Siem Offshore Contractors

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.

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

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

• Submarine cable installation
• Subsea cable repair
• Offshore cable maintenance
• Subsea umbilical installation
• Marine cable services

Headquarters

HQ city

Leer

HQ country

Germany

HQ region

Europe

Offices1 record

Markets served

GTM type

B2B

Offering type

Services

Cost components

Personnel, Infrastructure, Operations, Supply Chain

Revenue model

1. 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

Core 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

Named customers6 records

Segments2 records

Ideal customer profiles1 record

Technology focussed No

API detail

Has API

No

API docs

API detail

Core technology

AI maturity

App detail

Feature4 records

Partnerships

One partnership is on record.

• Subsea7 GroupcoreStrategic or Co-development PartnerSeaway7 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

Market position

Strengths4 records

Competitive moat5 records

Key highlights5 records

Customer concentration

Revenue estimate

Valuation estimate

Number of profiles

Funding overview

Funding rounds

Investors

Funding detail is available on the Subscription and Enterprise plan.Contact sales →

M&A

Investments1 record

M&A and investment is available on the Subscription and Enterprise plan.Contact sales →

Frequently asked questions about Siem Offshore Contractors