Docking device enhances efficiency and safety during transfers

One of the focus areas of the OWA is to improve operational efficiencies and advance technologies that enhance the accessibility and availability of offshore wind turbines. Enhancing the transfer of windfarm technicians from crew transfer vessels (CTVs) to offshore wind turbines – making that process safer, more efficient and less expensive – is one such focus and a process that could be significantly enhanced by equipment developed by UK-based Offshore Transfer Devices (OTD).

In early September 2024, OTD conducted a demonstration using its Tube Docking Device (TDD) at RWE’s Rhyl Flats windfarm in conditions that saw a maximum of 1.5 m wave height. The demonstration was a culmination of an ‘innovator support project’ delivered through the OWA programme. That project supported OTD in installing and testing the TDD onboard a 15-m South Boats CTV, as well as in designing and installing an integrated personnel access platform for technician transfer. 

The demonstration was attended by several members of the OWA’s logistics and O&M technical working group, including RWE, Scottish Power, Vattenfall and Ørsted, as well as Pelergy and Chartwell Marine, the designer and developer of the bespoke TDD personnel gangway.

The demonstration, undertaken in changeable conditions, highlighted the stability that the TDD can provide for technician transfer, with several successful approach and push on procedures being performed. 

Carbon Trust manager programmes and innovation Alistair Morris said, “Despite the conditions – which were above the operational limit for the vessel using a conventional fender arrangement – once pushed on using the TDD there was minimal movement along the ladder rung. 

“The vessel was able to maintain a stable platform, negating any possible slips and unpredictability with the conditions. During this demonstration, the vessel reduced its propulsion power by up to 50% while maintaining a continuous grip, which reduces CO2 emissions for prolonged push on activities.” Ahead of the demonstration, and as part of the project, the device was tested during an earlier trial period at Rhyl Flats Windfarm. The vessel and its integrated personnel access system allowed for push on tests maintaining a stable platform in conditions of up to 2 m Hs.

The TDD is a light, compact device used to effectively stabilize, pin and grip the transfer position to a structure offshore. It will also cushion and protect both device, vessel and structure in greater wave height in challenging adverse weather conditions. 

In operation, the TDD goes through a primary phase where the jaws take the shape of the cylindrical fender tube. This is shortly followed by a secondary phase known as ‘thrust-out,’ a combined dampened stroke of 750 cm enabled by hydraulic rams and accumulators.

The TDD can deploy onto a tube on the foundation of an offshore wind turbine whilst the vessel is simultaneously in a roll, pitching and off centre, whilst addressing all six motions of freedom – heave, pitch, roll, yaw, sway and surge. Conversely, due to mechanical advantage a vessel can obtain a higher level of grip with a proportionally reduced amount of propulsion, thus minimizing pushing force required to maintain a stable platform against offshore structures.

An additional, optional, hydraulic assistance mode can be implemented, which operates in a similar mode to applying a brake pedal of a car. This optional ability to add clamping will also allow substitution or minimal propulsion, enabling transfers to light anchored structures such as floating LiDAR’s, anchored barges or jack-up vessels. This optional ability, whilst using little or no propulsion, also enables transfers in adverse weather conditions to ships under dynamic positioning (DP), when CTVs and other windfarm support vessels push on with minimal propulsion as it can upset the mathematical model of the DP vessel. Another key feature of the system is the ability to alter the lateral position without disengagement. This can be achieved by reducing forward propulsion and re-applying when at the desired height, enabling clamping with its RG Seasight-Fenders.

OTD said the priority throughout the development process was to make the TDD fail-safe, ensuring that the risk of mechanical entanglement to any offshore structure is completely mitigated. The key features required from the design and model testing work undertaken earlier in the development of the TTD were to create a simple and lightweight device which can effectively stabilize, pin and grip the transfer position. Offshore Transfer Devices and Hercules Hydraulics created a cushioned approach which will minimize impact loads and offer protection to the device, vessel and offshore structures.

The OWA partners believe that the TDD ‘holds significant potential’ to benefit larger and smaller craft by increasing safety and operability for personnel transfer as well as increasing weather windows. And, in addition to enhancing safety and operability, the TDD also offers fuel savings, which could be of significant benefit not only to conventional vessels, but to electrified CTVs in the future. 

Pelergy spokesperson Mike Newman said the offshore trials with the TTD were ‘a huge milestone.’ “It isn’t easy taking technology to market in offshore wind, especially when you are a startup on a tight budget. The next steps for us are to work on immediate opportunities for commercial delivery and build-to-order of the TDD.”

“The TDD’s successful design, installation and testing demonstrates the importance of supporting innovation. The funding provided by the OWA has allowed for TDD to reach a major milestone in its development and has demonstrated its potential to change offshore wind access for the future,” the OWA concluded.