In 62 hours of rigorous offshore testing, tech scale-up Seaqualize completed trials for its inline Active Heave Compensator (iAHC), the Delta600. Together with partners Van Oord and research institute MARIN, the offshore lifting tool was tested for fixed-to-floating, floating-to-fixed and floating-to-floating transfers of 300-mT loads.

Since December 2019, Seaqualize has been developing the world’s first iAHC: a tool specifically designed for heavy lift, in-air load control. The tool can balance and transfer loads of up to 600 mT in mid-air, while the barge or crane vessel is heaving up and down in heavy seas with a significant wave height (Hs) of up to 2.5 metres.

This functionality is of great benefit during offshore wind turbine installations or when lifting delicate loads to and from floating supply vessels or barges. By engaging the Delta, operational time greatly increases, especially in the hard-to-work winter, autumn or spring seasons. It offers contractors greater planning flexibility, and lifting crew a higher level of control, safety and efficiency.

Also read: Seaqualize tool helps floating ships to install wind turbines in deep water

Trials with Aeolus

During the offshore trials, the Delta600 lifted a test weight to and from the floating supply vessel Rem Trader, using Van Oord’s jack-up crane vessel Aeolus in both jacked and floating conditions. These floating-to-floating and floating-to-fixed lifts were operational tests of typical challenges in the offshore wind industry: installing turbine components using a floating vessel, or picking up components from a floating supply vessel.

Such “feeder barge” operations are essential in for example the US wind market. Transferring the most delicate parts of a wind turbine offshore is new to the market, and such operations comprise demanding lifting conditions and a new set of tools. According to Van Oord the tests have shown the Delta600 allows for controlled offshore lifts during challenging feeder barge operations.

Also read: Van Oord orders methanol-powered mega ship to install 20-MW wind turbines

Compensating waves and heave motions

During the tests, several very gentle set downs and quick lift-offs have been performed. MARIN observed that the tool is able to control the load within an envelope of 5 cm, with minimal accelerations and dynamic crane forces.

Lift-offs where performed with a solid ninety per cent of the load already in the hook of the crane before lift-off, while still fully compensating all waves. This significantly reduces impact loads on the load, crane and rigging and results in a controlled and stable lift-off.

Finally, the tool showed off its “follow-mode”, where the test weight could actively match all heave motions of the target vessel, to further minimise set-down impact for floating to floating set downs.

This offshore trial was also the last step in full DNV product certification as a standard offshore lifting tool. The research project was executed with a grant from the Ministry of Economic affairs of the Netherlands, and included Dutch research agency TNO besides the offshore testing partners MARIN, Van Oord Offshore Wind and Seaqualize.


600 mT lifting may seem like a lot, but offshore wind turbine sizes are growing explosively, thus requiring ever bigger lifting tools for still very delicate components. Currently, Seaqualize is designing the next version, the Delta1000, equipped for all next generation wind turbine components.

Further conceptual improvements include the addition of single lifting points for quick-connect systems, and smart controlled tugger winches for supreme control in the horizontal plane. At the same time, the company will further develop its offshore operational support capabilities, by deploying the Delta600 in the field.