By TEBAOFLEX Jyen. Originally published on December 9, 2025.
An ROV main umbilical and an excursion tether perform different jobs. A load-bearing umbilical may connect the vessel launch-and-recovery system to a tether management system (TMS), while a more compliant tether connects the TMS to the vehicle. This arrangement reduces the vehicle’s exposure to the loads on the long surface cable. It is not mandatory for every ROV: direct surface tethers also exist.
Start with the load path
Determine which component supports the vehicle, cage and suspended cable during launch, operation and recovery. A communication tether is not automatically a lifting member. Record the allowable working tension of the cable and the complete terminations, not just the breaking force of a sample of armour wire.
- Main umbilical: suspended wet weight, hydrodynamic loading, vessel motions, winch traction, sheave bending and emergency recovery.
- Excursion tether: vehicle excursion, local currents, snagging, buoyancy, minimum bend radius and TMS handling.
- Both: cyclic load spectrum, torque response, abrasion, corrosion, pressure, electrical power and communication continuity.
Steel armour and aramid are design options, not universal ratings
Opposite-lay armour layers can be designed to reduce tension-induced rotation. Their balance depends on wire sizes, lay angles, stiffness and boundary conditions; opposite directions alone do not prove zero torque. Likewise, an aramid strength member does not establish a particular breaking load or service depth. The manufacturer must document the finished construction and its termination efficiency.
Specify the permitted rotation and torque under defined tension and bending conditions. Inspect for armour movement, local opening, crushing and termination damage using the equipment supplier’s procedures. Do not add a swivel unless the system designer has approved its effect on the umbilical.
Buoyancy and pressure must be checked together
Neutral buoyancy means the cable’s mass is approximately equal to the mass of the water it displaces under the relevant conditions. State the reference water density, temperature and pressure. A density near that of fresh water is not necessarily neutral in seawater, and pressure-induced volume change can alter buoyancy.
For a hypothetical fully displaced circular section, submerged mass per metre is approximately m_air − rho_water × pi × D² / 4. Actual design must account for flooded spaces, compressibility and components whose geometry changes under pressure. This expression is not a depth qualification.
A metal optical tube, water-blocking material or syntactic buoyancy layer needs pressure and fatigue evidence for the assembled cable. Do not infer that a tube material alone guarantees freedom from water ingress, hydrogen effects or optical attenuation change.
Standards and acceptance records
DNV identifies DNV-OS-E402 as a diving-system standard. It is not used here to assign a universal 5:1 safety factor to every ROV umbilical. Agree the applicable ROV, lifting, electrical and pressure requirements with the equipment designer and certifying authority.
- Approved construction and termination drawings, mass in air and water, pressure conditions and allowable working tension.
- Mechanical qualification covering relevant tension, torsion and bend-over-sheave duty, with sample identification and acceptance limits.
- Electrical and optical records at the specified test conditions; distinguish routine production tests from destructive qualification tests.
- Handling instructions, inspection limits and a documented basis for continued service or retirement.
Common selection questions
Must every tether be neutrally buoyant? No. The preferred buoyancy depends on vehicle control, route and deployment method. Must every umbilical have bare steel armour? No. Jacketed and exposed-armour designs involve different handling and environmental trade-offs; neither should be selected solely from depth.
A published manufacturer example, Nexans’ ROV cable range, distinguishes umbilical and tether solutions. It is supporting context, not evidence that a TEBAOFLEX cable has the same ratings or qualification.
Sources and application documentation
Discuss the application
Send the application duty, installation drawing and required acceptance criteria to TEBAOFLEX. WhatsApp: +86 185 9591 3361. Request the applicable product documentation before ordering.