I've never had an issue taking my BCD436HP on Carnival (Valor being one of them) & Royal Carribean (All three ships went out of Galveston). I had it in my carry on as I have never checked baggage before. Went through X-Ray just fine, one time I was asked if it was a battery bank and I said "No, it's a scanner" and just got an "Oh, Okay". The only things I was able to pick up was marine VHF going in and out of the ports, I didn't hear anything while underway and the onboard conventional DMR radio for housekeeping & engineering I believe. Nothing exciting by any means, but then again, I was more focused on eating, drinking, and attending shows.
Enjoying radio is a fun past time of mine so I can't fault you for wanting to take your scanner. I will say from personal experience, I thought I was going to listen to it a lot more but was distracted on other things. That might not be the case for you though or you might just want to set yours up to record if you so have that function.
That being said, I did see that it was on the prohibited items list and knew I was taking a chance. Not sure what I would have done if they said I couldn't have it. As others have mentioned though, a laptop with SDR dongle may be the way to go. You might get some hiccups if someone things your SDR is some type of device used to access the internet outside of their systems. Either way, Its a risk you take so it's only up to you what your willing to take or leave behind.