Which vessels are designed only for transporting offshore workers to and from job sites?

Crew boats are specifically designed for the purpose of transporting offshore workers to and from oil rigs and other offshore job sites. These vessels are constructed for speed and agility, allowing them to navigate through various sea conditions while ensuring timely and safe transfer of personnel. They are typically equipped with features such as large open decks for easy boarding and disembarking, and are built to accommodate a significant number of crew members.

Accommodation vessels, while they do provide living quarters for workers who stay offshore, do not primarily serve the transportation function. Instead, their main purpose is to provide a stable platform for housing personnel working on offshore projects.

Dive support vessels play a different role as they are equipped for dive operations, providing the necessary support and equipment for divers working underwater, rather than focusing solely on crew transportation.

Heavy lift ships are designed for the transportation of large and heavy cargo. They do not serve the specific function of transporting workers, but rather are geared towards moving large machinery or components used in offshore operations.

Thus, crew boats uniquely fulfill the requirement for transporting personnel, making them the correct answer.