The SS LEGO Island was a ship used to create LEGO Island.
When the Infomaniac recieved a Power Brick, he used it to create the SS LEGO Island. He had many adventures on the ship, and used his power brick to create Key Lime Island, Soup Island and Sandwich Island. However, he decided to make an island to be his home, and he created LEGO Island. It is unknown what happened to the ship after that, though it was presumably stored at LEGO Island.