I decided to copy the outline of the dolphin dorsal fin from the resource post made earlier today--mostly for a distraction, but also curiosity. I've attached some screen grabs of the outline--If you use Adobe Illustrator to make fin templates I can send you the actual .ai document. Otherwise, I can email you a PDF, but they are too big to attach at their actual size.
I estimated from the picture that the fin depth was about 5", depending of course on where the bottom of the fin was determined to be (you can see how I cropped it from the blue lines). 5" depth x 8.25" base--sounds like a fish keel to me.
If you look at the front view of the dorsal fin, in the resources section, you can see just how thick the fin is. It's really much thicker than I had imagined. The other thing I noticed was how 'flexible' it looked. Does anyone know what the flexibility of the dorsal is like and if dolphins have any control, as in muscular control, of the fin. I imagine that the fin is just cartilage. Any experts? The third picture is of a dorsal fin that looks quite flexible, but doesn't answer the question of control.