Rather than use a purpose-made gimble mount  for a depth finder, I decided to go with a more general-purpose  option. 

I found this choice on  Amazon.   (You need to Login or Register

It was designed to hold a camera (e.g., GoPro), but by swapping out the ball mount for the camera with the one for the depth finder, I have a solution that winds up being multi-purpose.    Of course, the base plate mount on the mount is replaced with a clamp that has its own ball mount.  Since I tend to rent canoes rather than transporting them 1000 miles each direction, I needed a "non-permanent" option.  This should be perfect for attaching to a thwart.

Beyond that, I how have a place to mount my iPhone.  Not only do I sue it with my inReach for communication purposes, my phone also has a number of maps of Quetico (e.g, Canada Topo, Garman, Gaia), that I take along.  They are more for reference purposes and used in addition to my printed maps, but non-the-less helpful.  So I've removed the GoPro style mount from the original top which leaves a threaded camera mount on top of a 1-inch ball.  I attached that to a swiveling cell phone mount.

So on fishing days, I'll mount the depth finder.  For travel days, I'll mount my iphone and with my bluetooth  remote, I can take photos while I travel.

dd