Negril is unique in many ways but the same as anywhere when it comes to danger. Traveling alone to NYC or LA or Paris for a female poses the same potential dangers as Negril does. I am surprised that your father, who himself has traveled to Negril doesn't have friends / contacts that he can put you in touch with to put himself at ease. It comes down in many ways to your ability to navigate the potholes in the road be it anywhere you might be, if your Dad doesn't have that confidence in you then you will have a tough time convincing him otherwise. I have two sons 23 and 20 and I doubt they would want to go on vacation with me simply because I've given them enough of my opinion over the years and they certainly wouldn't want to play by my rules in Negril. I think that only you can convince your dad that you are fine to travel alone. Good luck and hope you make the trip.