Topside Hollandse Kust (west Alpha) offshore platform ready to start journey to final destination

Today, the ‘sail out’ of the topside for the offshore platform Hollandse Kust (west Alpha) takes place. The steel construction will sail to its final destination about 50 kilometers off the coast of Egmond aan Zee where it will be installed on the jacket foundation.

The steel structure measures 47 meters in length, 35 meters in width, 25 meters in height, and weighs over 3,600 tons. It was built for TenneT by the Equans/Smulders combination.

Almost two years after the first steel cut, the topside was loaded out in the port of Antwerp at the beginning of August. During this relocation, the steel superstructure for TenneT’s ‘socket at sea’ was successfully placed on a floating pontoon.

Green light

“First, the floating pontoon is towed to the port of IJmuiden,” says Matthijs Knollenburg as construction manager on behalf of TenneT. “As soon as all weather conditions give the green light for the installation on the jacket, the pontoon will sail to its final destination at sea. At that time, the crane vessel Thialf of Heerema Marine Contractors is also on its way from the Norwegian port of Stavanger to that location.”


The topside will be placed on the jacket foundation which was installed off the coast of Egmond aan Zee last year. As soon as the two vessels meet at sea, the pontoon moors against the Thialf. “The topside is then ‘loosened’, after which the crane vessel lifts the construction into the air. Once the pontoon has been towed away, the Thialf will sail for another 500 meters towards the jacket. So-called cones are attached to the jacket. You can compare this with inverted ice cream cones with which you can lower the topside exactly in the right place without too much measuring.”


After installation, a hotel barge is placed next to the platform so that the Equans team can start the welding work to fix the topside. Earlier this year, the two sea cables, with which the green electricity from the wind farm will soon come ashore, were already installed by Jan de Nul Group. The ‘socket at sea’ will be ready for commissioning before the end of this year.


In 2025, Ecowende (a joint venture of Shell and Eneco) will place the 54 wind turbines in the offshore wind farm and connect them to TenneT’s ‘socket’. With an installed capacity of approximately 760 megawatts, Ecowende can green approximately 3% of the current Dutch electricity demand. The wind farm is scheduled to be commissioned in 2026. Source: TenneT Images: Crossing Zebra

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