the Suez canal opened on the 17 November 1869. So they probably went from Ireland, through the straights of Gilbralter, sailing across the Mediterranean sea to Egypt on onto the red sea and then the Indian sea.
Before the Suez canal opened it was a very long voyage, the original 1st fleet, sailed from Portsmouth, to the canary islands then to Rio de Janeiro, to the cape of good hope, and then Australia, this route avoided the much more dangerous Cape Horn.