Under these murky waters on the River Hamble lies some remains of a medieval ship, but this isn’t just any old ship. We’re hoping this is the Grace Dieu, Henry the Fifth’s huge flagship. In fact it was so big that no bigger boat was built for another 200 years. But amazingly she only ever had one voyage and after Henry the Fifth’s death she was just abandoned and left to rot. So, was she too big to sail, was she a failure, and how much of her lies under here? We’ve got just three days to find out.