A semi-submersible is a specialised marine vessel with good stability and seakeeping characteristics. The semi-submersible vessel design is commonly used in a number of specific offshore roles such as for offshore drilling rigs, safety vessels, oil production platforms and heavy lift cranes.
This vessel type can also be described as semisubmersible, semi-sub or just semi.
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Characteristics
Semi-submersibles are typically configured with large buoyant pontoon structures below the water surface and slender columns passing through the water surface supporting a platform deck at a significant height above the sea surface.
A semi-submersible vessel may be able to transform from a deep to a shallow draft by deballasting (removing ballast water from the hull), and thereby become a surface vessel. The heavy lift vessels use this capability to submerge the majority of their structure, locate beneath another floating vessel, and then deballast to pick up the other vessel as a cargo.
With its hull structure submerged at a deep draft, the semi-submersible is less affected by wave loadings than a normal ship. With a small water-plane area however, the semi-submersible is sensitive to load changes, and therefore must be carefully trimmed to maintain stability. Unlike a submarine or submersible, a semi-submersible vessel is never entirely underwater.
Early History
The semi-submersible design was first developed for offshore drilling activities. Bruce Collip of Shell is regarded as the inventor.[1]
When offshore drilling moved into offshore waters fixed platform rigs and submersible rigs were built, but were limited to shallow waters. When demands for drilling equipment was needed in water depths greater than 100ft in the Gulf of Mexico, the first jackup rigs were built.
The first semisubmersible arrived by accident in 1961. Blue Water Drilling Company owned and operated the four column submersible drilling rig Blue Water Rig No.1 in the Gulf of Mexico for Shell Oil Company. As the pontoons were not sufficiently buoyant to support the weight of the rig and its consumables, it was towed between locations at a draught mid way between the top of the pontoons and the underside of the deck. It was observed that the motions at this draught were very small and Blue Water Drilling and Shell jointly decided that the rig could be operated in the floating mode. The first purpose built drilling semi-submersible Ocean Driller was launched in 1963.[2] Since then, many semi-submersibles have been purpose-designed for the drilling industry mobile offshore fleet.
Applications
Mobile Offshore Drilling Units (MODU)
Semi-submersible rigs make stable platforms for drilling for offshore oil and gas. They can be towed into position by a tugboat and anchored, or moved by and kept in position by their own azipod propellers with dynamic positioning.
Drilling rig construction has historically occurred in boom periods and therefore 'batches' of drilling rigs have been built. Offshore drilling rigs have been classified in nominal 'generations' depending upon the year built and water depth capability as follows;
| Generation | Water Depth | Dates |
|---|---|---|
| First | about 600ft | Early 1960's |
| Second | about 1000ft | 1969-1974 |
| Third | about 1500ft | Early 1980's |
| Fourth | about 3000ft | 1990's |
| Fifth | about 7500ft | 1998-2004 |
The IMO MODU Code[3] is an accredited design and operational guideline for Mobile Offshore Drilling Units of the semi-submersible type.
Semi-submersible Crane vessels (SSCV)
After the drilling industry, the advantages were soon recognized for offshore construction. In 1978 Heerema Marine Contractors constructed the Balder and Hermod. These semi-submersible crane vessels (SSCV's) consist of two lower hulls (pontoons), three columns on each pontoon and an upper hull. After that J. Ray McDermott and Saipem also introduced SSCV's, culminating in the workhorses DB-102 (now Thialf) and Saipem 7000, capable of lifting respectively 14,200 and 14,000 tons.
During transit an SSCV will be de-ballasted to a draught where only part of the lower hull is submerged. During lifting operations, the vessel will be ballasted down. This way, the lower hull is well submerged. This reduces the effect of waves and swell. High stability is obtained by placing the columns far apart. The high stability allows them to lift extreme high loads.
Offshore Support Vessels (OSV)
Semi-submersibles are particularly suited to a number of offshore support vessel roles because of their good stability, large deck areas, and variable deck load (VDL). Some of the most prominent vessels are;
- Uncle John - Diving / Construction support vessel, built for Houlder Offshore in 1977[4]
- Seaway Swan - Diving Support Vessel built in 1977
- Tharos - Offshore Safety support vessel, built in 1979 and since converted into a drilling vessel.
- Stadive - Diving Support Vessel (DSV) built for Shell in 1982[5]
- Iolair - Offshore safety support vessel, built for BP in 1982
- Safe Karinia - Offshore operations vessel, built in 1982
- Q4000 - Offshore Multiservice Vessel, built for Caldive in 2002[6]
- Ocean Odyssey - Converted semi-submersible drilling rig used as a rocket launch pad.
Offshore Production Platforms
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When oil fields were first developed in offshore locations, drilling semi-submersibles were converted for use as combined drilling and production platforms. These vessels offered very stable and cost effective platforms. The first converted semi-submersible floating was the Deepsea Pioneer vessel in the UK North Sea in 1975.
