In adventure mode, I went to a part where the boat ran aground and when I get an iron ore the Diary opens but nothing appears there.
I wanted to know what would be written in the diary so I could complete this phase.

I actually don't remember what exactly you have to do at that point. Did you collect all iron pieces (I think there's more than one, right?) + swim back to the surface? If not try that.

You must now dive and get 7 pieces of iron from the sea floor to repair your ship. Once you have used the iron to repair your ship, [...]

And in the comments section:
If you have iron from island you have to get any piece from sea floor. When you get it a message will appear and ship will be repaired automatically