Captain Fin Co Christenson FG Keel Fin Set - Single Tab   Chris Christenson takes us back in his time machine with this classic keel fin design. The Christenson Keel is a fiberglass template that's a touch more upright than a traditional keel making them more versatile for down the line speed and control, which will complement your retro twin fin fish. A slightly upright keel for more control in a retro twin. Compatibility: Compatible with Futures fin system. Construction: Fiberglass Flex: Stiff