Whales

On the way here we had a amazing experience! We had small whales, 6 m long, swim under the boat and next to us! It was so scary, they came from behind swimming FAST and swam with us. We were so worried they would come up under the boat. They were black with white fins, and had a small dorsal fin. One turned over and it had a white belly. A very thrilling site. Still dont know what they were??