Take a look at a video with an explanation on how a Spar is transported and installed.
A spar is a type of floating oil platform typically used in very deep waters
A spar platform consists of a large-diameter, single vertical cylinder supporting a deck. The cylinder is weighted at the bottom by a chamber filled with a material that is denser than water to lower the center of gravity of the platform and provide stability. Spars are anchored to the seabed by way of a spread mooring system with either a chain-wire-chain or chain-polyester-chain composition.
March 8, 2013; Image: Technip