James Fisher Strainstall (United Kingdom) - James Fisher Strainstall (JF Strainstall) was selected to provide a subsea load monitoring solution for the O2 tidal turbine, which was recently constructed by Orbital Marine Power (OMP) and deployed off Orkney, Scotland. 

Weighing 680 tonnes and measuring 72m in length, the floating structure stands to be the most powerful of its kind in the world, with the ability to meet the electricity demands of 2,000 homes over the next 15 years. Following construction, the tidal turbine has since been established in an environment that holds some of the strongest tidal currents in the world.

The challenge:

• The subsea load monitoring pins provided by JF Strainstall had to function within the turbine’s splash zone area, in addition to being capable of withstanding temporary immersion.
• Due to the deployment arms of the turbines rotating around the axis of the load pins, JF Strainstall needed to ensure the pins could provide a wide, 90-degree range of angular movement.
• The load pins had to monitor both pushing and pulling forces in order to match the current’s changing direction.
• OMP required independent monitoring of the forces acting on each end of the load pins. This presented a particular challenge, in that the clevis joint they were designed to fit in had a total of five areas of contact, as opposed to the usual three.

The solution:

• The load pins provided by JF Strainstall were both XY and bi-directional, meaning they were capable of measuring the forces acting on the pins in a positive and negative polarity, in two independent planes of direction.
• Although the total length of a single load pin was just over 1.8m long, each was designed to effectively be two independent load pins, both sharing the same physical, high tensile stainless steel housing.
• Both of the load pins provided by JF Strainstall had a total of four independent, internal Wheatstone bridges, each of which was connected to an internal amplifier, providing a 4-20 mA analogue signal back to OMP’s control system.

The results and benefits:

• JF Strainstall supplied two subsea load monitoring pins capable of measuring forces up to 350 tonnes, which were positioned at the joint between the main structure and the turbine deployment arms.
• Due the load pins being bi-directional, OMP was able to calculate the resultant force acting on the structure alongside the changing tidal currents, while still allowing the turbine to remain in operation.
• The O2 tidal turbine stands to provide homes with predictable, clean power by harnessing the tidal stream in order to help combat climate change.