Got it at a garage sale. Base 8.5", overall length 11.25", height or depth depending on how you look at things 5.5" (not counting finbox insert). Control Fins, Venice, CA. Intended to be a sailboard or surfboard fin? Anyone know any more?
I've seen them on rescue/paddleboards too... the big yellow ones with a slot in the rail to hold on to them. I think Becker used to make them for the lifeguard crews.