Private chef
The cook can or doesn’t have to be included in the crew; it depends on boat size and guests’ wishes. If there is no chef on board, the captain, skipper or the hostess are taking care about a meals.
Chef like a member of the crew is completely in charge of food and beverages, planning menus, cooking according to guests’ wishes and serving the meals (if there isn’t anyone else who would do that) but also for buying and ordering groceries.