This Naiad fin is pressed onto its splined shaft, and stays put without fastenings. Removing it requires special equipment, though. Note the narrow winglet at the tip of the fin to make it more efficient.
This Memorial Day, remember those who were lost serving our country on the high seas in the U.S. Navy aboard PT Boats. Recently we were invited out for a ride on the only operational combat-veteran PT Boat, PT 305 in New Orleans.
See what it was like here. ▶