I have sometimes used the rod tip, but that of course has limited range. I have in the past used a line with a lead weight on but that just not practical when fishing. Pulling up a line, counting knots, cleaning off weeds, storing again etc.
I've looked into a sounder for the pontoon boat several times and there are several good ones out there, most of them require a transducer mounted to the boat, and the device itself also mounted to the boat. That makes it difficult to move from pontoon boat to float tube etc., and takes more time to setup on the water.
Then I saw a small, handheld depth gauge like a flash light you stick below the surface, press a button and then read the depth off a small LCD display on the device. Looked nice but was quite expensive.
In a video on YouTube, I feel over a little device called "Deeper". It looked just like what I've always wanted (in fact, much more), but it was a little on the expensive side as I had zero experience with it. YouTube- and online reviews looked promising, and so I decided that to get one.
I tried it for the first time yesterday. It's a little smaller than a tennis ball, charged via USB. There's an app for iPhone and it connects via BlueTooth. It turns on automatically when you dump it in the water and connects immediately to your phone . It might acutally be the best BlueTooth connection I've ever experienced. So stable is the connection that every time I dug out the phone from my pocket to check conditions, it was always just "on" - even though it was windy, wavy and the sonar hanging off the side of the pontoon boat. When you turn on the app, you get a really impressive representation of depth, bottom and weed height/depth. The app has a lot of different settings that I haven't explored yet, but it's a really great device.
Here's an image of the chart it produces in "Detailed mode". I'm not sure all the fish are really fish, but I was fishing pike and I'm sure some of them are real signals. I'll get a better feel for that as I gain some experience with it.
But that really doesn't matter much. I'm more interested in depth and bottm structure, and it also tells me water temperature, which is also very important. I didn't check the accuracy of the thermometer, becasue I had nothing reliable to test against, but I'll do that some day.
This completely takes the guess work out of choosing the right density flyline or weight on/for your fly.
This is a really great gizmo and there are a number of places I regularly fish that I really look forward to seeing on the sonar. If you're interested, this is the one I have. It has a 40m BlueTooth range depending on how much detail you choose in the app (which is more than I'll ever need, because I won't be using a rod to cast it over fishing spots, which is one of the intended uses) and it can scan to 40m of depth, which is more than I'll ever need too. But if you need it, you can get more powerful versions.
Sorry for the late FP - I just got back from a morning fishing trip. I'm camping on the island of Møn, where I'm once again attending the Møn Session-event, which is really great.
Have a great weekend!