Shipwreck/Structure

Shipwrecks are naturally-generated structures that generate underwater. They can generate right-side-up, sideways, or upside-down. Although oak is used in the blueprints, the wood planks, logs, trapdoors, and doors can be of any variant.

With Mast
The structure is called "with_mast." The chests have random loot.

Degraded
The structure is called "with_mast_degraded." The chests have random loot.