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Offshore piles on the straight and narrow

Demand for pile driving accuracy on the latest offshore wind developments has led Fugro to develop a system, called the Inclino Cam, designed to safely check the verticality of piles during installation.

“The need to measure verticality of wind turbines starts with the foundation,” explains Fugro Survey positioning and remote services manager Dieuwertje Smallenburg. “Most offshore wind turbines are founded on monopiles that typically measure 70m in length with a diameter of 6.5m and weigh in at around 850t. These monopiles are driven into the sea floor using a hydraulic hammer - a process which can take several hours - so verticality is a key requirement but difficult to achieve or measure.

“Previously inclinations of 1º were tolerated, but with the increasing size and developing technology 0.25º is now generally used as maximum tolerated inclination.”

According to Smallenburg, the conventional way to check the verticality is with a handheld inclinometer, but the irregularity of the outer pile surface may affect the accuracy of the results, so multiple measurements are needed to ensure the reading is accurate.

“This causes delays in the piling operations as the hammering has to stop for the measurement and processing of the information for the crane and hammer operators,” he says. “There are also health and safety issues associated with the manual measurement.”

Fugro’s Inclino Cam system is based on intelligent visual object recognition combined with vessel motion compensation.

Two high-resolution cameras are placed at an angle pointing towards the monopile to measure the inclination in two directions and to compensate for vessel movement the cameras are connected to inertial motion units (IMU).

The camera images and IMU data are synchronised using Fugro’s Star Port technology and processed by its Starfix.NG navigation software to give a visual display of the verticality during the driving process.

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