre-arranged victory declaration.

Despite early criticism of the aesthetics of the bridge's skewed shape, which were dictated by the northern location of the navigation channel and the need to span that from both sides with 244m of cantilevered sections, it was considered a fairly standard design of its day.

Derogatory comments about its appearance eased once it was complete and it could be viewed against its natural setting, although saddling it on each side with the world-pioneering clip-on additions in 1969 stirred up public opinion anew.

The builders struck major difficulties sinking the southern anchorage into reclaimed land at Westhaven, after under-estimating the number of boulders to be blasted out of the harbour bed, taking two years instead of a forecast nine months.

On the other hand, the quality of rock beneath the harbour floor proved higher than expected, leaving the bridge's six piers strong enough to support the future clip-ons as well as their original payload.

Local contracting firms were meanwhile flat out filling in Sulphur Beach for toll plazas and a 300m concrete viaduct sweeping over Northcote Pt to the bridge.

Setting aside disappointment that the bridge had been slimmed down from an earlier design, the Weekly News was able, by late 1958, to report that, "as compared with another pressing need - a new jet-age airport - it is a solid reality, not a controversial will o' the wisp".