Sub M_snb()
  activesheet.columns(6).replace "Bowen Marina", "Bowen Harbour",2
End Sub
You could have saved the trouble using a validation list containing all valid port names.
The string should have been split into 2 parts: the geographical part and the port name.

The Townsville item could be addressed by:
Sub M_snb()
  activesheet.columns(6).replace "Townville's", "Townsville",2
End Sub