Statoil’s oil transport studyStorting approves Statfjord B and C

First attempt at a tow

person By Trude Meland, Norwegian Petroleum Museum
Work on building and outfitting the concrete gravity base structure (GBS) for Statfjord A was completed in the Gands Fjord during the early summer of 1976. Preparations then began to tow the colossus to Digernessundet near Stord further up the coast, where it was to be mated with the topside under construction at Aker’s Stord Verft yard.
— Five large tugs at the front with full propeller force, pushed large amounts of water backwards, towards the cell structure and created a strong countercurrent. Photo: Unknown/Norwegian Petroleum Museum
© Norsk Oljemuseum

To prepare for the tow, the GBS was raised by deballasting the concrete cells until it floated stably with the cell domes above water. The mooring lines were cut, the towing hawsers attached, and the five large tugs could set off.

This operation began on 2 June, in ideal weather for a controlled tow across the open Bokna Fjord north of Stavanger. When the voyage began, however, the GBS sheared off to one side and became unmanageable. Fortunately, the crew succeeded in avoiding a collision with the eastern side of the fjord.[REMOVE]Fotnote: Lavik, Håkon. Statfjord. The largest oilfield in the North Sea . Stavanger 1997, p 28.

The only option was to shut off the engines and re-moor the GBS, while detailed efforts were launched to understand what had happened.

It turned out that several factors made the tow impossible. The GBS had been deballasted until the tops of its storage cells were out of the water, and resistance at the surface was too high when the tow started.

In addition, the five big tugs ahead of the structure were running their propellers at full revolutions. That pushed large masses of water backwards against the cells and created a strong counter-current. As a result, the forces balanced each other out and the GBS sheared off uncontrollably.

The solution was to lengthen the towing lines and obtain more powerful tugs. That job accordingly had to wait until the Brent D GBS had been towed to Vats in order to use the same vessels.[REMOVE]Fotnote: Status 1976 no.10, p 1. Tauingen av Statfjord A utsatt til august.  This delay was used for further work on mechanical outfitting of the shafts.

By then, everyone working for Aker on the A platform’s shafts had been sent home. The job in the Gands Fjord was over – they thought. But when it became clear that the GBS would be remaining where it was for a while, those who had not started new jobs were recalled.

The work was already delayed, so the time could just be used to complete the GBS.[REMOVE]Fotnote: Interview with Svein Jørpeland by Trude Meland, Norwegian Petroleum Museum. Six weeks later, everything was ready for a second attempt.

Statoil’s oil transport studyStorting approves Statfjord B and C
Published November 12, 2019   •   Updated December 11, 2019
© Norsk Oljemuseum
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