What do the ships, the Godspeed, the Susan Constant, and the Discovery represent for the colonists?

The colonists travel on three ships to the New World, the Discovery, the Susan Constant and the Godspeed. They are painted nicely when the leave London, but look battered by the time they arrive at James Town. The ships represent safety, though traveling upon them is extremely unpleasant for the passengers. When the Indians attack, the ships are the only place they can retreat to. They are the only means of escape back to England, and are also where prisoners are kept. New ships arrives with groups of new colonists, and bring food. However, when they leave, they also take most of the food the colonists have put together.