That’s not it. Look for pictures of early 60’s Hansen Surfboards. If anything it was more of a large “Pivot” fin. When Hansen went to fin boxes, they stopped using that design. It’s called a “747” because of its similarity in outline to a 747 Boeing vertical tail fin. If you go through the “Archives” you may find some mention or pics of the fin over the years. They were glass-ons done with Mahogany wood at center. So that when they were sanded the Mahogany wood at center formed a bead around the fin.
Do an archive search for; “Vintage Hansen Cardiff Mike Doyle” . There is a nice example of a Hansen board with that fin. Hansen’s people referred to that fin as a “Doyle Pivot Fin”. It’s funny because I don’t think 747’s were around in ‘64 &’65. So that name was probably given to in later years. ‘65 was like 707’s.
A guy from Australia was making and using that design. I can’t remember his name, but Chipfish (Ben Chipper). I think Ben posts as fins if he is still on Sways. Try going through the archive.
Ben sent me a bunch of fins a long time ago and several had the 747 shape. They look like an airplane wing. The back fins are from Ben, they have the 747 shape.