I am going to glass on a single fin to a 6 foot pintail I just built. What size fin would you guys recommend? I currently have a 6'2" swallow tail single fin and that uses an 8".
A 7.5" fin works well for a 13 inch tail. If the tail is narrower you can get away with a 7 inch fin. Wider, use a deeper fin.
I put an eleven inch tall marine ply flew fin in my 6 foot rounded pin. ( I put the board in the archives as the Pink Lady, resource 794). I loved the way it rode. The long flexy fin loaded up really well on bottom turns and sent you flying. If you give me some time i can get other numbers off the board because right now my buddy has it in Hawaii. Darren
It really depends on your size, the width of the tail, the rails, your surfing style, and the hollowness and speed of your most encountered waves.
For me, a 6' single fin can use fins from 7" to 12", depending on the above.
I'd settle for something closer to the lower end of the range, as you can always go bigger or install tri biters.
For backside surfing, probably an inch and a half longer, if you really like to push hard on the bottom turns.
Some friends of mine in the bunker board daze (1969-71) used fins a small as 4" finger fins, while I used fins as large as 12" sabres. They rode frontside only, I normally rode backside.