Welcome Aboard Flipster1998!!!! Whenever there is a question about a switch or a breaker slot, I try to start backwards. For example.....Do you have Auxilliary Blowers installed on the boat? If not, then I would not worry about Aux. Blowers breaker slots. There should be several Aux switches at the helm , as well as empty slots in the AC and DC panels for fuses and breakers. These are all there for explansion purposes.
I believe the Aux. Blower breaker is for a heater.