A powership is an existing ship that has been modified for power generation, a marine vessel, on which a power plant is installed to serve as a power generation resource. Converted from existing ships, powerships are self-propelled, ready to go infrastructure for developing countries that plug into national grids where required. Unmotorised powerships, known as power barges, are simply conventional power plants installed on a deck barge. These are sometimes called "floating power plants" or "barge mounted power plants". They were initially developed during World War II by General Electric for the War Production Board as a transportable large scale power generation resource.
Powerships can be equipped with single or multiple gas turbines, reciprocating diesel and gas engines, boilers or nuclear reactors for electricity generation. Bureau Veritas, an international certification agency with experience in overseeing both shipbuilding and power plant development, classifies such floating power plants as "special service power plants".
A total of about four self-propelled powerships are currently deployed around the world, while there are over 75 power barges worldwide, including over 600 MW of generation capacity in New York City. Power barges can be built very quickly in comparison to a powership or a land-based plant. A 100 MW gas turbine power barge can be built and be ready for deployment in about three months.
One of the earliest (if not the first) powership built was in 1931, the SS Jacona built by the Newport News, Virginia Shipyard and Drydock Company, for the New England Public Service Company of Augusta, Maine. The idea came to the president of the Augusta firm, when one winter a severe winter storm took out a lot of the New England major power transmission lines. The Jacona role would be to dock as near as possible to the affected area and hook into the local power grid restoring power. During the Summer months the Jacona would hook into vacation area power grids where power needs are extremely low during off season and extremely high during the Summer vacation season. The Jacona was fitted with steam boilers which drove two generators which could produce 10,000 kW each.
At one time the US Navy used its submarines when disaster hit a local community bring down the commercial power grid, this led to the idea of powerships for the US Navy, and an early US Navy powership was the USS Saranac, a former US Navy naval ship. Saranac was a 1942 built fleet oiler before her conversion into a powership following the Second World War to serve in the US Navy and Army. In 1957, she was sold to Hugo Neu Corporation of New York City and was used then as a power facility abroad by the International Steel and Metal Corporation. In 1959, she was renamed Somerset.
The first floating nuclear reactor ship was the MH-1A, in the Panama canal zone. This ship (the Sturgis) is due to be scrapped in 2015. Although the reactor and fuel have already been removed.
Power barges and power ships offer a number of advantages over other forms of power plants; due to their mobility, powerships can be connected to local power grids to temporarily cover demands whenever on site power plants are insufficient or the building of new power plants will take time, while dual-fuel engines on board can be powered by either liquid fuels or gas. The power barge and power ship are able to use any infrastructure available at the site on which she is required.
Some recently built power ships are existing large bulk carriers, which are fitted with used reciprocating engines and new state-of-the-art, large-bore dual-fuel diesel engines that run on heavy fuel or natural gas to generate electricity, relevant transformers and electric switchboards. The only other power ships were based on US Naval vessels. Power ships utilizing new purpose built ships would not be competitive to a purpose built power barge due to the higher cost of construction. The crew quarters and propulsion systems are under utilized during the power plant operational period which can be up to the life of the power plant.
It is expected that a power barge or power ship will moor at one place for an average duration of three to five years, or up to 20 years. For this reason, power ships are an ideal solution to bridge the gap for a certain time until a local power plant is built or the high demand in electricity supply is over.
Karadeniz Powership Co. Ltd., a subsidiary of Karadeniz Energy Group based in Turkey, developed and carries out a project named "Power of Friendship" that aims to provide a total of 2,010 MW of electricity to more than ten shortage-stricken countries in the Middle East, northern Africa and southern Asia with ten different ships by the end of 2010. The first powership of the project, which can supply 144 MW power, went into service at the beginning of 2010 off the shore near Basra in south-eastern Iraq, and the second powership is on its way to the same place. The company also signed a contract with Pakistan., but the Pakistani government terminated this project.
All other builders of power ships have gone out of business.
Power barges are in demand for their short construction cycles, flexibility in deployment, minimal land requirements. The capital costs of constructing and operating power barges are very competitive with their land-based equivalents.
Construction and installation
Power barges are typically moored in protected harbors, and may be entirely self-contained with step-up transformers or connected with land-based transformers that send electricity to domestic consumers. If the purchaser defaults, the manufacturer or intermediary can tow the barge(s) away and sell the plant to another customer. Floating power plants are usually constructed off-site at a shipyard, and then transported via dry tow to the end-use location.
