Why did Brian build a raft and what were Brian's problems at the end of chapter 17 of Hatchet?

In chapter 17, Brian works to recover from a moose attack and a tornado that touched down on top of his shelter. After repairing the shelter and gathering wood, Brian turns his attention to the tail of his plane sticking up out of the lake. He is sure that a survival pack is stored in the plane that would yield him many useful items. However, Brian must build a raft to reach the plane and retrieve the survival pack. Building the raft proves a difficult, long, tedious task of gathering and weaving branches. In his injured state, everything takes longer.

Eventually he finishes the raft. After sleeping and eating, Brian swims, pushing the raft out to the plane. This takes much longer than he thought. He is again exhausted. Though exhausted, he begins to search for a way into the plane. Again Brian faces obstacles. The chapter ends with Brian still trying to figure out a safe way into the plane.