In order to access the Captain’s Quarters on Club Penguin you need to have a special key. To obtain this special key go to the Book Room on Club Penguin. Look for the book titled The Journal of Captain Rockhopper.
Then go to the back. You will find a page with a key. Click on it to obtain the key.
Congratulations! You now have access to the Captain’s Quarters on Rockhopper’s ship!