Use a text editor such as notepad to edit the "playconsum.txt" file in the game's "\data\econ" folder. Set all values to zeros so the entries appear as:

Sup Weight(lbs) Per person
Food 0
Fruit 0
Pork 0
Rum 0

This allows you to sail as long as needed as long as at least one ton of those supplies are present. Note: The "Fruit" and "Livestock" commodities will still be used by the crew.