this is my fisrt post, so I would like to introduce briefly myself.
I'm Tiziano, from Italy, I'm 25 and I'd like to explore the seas of the Ligurian Gulf, that is where I live.
Ok, really short introduction, so we can discuss a bit about interesting things. :)
In these days I was thinking and reading about the tether, and I'm now studying a 4-wire tether solution.
So, I wold like to discuss a bit with you the idea, just to know if I'm wrong.
The idea is simple, and is nothing really new. I mean: 2 wires for the ethernet and 2 wires for power supply. Just to keep it simple.
First problem: how many Amps are absorbed by the ROV, at maximum? Well, doing some calculations I found something around 3.5 A. I'm right?
Supposing 3.5 A, for a 100 m tether, i was wondering using a PS wire of 16 or 18 AWG. It should be ok, I hope. But... the wire is heavy...
Also, for a safety purpose, I would like to add a nylon rope of 4mm diameter, in order to manually recover the ROV in case of failures, and also to strenght the connection. But, again, this adds weight.
For the moment I'm not thinking about the flexibility of the tether assembly. But it is a problem too!
A possible solution for the wire weight (and maybe for the maneuverability) with this kind of tether, is a scuba diver buoy. Here the thing I'm thinking: http://www.ebay.it/itm/BOA-SUB-SILURO-IN-PVC-PALLONE-DI-SEGNALAZIONE-SAGOLA-/110932259856?pt=Sub_scuba_e_snorkeling&hash=item19d413f410#ht_1816wt_1037
The tether can run from the ground to the buoy, then, with a pulley, down to the rover. In this way, we can reduce the tether weight over the ROV. An other advantage, is that I can run the rover some tenths of meters off the shore and signal the position to the people around me. Last advantage, is that in case of problem, I can pick the ROV first UP, and then BACK to the shore, that is good in presence of underwater stones that can stuck the ROV in case of recovery.
Waiting you for better ideas, and to know if a 18 AWG wire should be ok over 100 m (and over 200 m tether?).