You can book passage on a container ship. I flipped through about 1/3 of their list of voyages, and the longest one I found is 97 days (London - Adelaide - London round trip), although it includes numerous stops enroute. The longest single leg of that journey is 13 days, between Pointe Des Galets, La Reunion (near Madagascar) and Sydney, Australia. All for the low low price of 12,742 Euros.