QED Naval returned to Subhub following the completion of the tow on a cold but bright winter’s morning to tidy things up and secure Subhub for the initial ballast system and flow augmentation trials.
The moorings were re-set so that Subhub now aligns to flow on the flood and ebb tides where flow speeds of up to 1m/s are experienced which is ideal for conducting the initial ballast system trials.
Some of the marker buoys were reset and the umbilical and operations tether unraveled and stretched out. The umbilical allows the remote control of the Subhub platform from the support vessel which is a barge in this case.
The video below you can see the umbilicals are tough outer pipe used to protect all the service lines to operate the Subhub remotely. The service lines are further protected by bundling them into a tough PE coating . The service lines include:
- Hydraulic lines to control the seawater inlet and tank vent valves;
- Low pressure air to pressurise the tanks to deballast all the seawater which provide the required on-bottom weight to overcome all the wave and tidal forces;
- Data/coms cable for monitoring the Subhub and control the operational condition of the Subhub;
- Main export power cable.
The umbilicals are connected into the Subsea Manifold which is an subsea junction box so when the Subhub is installed all the services can be disconnect from the support vessel housing the air compressors, HPU, generators and control panels. It can then be lowered to the seabed so the support vessel can demobilised and site cleared of any visual impact. Equally, the Subsea Manifold can be easily retrieved and the systems connected up to take control of the Subhub again.
The video below also shows the final action of the day which was to make some modifications to tidal turbines. Supported by Cuan Marine’s small multicat, Cuan Cat, it made for easy access to the tidal turbines.