Vibration and thermal growth
Gas turbines and diesels generate substantial amounts of vibration both during start-up and operations. The gas turbine generator coupling is very sensitive to alignment and therefore, controlling deflection is paramount. Foundation designs seek to either isolate the deck barge and the power island raft or to combine the structures of the power island and deck barge to gain the same structural rigidity. The difference is that the integrated structural approach yields a direct path for vibration, while the isolated structural approach seeks the rigidity in an independent foundation and utilizes spring mounts or other mat type vibration dampening.
The deck barge will tend to exhibit thermal growth during the diurnal cycles and possible out-of-trim conditions referred to as hogging and sagging caused by changes in ballast or fuel.
The power island design requires certain deflection limitations at the generator coupling and vibration dampening from start-up or out-of-phase operations, as well as significant trip loads mostly in the generator section. The power barge systems engineer must integrate power island engineering with naval architecture and marine engineering.
From New York City to Bangladesh
During the 1990s, power barges became a popular way of providing energy to developing nations, with companies including equipment suppliers like General Electric, Westinghouse, Wärtsilä, and MAN; by developers such as Smith Cogeneration, AES, GMR Vasavi, which operate floating power plants for customers located in New York City (USA), Khulna (Bangladesh), the Dominican Republic, Brazil, Ecuador, Angola, Nigeria, Thailand, Effassu (Ghana), as well as in the Philippines, Jamaica, Kenya, and Malaysia. Engineering, procurement and construction companies such Power Barge Corporation, Waller Marine Inc, Hyundai, IHI Corporation and Mitsui offer gas turbine power barge construction programs, and Karadeniz Energy, MAN and Wärtsilä offer medium speed engine power barges.
Today there are over 75 power barges deployed and operating around the world. The utilization rate of power barges is around 95% with only one or two power barges available in the global market at any one time.
In April 2011, Waller Marine finalized installation in Venezuela of two large floating power generation barges into a prepared basin at Tacoa. The two 171 MW barges, each supporting a GE 7FA dual fuel industrial gas turbine, are connected to the grid and soon supply much needed power to Caracas. Power Barge Corporation recently delivered a 96 MW gas turbine power barge to Angola, a 72 MW Wartsila power barge to Panama and a 105 MW gas turbine power barge to Venezuela.
Year of conversion given in parenthesis.
- USS Saranac (1957)
- MV Karadeniz Powership Doğan Bey (IMO 8117031), 144 MW, 2010, serving in Basra, Iraq.
- MV Karadeniz Powership Rauf Bey (IMO 7925522), 200 MW, 2010, serving in Basra, Iraq.
- MV Karadeniz Powership Kaya Bey (IMO 7925546), 220 MW, 2011, serving in Pakistan.
- MV Karadeniz Powership Ali Can Bey (IMO ?), 110 MW, 2011, serving in Pakistan.
- MV Karadeniz Powership Irem Sultan (IMO 8222252), 110 MW, 2012, serving in Basra, Iraq.
- MV Karadeniz Powership Fatmagul Sultan (IMO ? ), 205 MW, 2013, serving in Beirut, Lebanon.
- MV Karadeniz Powership Orhan Bey (IMO ? ), 136 MW, 2013, serving in Beirut, Lebanon.
Notable power barges that Power Barge Corporation has worked on
- SS Jacona (20 MW) 
- Osagyefo Barge (125 MW), located at Effasu, Ghana
- Iuka 101/102 (30 MW) Frame 6B power barges (part of a fleet of 9 power barges in Lagos) Nigeria
- Dymani III (48 MW) W251B11 Kenya
- Gantisan One (50 MW) LM2500 Malaysia
- Dynami I (105 MW) W501D5 Venezuela
- Dynami II (96 MW) W251B11 Angola
- Dynami iV (116 MW) W501D5A Ecuador
- Victoria 8 (144 MW) W251B11 CCGT Bangladesh
- Rio da Luz (100 MW) P&W FT4C-3F (decommissioned)
- Power Barge II (50 MW) MAN 51/52 Panama
- TBGMR (250 MW) LM6000PC CCGT Mangalore
- SmithEnron (185 MW) Frame 7 CCGT Dominican Republic
- Estrella Del Norte (40MW) Dominican Republic
- Estrella del Mar (72 MW) Dominican Republic
- Estrella del Mar II (108 MW) Dominican Republic
- Santa Ines (55 MW) Guatemala
- Santa Elena (55 MW) Guatemala
- MH-1A, a floating power station constructed as part of the Army Nuclear Power Program
- Russian floating nuclear power station
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