Remotely Operated Vehicles (ROVs) are transforming how we explore, inspect, and operate beneath the ocean’s surface. Yet one critical component often determines whether a subsea project succeeds or fails: the ROV cable. It’s the vital connection that transmits power, data, and control. While also physically linking the ROV to the surface. Choosing the right cable isn’t just a technical decision; it’s a strategic one.
Introduction
Remotely Operated Vehicles (ROVs) are essential to modern subsea operations, from offshore energy and scientific exploration to defense and inspection. Their success depends on many components working seamlessly together, and one of the most critical is the ROV cable. The cable is more than a link between vessel and vehicle. It provides power, transmits data and control signals, and carries mechanical loads during deployment and retrieval. Selecting the wrong cable (too short, too weak, or unsuited to the environment) can jeopardize an entire subsea project.
This guide explains how to choose and design ROV cables that are fit for purpose. It explores the latest developments in the ROV industry, the principles of cable construction, the relationship between system and cable requirements, and how to optimize lifespan and minimize downtime.
1. Subsea ROV Trends and Their Impact on the Cable
1.1 Going Deeper with ROVs
As offshore activities extend into deeper waters, cables must reach greater lengths and withstand higher pressures. Longer cables weigh more, which means they must also be strong enough to lift their own mass along with the ROV. Traditional steel armor becomes impractically heavy beyond about 4,000 meters, so alternative strength materials such as aramid fibers are being used. These materials reduce weight but pose new challenges: they are less heat-conductive and can be more brittle than steel. Deeper operations therefore demand careful material selection and precise balancing of strength, weight, and heat management.
1.2 Less Downtime, Longer Lifespan
Downtime is costly. Predicting when a system or cable will fail requires deep understanding of materials and fatigue. For steel components, established inspection methods exist, but synthetic fibers are less predictable. Research is ongoing to measure fiber degradation and remaining service life. New technologies, such as fiber-optic sensors and even self-healing materials, promise better monitoring and extended cable lifespan. Keeping up with these developments helps operators reduce maintenance costs and unplanned interruptions.
1.3 The Sustainability Trend
The global shift toward renewable energy, particularly offshore wind, is reshaping subsea cable requirements. Floating wind farms operate farther offshore and in rougher conditions, where cables must tolerate constant motion, bending, and exposure to extreme weather. Dynamic marine cables, capable of both power transmission and mechanical endurance, are therefore crucial. Sustainability also means designing cables that last longer and require fewer replacements. Longer lifespans reduce waste, minimize environmental impact, and improve lifecycle economics.
2. ROV Cable Construction
Every subsea project has unique demands, and no standard catalog cable fits all applications. Cable design depends on the ROV’s function, depth, deployment method, and power requirements. A typical ROV cable includes electrical conductors, optical fibers for data transfer, strength members, and protective sheaths. Conductors are usually copper, insulated with thermoplastic materials. Optical fibers are placed in the cable’s core for maximum protection against crushing forces. Around the core lies the strength member, often steel or aramid, which bears the mechanical load.
The cable’s geometry is designed to balance flexibility and strength. The helical structure allows bending and stretching without damaging internal components. Load is transmitted primarily through the strength member, not the conductors or fibers. For deepwater cables, elongation must be limited, generally no more than 0.6% at maximum working load, to prevent permanent deformation or internal stress.
3. System vs. Cable Requirements: Fit-for-Purpose Design
A successful ROV project depends on how well the cable’s design matches the system’s operational needs. Seven key system parameters directly influence cable requirements:
- Function: whether the cable must transmit power, control signals, or data defines its internal geometry.
- Deployment: launch and retrieval methods affect the required flexibility, bend radius, and crush resistance.
- Depth: operating depth determines cable length, pressure resistance, and allowable voltage drop.
- Power: the required current and voltage define conductor size, insulation thickness, and cooling needs.
- Downtime: reliability considerations dictate redundancy (e.g., extra fibers) and repairability.
- Design life: fatigue and material stress analyses ensure the cable meets expected operational lifespan.
- Budget: cost affects material selection and production complexity, but the cheapest solution often proves most expensive over time.
Let's dive a bit deeper into three of these parameters.
Function and Deployment
The function of the ROV cable determines both its electrical and mechanical configuration. Deployment conditions (winch type, bend radius, and handling system) dictate geometry and choice of armor. Steel offers superior crush resistance and is often used for work-class ROVs; lighter synthetic options suit smaller or deep-diving vehicles.
Depth
At greater depths, longer cables are needed, but increased hydrostatic pressure and weight complicate design. Air voids must be eliminated to prevent collapse under pressure, and buoyant materials like foam may be used to offset weight in water. However, these materials behave differently under compression, so careful testing is required.
Power
Power transmission drives cable diameter. Heat generated by current is typically dissipated by seawater, but in shallow or multi-layer winch storage, cooling can be limited. Thermal analysis helps prevent overheating. Voltage drop, usually limited to around 10%, and electrical stress must also be managed. Filling internal voids reduces the risk of discharge and insulation failure.
4. Downtime and Life Expectancy
4.1 Preventing Downtime
Because ROV cables are mechanically and electrically complex, they are often the most fragile part of the system. Downtime can be reduced by using spare optical fibers, protecting delicate elements in the cable’s inner layers, and choosing materials with proven fatigue performance.
Steel-armored cables are easier to repair at sea, while aramid-armored designs require specialized tools and training. Considering repairability early in the design phase can prevent long interruptions later.
4.2 Prolonging Life Expectancy
Cable life is primarily limited by fatigue and bending stress. The ideal design balances tensile strength with flexibility. Longer helical lay lengths increase tensile strength but reduce flexibility; shorter lay lengths improve bending performance but can shorten lifespan. Modeling these trade-offs helps engineers predict fatigue life under real operational conditions.
4.3 Budget Considerations
Cable cost depends largely on manufacturing method. Unilay construction twists all components together at once, producing a compact, low-cost cable but introducing torsion. Concentric lay builds each layer separately, improving stability but raising cost. Group lay combines subcables into one structure, offering maximum flexibility at the highest cost. Cost optimization should never outweigh reliability. A slightly higher investment in cable quality often saves significant expense by avoiding downtime or premature failure.
5. DeRegt as Strategic Partner
Cables are just one part of the ROV system, but their complexity and importance demand close cooperation between engineers, manufacturers, and operators. Early Supplier Involvement allows cable experts to contribute from the design stage, ensuring all system components fit together seamlessly. A true strategic partner goes beyond supplying cables — they think alongside you. Through co-creation, manufacturer and client jointly develop the optimal solution for the application. This collaborative approach reduces technical risk, accelerates design, and maximizes system reliability.
DeRegt combines in-house expertise with field support. Engineers and service teams assist on location to troubleshoot issues and perform repairs, minimizing downtime and maintaining performance throughout the cable’s service life.
Conclusion
An ROV cable might seem like just one component of a larger system, but it directly influences mission success, safety, and cost. Depth, power, deployment, and lifespan requirements all interact, and each project calls for a customized solution. By understanding how cable design, materials, and construction relate to system performance, and by partnering early with experienced engineers, operators can achieve longer lifespans, lower downtime, and greater operational reliability.
