The real test tube is when you fly inside a closed titanium tube called passenger aircraft. The large ships have more open spaces than my single family home. The recent cruise on RCCL ship Oasis of the Seas was so big, it had a living forest on the ship with hundreds of mature trees and thousands of bushes. Birds were living there permanently. I measured the walking distance from our cabin to dining room and back, and it was half a mile of walking. The ship also had a artificial water fall where passengers could water ski. Try that inside of a aircraft flight, a train or a bus.
Enjoy your cruises. I do not plan to get on an airplane either I don’t think they’ll let me because I don’t have a “vaccination”. I will watch all this from afar.