Installation and Removal

The advantage of buoyant designs is that they can be floated into place, removing the need for craneage and barges which are impractical anyway in the tidal flows found in the Pentland Firth. With the SST concept no cranes, barges or jack-up rigs are required for any part of the operation - only a workboat with moderate lift capabilities.

For installation, the swinging arm of the SST is stowed against the main spar buoy so that the turbine can be towed into position with minimum draft. The spar buoy comprising the main body of the SST is at full buoyancy for float-out. The base in the images below has been pre-installed on the seabed and is marked by a guide wire and buoy.

The workboat tows the SST into position at near to slack water, into the prevailing flow.

The gravity base has been pre-installed with electrical cables in place. This base is either a piled structure or, if as in the Pentland Firth the seabed is too rocky to allow this, a gravity base consisting of a flooded concrete chamber - as shown here - or a tray that is filled with rock ballast once in position. The base is equipped with a stabbing guide to accept the swivel ring at the end of the SST swinging arm.

The swinging arm is lowered down the guide wire and electrical cabling (not shown).

The swivel ring fits over the stabbing guide and is locked in place. The SST swing arm is locked and the cable connections made. The SST is now in its maintenance position and ready for first stage commissioning.

For the SST to assume its operating position, water is let into the main spar buoy. As the SST sinks, it starts to roll over ...

Finally, the SST ends up its operating position. With the rotors stopped and only static thrust on them, the SST rides a few metres higher than it does when running and with full thrust on the rotors (see below):

Removal of the SST is carried out by reversing the steps above.