Floating Tether


I have been having issues with my tether getting caught on things deep in the ocean. Booo!

A neutrally buoyant tether would be best but, I will settle for positively buoyant.

There have been some posts about using hollow braided polypropylene rope and decided to give that a try.

A quick test today:

I cut the rope so that, when stretched out tight, it was the same length as the solid core, cat5, single twisted pair wire. This is what I use for my tether.





The 1/4" hollow braided polypropylene rope is sufficient to float an equal length of solid, cat5, single twisted pair.

Now to buy the rope.


Good idea. The only thing I can see that might be problematic is that as you add the rope you also increase tether drag. This may affect how the ROV maneuvers in the water... Please let me know how it works out because I have been considering doing the same thing....


Ron sends


The rope would also double as a strain pull point (as in when you pull on your tether it won't pull on the wires inside). So its a nice two for one!


Ya, concern about drag is why I haven't tried this before now.

The rope arrived today so I hope to have this ready to go soon. I will post results in openexplorer for sure, but I plan to post here as well.



The pricky part is making sure that the rope is not longer (and it will stretch) than the tether.

I could leave a loop of extra tether on the rov end, but that invites snagging. Perhaps I could have the exta tether length inside a protective sleeve...



Are you planning to thread the cat-5 cable through the center of the rope? If so, how are you planning to accomplish this? A few feet would be relatively easy, but I'm thinking that 100m is a lot of work...


I will use reasonably thick bolt (or something like that) like a needle (maybe a knitting needle). The rope is like the mesh that goes around the rov wires. When you bunch it up it widens, but crucially, it also shortens the rope. So like warp travel, I will compress the space in front of my spaceship (needle thingy) and have less distance to travel!

Even with warp drive technology, it will still take a really long time. I will do in on a near by street that has an extra long block. I will sit at one end with the spool of rope, and the tether will be stretched out down the block

My tether is 300m, and to benefit from the strength of the rope, i will need it to stretch along the whole length.


Also, to be clear, it is a single twisted pair, just like the standard rov cable. The difference is that it is solid core (there may be other differences too).


Ok, Cool... I understand now.... Thanks... :)


May I recomment using a Marlin Spike to work with the rope. They can be found at most hardware and marine stores. I have one to work splices in rope and it makes things a lot easier... http://en.wikipedia.org/wiki/Marlinspike


That looks perfect! Thanks!


I think your idea of doubling it up inside the actual rope itself would work great, but let us know how it goes. I would just be careful, because having done one of these (with a much larger tether mind you) it takes forever and it can be a royal pain.


Hi Darcy

We have done a bit similar with one of the magnetometers and it seem to work fine

As you imply the braided rope acts as a bit of a Chinese finger trap and pulls down on the cable. At a guess you don't have the full strength or the rope but you do get a lot more strength than the cable

As a bit of the side issue have you considered only making the bottom section of the cable neutral/+ve buoyant (eg say the bottom 50m) as most of the rest of the cable would be supported from the surface and it only the bottom section that can get caught up in objects on the bottom

Interested to hear how you go as I'm looking at exactly the same thing (the tethers here but life is getting in the way of the implementation)


In cases where I can position my self above the site, that would work really well I think. I am usually anchored in a shallower area though and so the ROV has to travel horizontally for some distance. It would help if I knew the distance (for proper tether management) but so far I am mostly guessing after the mission by looking at the gps trace.

The other reason I want to cover whole tether is so that I have the extra strength of the rope when I pull the rov back.

If it is too difficult to thread the whole 300m, I will take what I can get! :)


I build umbilicals like this often. It takes a long time. You will need a hallow splicing needle. Smaller the better. Hot melt glue the wire into it and then start stuffing. 10 hyperactive children are needed to help move the rope down the wire. They seem to love helping. The rope will pinch down on the wire. Good luck


It took me more than 6 hours to feed the wire through 152m of rope yesterday. Many of my thoughts were wishes. Wishes for minions to move the rope down the wire! heh.

Its was raining, which was in at least one way, a blessing.

I used a thick crochet needle, which I drilled a hole in the back of to thread the wire through. I pushed the crochet needle into the rope and bunched up the rope ahead of it. When the backlog of rope needed to be pushed down to the reel, the hooked the crochet needle, very handily, hooked into the rope and held its place. I don't see how I could have accomplished this solo with out it.

Where the rain came in handy was while pushing the rope towards the spool of wire. I didn't have gloves, and the water must have lubricated the rope enough to spare my hands. My hands are now extremely smooth. :) I did get one very small blister. I am very very sure I would have quickly ruined my hands and then grabbed some gloves (in that order) if the weather was dry. I'm not sure if it hindered or helped the wire pass through the rope.

Another crucial bit of help came from the benches in Jericho (the park I did the work). I was able to tie the loose end of the rope to various benches as I pulled the rope down the wire.

I had a lot of time to think about all the ways 152m would be more than sufficient. :D


I just thought I would add something to this older thread just to give a bit of completeness and an alternative approach

Over the weekend I was playing around with a new Tether and I wanted to make it “sort of” neutrally buoyant to keep out of the way of the bottom and obstacles

I had been tossing around the concept of having basically permanent floats on the tether to both mark distance of cable out and to provide buoyancy. I was after something relatively incompressible with depth (a little was OK) and that could be strung onto the tether like beads

I had the thought of using Corks (VH8 Colmated Corks 44mmby 22mm purchased from a local home brewing supply shop). After putting an approx. 3mm hole down through the middle of a plastic pack of corks, it was time for a bit of experimentation

After conducting a simple bucket test I found that with 21 Standard 100m of tether sunk but with 22 Corks it floated

Given a bit of simple math that’s about 1 cork every 5m of tether simple

Next I made up a way to thread the corks onto the tether

A simple bit of Line Trimmer / Lawn Edger cable heat shrunk on to the end of the tether to act as a threading needle (give yourself plenty of lead in)

Thread them onto the tether

Side them down the tether and fix them into position with hot glue

Pack it all away - all up less than 1hr

[HELP] How improve standard tether cable buoyanancy with classic corcks?