drillship

A drillship is a ship-shaped mobile offshore drilling unit (MODU) equipped with a full drilling package mounted on a derrick located amidships over a moonpool — an opening through the vessel's keel through which the drill string, riser, and subsea equipment are deployed to the seabed. Unlike semi-submersibles and jack-ups, drillships are self-propelled and transit between locations without tug assistance. Station-keeping during drilling operations is achieved using DP-3 dynamic positioning systems (three independent DP controllers per IMO MSC/Circ.645), making them suitable for locations where mooring is impractical. Drillships are the preferred unit for ultra-deepwater operations (water depths exceeding 1 500 m, with modern vessels capable of 3 600 m or more) and high-specification exploration drilling in remote areas such as the deep Gulf of Mexico, offshore Brazil, West Africa, and the Arctic margins. Key contractors include Transocean, Valaris, and Seadrill. Drillships are regulated under the IMO MODU Code and flagged under SOLAS for the purposes of safety construction, fire protection (SOLAS Chapter II-2), and security (SOLAS Chapter XI-2). Structural and machinery requirements follow SOLAS Chapter II-1. MARPOL Annex I applies to oily water discharges, and the ISM Code (SOLAS Chapter IX) mandates a Safety Management System. Classification is typically by ABS, DNV, or Lloyd's Register. See the /reference/ship-types page for comparison with other drilling units.