I used to ride single fins. You had to have a long enough fin so it wouldn't pop out on bottom turns. The tail couldn't be too wide or it would break loose as the wall of a barrel got too steep.
I took care of those probelms by narrowing the width of the board and, thus, the tail, riding a 12" flex fin and adding two, 2 inch tri fins on the rails.
The boards were fast and rode barrels well but did not surf small, wimpy waves very well or cutback without the tail sinking.
The one I am looking at is a Jacobs shaped by Wayne Rich. Has to be an 80's board....It looks like a cross between a longboard and a kneeboard, and is about 5' 8".
As far as long and thin fins go - windsurfing fins have to take the cake there....
The picture is a board from the 70's, and is 5' 2". I think it is onsale at Aloha-Cruz or Chubbysurf or something....
The board I am curious about is also a Jacobs but about 5'8" 22.75 x 2.5ish and was shaped by Wayne Rich - who worked as a shaper for Jacobs from 1980 - 1992 or so...*not* before.
And, as I said, it looks like a longboard with a kneeboard diamond tail.
So, the board I am curious about (no picture of it) is from that period, and is a kneeboard, and does look like the one pictured except for the nose and is bigger, wider, and thicker.
Sorry for any confusion!
Probably made out of a blown blank for a longboard.
I got a reply from the shaper - Wayne Rich - I will call him for more details...
"I think around 1987 or so I shaped this particular kneeboard
for a good friend - "Dick Leach". Ray Lucke glassed and airbrushed it in our
shop at 643 Cypress Ave Hermosa Beach."