So, I was out two days ago on the bay heading back to shore about half a kilometer out coming back from a long tack. Going at a pretty good rate of speed. I feel this hit and loud knocking thump sending a shockwave through my surfboard. I look around and can't see anything that I have hit, and because it was so loud and threw me off balance I assumed it was a piece of driftwood. I get back to shore, land my kite and pick up my board and see a gash on the rail of my board. Except the gash is on the edge that was not in the water on the tack. And its deep. And it is the perfect shape of a dorsal fin. Whatever hit me was going at a pretty good rate of knots to leave a big slice on the rail that was about a third down from the nose so it would have for sure been out of the water. I could not see any dolphins around, (and I see them often and ride with them whenever they are around), so I can assume it was a very large fish with a big dorsal fin. When I went to repair the board yesterday I pulled some greyish black flesh out of the gash. Pretty sure it was a shark, but if anybody knows of any other fish that would have a strong dorsal fin and can penetrate a tough epoxy board please let me know. Very curious.