Changes

===Jackups===

===Jackups===

''Jackups'' are similar to platforms except that the support legs are not permanently attached to the seafloor ([[:file:offshore-rigs_fig2.png|Figure 2]]). The weight of the rig is sufficient to keep it on location. The rig's legs can be jacked down to drill and jacked up to move to a new location. When under tow, a floatation hull buoys the jackup. The derrick is cantilevered over the rear to fit over preset risers if necessary.

''Jackups'' are similar to platforms except that the support legs are not permanently attached to the seafloor ([[:file:offshore-rigs_fig2.png|Figure 2]]). The weight of the rig is sufficient to keep it on location. The rig's legs can be jacked down to drill and jacked up to move to a new location. When under tow, a floatation hull buoys the jackup. The [[derrick]] is cantilevered over the rear to fit over preset risers if necessary.

[[file:offshore-rigs_fig3.png|left|thumb|{{figure number|3}}Semisubmersible rigs, (a) Pontoon type semisubmersible. (b) Twin hull semisubmersible. (From <ref name=pt03r50 />.)]]

[[file:offshore-rigs_fig3.png|left|thumb|{{figure number|3}}Semisubmersible rigs, (a) Pontoon type semisubmersible. (b) Twin hull semisubmersible. (From <ref name=pt03r50 />.)]]