Yes, this is normal. Each time the raft hits or sounds like it hits a rock in water, it will damage raft as well as night critters hitting on it. Best to keep a crafting table next to it and repair raft often. I have buildt a raised flat floor next to water and put raft on it when put in right place as to be docked. Then I destroy raft with axe, pick up pieces and drop in water when I want to use it.