Floating installation

To keep a heavy load still, in-air, while the cranehook is heaving up and down, is one of the holy grails of offshore heavy lifting.

Seaqualize offers full Active Heave Control, to be placed independently in any standard lifting crane, and can be combined with XY control. For self-geared vessels on DP, this offers a major workability increase

AHC cranes; not good enough

Our client was looking for a solution to improve the workabiliy for installing transition pieces (TPs) onto monopiles, using their floating heavy lift vessel. The TP's had to keep a steady vertical position, as otherwise the TP flange might slip off the guiding pin that ensures the right rotation of the TP. The active heave functionality of the vessel crane was not accurate and safe enough, so they were looking for a device specifally for this operation. Seaqualize offered that functionality, on a rental basis, and could combine it with feeder functionality in the same operation.

“Got to be one of the best ideas I´ve ever seen in heavy lifting, as complex as these lifts are” - Client lifting supervisor

Our Heave Chief 750, was used to install ~600mt TP's for the installation of TP's on the CVOW project. Based on the internal MRU in our machine, we could keep the TP's still to within max. +/-10cm, usually even within +/- 5cm, even in waves of Hs 2.0m. This way, the crew could keep installing, even in winter conditions from November till March. On this project, passive bumpers were used for horizontal allignment, but on future project, the next generation HC's by Seaqualize, will be able to dampen XY pendulum swing motions as well, making installation even simpler, safer and quicker.

Hundreds of tons easily balanced at +/- 5cm

During the project, we gathered plenty of field data and footage. The below footage and graph shows the peformance during two distinct phases where workability is increased:

1. The approach of a TP towards the MP (Video below)
   Keeping the TP still in vertical direction makes placing of the TP around the MP much easier. The crane operator can concentrate on getting the TP guiding pins against the monopile flange for horizontal alignment.
   
2. Gently placing the TP flange onto the MP flange (graph below)
   When placing the TP flange onto the monopile flange its important to have:
3. • A minimal set down velocity
   • Reduced motions to a minimum to not 'loose' the rotational allignment pins whenever the crane tip moves up again
   • Once contact is made, to 'stick' to the MP, and not lift the TP again.

All these criteria are met: the setdown velocity is reduce to max 7,5 cm/s and the load is always balanced in the tool, so never more contact force than ~0,2G or 0,3G. The motions are kept within the bandwidth of ~+/- 5cm, and once contact is detected, the system automatically keeps contact to make operations much more safe.

Crane hook compensation reduces TP motions to +/- 5cm

The TP is lowered onto the monopile flange, while the waves acting on the crane tip are compensated

Workability can be doubled, especially if XY control is added

Keeping loads this stable can significantly help workability. With heave control only (as done in this case with the Heave Chiefs), operations in heavy seas already run much smoother.
But what if you add XY control on top, such as in our Full-Motion Chiefs? An example of that control can be seen in our prototype, but we also analyse workability with such control for specific locations.

Below you'll see the workability gains for a German North sea location, for a wide range of seastates. Depending on the heading, this gain can be almost double.

Workability is doubled when using heave + XY compensation

Workability analyses for using full-motion compensation on a 800mT floating installation with a DP2 vessel. Using compensation increases workability upto a factor 2.