To get to Antarctica, you have to cross one of the roughest bodies of water on the planet, the Drake Passage. Depending on the speed of the ship and the weather conditions, it is approximately forty hours from Ushuaia to the South Shetland Islands. In that time, it is possible that the ship will experience some motion.
If you are prone to seasickness, we recommend that you consult your doctor to advise you on the best medicine to take with you. Once in Antarctica, the ship becomes a stable platform.