Knud E Hansen has developed a new design for an offshore wind turbine maintenance vessel, known as the “Jack-up on Jack-up” concept, according to the company's Sept. 3 news release.

The 154-m-long, 64.4-m-wide, four-legged jackup vessel is designed for all types of maintenance on wind turbines up to 20 MW, including replacement and handling of nacelles weighing up to 1,000 t at a hub height of 175 m, and managing blades up to 130 m long.

All tasks can be performed while the vessel is jacked up in up to 80 m water depth. Its 15-m-wide working area can be elevated to the height of the nacelle, providing a stable platform for maintenance of blades and dispensing with the need for hazardous rope access.

A telescopic weather cover fitted on the platform allows work on the blades to be performed in most types of weather conditions, day or night.

This should enable more working hours per year than with conventional maintenance vessels and rope access, the company added, facilitating a reliable schedule for planned maintenance.

A large, air-conditioned workshop is at the aft end of the work platform. When the weather cover needs to be in use, a “virtual” factory hall can be created around the blade, so various types of work can be conducted on the blade.

This reduces the need to remove the blades and transport them to shore for repair. There also is potential to insert an X-Y motion compensating system between the work platform and the platform carriers, so the “factory hall” can remain geostationary.

A “cherry picker” located on a hammer head at the platform’s opposite end provides access to the nacelle.

The main crane is fitted on the elevating structure; this is said to allow for use of a conventional pedestal-mounted crane with a boom roughly 30% shorter than on a conventional wind turbine maintenance vessel, while reaching the same height.

This arrangement provides an improved view of the blades and the nacelle from the crane driver’s cabin, the company claims.

Two crew access vessels are secured in davits on the aft deck. A retractable boat landing can reach the water when the vessel is jacked up, allowing the vessel to also serve as a mother ship for crew transfer vessels working in the area.