We sailed across the Atlantic from New York to Bremerhaven Germany in 1963 on the USNS Geiger (a Military transport ship). At times, there were 40 foot seas, and they closed the outer doors of the ship to prevent anyone from going outside (who would have wanted to anyway?). It was a long 12 days of sea-sickness. I'm sure today's Cruise Ships can handle the rough water better, due to their stabilizers (the transport ship didn't have them).