Well as a few of you may know we have been extensively testing our OpenROV up at BC Robotics (#049)the past 2 weeks. We decided to go with a Cat5e tether on our build - i am not sure if anyone else has gone this route yet?
Our test tether is about 65' long , cat5e patch cable. One thing to note is that in the colder PNW waters the cable does get very stiff, and definitely affects the maneuverability of the ROV. The weight is also a concern as even a short run of this cable will weigh the ROV down. Floats attached to the line do help a lot!
Also another thing to note... We happened to have a small pinhole in our cable about 3' up the tether from the ROV .. on a dive to 15' depth and found a good 4 ounces of water in the tube after only 2 minutes!! The Cat5e will work like a pipe.
Standard wire will do this also if it is not solid core - be sure to allow solder to wick into the jacket and use heat shrink tube and liquid electrical tape!
If you have a leak in your ROV during testing and cant seem to find the source.. check the wires! And if you are going the Cat5e route - be prepared to fiddle with the flotation a lot!