Convertible Semi Submersibles

This revolutionary semi-submersible hull operates in two modes, with the same vessel operating as a high speed supply ship during passage in its ‘Transit’ mode and then converting into its semi-submersible ‘Platform’ mode when it arrives on station.


  • Fast vessel transit in closed ‘Transit’ mode
  • Upon arrival, Subamarine converts into a semi-submersible platform
  • Sponsons ballasted underwater while hull deck is raised clear of surface waves for unmatched platform stability
  • Working stability in 3m plus seas
  • Fewer lost days due to sea conditionsROV & DP Work
  • Personnel Transfer System
  • Engineering platform
  • Wide range of offshore duties for Installation, Maintenance and Decommissioning
  • Improved availability = fast payback

The OSSeas-patented SSH hull uniquely integrates two separate hull-structures into one versatile craft.

The two sections are engineered to nest together during high speed Transit mode and then to elevate and lift apart as the vessel transforms into its semi submersible Platform mode. The vessels lower hull section is designed to ballast down to below the surface and under the areas of swell and high wave energy, while the upper hull superstructure is simultaneously raised out of the water completely.


Subamarine offers a truly unique solution to get high value people and equipment on site quickly and provides an all weather platform with unmatched stability for better programme delivery and more days at sea.

More Capability

The craft has high capacity with plenty of internal area available for people, good amenities for daily runs to the field, such as showers, bunks for rest, lounge area, etc., accommodation for longer field durations and plenty of space for engineering equipment and ROV’s.

A large aft upper deck allows room for FRCs, Life rafts, survival suits, and light equipment/freight, as well as two to four ‘daughter’ maintenance craft for use in good weather to maximise the number of duties – towers, platforms, survey sweeps etc – which can be serviced.

The deck also provides a highly stable platform where a transfer system is mounted to provide walkway access on the platform or wind tower. This could be a hydraulically stabilised gangway or ‘cherry picker’ system as shown.



The vessel is envisaged to be long and wide, typically 70m – 100m long with a wide beam. This provides comfort in Transit mode, gives greater stability and further dampens residual wave induced motion when in Platform mode with the hull submerged. This gives spaces for accommodation, workshops and deck areas.

  • 70m Subamarine
  • 80m Subamarine
  • 90m Subamarine


  • Installation & Maintenance of Offshore Platforms
  • Windfarm platform servicing
  • Offshore Supply
  • Safety Standby Vessel
  • Hydrographic Survey
  • Marine Engineering Support
  • Decommissioning Vessel
  • Coast Guard and Naval Surveillance
  • Military platforms


Please Contact us for information or to discuss your requirements.

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