From Bulbapedia, the community-driven Pokémon encyclopedia.
The S.S. Spiral (Japanese: ラセンまる S.S. Spiral), known as the S.S. Sinnoh (Japanese: シンオウまる S.S. Shin'ō) in Pokémon Diamond and Pearl, is a ship that travels between Snowpoint City and the Fight Area. After the player has defeated the Elite Four, the ship will take passengers.
Differences between games
In Pokémon Diamond and Pearl, the ship is known as the S.S. Sinnoh and appears as the generic ship. A horn sounds upon departure from Snowpoint City. The sea that it travels through has a current too strong to Surf on. When disembarking at the Fight Area, the player arrives directly above the sailor.
In Pokémon Platinum, the ship was renamed S.S. Spiral and was vastly redesigned. It is now red-orange and silver in color, as opposed to the previous white and brown. It includes two rotating drills at its prow to plow through the icy waters, which did not have ice in Diamond and Pearl. There is a winch at the back of the ship. The horn no longer sounds upon departure from Snowpoint City. When disembarking at the Fight Area, the player now arrives at the edge of the pier instead of directly above the sailor.