Longer Tether


Hello there everyone!

Our expedition on openexplorer (https://openexplorer.com/expedition/northwalesmineexploration) has been lucky enough to be sponsored by the Betty and Gordon Moore foundation and the kindness of OpenROV, as such our little ROV is going to be busy exploring flooded mine passages, that brings me to my question.

How long can the tethers be before you start having problems?

Reason I ask is because the way some of our mines have been driven you're going to be losing a lot of the tether diving down inclines before you can start exploring passages.


Hi Paul:

Here at OpenROV we have been using 200m of tether on some of our ROVs, seemingly without problems. We have heard anecdotal accounts of HomeplugAV (that's the protocol being used) working out to about 400m. However, we have not done any formal testing of this yet.

If you experiment with longer tethers, please post something here on the forum to let us know what kind of results you are achieving.



I use a 300m tether. It works great.


What is your strategy organizing the tether when the ROV is getting closer?

How do you know how much you can reel-in?

Anybody tangled the tether around obstacles (or other traps)? And how to get this sorted?


slightly off topic:

And who is the (...) person in charge who decided to send the tether cable in a way that you need a lot of time and a lot of patience to get it usable instead of sending it on a reel?


Thanks for the replies! 300 meters sounds great, we'll be to see a lot more that way.


How long is the tether as supplied in the kit ?


100 meters


Can I order e.g 100m more?
or can I use another tether cable?


If your going to extend the tether I would make sure to make some type of tether management system. These tethers can get tangled very easily if you are not careful.


I have had issues with the tether getting tangled together, but the main issue I have had is in knowing how much tether to let out. When you let out tether, you can, for a while, tell if the ROV needs more by the tug on the tether. But, because the tether is negatively buoyant, the more you put out the less information you can receive in that manner. The tug on the tether from the ROV will quickly be replaced by the tug of the tether as more and more of its weight goes into the water.

I have tried using floats. In a long tether they don't solve the issue and can increase the chance of tangles since the floats cause loops in the tether.

In another post : http://community.openrov.com/forum/topics/floating-tether-1

I am posting about the attempt to use hollow braid polypropylene rope, with the tether run through the center, to float the tether. I would prefer neutrally buoyant tether, but that is trickier to come by. I hope that positive buoyancy will be an improvement.


Hi Darcy

but the main issue I have had is in knowing how much tether to let out

Length of cable out is always a bit of an issue for the side scan we mark the cable (and will do the same for the upgrade of the ROV to the longer tether)

For the side scan cable we have numbers every 10m (on a much larger diameter [14mm] multicore cable) covered with clear silicone emergency tape

On the extended ROV tether I've been tossing around the idea of using heat shrink and / or electrical tape to form a banding system (similar to Roman numbers) every 10 metes (eg 40m out would have the cable marked with 4 bands say 50mm band 50mm space by 4) and maybe a mid point mark of a different colour for the 5m. (its what we had on the SSS cable before we swapped over to the numbers)

Keen to hear how you go



I tried in the past to use zap straps to mark length, they got caught in the pullys and a wheel that marks distance, it needs proper mounting, which I haven't done!

Heat shrink is a really great Idea. I will have to do that.



If you want to extend the tether, you can splice on pretty much any kind of wire- if you have some tether from another openrov, that would be fine.

I don't believe we sell tether cable in the OROV store, but it's a possible idea. I'll look into it.



I would buy some.



If additional tether is not available through OpenROV, could you provide the source and part number for those of us who would like to get additional lengths ?




Zack with OpenROV here.

I'm happy to see interest in this! I will add this to the store as soon as I can...hopefully not very long wait, maybe a day or so.

In the mean time there's one other option, buy an Ethernet cable and cut off the jacketing. The twisted pair inside the cable works just fine for this and is actually what we used originally. It is a bit weaker, though, and more likely to break.

Hopefully I will have it in the store shortly. Thanks for the feedback.






I would also be interested in the new battery tube endcaps. The laser cutter I use cuts on a bit of an angle. It is normally not an issue, but the bt endcaps are small enough, that it is an issue.


I haven't got the kit in the mail yet, so this might be a silly question, but how do you extend the 100m cable? Do you have to solder two together or do they attach mechanically? Thanks.


Hello Grace,

In order to extend the length of tether you would simply solder two lengths together.

-Brian G.