I fish out of canoes a bit and I built myself a portable unit by getting one of the $99 ones, (a Bottom Line - no longer made) - mounting it on a plastic box with a 12V drill battery in the box and using tye-wraps to attach the transponder to a block of foam. When I got underway I just threw the the foam block in the water. It gives me depth and surface temperature which is all I wanted. I use mine in both my canoes, my 10' jon boat and while I haven't tried it yet I could take it with me in my belly-boat (float tube).