How does Pi's voyage compare to the biblical story, Noah, who was spared from the flood while God washed away the sinners?
There are some similarities. Pi is onboard a small ship with a few animals who are all in some state of difficulty. There is a struggle for survival; Noah has to care for animals he has no real experience with. Pi is also on the open seas for months, floating along, until he finally gets some indication that there is land (the floating island). He eventually washes up on shore, of course, and is saved. There are also many moments when Pi thinks about God's influence on his life, as he drifts along. And in one important sense, Pi's life on the water with the animals is out of his hands; he hasn't chosen this venture, any more than Noah did.
However, the story of Noah is, to a large extent, about redemption and hope, but also the kind of sacrifice faith forces on you if you are going to consciously accept the Divine into your experience, and I think we'd have to ask, to what extent is Pi's story about a sacrifice that is forced on him, that he is not a willing participant in, that he cannot avoid? Noah has this theme running through his story, but Noah's duties are to God, and although Pi talks about religions and God, I wonder to what extent he is truly religious or spiritual? It is a process of belief for Noah; he cannot escape his fate, because he has chosen to believe in God. Pi cannot escape his fate either, but is he a true believer, or is he someone who clings to faith as a way out of his doubt? I think these are valid questions, given his ambivalence.