GTA Vice City
The Yacht is owned by Juan Cortez, and is featured in all the missions Tommy Vercetti does for him. In the mission All Hands On Deck, Tommy must defend the boat from the attacking GIGN and DGSE agents. You can enter the Yacht using a helicopter, land it next to the boat and then jump on the Yacht.
The Ballad of Gay Tony
Luis Fernando Lopez is ordered by Yusuf Amir to steal the Buzzard helicopter off the boat and destroy it. This time, the Yacht is larger and has a helipad. Unlike in GTA Vice City, you can now enter it.