I contacted a subsea cable supplier (Elmeridge Cables Ltd, they have been very helpful) in the UK and asked if they could supply a neutrally bouyant tether for the Open ROV.
I specified a single twisted pair, 24 AWG, neutrally buoyant, yellow colour sheath, with as small an outer diameter possible.
This is what they came back with:
M.O.Q is 2000mtrs
Neutrally Buoyant 1 x 2 x 24AWG
conductor: tinned copper class 6
Tape: non woven tape to hold the conductors in place
Pulling Element: open Braid yarn
Jacket: bright Yellow PUR
Cable Weight 37.5kg/KM
Price 1.81 GBP per/mtr
I have posted this here so that everyone can see this and have a chance to offer some feedback. As the minimum order quantity is 2000 m (there are, of course, substantial costs in providing a bespoke production run of cable, hence the M.O.Q.) a group purchase could be an option if we have enough interest.
Tether management is one of the most important aspects of piloting a ROV and a neutrally buoyant tether, with a smooth profile (floats can add bouyancy but they also encourage entanglement and create tether handling issues.) would have many advantages.
Of course, like anything, there are downsides with a larger tether spool required, more weight during transport, increased tether drag subsea, inherant stiffness of the tether - which could put a turning moment on the ROV etc.
I thought I would post this here so that the Open ROV community can give their opinions. Any feedback is appreciated.
One thing I forgot to ask them is the minimum bend radius, which will have implications for our spool sizes. I can find this out if there is interest.
Cheers guys and happy ROVing!