Deep / Surface

World-class marine engineering has been carried out in Mäntyluoto, Pori, for more than fifty years. The area was originally intended for automotive and nuclear power industries, but its future changed course in 1972, when the French company Forex Neptune commissioned a Pentagone-type offshore oil drilling platform.

Demand for offshore drilling platforms had already begun to grow in the 1960s and accelerated rapidly with the first oil crisis and the North Sea oil boom in the early 1970s. As a result, the Mäntyluoto works expanded in both scale and operations. The second oil crisis in 1979 brought further major orders, including three ice-reinforced drilling vessels built for the Soviet Union.

At its peak in the early 1980s, the facility employed more than 1,500 people, along with a similar number of subcontractors.

Over the decades, the Mäntyluoto works has designed and built a wide range of structures, including various types of offshore drilling platforms, ship hulls, and specialised vessels. Of the approximately 25 spar‑type deepwater drilling platforms built worldwide, the hulls of 17 were manufactured in Mäntyluoto between 1997 and 2009.

As demand in the offshore drilling sector declined, the Mäntyluoto works redirected its expertise toward offshore wind power structures. A landmark example of this transition is the world’s first offshore wind farm designed for Arctic conditions, constructed off the coast of Tahkoluoto in the 2010s.

The history of the Mäntyluoto works, later the Mäntyluoto yard, is marked by continuous adaptation and renewal – a long journey from the oil industry to offshore wind energy and the construction of structures for Arctic icebreakers.

Plater, welder, pipe fitter, scaffolder, crane operator, maintenance worker…

Mäntyluoto Works employed workers from a wide range of heavy industrial trades. Demanding working positions, heavy tools, and changing weather conditions put a constant strain on the body. Knees went numb and necks stiffened in awkward postures among massive steel structures. Some welded inside pontoons, while others worked at heights of more than one hundred metres.

The responsibility was considerable. The structures of offshore drilling rigs had to withstand extreme conditions at sea. The quality of welds and the precision of installations were essential parts of a larger whole. Workdays began with the allocation of tasks or continued from where the previous day had ended. During breaks, workers queued for the canteen or ate their own packed meals in break rooms filled with cigarette smoke.

Work crews developed their own forms of humour, helping to lighten the burden of physically demanding labour. At sauna evenings and at the traditional end-of-project celebrations – known as “pig feasts” – refreshments were rarely in short supply. Many workers remained at Mäntyluoto Works for decades, despite the industry’s recurring cycles of boom and decline.

The quieter side of work at Mäntyluoto Works was carried out by engineers. At their drawing boards they produced the calculations and technical drawings that ensured the rigs’ seaworthiness and structural performance. The challenges were considerable: in 1974 engineers adapted what was then the world’s largest offshore drilling rig, the Ocean Ranger—originally built in Japan—to suit local production conditions.

In the mid-1980s, design work moved onto computers. The yard invested four million Finnish marks in a CAD system that improved dimensional accuracy and the overall quality of structures. In 1986, welding robots arrived in Mäntyluoto to manufacture leg structures for Arctic jack-up rigs destined for the Vyborg shipyard.

The work demanded precision and strong control of complex design processes. At times engineers worked on the shop floor or even at sea to ensure that their plans functioned in practice. The social dimension of the work was equally important: engineers needed to collaborate effectively with both local heavy industrial workers and international clients.

The office of the Mäntyluoto Works was staffed mainly by women working as payroll clerks, switchboard operators, and office staff. The work was learned on the job, and many came to the yard directly from lower secondary school.

At first, wages were calculated by hand. Even as office computing developed, manual calculation remained an essential safeguard – accuracy depended on staying alert and checking the figures oneself. Computers were long regarded as unfamiliar and difficult, but in time they came to ease the workload. Switchboard operators recognised the voices of shipyard workers, directed visitors to the right person, and handled calls and visits from abroad.

