tethered camera sub

[TAG caver]

I'm interested in building a small camera sub to push and survey a sump in my project cave. I plan to adapt the steering system off of a decent RC sub to a body Im going to machine out of either aluminum or really dense plastic, probably in the shape of a torpedo. A USB webcam goes up front with a REALLY bright light to show the way. I've got a wicked electric model airplane motor to swim thru all but the strongest underground rivers (I hope) I'm gonna use the power / steering / video tether to fish it out if needed but I wonder what kind of length I can get away with before signal loss starts to mess with USB? Has anyone else played with concept? Any ideas or info would be greatly appreciated. Thanks

[self-deleted_user]

Not sure if this is anything like what you want, but perhaps it could be of use? http://blog.xkcd.com/2010/11/05/submarines/
For camera, on the UK forum apparently this headmount camera is very good for cave filming: http://gopro.com/ apparently the other popular HD camera (the Contour) has issues with the frequency of LED lights and the recording is not that great in caves hence the preference for the GoPro. Everyone so far over there from what I hear likes the GoPro.

[LukeM]

Apparently the reliability of USB cables is pretty shaky over 15 ft. Depending on what you're doing you may be able to push beyond that, but not by a whole lot I'd suspect. There are booster extension cables though. I've never tried them. http://www.datapro.net/products/usb-active-booster-extension-cable.html Sounds like a cool project!