Tomb Raider: Underworld; Mediterranean Sea Help?

I just started playing this and I'm at the Mediterranean Sea part where you have to go back to Lara's boat by follow your route back to the surface. I saw the clip of Amanda's soldiers leaving. I got back on the boat and nothing is happening. I've gone back numerous times and retraced everything and still nothing happens when I get on Lara's boat, what do I do? Did I miss something?