The largest yachts (Catamarans 48+) have mandatory skipper, while any other yacht can be rented with or without, depending on the captain's skills, experience and confidence, who, in any case, must give proof of having a valid sailing license.
The Skipper needs a single room (or the front bunk) and food provisioning from Guests. We can suggest some professional ones, very expert about specific sailing areas, but the final payment and agreement will happen between Guest and Skipper at check-in.