Hint 1
Hint 2
Hint 3
As Magnus said in the note you found behind the toy cupboard in his cabin --
How do I arrange the dog toys?
-- you need to scrape away the barnacles on the pier supports. You can use the hook you got from the fish gutting station for this. (Told you it would be useful.)
Don't see any barnacles? Then maybe it's still high tide.
How do I change the tide?