I know this thread is a little old, but curious if there are any updates?
I am planning to start building a boat for lake/stream/river mapping as well. Mostly for streams and rivers.
Currently, I'm researching depth transducers and looking to use a Raspberry Pi3 for data logging.
@Michelle I'm curious about why you are going with a $3k transducer over a $150 version? The only advantage I see in your sensor is the update rate? Not sure how fast you are planning to have your boat move when mapping?