My son and I dove off a cruise ship once (Belize, Roatan, Cozumel - not organized via the cruise ship). Brought all our gear etc, except for knives (were expressively listed as not allowed). It started out with my son staying in a cabin with my daughter and I with my wife. After all the dive gear got rinsed the first time in my shower and pretty much took over the bathroom + hallway for drying it turned out the cruise continued with my son and I sharing a cabin and the girls the other one... I brought some string to hang stuff from ... for drying good thing I did.
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I struggled with what to do with the passport - something that had to be taken on land (even if not checked, what would you do if you missed the boat or had other trouble), but which I was not willing to leave on the dinghy or boat we dove from locally - I just was too worried about potential loss. So, I took mine and my sons with us diving together with some cash in a waterproof cell phone vinyl pouch. I figured if all air is out it should hold up nice and stay dry. Did so successfully the first to dive days. Not the third. Lessons learned:
An older fabric covered passport binding de-laminates pretty good in saltwater. Some ink from some stamps runs pretty good. Not much harm to more modern style passports (like US or the newer German ones) except for running ink from some stamps. Saltwater logged paper and money dries very slowly in a cruise ship cabin, even when well pressed (page by page, bill by bill) between (changed several times) toilet paper sheets. Maybe rinsing in non-salt-water first might have been the brighter thing to do.
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Afterwards I was wondering if it was worth the hazzle and the carrying of gear through ports and quite a ways down roads (e.g. Belize) ... but whom am I kidding, compared to going shopping with the girls... in a tourist filled cruise port ... or taking a cattle tour to a beach, ... no contest... sure it was worth it!