how not to install a transducer...got a few pictures here...
first...
a thru hull transducer,it needs a fairing block,the block is a two fold,first,it allows the 'ducer to be mounted correctly into the hull.by this i mean it will read straight down,rather than off to the side-due to the "v" of a hull...second,it makes a sealing surface for the 'ducer.the 'ducer needs the block to have a good sealing surfce,without the block,most 'ducers have a very tiny area to seal the hull.
use the blue composite blocks,avoid using wood.i cut the block,after i find the correct angle,using a table saw.again,i don't reccomend wood...after you drilled the hole in the boat,remove the bottom paint in the area where the block will rest,rough up the gel coat too.by doing this,you will assure a good adhesion for the 5200.remember,nothing sticks to bottom paint,so remove it...
sealers...i use and reccomend only one sealer,3m 5200,do not believe what other's tell you,it's removable,it's not as permanent as some will tell you-i've removed and reinstalled numerous items set in 5200...do not use a silicone sealer ever !!!

here's a thru hull 'ducer installed by the owner...i removed this using no tools !!! i grabbed the 'ducer and twisted it out of the boat-i kid you not !!!
the owner purchased a raymarine "c" series unit and i was installing it,the reason the remove the 'ducer...the 'ducer was also turned slightly,as you see in the pictures,this is exactly how it appeared when i pulled the boat...scary thought huh ?




here's the fairing block this gentleman made,it was only on the inside of the hull...




this is the ducer...not the small sealing area...





look close at the pic,you can see the marks where i twisted the ducer around to unscrew it...