I originally purchased a $500+ Humminbird fishfinder and ended up returning it. After having problems figuring out how to rig a transducer, plumbing wiring, and dealing with batteries I decided to buy a $180 Humminbird Fishingbuddy. A through the hull wouldn't allow accurate water temperature and having a transducer mounted through a scupper hole has potential problems of snapping off if hit from below.
So far I've been super impressed with the Fishingbuddy. It has side imaging plus an accurate vertical cone that shows bottom contour, size, and depth of fish. Another plus is I don't have to deal with recharging batteries (takes AA's). I can turn the direction of the side imaging by rotating the unit without having to actually turn my PA to locate fish in front or beside me. It has an alarm when fish are below me. It is possible to mount the FB on the side right next to the seat where I can view it while sitting or standing. It simply bolts to the side of my PA and easily removes. I have a pontoon that I sometimes use and I can easily transfer it from my PA to pontoon in a matter of a minute.
The FB may not be as extravagent as other models but for $180 it does a great job. http://store.humminbird.com/products/27 ... hin'_Buddy