During your stay on the ship, you will get the mission Rogue Games. It is part of the story and cannot be missed. You have to collect three packs of medicine on the deck of the ship. The goal for this achievement is to get the packs without alerting and having to kill the guards. As the packs are close to the entrance and the guards are also not very alert, it is relatively easy. A good tip is once you finished the mission, go back to the deck and kill the guards for the extra experience. Also, the deck is full of vases to break and definitely helps you to get the Sherd Master achievement earlier.