We were sailing along Chatham Strait when some Dall’s Porpoises came towards us. As we picked up speed, they began to ride the bow wave. They are unbelievably fast (this film shows them in slow motion). We could see them quite clearly as they swam under the bow and around the boat. We could even see the difference between males and females: males are overall much chunkier than females with a deeper tailstock and keel and often have convex flukes whereas females have slightly concave ones.