Eric drew up this great visual of the different tether strategies. What do you think? I've started a discussion on the forums, feel free to chime in there.
I have to say, I like the current solution a lot. However considering an alternative I have to go with 'Standard Ethernet"
My thought is that the tether is probably the part mostly likely to get cut, tangled and otherwise broken and replacing it might as well be as easy as possible. since there are separate Tx/Rx pairs the low-latency/low-bandwidth control down link will not have to be shared by Rx and I think this is important for ROV control. It looks like the Rx-uplink pair is going to be pretty busy with video, but if that hiccups every now and then it isn't critical.
Length is always a consideration and I believe with a decent driver you can get a maximum of 328-ft at least per spec. So count on about 200-ft. A float based battery operated range extender could be inserted between multiple 200' segments if needed, but honestly I think a 100' length is more than enough. Perhaps those needing extended range might use an altogether different tether? I don't think it is necessary to accommodate everyone with a 'standard' tether, more range and thus more expense could be available for special needs.
Obviously the connection points (connectors) at least at the ROV end will be special, but the rest of the wire length is nothing special. Replacing it is very easy and very familiar to nearly everyone.
Although not a fun thing to do, excess weight could be compensated for by floats, the rigidity might actually be welcomed. Just my $0.02.
So for those reasons I would favor the 'Standard Ethernet' approach.
With the current design, what is the maximum length of tether that can be used with the open ROV? What would be currently available for a battery range extender beyond 200 ft?
If tether breakage is possible, with resulting open ROV loss, would a fail safe float/reel system with a simple 24 hour galvanic time release ( http://www.reddenmarine.com/neptune-marine-products-galvanic-time-release-1-day.html ) be a consideration? For under $15 in parts it may be nice to wait 24 hours to have a buoy pop up to enable you to pull up your openROV.
We've had the signal running through 70m of tether, but all of supplier specs indicate we should get 100m.
Fail safe system - yes! That's definitely something we talk a lot about. A few folks have expressed intent to build one. The galvanic time release seems like a great part for that system. Thanks for the link!