Although the name of the Mäntyluoto yard changed over time and many office workers worried about their jobs during periods of transition, the work itself continued largely unchanged. Office work was valued, and there was trust in the employer. Even demanding tasks were managed together with colleagues. The shipyard was widely regarded as a good place to work, as reflected in careers that lasted for decades.

Statutory occupational health services at the Mäntyluoto yard began to develop systematically in the early 1980s, when the yard expanded and the workforce grew rapidly. The first years were hectic: ships and offshore drilling rigs were built simultaneously, and at peak times as many as 3,000 people worked on the site.

The occupational health clinic was located at the heart of the yard. Its staff included a physician, two occupational health nurses, a secretary, and a physiotherapist. Workdays began with clocking in at 8:00 a.m. and ended at 4:00 p.m., although flexibility was applied when needed.

In the early years, there were no established practices or systematic induction. Much of the work focused on treating workplace accidents, conducting health examinations, and addressing everyday ailments. During the 1980s, the occupational health unit became a forerunner in its field by introducing its own electronic patient record system. The work was continuously developed: rehabilitation groups were established, comprehensive health screenings were carried out, and staff actively participated in improving workplace safety together with the rest of the yard personnel. Occupational health was regarded as a shared responsibility of both employees and management.

As activity at the yard declined in the 1990s, occupational health services were increasingly offered to external clients as well. Eventually, the yard’s own health clinic became part of a private medical centre.

The enormous size of offshore drilling rigs made the work physically demanding and at times dangerous, especially under tight schedules. Working alongside dozens of subcontractors complicated the supervision of workplace safety. In the early years, protective equipment was rarely used, and accidents ranged from minor injuries to serious incidents.

By the 1980s, workplace safety had improved markedly. Safety representatives, an on-site fire brigade, and regular inspections became part of everyday operations. Scaffolding grew safer, greater attention was paid to ergonomics, and the use of personal protective equipment became mandatory.

International clients further tightened safety requirements. In the 1990s, the Norwegian owner Aker Maritime introduced weekly safety inspections. In the 2000s, the yard’s French owner Technip, together with American clients, elevated the safety culture to an entirely new level.

Ultimately, safety became part of the workers’ identity – being without a helmet felt almost as if one had left home without trousers.

The socialist Soviet Union, already among the world’s largest oil-producing countries in the 1970s, was an important trading partner for Rauma-Repola. Trade was governed by the rules of bilateral trade, which required exports and imports between the two countries to be roughly equal in value.

The Soviet economic system operated according to five-year plans. This facilitated trade, as forthcoming purchases by the neighbouring country were known well in advance. Finnish companies each had their established fields of operation: Wärtsilä built icebreakers, Hollming specialised in marine research vessels, and Valmet produced accommodation ships. Rauma-Repola was responsible for offshore drilling rigs and drilling ships, as well as tankers.

Nevertheless, the most decisive factor driving offshore drilling projects was the global price of oil. When prices were high, it became profitable to search for oil in increasingly challenging locations, creating demand for drilling equipment.

Negotiations in Moscow resulted in major orders for Pori. The drilling ship Valentin Shashin was completed in December 1981, Viktor Muravlenko in June 1982, and Mikhail Mirchnik in September 1982. The drilling rigs Kolskaya and Sakhalinskaya were both produced in 1985. This same peak period also coincided with the secret construction preparations of the Mir deep-sea submersibles.

Trade with the Soviet Union came to an end in 1991 with the dissolution of the Soviet state.

The construction of offshore drilling platforms began in Mäntyluoto in 1972. The first platforms were delivered to the North Sea for oil exploration and were floating, movable semi-submersible units.

Later, the focus shifted to Soviet orders for the Caspian Sea, where jack-up platforms designed to be transported by floating were built. In addition to platforms, ice-reinforced drilling vessels were constructed for the Soviet Union. The next phase of development led further north, toward Arctic regions. In the 1990s and 2000s, Mäntyluoto became a significant builder of SPAR platforms for the Gulf of Mexico. SPAR platforms are floating structures designed for deep-water drilling.

