I have a 998 HD si unit that I am using with two transducers on an aluminum boat with rivets. I am using the HD side imaging transducer and a 2d for high speed operation using a y splitter cable. My question is which transducer is being used for 2d during slow speeds. Also when the 2d transducer is being used is it as precise as the 2d imaging that would come from the HDSI transducer.