1. The symbolism of the raft
PPT3 Life of Pi
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2. Pi's raft starts as a humble pile of life jackets and oars
Pi's raft starts as a humble pile of life jackets and oars.  It is his shelter, and, like any shelter it should keep him safe.  At first it is not very effective.  It rolls and dunks him and he struggles to balance on it.  But as the film progresses, Pi improves the raft.

3. The raft can be seen as a symbol of man's desire to build and expand his shelter.  In reality we try to protect ourselves from danger and the unpredictable nature of life with material possessions and wealth, symbolised by the raft.  The storm that destroys the raft leads to our discovery that such safeguards are fragile and futile in the face of the metaphorical storms that may come our way in life.  (The film suggests that faith in God is a much better defence against life's harsh realities and unpredictable twists and turns).

4. The raft can also be seen as a symbol of separation
The raft can also be seen as a symbol of separation.  Pi discovers that he can remain separate from the 'tiger within' so that he doesn't lose his humanity.  Metaphorically, it is his life preserver, protecting his soul and humanity from the ocean and from being consumed by his primal self.