ROV Tether Winch

Build/Make DIY ROVs
1

Hi everyone,

I’m currently designing a tether winch system for an ROV, and I’m looking for some advice from people who have experience with ROV tether management or winch systems.

The main goal is to continuously measure the tether tension and use the measured tension to automatically control the winch. For example:

- If the tether tension becomes too high → the winch should pay out some cable.

- If the tether tension becomes too low → the winch should reel the cable in.

- The system should maintain the tether tension within a defined range.

My main question is about the mechanical arrangement for measuring the tether tension.

Where is the best place to install a load cell or tension sensor in the tether path? I’m considering different arrangements such as a dancer/tension arm, pulley/sheave with a load cell, or an inline tension load cell, but I’m not sure which approach is most suitable for an ROV tether.

I’d also appreciate advice on:

1. What type and capacity of load cell would be appropriate?

2. Where exactly should the sensor be positioned relative to the winch and guide rollers?

3. What mechanical mechanism would you recommend for transferring the tether tension to the load cell?

4. How can I avoid introducing excessive friction or damaging the tether?

5. How should the tension measurement be integrated into the winch control system?

6. Are there any practical issues such as vibration, dynamic loads, cable movement, or sensor protection that I should consider?

If anyone has built or used a similar ROV tether tension monitoring/control system, I would really appreciate hearing about your design, especially any photos, diagrams, or lessons learned from your experience.

Thanks in advance for your help!

2

Hi @shervin-

That sounds like a cool project! Some feedback:

  1. I’d think a load cell with 50-100lb max capacity is a good starting point, given the workling load limits of the Fathom tether.
  2. I’d think you’d either place the load sensor in a mechanical level wind, or on a pulley that routes the tether from the motorized spool to the water. It can be quite tricky to route the cable cleanly from the water to the spool, and if it runs over the edge of the boat getting consistent readings seems challenging. Suspending a pulley out over the side of the boat with a load cell should work well in my opinion!
  3. Using a simple hanging pulley lets you use a crane-scale style load cell.
  4. Fathom tether is fairly robust - I only find it is damaged by extreme tension or razor sharp edges. Making sure the pulley goes cleanly across a pulley or whatever you’re measuring tension with should be enough! The tricky aspect is winding when little tension is present - you don’t want to pinch the tether if the loops jump off the spool!
  5. The idea of paying out/in when tension is above/below a threshold is interesting - but generally I’d think a simpler solution is a simple “free-spool” out option, where the ROV will pull the tether it needs, and an operator controlled, winch in button, for when the operator wants less tether in the water.
  6. Yes! The Marine environment is tough! A good slip ring, protection from the elements, and avoiding galvanic corrosion are all important to remember!

I’m only aware of this system from Hybrid Robotics, and while quite nice, it is also quite expensive!

3

Hi Tony,

Thank you very much for taking the time to give such a detailed and helpful response. I really appreciate you sharing your experience and practical suggestions.

Your recommendation of using a suspended pulley with a load cell, especially the crane-scale style arrangement, is very helpful. I had been considering several different ways of measuring the tether tension, and your explanation gives me a much clearer direction for the mechanical design.

I also hadn’t fully considered the problem of low tension during winding and the possibility of the tether becoming loose, jumping off the spool, or getting pinched. That is definitely something I’ll need to address carefully in the design.

Your suggestion regarding a free-spool system and operator-controlled winch-in is also interesting. I’ll compare that approach with the automatic tension-control system I’m currently considering.

I’ll also take a closer look at the Hybrid Robotics system you mentioned. It would be very useful as a reference for understanding how a practical commercial system handles tether management.

Thanks again for your time and for sharing your experience. Your feedback is extremely valuable for my project!

Best regards,

Shervin

4

Hi Shervin,

I operate Falcon ROV’s professionally, during operation we will normally manually handle the tether. We have discussed this idea internally a few times and I thought I’d share some of the challenges you might encounter when setting up the control loop.

  • Current can really affect the amount of tension on the tether, If the system isn’t able to account for the length of tether currently in the water and the strength of the current, I could foresee the possibility of a runaway situation. This could possibly be resolved my having the pilot control the level of tension.
  • During operations, especially around any entanglement hazards, we find it extremely useful to have direct feedback on the “feel” of the tether (If its rubbing or being pulled ect.). Losing that feedback could possibly cause the tether to be put in more risky positions.
  • Pilot mental load is extremely important to keep in mind and minimising it as much as possible, too many things to keep track of as a pilot are where mistakes happen. Obviously, this is dependent on the individual but something to keep in mind.

I think this is a really cool project though and I wish you luck on it. Feel free to ask any questions.

Regards,

Jasper