I have a pinnacle std with a garmin echo 200. I've mounted my transducer on the outside behind the rudder. I have perfect water temp and echo readings. I launch in the surf, in rocky kelp gullys and in two years I've had no problems. The downside is I had to put an inspection hatch in the rear of the kayak to pull the cable through and mount the transducer bracket. Your other option is to mount it in in your fishbox. With the pinnacle I would have had to cut a hole in the side of fishbox and then glue the transducer to the inside of the hull. But then you do loose the accuracy of your water temp and sound strength. I have a large unit on my boat with a 1kw transducer which work perfect thru the hull, sound quality lost is about 20% but a smaller 200w transducer will loose a lot more of its power, even thru a thin kayak hull. I've made an aluminium "u" shaped bracket, attached it with 2 4mm bolts thru the hull. The transducer is bolted to that, BUT, the transducer can still tilt in the bracket if i push hard on it. Should I strike sand, kelp or something, the movement will stop it from braking out. The transducer is also protected by the rudder as the rudder is far deeper than the transducer , so the risk of hitting the transducer is minimal. I've had many "swimming lessons" in the surf, got separated from the kayak, kayak gets rolled and washed out and all of those fun things, no damage yet. Just make sure when you mount it that it has a clear view / that no part of the rudder moves underneath the transduce. If you want to, I'll send you pics.
