Termination of Neutrally Buoyant Tether


A few months ago we added Neutrally Buoyant Tether to the experimental part of our store. We sold through out stock faster than expected, but more is on the way and we should have back in the store by the end of the month.

We have had a few of our community members already start testing it out with their own ROV systems including @Darcy_Paulin and @Kevin_K. Read more and see their video here.

We have had others ask about how the termination of the tether works. I wanted to get the conversation started about the best way to go about this.

Here in the lab @Eric_Stackpole and I have made separate terminations with the tether on v2.8 ROVs. We each did it separately but our approach was very similar. When we took these out in the field we were noticing that when at depth the tether would begin to sink. We suspect this is due to water either hosing or wicking up the inside of the tether (this is still unconfirmed).

We are going to conduct more tests here in the lab in the pressure vessel to figure out the cause, as well as a better way to terminate the tether.

Here is a step by step that @Eric_Stackpole did.

Step 1: Strip back the outside jacket and cut the wires in order to expose a length of the kevlar strain relief.

Step 2: The tether wire was soldered to a quick disconnect. It was then looped around itself in order for no strain to be applied on these joints when the tether is pulled.

Step 3: Use knots in order to attach the kevlar member to the quick release in order to provide the strain relief.

Step 4: String was tied around in order to keep the kevlar in place and then hot glue was applied.

Step 5: Use electrical tape to cover the connection.

Step 6: Put sleeving over the connection in order to protect it.

We would love to hear what other people have tried so the design can improve for everyone!


@Brian_Grau Thanks for posting this tutorial, I never had a termination on my cable when I made it up, but I most likely will when I redo both ends of the connection.

One thing I might do differently is use black heat-shrink tubing vice black electrical tape to cover it on the quick disconnect. It might make for a neater appearance that might hold up better.


Which quick release is used? I want to get some, but there seem to be a few different options.


These connectors by LEDJump are what we’ve been using for the experiments. They’re pretty good quality for the money, though they still occasionally leak a little. It would be cool if somebody could figure out some modification steps to make them truly waterproof.


First dive. 2.8. West of Scotland

Hi Brian
Great that you looking at this, I had been thinking about this a bit of late
I have spliced together a few of Kevlar stranded towfish cables together so as to maintain their full towing capacity and typically you bind and then flood fill with a urethane potting agent

(Can’t recommend Flexane 80 strongly enough as a potting agent)

A couple of things
Are you really sure you want to transfer all of the force through the plug rather than taking the force off the plug (this is sort of standard for most other connections)

Given the Kevlar whip you have pulled off how about connecting something like a 400lb fishing snap to the Kevlar strand and then connecting that to the ROV (either direct or through a lanyard). If the Kevlar whip is shorter than the plug length this will remove all of the force from the plug. Additionally this strategy would also then allow cable to be connected together (sorry for the bad mock up - and yes I can see that one would have to be a male plug)

If you are wanting to transfer the force through the plug rather than electrical tape or heat shrink how about a “silicone hose” (or comparable flexible hollow thing) slid over the top of the splice and down hard onto the plug and then filled with a urethane to bind it as this will also stop wicking in the cable where you have pulled the Kevlar from the sheath

Ideas for WiFi Topside Float design

Hi Scott:

Nice post. We should try out the potting stuff you recommend.

As for the strain relief, we’ve been using cable ties around the body of each connector half to form a strain relief point, and then, after joining the connectors, we use another cable tie to hold the pair together. Difficult to explain, easy to see in photos- maybe I can get Brian to take some more photos tomorrow. The way we do it now, the connector is still the primary load path- the cable ties just serve to hold things together if you need to haul in a dead ROV. I’m sure there are easier and better ways to do things, we just need to get more folks experimenting with the tether.



Have you already tried Self fusing tape? It is used as insulation for underground High voltage cables and should seal any connection or termination very well.
Here you can find the manufactured by 3M, that I always use, but there are several others in the market. http://www.amazon.com/3M-19MMX9M-FUSING-SCOTCH-PREMIUM/dp/B00DK86184/ref=sr_1_9?ie=UTF8&qid=1444212704&sr=8-9&keywords=3M+self+fusing+tape

Sorry if you already tried it, I am new in underwater issues!

Best regards,


@Brian_Grau / @Walt_Holm et al
I have been thinking a little more about this and have a few more thoughts (sorry if they are a bit disjointed and random just multiple thoughts on the subject and an insight into my scattered mind)
In no particular order

  1. Given you are looking to transmit the stress through the plug and elements of the plug no matter what will not be connected to the Kevlar core maybe some destructive testing of the plugs to see what they can take (i.e. what is the use of a 300lb tether if the plug can only take say 100lb)

  2. Increasing the water proofing of the plug simplistically from seeing this style of plug previously look at replacing the O ring

From the image it is a Static axial seal (face seal) [by the look of it with a non-constrained outer diameter] which acts similar to a gasket in that it is squeezed on both the top and bottom of the O-ring’s cross section. The tighter the squeeze the more effective the seal. Additionally the “softer” more deformation / elastic the O ring the better the seal for the same tensioning if the screw fitting

So I would also trial a few softer O Rings (say Shore A 60 (or even lower) rather than standard Shore A 70 O rings) I would also look at some “Square” O Rings (section) to give better contact face

  1. Simplistically looking at the Kickstarter you are looking at say 700+ kits with then at least 2 terminations for the tether (more still for the 100m Adventure Packs) so say near 2000 terminations

Given that how about just setting up for an Room Temperature Vulcanization Over Moulding (yes I get that you still have to prototype to get the best answer)
Sort of a bit like this


@Scott_W and @jo_tanaami thanks for the great comments and suggestions.

We will have to give some of these a try in the lab and in the pressure vessel :smile:

I love destructive testing! I will try to get this done in the near future.

This should be a relatively easy test which should not take too much time.

In regards to the kickstarter tethers we are working on a custom connector that can be mass produced, handle the strain, and be easy to connect and disconnect.

Thanks for the link that looks like a pretty cool way to make connectors.


Thanks for the update Brian - Yep got to love destructive testing

Can you share any more info on the kickstarter custom connector

I’m down for the Std + Adventure pack and had been thinking strongly about cutting the tether into chunks

Ideally I would see a 125m total tether cut into 15m 35m & 75m giving a lot of versatility in depth range if we have strain relief across the joints (worst case using lace on kellums if need be if we cant get to the Kevlar core)
50m (15 +35)
90m (15+75)
110m (35+75)
125m (15+35+75)


I can’t share any more information about the Trident tether connection at this time. When we are able to share, we will share the information.

I really like the breakdown of tether options for the versatility. In the future we have talked about selling custom lengths and this is a good starting point to know what the community wants.