It's not a crazy idea... I've used an off the shelf fish finder/depth gauge.. The transponder took many trips to 300 feet with out any problems. I dident realize that the digital world had evolved to equal the reliability of the analog world. But now that I think about it, we rely on it from the time we take off in an air plane till the time we land. We spend billions on resurch and development for air craft ( fly by wire ) and there's no reason we shouldint take advantage of it in our subs....Thank you, Warnn for bring it to my attention.
djb