The Port of Motril has confirmed that the oil platform just in sight off our coast is one that is on its way to Almería from Algeciras.
It’s probably being towed but the vessels that are doing it are too low on the horizon to be seen (hull down).
It appears to be from the photo a semi-submersible, which is a fully-floating rig, They can be set up in up to 2,500 metres of water depth but normally anchored over the chosen location at about 1,500 metres. If the water is deeper, then they use directional thruster working on GPS and Sonar Beacons to maintain station.
These Mobile Offshore Drilling Units (MODUs) are called Semi-Subs because they have a large ballast structure beneath them that can be filled or emptied to elevate or lower the structure. When they are being moved, as in the case of the above photo, the ballast is pumped out to get the rig as far as possible out of the water to reduce hull drag.
Once they reach their destination, the ballast tanks are filled, which gives greater stability to the structure and makes them less prone to wave action – the lower the centre of mass is below the centre of buoyancy; the greater the stability of the platform.
(News: Costa Tropical, Granada, Andalucia)