Re: transducer mount recommendation
In my opinon you have it lined up with one of the skegs. The skeg or step is going to create air bubbles at some speed. When you get air bubbles then it will not get good readings.
If it was my boat I would do 2 things. First I would move your bow stop toward the stern so the end of the bunk is flush with the back of the transom.
If this affects your tongue weight too much then you may need to move your axel back a little.
Then I would move your transducer so it is almost lines up with the bunk. Right now you have your transducer pointed straight down which is very good.
One other thing is if your are going to drill more holes drill them so that both holes are in the middle of you mount so you can loosen and then raise or lower the transducer.
With what you have try moving it to port enough that the starboard bolt will go in the left hole. Put some silicone seal under the mount and let it cure for 48 hours before testing. This may be enough to get away from the air bubbles.
Also you do understand that from speed to stopped in the water on many boats you need to readjust the sensitive. The new units in auto sensitive will try and adjust for you.
http://www.lowrance.com/en/Support/Tips-and-Tutorials/Installation-Guide/