Keel laid for ground-breaking offshore installation vessel

The shipowner said the keel was laid “weeks ahead of schedule” and prefabricated blocks are now coming together for assembly in the drydock at the yard. A steel cutting ceremony for the vessel took place on 1 March 2019.

Offshore Heavy Transport’s (OHT’s) chief executive Torgeir Ramstad said the company’s customers have described the new vessel as “ground-breaking.”

The Alfa Lift design vessel will be the largest and among the most innovative, custom-built installation vessels for the offshore wind industry and is due to be delivered early in 2021. The next major milestone will be the launching ceremony, planned for March 2020.

Compared with a jack-up or a floating vessel, an installation vessel that can submerge like a semi-submersible heavy lift ship of the type that OHT is used to operating has important advantages.

These include being able to submerge to reduce motions and increased workability in installation mode. Submerging also provides the vessel with a secondary role as a heavy transport vessel capable of transporting heavy modules, jack-ups and other cargoes.

The key to the concept is the fact that a submersible vessel has better motion characteristics when submerged than a typical monohull vessel. When the vessel is submerged, cargo doesn’t have to pass through the splash zone during lifting operations, which has a positive influence on crane dynamics.

The dynamically-positioned, 48,000-dwt vessel has a 3,000-tonne lifting capacity main crane from Liebherr that matches the future requirements of the offshore wind industry, allowing the vessel to transport and install up to 10 1,500-tonne ultra-large jacket foundations or 11 2,000-tonne XXL monopiles, plus transition pieces for next-generation wind turbines.

It is designed to install components such as the these without submerging, in significant wave heights of up to 2.0 m (Hs 2.0 m). If conditions become more challenging, the vessel can submerge and continue to work in Hs 2.5 m.

Having submerged, the Alfa Lift vessel remains in that state until all foundation installation work is finished, remaining submerged and moving in DP mode to the next foundation. The vessel only comes back to the surface if the weather picks up significantly, or if operations have been completed and a new batch of foundations needs to be loaded in port. In this way, the vessel’s design and operation saves time while also providing a very stable platform.

OWJ’s description of the vessel can be found here.