- Any of various self-propelled water vessels designed so that most, but not all, of the structure is submerged, including vessels with decks close to the waterline for transporting large structures such as oil rigs and disabled ships, and vessels with minimal structure above the waterline for avoiding detection.
- A seagoing, self-propelled barge that has partially submerged vertical legs attached to underwater hulls or pontoons and serves as living quarters and a base of operations in offshore drilling. In this sense also called semisubmersible rig.
offshore drilling rig
semi- +â€Ž submersible