This assumes you're checking it for work reasons, and not for, say, healthcare, or financial reasons.
Plenty of people have reasons to check email that are not about work, and where they could reasonably need to be contactable. It's quite a privilege in many ways to be able to fully disconnect.
If you're in a situation where you might urgently need to check an email then boarding a boat and going out in to the middle of the ocean as far from an Internet connection as humanly possible is probably an less than optimal IT strategy.
If you or a loved one has potentially urgent healthcare issues - then a cruise is not sensible.
I've had relatives who have had to cancel in the past because of this - travel insurance is a good investment (and there's a reason it gets more expensive the older / sicker you get...)
My general point here is, something, anything, urgent has come up. What're you gonna do? Swim to shore? I can think of the convenience of forgetting to pay a bill and then doing it online - in which case it's up to you to figure if whatever internet fee you pay would save you on potential late fees.
Being out of contact was often the absolutely normal state of affairs until 25 years or so ago. If you must be reachable, stay by the phone. Otherwise, someone may not be able to get in touch with you right now in many circumstances.
Plenty of people have reasons to check email that are not about work, and where they could reasonably need to be contactable. It's quite a privilege in many ways to be able to fully disconnect.