Remember the cruise line world can be a small one - and if you're a US citizen, they really DO all know each other - most of the hiring parters have come from shipboard jobs themselves and have worked for a couple different companies.
Number one rull is donn't say you'll quit your job to come work for the next cruise line. BIG no-no!!
They usually won't even offer to interview you if they know you're currently employed by a competitor, but will ask you to call the the moment you get back home.
I was with NCL when I got calls from HAL and Princess, neither would even offer me a gig until I was off contract. RCCL called me a week or two before sign off, so I was able to do a quick phone interview and then asked to come to Miami for a 'hiring event' the weekend after I signed off the Sun. I was offered a job the following day and on the next ship of the next line the next weekend.
Then in 3 months, C-Deck called offering me Silversea/Radisson/Crystal vacation fills, but by this time, I was just offered a managment gig with RCCL and decided to go with the porthole, own room and medical coverage, instead of the world itineraries and a job I was getting tired of.
What was getting the calls was the ship experience (esp doing a take out, i.e. brand new ship) and solid resume with references.