On my Maristar it has a Somewhat Universal Guage in that it requires a 2 1/8th" hole to install. Mine is the Lowrance 3500 which is now replaced by: LST-3800
My 3500 Also, has a Stock Transducer that blinks quite a bit while I'm underway. (Blinking means it's not giving you depth at that time and Blinks the last recorded depth). I have heard that one can buy a High Speed Transducer that minimizes this issue.
Go here to read about them>>Lowrance Website<<
Here is the In-Hull Transducer.