Hi been a while since I posted. I've searched the interwebs and talked to a few people I know without finding too much insight.
What I've noticed over the years is different fins and their placement and how it affects the planing speed or trim speed of a surfboard. A few examples,
I've got a 7'2'' egg that was always a single fin, it felt soooo slow and I could barely get it down the wave to do a bottom turn. It had an 8 inch fin similar to a 4a. I added side bites and put in a 6.5'' fin with a bit of rake and the board takes off like a rocket but is too loose. So I move the new 6.5'' fin back in the box and I'm dragging anchor again.
I've got a 9'6'' Velzy Pig. I'm surfed it with a 9'' Takayama Cutaway fin for years. It's smooth, fast and awesome. I decide to try a wide base pivot fin in it one day and I'm dragging anchor and can actually barely catch a wave with it.
Last I've got a Takayama Howard Mini 6'6'' 2+1. I moved the fin back in the box on a bigger day and couldn't get the board past the mid face of the wave. I move the same fin forward again and it comes back alive.
Has anyone else experienced something like this? It has always made sense to me why twins and quads are faster and the affect fins can have on turning and drive. But I don't understand why the same fin, further back in the fin box can produce so much drag. Or why a different fin shape(same size & placement) can create so much drag. Does anyone have any insights?