I just installed a Garmin 168 in my Oday 22...
...it came with a transom mount 'ducer which I just bedded in silicone inside the hull. It seems to work just fine, even gives me both bottom and "fish" as advertised. Water temp is probably a degree or two off (on the high side) since it is inside the hull and not in the water. My 'ducer is mounted in cabin under the forward half of the starboard quarter berth, close to centerline. It is bedded in silicone, but pressed close to the hull so not a lot of energy is absorbed by the rubber. Here are some things to consider (not a comprehensive "how to"): 1. Test the location you want to use by placing the 'ducer in a platic bag full of water. We the deck and put the bag on the wet area. If you get a good "known" depth then you're good to go. 2. Sand the area smooth before mounting the 'ducer. I have seen instructions that say to sand the 'ducer surface too, but I did not. 3. I bedded mine in silicone. If you search the web you'll find lots of info on other methods. You can use epoxy (the best way, but very permanent). You canuse plumber's putty, you can even use a wax toilet seal. You can mount a standpipe and fill it with water or mineral oil. Lots of ways to do it. I think epoxy gives the least sensiivity loss (stiffer material) but my reason for getting a depth sounder was to detect shallow water, not deep water. If I can't see the bottom at 1000 feet, that's okay, my Oday 22 isn't going to ground there anyway. 4. I mounted some wire guides to keep the cable up under the top surface of the lazarette and not get fouled on gear stored inside. I plan to mount a cut down container around the 'ducer so nothing knocks into it. 5. I have read some advice not to mount it next to the keel because it will be shaded/ blocked by the keel when you heel. This is ridiculous - the 'ducer will be fixed with respect to the boat, so it will heel too.
