Is it possible to rent a yacht without a skipper?

 Yes, bareboat charters are possible, but not for every boat.  Typically, sailing boats and catamarans of a certain size can be operated independently, while larger yachts often come with a dedicated crew of two. 

To embark on a skipper-free voyage, you must hold a valid International Certificate of Competence (ICC) for boat handling or a local certificate of boat operator proficiency. Not for every boat. Usually it is possible for sailing boats and catamaran certain size while bigger yachts come with crew of 2 or more