Siem Offshore Contractors
Siem Offshore Contractors is a submarine cable installation, repair, and maintenance contractor headquartered in Leer, Germany. Founded in 2003, the private company employs 1,001-5,000 people and serves offshore wind and energy clients globally using specialized marine vessels.
- Company typePrivate
- Founded2009
- HeadquartersLeer, Germany
- Headcount1,001–5,000
- GTM typeB2B
- OfferingServices
What Siem Offshore Contractors does
Siem Offshore Contractors is a submarine cable installation, repair, and maintenance contractor headquartered in Leer, Germany. Founded in 2003 as a private company, the firm employs between 1,001 and 5,000 people and operates within the offshore energy services sector. The input references a related entity, Seaway7 — the dedicated offshore wind installation arm of Subsea7 Group — which provides integrated Engineering, Procurement, Construction, and Installation (EPCI) solutions spanning cable laying, WTG foundation installation, offshore substations, wind turbine generator installation, floating offshore wind, and heavy transportation. Together the activities position the company across the full lifecycle of offshore wind farm execution.
The technical platform is anchored in a specialized marine asset base. The fleet includes the custom-built foundation installation vessel Seaway Alfa Lift, the DP3 Heavy Lift Vessel Seaway Strashnov with a 5,000-tonne crane capacity suited for offshore substations, the next-generation jack-up installation vessel Seaway Ventus for wind turbine generator installation, and six semi-submersible heavy transportation vessels (Eagle, Falcon, Hawk, Osprey, Swan, Albatross) suitable for oversized cargo. Supporting capabilities include submarine cable and subsea umbilical installation, repair and maintenance, dive and ROV support, marine survey, UXO investigation, and remedial cable protection. The company draws on three decades of offshore energy experience originally developed in oil and gas, now redeployed to the offshore wind market since its first UK monopile installation in 2009.
The business operates on a project-based enterprise model with revenue generated through direct contract awards for large-scale offshore installation projects. Customers are primarily offshore wind developers across European, Asia Pacific, and North American markets, including developers such as Skyborn Renewables and Ocean Winds. Pricing is not publicly disclosed; contract values are determined per project based on scope, vessel requirements, and project duration. The track record cited includes 800+ WTG foundations installed, 30 substations installed, 2,500km of inner array cables installed, and 50+ completed projects. Operating as a wholly-owned subsidiary of Subsea7 Group, the company leverages group-level engineering, vessel, and execution resources while maintaining a focused offshore wind mandate.
Siem Offshore Contractors firmographics
Firmographics- Name
- Siem Offshore Contractors
- Legal name
- Seaway7
- Website
- https://siemoffshorecontractors.com
- Company type
- Private
- Founded year
- 2009
- Operating status
- Operating
- Headcount range
- 1,001–5,000 employees
- Short description
- Siem Offshore Contractors is a submarine cable installation, repair, and maintenance contractor headquartered in Leer, Germany. Founded in 2003, the private company employs 1,001-5,000 people and serves offshore wind and energy clients globally using specialized marine vessels.
- Ownership category
- akta.pro rank
Siem Offshore Contractors industry classification
Industry- Product category
- Offshore Cable Installation Services
- NAICS
- Site Preparation Contractors (23891), Other Specialty Trade Contractors (2389)
- SIC
- Heavy Construction Other Than Bldg Const - Contractors (1600)
- akta.pro primary industry
- Subsea Cable Construction, Marine Installation & Repair Services (HDAIALAC)
Keywords
Where Siem Offshore Contractors is headquartered
LocationHeadquarters
- HQ city
- Leer
- HQ country
- Germany
- HQ region
- Europe
Offices1 record
Markets served
Siem Offshore Contractors business model
Business model- GTM type
- B2B
- Offering type
- Services
- Cost components
- Personnel, Infrastructure, Operations, Supply Chain
Revenue model
- EPCI Contract Services: Seaway7 generates revenue through Engineering, Procurement, Construction, and Installation (EPCI) contracts for offshore wind projects. Services include cable laying, WTG foundation installation, offshore substation installation, wind turbine generator installation, and heavy transportation. Revenue is project-based, earned through awarded contracts for specific project scopes.
