Semi-submersible vessels were prominent in maritime news during December 2025, with completions, orders, and operations underlining their versatility across offshore energy, transport, and security applications.
Sembcorp Marine Delivers World's Largest Semi-Submersible Crane Vessel
Sembcorp Marine recently unveiled Sleipnir, the world's biggest and strongest semi-submersible crane vessel (SSCV), at its Tuas Boulevard Yard for Heerema Marine Contractors. Aptly named after Norse God Odin's eight-legged stallion, this vessel features a 220m by 102m reinforced deck area - the largest among all crane vessels ever created - as well as two 10,000-tonne revolving cranes that can lift 20,000 tonnes simultaneously - no other vessel matches this capacity!
Sleipnir can accommodate 400 persons and supports global deployment for installing and decommissioning jackets, topsides, deep-water foundations and moorings used in oil, gas, renewables or any combination. With its single lift capability reducing offshore assembly times while still offering traditional flexibility. Furthermore, Sleipnir pioneered dual fuel engines running off Marine Gas Oil (MGO) and LNG with an IMO- and US Coast Guard-approved ballast system to enable eco-friendly operations.
Soon to enter service, Sleipnir elevates heavy-lift capabilities for larger integrated structures.
Allseas Secures Order for Grand Tour Semi-Sub Heavy Transport Vessel
Allseas signed an agreement with Guangzhou Shipyard International (GSI), China for the semi-submersible heavy transport vessel Grand Tour on September 11th 2025 - expanding their fleet for integrated transportation and installation operations.
Grand Tour was engineered to fit seamlessly into Allseas' Pioneering Spirit's bow slot for seamless load transfers and one-stop service for clients. Supporting Europe's energy transition initiatives such as TenneT's 2GW offshore wind program with 28GW by 2032 goals, as well as transporting large converter stations from Asian yards to Dutch and German North Sea sites, Grand Tour provides clients with one stop solutions.
With its semisubmersible hull, 57m beam for stability, shallow-draft access and 24,000 m3/hour ballast system, Allseas Project Director Pieter Kambier noted it reduces risk while streamlining schedules on complex projects.
Vuyk Engineering Creates Allseas Grand Tour
Allseas contracted Vuyk Engineering of the Netherlands for their Grand Tour semi-submersible HTV design. Scheduled to arrive at GSI by Q1 2028, it was optimized to carry up to 60,000-tonne payloads while accommodating for 40,000 tonnes in topsides at the stern, and integrated seamlessly with Pioneering Spirit.
Main dimensions for this vessel include LOA 229.9m, beam 57m, depth 14.8m, summer draught of 11.1m (DP2 positioning), deadweight at 11m draught and deadweight of 73,000t at 11m draught. Features of note include 180x57m cargo deck for skidding/float-on/off, methanol-ready propulsion with air lubrication for better fuel economy as well as podded propulsion with high capacity ballast capacity and air lubrication to reduce fuel usage for optimal fuel economy in low light environments.
Transport capacities depend on load center of gravity (COG). At 20m COG, transport capacities range from 60,000t down to 38,500t at 45m COG allowing greater flexibility for heavy offshore infrastructure projects.
China Unveils Mysterious Semi-Submersible Trimaran
On December 6, 2025, China unveiled an intriguing semi-submersible trimaran at its Huangpu Shipyard in Guangzhou that combined surface vessel and submersible characteristics in a 65m trimaran layout with central hull and outriggers, painted submerged grey.
This craft features a minimal superstructure with sail-like tower possibly used for snorkeling or antennas, depth indicators, and pump-jet propulsion pump-jet propulsion that may provide quiet high-speed operation. According to experts such as H.I. Sutton who first noticed it on October satellite imagery, this craft may be an uncrewed or minimally crewed hybrid USV/UUV.
Theories regarding its purpose range from being a semi-submersible arsenal ship for missiles and launchers, drone mothership, special operations platform or experimental testbed; though no weapons or accommodations have yet been confirmed.
JSI Alliance Concludes Inaugural Semi-Sub Cargo Operation
JSI Alliance recently completed their inaugural semi-submersible cargo operation on deck carrier MV Zhong Ren 122 successfully and demonstrated their expanding expertise in heavy lift logistics.
U.S. Raid on Suspected Narco Semi-Submersible Device
U.S. forces conducted an air strike against a semi-submersible suspected of drug trafficking in the Eastern Pacific on December 23rd 2025, leading to one fatality and reinforcing ongoing anti-narcotics efforts.