I put a thru hull gt-21 in with my 741xs and could not be happier, keeps bottom at all speeds and very sharp picture.
Gt-21 is traditional 50/200 & chirp down vu, did not want side vu. From what I understand if you want side vu you will need 2 transducers.
Mine is mounted just off center where the cabin meets the deck pretty much. Needed to put 2 small access hatches in the cabin floor to install and run the wiring. Reason for putting it there I did not want to redo the battery tray. These new transducers are quite large and with the bilge pump plus live well it would have been tight.
Like I said I couldn't be happier with it, just need to replace the crap transom mount that is connected to the 541s that came with the boat. Going to put an Airmar p66 on.