Mark,
If you do decide on a depth finder, I'm with Mary Lou, get a combination  
fish finder/depth finder. We have one on the Chris Craft and they are nice  
because you can see what's on the bottom. Ours also tells us the water  temperature 
and the unit is mounted on the transom of the boat. You might ask  Mary Lou 
where they have the transducer mounted on the R22.
 
Rummy