I believe it's ethical, and have seen other fly fishermen using them.
A depth finder or fish finder what ever you want to call it, would be really effective when fishing chironomids, so you can find the depth the fish are at.Just my opinion.GOOD LUCK.
In very large bodies of water or when the water tempature is cold so the fish are not moving much. I will use a depth sounder to find fish. Never on small bodies of water or when the water temp is good and the fish are active. Mostly this means I use it on Puget Sound or Lakes such as American Lake. The other use is to find out a lakes structure when a lake is hard to read. Smaller lakes are most of the time easy to read, larger bodies of water are not.
I have a fairly inexpensive unit by Hummingbird that is portable, water proof, and battery operated. I can mount the trasducer to the bottom of my canoe via special suction cup mount, or to my tolling motor.
If I were to buy another one, I'd get a 'fishing buddy'. They are portable and can be used with a float tube or bigger boat.
I know guides that use them for still water fly fishing...
For the purist needing a depth finder, I would suggest attaching a hemastat to the end of your leader and lowering it to the bottom and noting the depth. It's cheap and easy and tells you where on your leader to attach your strike indicator (for chironomids). As for a fish finder, well, that's up to you.
Since I use a anchor I have marked the rope off every 2ft then when putting down the anchor I just count the marks a get the depth that way. This works well from my kayak. When I am out on the sound or American lake I have a fully loaded 15 foot boat with a depth sounder that came with the boat. I also have another depth sounder that I have made portable by installing the tranducer on a 1 x 4 board that I can c clamp in place and the unit installed on an old small kids tackle box, with a motor cycle battery inside for power.I have not used the home made portable unit much because its to bulky for the kayak and the large boat has one but it comes in handy when going out on friends boats who may not have a sounder.
I've used one for the past 3 years. Is it great for finding bottom and/or structure? Yes. Is it great for finding fish? Not really. Mine has a sidefinder and occasionally I'll get a hook-up after casting towards a blip, but I think most trout are to small to give an accurate sounding. It's great for locating bottom on new water. I would much rather get right into fish with my c-mid/strike indicator set up than spend a couple of hours trying to dial it in. As far as ethics go, who's to say. My fishing partner gives me a raft of sh** everytime I bring mine along, but he is also the one who asks me how deep was I when I hooked that last one. Check out Cabelas for the FISHIN BUDDY. I think they run about $150-$175.
:THUMBSUP I look at it this way. In today's hurry-up world, most people have very little time for recreation. I bought an Eagle fish
finder about 6 years ago and have it on my South Fork Pontoon. It is one of the best investments I have ever made. When I find time to go fishing, I want to know where they are. Once I locate them, I can then concentrate on what they are feeding on.
I have seen many a frustrated fisherman "working" an area of a lake where the fish are not holding up in.
I use my finder as an educational tool. Along with using a thermometer, observing what is on and in the water, and keeping records I have learned so much about the lakes I have fished. My daily catches since buying the fish finder have increased greatly. I go fishing with 2 guys that have the same set up. We get on the lake, split up in different directions and locate where they are. When one guy finds where they are, he calls the others on the walkie talkie :EEK instead of shouting half way down the lake.
Ethical? Cheating? After having a successful day,I meet many "highbrows" coming in off the lake at the end of the day, :CONFUSED :MAD stating they just didn't have a very good day. When in fact they had been fishing the wrong spot and depth. I usually tell them that maybe they will have a better day next time.
We live in a world filled with technology. I say use it and have fun.