Hybrid riser tower and method of installation thereof

A method of installing a subsea structure, such as a hybrid riser tower, is disclosed. The riser tower includes a main portion and a buoyancy portion. When installed, the riser tower extends substantially from the seabed towards the surface with the buoyancy portion attached at a top end. The method includes taking the riser tower to an installation site in a substantially horizontal configuration with the main portion containing a first fluid and the buoyancy portion containing a second fluid, the second fluid being more dense than the first fluid. Then, tilting of the riser tower is performed such that it takes a substantially vertical configuration by allowing the first fluid in the elongate portion to interchange with the second fluid in the buoyancy portion. Also disclosed is a suitable apparatus for performing the method.