Alongside offshore drilling platforms and vessels, Mäntyluoto has also produced a service platform, Arctic tankers, a catamaran-type passenger vessel, and a dry cargo ship. In the 2010s, production shifted toward offshore wind power structures. In November 2025, construction began on hull blocks for the Polar Max icebreaker.

The construction of offshore drilling platforms brought economic security and jobs to Pori. Environmental concerns were rarely raised in local discussions. Finland—and the world—depended on oil. Gradually, however, awareness grew of the risks and dangers associated with oil production.

Concern over pollution in the Baltic Sea had already emerged in the 1960s. At Finland’s initiative, the Baltic Marine Environment Protection Convention was signed in 1974. The grounding of an Italian tanker off Helsinki in 1957 and that of the Soviet tanker Antonio Gramsci in 1987 exposed both the risks of oil transport and shortcomings in emergency preparedness.

The Pentagone 84 platform built in Mäntyluoto became a focus of environmental concern among residents off the coast of Finistère and the Iroise Sea in north-western France in 1975 during oil exploration, although no oil was ultimately found. The Kolskaya, completed in Pori in 1985, capsized and sank in the Sea of Okhotsk in 2011.

By the 1990s, environmental organisations had become increasingly concerned about the oil industry. In 1995, Shell planned to dispose of the Brent Spar offshore structure in the North Sea, prompting Greenpeace activists to occupy it. Preparations for the operation were carried out from the multipurpose barge Stadive, built in Mäntyluoto.

The MIR research submersibles opened a new dimension in oceanographic research. Their mobility and functionality at depths of up to 6,000 metres were excellent.

The roots of the submersible project date back to 1982, when the Academy of Sciences of the Soviet Union was searching for a manufacturer capable of building a submersible that could dive to a depth of 6,000 meters. On 8 January 1983, leaders and designers from the metal industry gathered at the Lokomo Works in Tampere at the invitation of Jouko Sere, Director General of Rauma‑Repola, to consider whether constructing such a vessel would be possible. The position of the Lokomo Steel Works was that the crew sphere could be manufactured. The assessment of producing the entire submersible itself was also positive. As a result, the project was transferred entirely to the Lokomo Marine Engineering Works.

The submersible project was kept secret from beginning to end. The chief designer of the project was M.Sc. (Eng.) Sauli Ruohonen, who had a long career at Lokomo. In total, about fifty people worked on the project. In addition, both domestic and foreign subcontractors were used.

The MIR‑1 and MIR‑2 submersibles were completed in October 1987. Deep‑water trials departed from Mäntyluoto, Pori, on 11 November 1987. The surface support vessel was R/V Akademik Mstislav Keldysh, which had been completed in 1980 at the Hollming Oy shipyard in Rauma. The actual deep‑sea trials were carried out near Cape Verde on 13–15 December 1987. The dives were conducted by a three‑person crew, with Pekka Laakso serving as the pilot. The vessels were handed over to the client on 17 December 1987.

The Mäntyluoto yard entered a new phase in 2025, when the Canadian company Davie Shipbuilding acquired Enersense Offshore Ltd from Enersense Plc. Following the acquisition, the company was renamed Sata Shipbuilding Ltd.

Current projects at the yard include hull blocks for the Polar Max icebreaker commissioned by the Government of Canada. The blocks were scheduled to be shipped to Helsinki Shipyard for further assembly in spring 2026. Production also includes foundation solutions for offshore wind turbines.

In spring 2026, the yard employed about 150 people, with the workforce expected to grow by roughly one hundred more. A continuing challenge has been the availability of skilled labour for demanding yard work, as the metal industry faces a wider shortage of professionals. One response has been the use of apprenticeship training, with a new training period underway in early 2026.

The long maritime-industrial story of Mäntyluoto Works and the yard continues through new projects.