Phillip and his mother were on a ship called the S. S. Hato. In later chapters, sometimes he simply calls it "the Hato." ("S. S." means "Steam Ship," and "Hato" is the name of an airport on Curacao; it's also a last name. So the name of the vessel basically means "Steam Ship Hato.")
As he's narrating the story, Phillip describes this ship as a small freighter that often emits thick, black smoke, and it's a ship that Phillip is particularly familiar with, since he often sees it in the bay. It seems to be well-equipped with life boats, as he and his mother are familiar with how to follow a drill and make their way onto a lifeboat.
Before he and his mother board the ship, Phillip's whole family notices that only some of the ships that leave the islands actually make it to the mainland. Others are torpedoed during the journey. So it's actually a terrifying decision between making the journey on the S. S. Hato, or staying home in Curacao and risking being attacked there, on land.