Last panel being 1st v or closest to bottom. Duh.

So half way up the step closest to bottom ?

I like the transom mount but my only concern would be routing the cable with it mounted under a 30' set back bracket.

30" set back. I hate proof reading.

Routing cable is no big deal for me. Just trying to confirm gt51 can be about 6" up off flat spot on keel. I beach boat a lot and would like to keep it up if I can.

I am no expert on the matter but it seems that if the transducer remains in the water at all speeds and is within the first step of the hull it should work fine.

Yes, I could of and have on a GT 52 I was testing. What I have found with these sidescan transducers is the lower the better as they need the both sides in clean water. I had issues with one side not getting clean water, or as clean a water as the low side at higher speeds. The 51 mounted dead center give the best results by far and I have good returns at 30+ knots on sidevu. On my next build I will mod the stringer and go to a through hull on the back end of the keel but where I have it now is great.

It's really not about being in the water but how clean the water is moving around the ducer. The higher up you are and closer to the strake the more chance of aeration at higher speed. Also consider the angle of the hull in front of the ducer. Regular transom mount ducers shooting down are not near as fussy about clean water across the side but the sidevu ducers are. If you're getting good returns to each side then all is good but if one side is better than the other a keel location works great.

As far as beaching goes... that would be an issue to consider when mounting but I have my trim range set to not let the back of my boat get into shallow enough water without my lower unit protecting it.

Thanks all. Sorry for the hijack. I will mount 1/3 up the bottom panel away from keel on port side and report back. I will be sure to leave just adjustment for down. I won't be able to check for clean water under a bracket :(

Please report back your findings with your mounting locations The Hermit. How did you decide to run the transducer cable under the bracket?

I found out that the vender for the Thru hull pair of transducers will allow me to return them with the purchase of another style transducer. The only other option that I know of with side view capabilities is the transom mount. Looks like I will have to make this design soon in order for them to accept the return. I am thinking about returning them for the transom mount and install it similar to Kmoose and the Hermit's installation. I really wanted to make the thru hulls work but there are too many unknown factors in this application (aeration/cavitation).