The canoe helps against starvation as it enables Kino to make his living. He is a pearl-diver; he fishes for pearls to sell. The canoe is thus absolutely vital to Kino; without it he and his family could not survive.
When the canoe is wilfully damaged by Kino's enemies, he is devastated by its loss.
The killing of a man was not so evil as the killing of a boat. For a boat does not have sons, and a boat cannot protect itself, and a wounded boat does not heal. (chapter 5)
We can judge from this quote just how much the canoe means to Kino. Its being damaged is more than he can bear. It is as though the canoe were a living thing; in fact it seems to assume even more importance than a person: 'the killing of a man was not so evil as the killing of a boat'.
It is the loss of the canoe which finally pushes Kino over the edge; henceforth he becomes as an 'animal' (chapter 5), driven beyond all reason and restraint.