These are some great ideas. We're using a single-twisted-pair (STP) instead of Cat5/6 along with two Ethernet to STP converters. The trade off is we get much lighter tether with less drag at the cost of much slower network speeds (limited to 10baseT). Also, one problem with PoE is the size of the components - it's a matter of fitting everything inside the tube at this point. We have discussed moving to fiber optics someday (for greater range and higher network speeds), but this would be significantly more expensive and not "off-the-shelf" - which is one advantage of almost every component we're using.

Thanks for your insights. We'd love to make it cheaper - our bill of materials is listed on the website http://openrov.com/page/openrov-2-0-overview. I believe we are going for slightly positive buoyancy so that if the connection is lost, the ROV will slowly drift toward the surface. This can easily be changed to fit the condition by adding small washers or foam to the screw beams.