F8-425FT TWIN This is the smaller fin of the F8 series, and it serves primarily as the back fin in a quad setup. However, it could also be used as a smaller thruster side fin or a side bite in a 2PLUS1 setup.
It features the same FLIPTWO tips as the larger version and generally is a scaled-down version of the shape. However, it does not have a cutaway at the bottom. This is primarily due to the size of the fin, where there is no need for the cutaway.
The fin has an interesting trailing edge profile that opens towards the bottom to better control the flow of water off the fin. The attached image shows the shape of this edge. It couples with the HOLOFOIL to make the central section of the fin work to generate as much lift as possible. Like the larger version of this fin, they carry speed through dead spots on the wave due to the lift generation.
The FLIPTWO tips help the fin transition into and out of turns, plus they add to the efficiency of the HOLOFOILS by allowing the foil to extend to the tip transition. The shape of the tip and the back extension improve the holding power of the fin and help it power through the end of a turn.
This fin could also be used as a side bite in a 2PLUS1 setup, providing a lot of pivot and speed.