Having decided that the ROV will have its own power and not be powered by the tether, I finally built a prototype topside tether. The purpose of this is to take the homeplug signal, convert it to ethernet, and connect it to my laptop. As it happens, my laptop doesn't have an ethernet connector, so I'll also need a USB-to-Ethernet converter. And this made me thing that perhaps I should just put that converter into my topside tether also. The result looks like this:

The USB hub+ethernet plugs into the laptop, and the ethernet connects to the homeplug box. I also added a USB powered 5v-to-3.3v buck converter to power the homeplug board from USB. The result is a simple one-cable topside tether. Now I need to mount this all.

Update: Mounted