emmafoils said..
I wonder why you don't see them on more of the shorter foil SUPs? Kalama uses a single one in the front and Ride Engine seems to have borrowed that idea but I don't see them on other production boards.
Because a lot of people in surfing (a bit less in foiling) are awfully conservative and are afraid of trying things they do not see pros using.
In this case however, it is because if you have a "whistle tail" (bevel on the tail), you have no room to put a fin, and also sub-6' boards have the foil mast too close to the tail for a fin to have significant leverage anyways. Plus most dedicated SUP foil boards seem to have enough yaw-countering properties nowadays?
Also, if you have enough dihedral in your stabilizer (or up/downturned tips), it can acts as small rudders.
I added a small fin on a flat stabilizer, and it worked well, except that the force on it was building like the square of the speed, so it was stiffening too much the foil at speed. Which is not an issue for fins as they are out of the water at speed.
I didnt try a fin in front, I would be wary of veering away the nose hard on touchdowns, but I didnt try it yet.
On a quad setup I would just use the 2 rear ones for maximum leverage. I have seen pics of Kahei kite foiling with the quads still on, he told me that he was just being lazy and did not bother to remove them for a foil session :-)