I currently have a garmin 551s in built into my dash. It is an adequate gps but hopeless sounder. I have purchased a humminbird 898cx si and I am going to install it on a bracket provided and use the garmin as a plotter only. My questions are:

1) is there any point keeping the transducer for the garmin?

I was going to keep it as a back up but a mate suggested I remove it and use the hole for the new transducer saving a new hole in the fibreglass.

2) if I was to keep it can you turn the sounder on the garmin off so that it doesn't interfere with the humminbird?

anything else I should consider?