It really depends on the perp. But you're right conviction rates are low. I wonder why that is.
Maybe because it's hard to prove the sex wasn't consensual? Unless she sought medical attention right away, and there was evidence that pointed to forced sexual entry and emotional trauma and it was documented, how else could she prove she was raped? Plus, a lot of women don't speak out for fear that people won't believe them. So if there's no case, no conviction.