Semi-submersible or Column-stabilised Units
Semi-submersible or column-stabilised units have working platforms supported on widely spaced buoyant columns. The columns are normally attached to buoyant lower hulls or pontoons. These units are normally floating types but can be designed to rest on the sea bed, see also 2.2.3.
Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 1, Regulations, June 2013, Lloyd’s Register, Global Standards