I came across this today and thought it was interesting:

"Deeper" link

$149? Hmmmmm? The question is how will the apparatus needed to power this device and my phone compare weight-wise to conventional battery powered fish finders?

I would think that you could charge this with a solar mat but the question is how long would it take? You also have to factor in the battery life and charging of your phone. I think it would be handy for extended trips if a solar mat works for charging. It would be a bit of a pain to have to be charging that frequently though. I see a lot of potential.

Also, you'd be subjecting your cell phone to some potential water damage...

One issue is trying to use your smartphone in direct sunlight. You would have to turn it up to full brightness which would drain its batteries fast all while protecting it from water.

No phones in my canoe not smart, dumb or fish finding

JB

Just get it over with and tie your phone to a line and use it to plumb the depths. About the same price and I imagine just as effective.