fin placement help for a twin to quad kneeboard conversion

I know the board looks like an easter egg, with its pastel paint job. This was a kneeboard (5’7"x22.5) I bought from someone many years ago and surfed on (really fast and loose) until one of the ofishl fins popped out. This was almost 10 years ago and at the time I couldn’t find the full size ofishl replacement so being young and impatient, I glassed in two standard fins into the ofishl boxes, the board also had a long keel that you can see in the picture, which i glassed a third cut down fin into.

I’m gonna sand down the keel and want to put fcs plugs in (i know futures, lokbox etc are better but im going to use fcs plugs) so I can experiment with the board as a quad. I was hoping some could advise me as to the placement of the fins.

thanks in advance.

Hi friend, we (I and my son) use this placements on two eps/epoxy quads ( 5’ 5" & 5’ 10") that we made, shaped by Neco Carbone, and it works very well. Back fin: 5 1/2" to 6" inches from tail, 1" to 1 3/8" inch from rail and 0" to 1/8" toe-in. Front fin: 11" to 12" from tail, 1 3/8 from rail and 1/8" to 1/4" toe-in.