Heavy-lift ship (Dockwise type)

A heavy-lift ship of the Dockwise type is a semi-submersible transport vessel that carries oversized floating cargo by float-on/float-off, ballasting down until the deck submerges, floating the cargo over it, then deballasting to lift the cargo clear of the water. This moves drilling rigs, jackup units, semi-submersibles, dredgers, and even other ships that cannot make a long voyage under their own power. The deck is long, flat, and obstruction-free, with high casings forward for the accommodation and machinery. Dockwise, now part of Boskalis, operated the type’s best-known ships, including Blue Marlin and Black Marlin, which carried payloads above 50,000 tonnes.