Tight tolerance for anode lift

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When it comes to wind farm construction, a floating vessel has an advantage over a jackup as it has no need to put its feet down. But despite its efficiency, there are still challenges to overcome.

In fact, a floating-deployment contract meant lift specialist Eager.one had to think again about monopile anode installation. Its established tool, a crane-mounted three-armed spreader with eye-to-eye slings “just wouldn’t work in this situation”, explained commercial director Robert Vaessen.

“The tolerances on this particular design are tight enough that it would have been tricky to lower the anode cage over the monopile, even using a jackup,” he remarked, and added that for a floating vessel “it would be nearly impossible”.

Therefore, the company developed an Anode Cage Installation Aid (ACIA). It’s an interesting piece of kit: the anode cage is sling-fastened to a lowering ring. This moveable hoop is attached to three winches seated on the main frame of the ACIA.

Firstly, slide pads help guide the device into the top of the monopile. At this point the winches get to work; the lowering ring and its load glide from the frame onto the tower, mounting the anode cage like a new wedding band slipping onto a finger – three sets of wheels keep the motion in parallel with (and safely away from) the monopile walls.

Then the lowering ring is retracted leaving the anode cage in place; once it’s returned to the main frame, the ACIA is lifted off and back to the ship for reloading.

The hydraulics, electrics and instrumentation fitted onto the lowering ring are powered via an umbilical winch, but it should be noted that reliability also requires multiple layers of control. For example, cameras and lights give a visual oversight during deployment but the winch readings include an accurate pay-out measurement. Further, while pin-pushers unfasten the eye-to-eye slings, in case of a jam a secondary mechanism can free the rest.

According to Vaessen, its deployment on Van Oord’s Svanen has given rise to interest in alternative versions: for example, adapted designs for specific locations, with investment costs shaved for broader operational tolerances.

By Stevie Knight