Submarine cables, or subsea cables, are purpose-built systems laid along the seabed to carry data, telecommunications traffic and, in some cases, electrical power. Although largely unseen, they underpin modern global connectivity: more than 95 per cent of international data transmission relies on submarine cable networks. These systems range in scale from short coastal links to intercontinental routes, as well as connections between land-based networks and offshore installations.
In this guide from CDC, we’ll explain everything you’ve ever wondered about submarine cables, including how they’re used, their main types, and how they’re designed and constructed.
How are submarine cables used?
Submarine cables support a wide range of critical functions, particularly in telecommunications and data transmission. These include:
- High-speed internet links between continents
- International voice communications
- Financial trading networks
- Cloud services and data centres
Beyond communications, submarine cables play an important role in offshore and industrial environments, supporting:
- Offshore wind developments
- Oil and gas platforms
- Subsea production facilities
- Remotely operated vehicles (ROVs)
Subsea power cables are also used to transmit electricity, such as for exporting power from offshore renewable energy projects to shore and interconnecting national and regional power grids.
Main types of submarine cables
Submarine cable systems generally fall into three main categories.
Submarine fibre optic cables are designed for telecommunications and data transmission. Using optical fibres to carry light signals, they offer exceptionally high bandwidth and minimal signal loss over long distances.
Submarine power cables are used primarily for the transmission of electrical energy. These cables are common in offshore wind, tidal energy, and oil and gas projects, and can carry high-voltage alternating current (HVAC) or high-voltage direct current (HVDC).
Hybrid submarine cables combine fibre optic communication with electrical power transmission. They are typically deployed in offshore energy, monitoring, and control applications where both data and power are required.
Like other types of marine cables, submarine cables are designed to be waterproof and highly durable, able to withstand the harsh conditions of marine environments.
Core components of a submarine cable
At the centre of every submarine cable is a core designed either to transmit data or carry electrical power. Data cables contain optical fibres, while power cables use copper or aluminium conductors. These cores are insulated to protect against water ingress, pressure, and temperature variation.
Surrounding layers provide additional protection. Steel wire armouring is often included to guard against external threats such as fishing gear, anchors, and seabed movement. An outer sheath offers resistance to corrosion and long-term exposure to the marine environment, contributing to operational reliability over decades.
How are submarine cables designed?
Subsea cables typically feature a custom design. Everything is precisely matched to the cable’s intended application, from the fibre count, voltage rating, and cable diameter to the insulation materials used.
Submarine cable design is shaped by several key factors, including:
- Water depth and salinity
- Seabed composition
- Environmental and mechanical risks
- Required electrical or data capacity
Cables intended for shallow waters typically require heavier armouring to withstand human activity, while deep-sea cables prioritise flexibility and reduced weight.
Design variables can include cable diameter, armouring configuration, insulation systems, and connector arrangements, allowing each cable to be matched precisely to its operating environment. Designs are validated through testing to ensure long-term performance.
Installation at sea
Subsea cables undergo a range of electrical, mechanical and environmental tests to verify their performance and durability prior to deployment. Once approved, installation is carried out by specialist cable-laying vessels that deploy the cable along a carefully surveyed route. Detailed seabed assessments are undertaken in advance to identify obstacles, geological risks, and environmentally sensitive areas.
In shallower waters, cables are often buried using ploughing or jetting techniques to reduce the risk of damage from anchors and fishing activity. In deeper waters, cables are generally laid directly onto the seabed, where natural conditions offer sufficient protection.
Environmental considerations
Modern submarine cable projects are developed with environmental responsibility in mind. Installation methods aim to minimise disturbance to the seabed and surrounding ecosystems, and all works are carried out in accordance with regulatory and environmental standards.
Contemporary designs increasingly focus on the use of non-toxic materials, reduced electromagnetic emissions, and long service life, helping to limit both environmental impact and the need for replacement.
Durability and service life of submarine cables
Generally, submarine cables are designed for minimal intervention. They’re engineered to operate reliably in demanding underwater conditions for extended periods, typically 20 to 30 years. They are built to withstand high pressure, temperature fluctuations, and continuous exposure to saltwater.
Performance is monitored throughout the cable’s lifespan, and where faults occur, specialist vessels can recover and repair affected sections, extending operational life.
Challenges in submarine cable systems
Throughout their service life, submarine cables face a range of challenges. Physical damage from fishing equipment and ship anchors remains one of the most common risks, particularly in coastal waters. Geological activity, including seabed movement and seismic events, can also affect cable integrity.
At the same time, growing global demand for data and power continues to push capacity requirements higher, increasing the importance of robust, well-engineered cable system
About Custom Designed Cables
Custom Design Cables specialises in the engineering and manufacture of bespoke cable solutions for complex and demanding environments. With experience across subsea, offshore energy, telecommunications and industrial applications, we focus the company focuses on designing cables that respond directly to real-world operating conditions rather than relying on standardised specifications.
Each project is approached from a technical and environmental perspective, ensuring that cable construction, materials and protection systems are aligned with long-term performance, safety and reliability requirements in harsh marine settings. To learn more about our custom subsea cabling solutions, speak to our team today.