As the oil industry has progressed into deeper water and harsh environments, purpose-built production semi-submersible platforms were designed. The first purpose built semisubmersible production platform was for the Balmoral field, UK North sea in 1986 [7].
A summary of offshore semi-submersible oil production platforms is given in the following table.
| Vessel
Name |
Oilfield
Name |
Region | Water
depth (m) |
Displacement (Te) | Current
Operator |
Startup
Year |
Designer | Constructor | Notes |
|---|---|---|---|---|---|---|---|---|---|
| Deepsea Pioneer FPU | Argyll & Duncan Oilfields | UK North Sea | 150 | 34,000 | Agip | 1975 | Converted from Transocean 58 MODU [8] | ||
| Buchan A | Buchan oil field | UK North Sea | 160 | 0,000 | Talisman | 1981 | Brown & Root | Scott Lithgow | Converted from Drillmaster MODU for BP |
| Balmoral FPV | Balmoral oilfield | UK North Sea | 150 | 34,000 | Agip | 1986 | GVA | Götaverken, Sweden | First purpose built production semsi-submersible. |
| Veslefrikk B | Veslefrikk oilfield | Norwegian Sea | 0,000 | StatoilHydro | 1989 | Stavanger, Norway | Converted from West Vision drilling semi. First floating production facility in Norway. | ||
| Emerald Producer | Emerald oilfield | UK North Sea | 0,000 | Sovereign Oil Company | 1989 | Newcastle | Converted from Alibaba Drilling vessel | ||
| AH001 | Ivan Hoe Rob Roy Oilfield | UK North Sea | 0,000 | Amerada Hess | 1989 | Brown & Root | Highland Fabricators, Nigg | Converted from Philips SS Sedco700 drilling vessel | |
| P-7 | Brazil | 207 | 0,000 | Petrobras | |||||
| P-8 | Brazil | 423 | 0,000 | Petrobras | |||||
| P-9 | Brazil | 220 | 0,000 | Petrobras | |||||
| P-12 | Brazil | 100 | 0,000 | Petrobras | |||||
| P-15 | Brazil | 243 | 0,000 | Petrobras | |||||
| P-18 | Marlim | Brazil | 910 | 0,000 | Petrobras | 1994 | GVA | ||
| Troll B FPU | Troll gas field | Norwegian Sea | 339 | 55,000 | StatoilHydro | 1995 | Doris | Aker? | Concrete construction. |
| Nanhai Tiao Zhan | Luihua | South China Sea | 300 | 0,000 | Amoco | 1996 | Converted drilling modu | ||
| Innovator | Marlim | Gulf of Mexico | 914 | 0,000 | ATP | 1996 | GVA | ||
| Njord A | Njord Oilfield | Norwegian Sea | 330 | 45,000 | StatoilHydro | 1997 | Aker | Originally built for Norsk Hydro Design based on P-45 ? | |
| P-19 | Marlim | Brazil | 770 | 0,000 | Petrobras | 1997 | GVA | Converted from drilling unit. | |
| Northern Producer FPF | Don Oilfield | UK North Sea | 0,000 | Petrofrac | 1998 | McNulty, Newcastle | Re-use of Emerald Producer vessel. | ||
| Janice A | Janice Oilfield | UK North Sea | 0,000 | Maersk | 1999 | Converted from drilling vessel | |||
| P-20 | Marlim | Brazil | 620 | 0,000 | Petrobras | GVA | Astileros, Spain | Converted from Russian built Illiad drilling semi. | |
| P-25 | Marlim | Brazil | 575 | 0,000 | Petrobras | ||||
| P-26 | Marlim | Brazil | 990 | 0,000 | Petrobras | ||||
| P-27 | Voador | Brazil | 533 | 0,000 | Petrobras | ||||
| PNA-1 | Brazil | 145 | 0,000 | Petrobras | |||||
| Visund | Visund | Norwegian Sea | 0,000 | StatoilHydro | 1999 | GVA | Daewoo, S. Korea | ||
| Troll C FPU | Troll gas field | Norwegian Sea | 339 | 55,000 | StatoilHydro | 1999 | GVA | ||
| Åsgard B | Åsgard | Norwegian Sea | 320 | 85,000 | StatoilHydro | 2000 | GVA | Daewoo, S. Korea | |
| P-36 | Roncador | Brazil Campos Basin | 1360 | 0,000 | Petrobras | 2000 | SBM Atlantia | Davie Shipbuilding, Canada | Converted from Spirit of Columbus and sank in 2001 |
| Snorre B FDPU | Snorre Oilfield | Norwegian Sea | 350 | 56,400 | StatoilHydro | 2001 | Aker | Originally built for Saga | |
| P-51 | Marlim Sul Oilfield | Brazil Campos Basin | 1255 | 80,114 | Petrobras | 2001 | Aker | ||
| Nakika | Kepler, Ariel, Fourier, Herschell & E. Anstey | Gulf of Mexico | 936 | 64,000 | BP | 2003 | ABB Lumus | HHI, S.Korea | Constructed for Shell, but operated by BP |