Go-to-market motion1 record
Distribution channels1 record
Marketing channels4 records
Siem Offshore Contractors product offering
Product offeringCore offering
Siem Offshore Contractors is a submarine cable installation, repair, and maintenance contractor. The company provides subsea cable and umbilical installation, repair, and maintenance services, supported by dive and ROV operations, marine survey, UXO investigation, and remedial cable protection work for offshore energy and infrastructure clients.
Product overview
Seaway7 offers a comprehensive portfolio of offshore wind project services centered on EPCI (Engineering, Procurement, Construction, Installation) solutions. The company provides six core service lines: Cable Laying Services (submarine cable installation, repair, maintenance with ROV support), WTG Foundations (foundation installation using vessels Seaway Alfa Lift and Seaway Strashnov), Offshore Substations (transportation and installation of jackets and topsides), Wind Turbines (integrated T&I services using jack-up vessel Seaway Ventus), Floating Offshore Wind, and Heavy Transportation (using six semi-submersible vessels: Eagle, Falcon, Hawk, Osprey, Swan, Albatross). These services work together to deliver complete offshore wind farm projects from foundations through turbine installation and cable systems.
Differentiator
Problem solved
Functional benefit
Products and services
- Submarine Cable Installation
- Submarine Cable Repair
Quantifiable outcome
- 800+ WTG foundations installed
- +4 more outcomes
Companies that use Siem Offshore Contractors
Customer profileNamed customers6 records
Segments2 records
Ideal customer profiles1 record
Siem Offshore Contractors technology and API
TechnologyTechnology focussed No
API detail
- Has API
- No
- API docs
- API detail
Core technology
AI maturity
App detail
Feature4 records
Siem Offshore Contractors partnerships and signals
Strategic signalPartnerships
One partnership is on record.
- Subsea7 GroupcoreSeaway7 is a wholly-owned subsidiary of Subsea7 Group. The company operates as the dedicated offshore wind installation arm within the Subsea7 corporate structure, with Stuart Fitzgerald (outgoing CEO of Seaway7) transitioning to CEO of Subsea7 Group. Lloyd Duthie appointed as new CEO of Seaway7 effective April 1, 2026, bringing over 25 years of experience with the Subsea7 Group.
Scale indicators9 records
Recent moves5 records
Expansion highlights5 records
Siem Offshore Contractors competitors and assessment
Company assessmentMarket position
Strengths4 records
Competitive moat5 records
Key highlights5 records
Customer concentration
Siem Offshore Contractors financial estimates
Financial estimateRevenue estimate
Valuation estimate
Siem Offshore Contractors leadership team
Management profileNumber of profiles
Siem Offshore Contractors funding detail
Funding detailFunding overview
Funding rounds
Investors
Funding detail is available on the Subscription and Enterprise plan.Contact sales →
Siem Offshore Contractors M&A and investment
M&A and investmentM&A
Investments1 record
M&A and investment is available on the Subscription and Enterprise plan.Contact sales →
Frequently asked questions about Siem Offshore Contractors
What does Siem Offshore Contractors do?
Siem Offshore Contractors is a submarine cable installation, repair, and maintenance contractor. The company provides subsea cable and umbilical installation, repair, and maintenance services, supported by dive and ROV operations, marine survey, UXO investigation, and remedial cable protection work for offshore energy and infrastructure clients.
Is Siem Offshore Contractors a public or private company?
Siem Offshore Contractors is a private company. It is classified as corporate owned and is currently operating.
When was Siem Offshore Contractors founded?
Siem Offshore Contractors was founded in 2009. It employs 1,001 to 5,000 people.
Where is Siem Offshore Contractors based?
Siem Offshore Contractors is headquartered in Leer, Germany, in the Europe region.
How does Siem Offshore Contractors make money?
One revenue line is on record: EPCI Contract Services.
Does Siem Offshore Contractors have an API?
No public API is recorded for Siem Offshore Contractors.
What industry is Siem Offshore Contractors in?
Siem Offshore Contractors's product category is Offshore Cable Installation Services. Its primary akta.pro industry code is HDAIALAC, Subsea Cable Construction, Marine Installation & Repair Services. Its NAICS code is 23891 and its SIC code is 1600.