I was on a Princess cruise back in February, and spent a lot of time in the casino. I got to hear quite a few stories from the dealers and pit critters, so I can chime in with some relevant info. (Long story short - your idea is highly likely to be shut down quickly by the casino staff.)

In theory, your idea should work. In practice, no.

It is true that you can charge up to $3k/day (max $21k/cruise) on the slots to your shipboard account, with no cash advance fee. In fact, on Princess (not on all CCL lines), you can even do this with table chips. You could then go down to the main desk, have them run your card for the current room balance, and switch the card on file for the next day. Lather rinse repeat.

Your problem is going to be getting the cash off your room key card, since, as I recall, Princess doesn’t have TITO - everything goes to and from the casino account on your card. You have to go to the cage to get cash.

If you charge, say, $1000 to your casino account, play $15, and try to cash out the remaining $985, they’re going to catch that no-play right away. The first time, they’ll let it slide. The second time, you’ll just get a warning. The third time, they’ll freeze your charging privileges in the casino, AND ding you with a cash advance fee, same as if you did it at customer service.

You might have better luck doing this with chips at the table, but they will still notice that you’re no-playing them and tell you to get stuffed after a day or two. These guys are there all day, every day, and they’ve seen all the attempted exploits.