| P-40 | Marlim Sul | Brazil | 1080 | 0,000 | Petrobras | 2004 | |||
| Kristin FPU | Kristin | Norwegian Sea | 320 | 56,000 | StatoilHydro | 2005 | GVA | ||
| Atlantis PQ | Atlantis oilfield | Gulf of Mexico | 2156 | 89,000 | BP | 2006 | GVA | DSME, S.Korea | |
| Independence Hub | 10 fields | Gulf of Mexico | 2015 | 46,160 | Anadarko | 2007 | SBM Atlantia | Dynamac, Singapore | |
| P-52 | Roncador | Brazil | 1795 | 0,000 | Petrobras | 2007 | GustoMSC | Keppel FELS | |
| Thunder Horse PDQ | Thunder Horse | Gulf of Mexico | 1849 | 130,000 | BP | 2008 | GVA | DSME, S.Korea | Largest semisubmersible platform |
| Blind Faith | Blind Faith | Gulf of Mexico | 1980 | 40,000 | ChevronTexaco | 2008 | Aker | Aker Verdal | |
| Thunder Hawk | Thunder Hawk | Gulf of Mexico | 1740 | 0,000 | Murphy | 2009 | SBM Atlantia | DSME, Korea | |
| Gjoa | Gjoa | Norwegian Sea | 360 | 0,000 | StatoilHydro | 2010 | Aker | Samsung, S. Korea | To be operated by Gas de France |
| Gumusut Kakap | Gumusat Kakap | Malaysia | 1220 | 40,000 | Shell | 2010 | MMHE, Malaysia | MMHE, Malaysia | First production semisubmersible in Malaysia |
| P-56 | Roncador | Brazil | 1828 | 50,000 | Petrobras | 2011 | Aker | Keppel FELS | Copy of P-51 platform. Built in Brazil. |
See also
- Submersible or Midget submarine - for small submarine craft.
- Submersible drilling rig - for submersible drilling vessels.
- USS Monitor - the U.S. Civil War warship considered to be the earliest semi-submerged ship.
- USS Spuyten Duyvil - another U.S. Civil War semi-submerged ship.
- Sea Shadow (IX-529) - a craft designed and built by Lockheed Corporation with the superstructure joined to the hulls with continuous members.
- Welfreighter - a submersible designed by Britain during the second World War to carry combat swimmers.
- Small waterplane area twin hull – a "SWATH" vessel consists of two submarine-like structures supported on streamlined pylons.
- RP FLIP (FLoating Instrument Platform) - a tilting craft designed to form a stable platform for scientific data collection.
- Drydock - facility used to repair and maintain ships; some are floating and can be submerged to load vessels.
- Narco submarine - low profile vessels used to smuggle cocaine from South America to the United States.
References
- ^ Ocean Star, Bruce G. Collipp
- ^ 60 Years in the Gulf of Mexico, E&P Magazine, 2007
- ^ http://www.imo.org/publications/mainframe.asp?topic_id=740&doc_id=2512
- ^ BMT Study of Uncle John Semi-submersible : http://www.hse.gov.uk/research/othpdf/200-399/oth363.pdf
- ^ Shell history : http://www.shell.co.uk/home/content/gbr/aboutshell/shell_businesses/e_and_p/introduction/thehistory_01041405.html
- ^ Helix brochure : http://www.helixesg.com/Portals/0/PDFs/q4000.pdf
- ^ GVA website http://www.gvac.se/gva-500/
- ^ http://www.offshore-technology.com/features/feature40937/
- ^ Offshore Technology Website http://www.offshore-technology.com/projects/
- ^ GVA Consultants Website http://www.gvac.se/floating-production/
- ^ Aker Solutions Website http://www.akersolutions.com/Internet/IndustriesAndServices/OilAndGas/FieldDevelopment/DeepwaterSolutions/SemiSubmersibleProductionPlatforms/default.htm
- ^ Petrobras Platforms http://www2.petrobras.com.br/Petrobras/ingles/plataforma/pla_plataforma_operacao.htm
- ^ UK DTI Data http://www.databydesign.co.uk/energy%5Cukdata/book.htm
External links
- [1] - GVA Consultants designers
- Dockwise website - Info on Dockwise transport ships
- Naybook website - Photos of Mighty Servant 2 hauling USS Samuel B. Roberts (FFG 58)
- Collection of photos of semi-submersible transport ships
- IMO Website - International Maritime Organisation
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