Bespoke ROV Tether Cables

An ROV tether is the flexible, dynamic connection that allows a remotely operated vehicle to receive power and commands and return telemetry, video and sensor data. On a free-swimming vehicle, it may run between the surface system and the ROV. On a work-class system, it will typically connect the vehicle to a tether management system (TMS), while a separate main-lift umbilical connects the TMS to the vessel.

That distinction matters. A vehicle tether is primarily engineered for excursion, manoeuvrability and repeated movement. It must transmit the required services while limiting the drag, weight, stiffness and mechanical disturbance imposed on the ROV. It should not be treated as a lifting cable unless the assembly has been expressly designed and qualified for that duty.

Fibron designs and manufactures bespoke ROV tether cables around the requirements of the complete system. Our engineers develop the conductor configuration, optical package, strength members, lay geometry, fillers and outer jacket as one coordinated construction. This supports new ROV developments, upgrades, replacement requirements and specialist vehicles for which an off-the-shelf tether is unsuitable.

Depending on the vehicle and payload, an ROV tether can incorporate:

• electrical conductors for vehicle power and auxiliary loads;
• control, telemetry and data elements;
• fibre optics for high-bandwidth video, sonar and sensor communications;
• screening and component separation appropriate to the signal architecture;
• synthetic-fibre strength members to carry operational tension; and
• protective polymer layers selected for handling and subsea exposure.

These functions cannot be designed independently. Conductor area influences voltage drop, current capacity and diameter. The number and arrangement of optical fibres affect space, bend performance and termination design. Strength-member selection influences breaking load, axial stiffness, weight and flexibility. Component lay and jacket construction affect how the tether bends, twists and behaves on a reel or within a TMS.

The aim is not simply to fit every service into the smallest possible diameter. It is to produce a balanced cable that remains practical to manufacture, terminate, deploy and operate throughout its intended duty cycle. Fibron’s wider composite and electro-optical cable capabilities allow electrical, optical and mechanical requirements to be considered together rather than as separate subsystems.

Tether behaviour in the water can directly affect ROV performance. A larger outside diameter creates more area for current to act upon. Excessive submerged weight can reduce mobility, promote seabed contact and transfer unwanted load to the vehicle. Too much positive buoyancy can also create an unsuitable tether shape or complicate management.

Fibron therefore designs to defined targets for diameter, weight in water and buoyancy rather than treating neutral buoyancy as a universal requirement. Neutral or positive buoyancy can be developed where needed, but the construction must also satisfy requirements for tensile strength, flexibility, operating depth, abrasion resistance and handling.

Fibron can process Vectran™ and other high-performance synthetic fibres together with specialist polymeric materials. This gives our engineers scope to adjust the balance between strength, mass, flexibility and outside diameter around the vehicle, depth, current environment, excursion length and deployment method.

ROV tethers can experience cyclic bending, fluctuating tension, reeling, twisting, local compression and repeated deployment and recovery. Damage may concentrate at connectors, terminations, clamping points and bend-transition zones.

The tether should therefore be considered alongside the equipment that controls it. Fibron can review minimum bend radius, reel and sheave geometry, TMS routing, termination envelopes, expected line loads and operating cycles. Lay configuration, strength-member arrangement and jacket selection can then be developed for the required flexibility and mechanical stability.

The optimum balance varies by ROV class. A compact observation or inspection vehicle may place a premium on low drag, low weight and manual handling. A larger or work-class vehicle may require more power, additional fibres, greater tensile capacity and compatibility with a powered TMS. Specialist survey, research, defence or intervention systems may add further requirements for payload communications, depth or environmental resistance. Fibron supplies cables and umbilicals across observation, inspection, medium and work-class ROV applications.

Early technical engagement helps prevent the cable becoming an interface problem late in an ROV programme. A useful specification will normally define:

• ROV class and whether the cable runs surface-to-vehicle or TMS-to-vehicle;
• maximum operating depth, excursion and required tether length;
• electrical loads, voltages, current demand and allowable voltage drop;
• control, video, telemetry and data requirements, including fibre count and type where applicable;
• target outside diameter, weight in air, weight in water and buoyancy behaviour;
• working tension, peak loads, minimum breaking load and axial-stiffness constraints;
• minimum bend radius and details of reels, drums, sheaves, guides and TMS routing;
• deployment frequency, expected bend cycles and design life;
• temperature, abrasion, chemical and other environmental exposures;
• connector, termination and bend-protection interfaces; and
• factory acceptance, qualification, certification and documentation requirements.

Where every value is not yet known, Fibron can work with the customer’s engineering team to identify the governing parameters and establish a practical design basis. Considering the cable alongside connectors, mechanical terminations, deployment equipment and other interfaces at an early stage can prevent one part of the system constraining another.

Tether development often proceeds in parallel with the ROV, telemetry package, topside equipment and TMS. Fibron can manufacture prototypes and short qualification lengths so that electrical, optical and mechanical assumptions can be tested before the production design is frozen. Results can feed directly into conductor sizing, component layout, strength-member design, jacket selection and termination details.

For an existing vehicle, available interface data, operational history, reel or TMS constraints and the revised service schedule can be reviewed together. This allows a replacement or upgraded tether to be engineered for the system in which it will operate, rather than selected solely by matching an outside diameter or conductor count. Fibron’s wider ROV capability includes replacement cable and umbilical systems as well as products for new vehicles.

Once agreed, the design moves into controlled manufacture at Fibron’s UK facility, with cable engineering, production, testing and project coordination remaining closely connected. Fibron has designed and manufactured specialist cables and umbilicals in the UK since 1986.

The test programme should reflect the risks and duty of the particular tether. Depending on the construction, Fibron can undertake electrical verification, optical continuity or attenuation measurement, tensile or break-load testing, cyclic bend or bend-over-sheave testing, crush and clamp assessment, bend-stiffness measurement and torque or rotation evaluation. Testing may be performed on samples, prototype lengths or the completed terminated assembly, with independent testing coordinated where required.

For development programmes, qualification is part of the engineering process rather than simply a final pass-or-fail exercise. The results can be used to refine the design and demonstrate that the manufactured tether meets its specified electrical, optical and mechanical requirements.

Fibron can also coordinate the cable with mechanical terminations, electrical and optical connectors, bend protection and associated interface hardware. Treating these elements as one assembly helps manage load transfer, bend control, sealing, connector alignment and installation space while giving the customer a single engineering partner for the cable and its interfaces.

Fibron’s experience spans ROVs, deep-ocean research, defence, offshore energy and other applications in which electrical, optical and mechanical performance must be maintained in harsh environments. For tether projects, that experience is combined with flexible manufacturing, in-house materials processing, prototype support, testing and termination engineering.

This makes Fibron more than a supplier of an individual length of cable. We can support the development of the tether as part of the wider ROV system—from the initial service schedule and mechanical design basis to prototype manufacture, qualification, terminations and the final production assembly.