Apple Watch with cellular on a cruise

I have an Apple Watch with cellular service and will be going on a cruise in a few weeks. I have added the cruise data plan to my iPhone, so I will not be charged roaming fees, however I did not do this for my Apple Watch. My question is how do I avoid being charged roaming fees by my cellular provider for my Apple Watch? Do I need to put my watch in airplane mode? I like to use my watch with my AirPods when I’m working out, which is the primary reason for taking my Apple Watch.