If you only want to do bottom (z) mapping, the precision of the RTK unit will be wasted.
Since the cone angle of the transducer, which is 20° will offset by a good margin the precision of the positioning data.
And remember, doing GPS position import in the 1197 will induce a delay in the NMEA sentence, which will
further degrade the precision of the map.
HB don't produce a pencil beam transducer in the <10° range. If you want a real precise map, look into lowrance units will special Airmar transducer which can be 9° of cone angle to really put the RTK signal in use.