Offshore unit and method of installing wellhead platform using the offshore unit

An offshore unit includes a hull and/or a deck frame, a mat attached to at least one connecting leg or a spud can attached to each of at least one connecting leg or lower hull attached to at least one connecting means. A wellhead deck is removably attached to the hull and/or deck frame and a sub-sea clamp in conjunction with a caisson or a sub-sea conductor frame is removably attached to the mat or to the at least one connecting leg, where a spud can is attached to each of the at least one connecting leg, or to the lower hull. The offshore unit is relocatable and is a platform or a rig capable of performing drilling, production, construction, accommodation, hook-up and commissioning or a combination of any of these functions thereof. The offshore unit is a self-elevating mobile platform or submersible platform or semi-submersible platform.