I was just getting ready to mark out where my fins are going on a new board and I realized that because you can adjust the fins up to about 1/2" in the ProBox boxes, I don’t know where they should start.
I’ve never installed fins on a thruster before, so I took some measurement from the archives, 3 1/2" inches for the rear, 11" for the sides, toed in 2" off the nose. Marking that out seems pretty easy to me, but I wanted to know if I should set the boxes so that the furthest back you can put the fin is 3 1/2" and allow movement only forward of that, or set it up so the furthest point forward you can have it is at 3 1/2".
The big issue is that I haven’t chosen a set of fins to go with board. It’ll be traveling with several people, all of whom will have to provide their own fins, and I’m sure the base lengths will be different. Any help would be appreciated, I’m not planning on picking up a router for another 3 or so hours.
I always measure to the back of the box - fins can differ a lot in their overhang anyway, so measuring from the back of “the fin” is just the back on “that particular fin”… with your measurements (3.5 and 11) that seems about right to me anyway. So w/ probox jigs you’d just see your measurement pencil dot or cross right in the back of the hole that you’re going to drop the router into (ie. don’t line up with the back outside of the jig…)
so far I have set mine where the back of fin, not the box, is the mark for the dimension. That way you have the 3.5 and 11" at the fin not the box. You could set the fin in the middle of the box and make your mark so you have 1/4" play up or back. So anyway, I’d put the fin in the box and make the mark from the back of the fin.
What size board? Would you want more than the 1/4" play for greater drive (fin forward) or looseness (fin back).
I’ve made two semi guns at 8’ with proboxes at 3.5" for the trailer and 11.5" for the sides at 1" inch from the rail; toed 3/16". This was input from Resinhead. The boards have worked great.
As far as thruster cluster goes, you’re in about the right numbers for measuring from the trailing edge of the fin; this is for “standard” fin size (~4 1/4" base). If you use those numbers for the “dot” holes on the jig, you’ll be in the right ballpark. Measuring from the box is definitely more reliable, so if you’re dup’ing a board, figure out how far it is to the rear most slot on the back FCS plug and use the same measurement - 1/4" (accounting for the movement in the box slot) to set the back of the slot on your pro-boxes if you’d like to be able to adjust your fins rearward; otherwise, just use the same measurement knowing that you’ll only be able to move the fins forward of the “basic” measurement…does that make sense?
Sorry 4fins; moving the cluster forward will loosen the board up. Moving it back will increase drive. Spreading it out will provide a larger sweet spot for the back foot, but will also draw out the turns. I verified this with three cluster adjustments during a very fun surf session in Washington on Sunday.
It’s been my experience with Pro-Box that if you plant the fins close to the rail with your mark that when you use the “rearward” adjustment, your fin will be VERY close to the rail; remember, it’s angled so when you move the fin back, not only is the tail of the board curving in relatively abruptly in that area on a thruster (especially a good “hippy” thruster), but the toe-in angle accentuates the movement of the trailing edge towards the rail. Something to consider with regards to your placement and you might do well to move your fins in 1/8" from where you might usually place them.
The board is 6’3". What I had in mind would put the rear of the side fins 1 1/8" off the rail. I might change that to 1 1/4" so I can move them forward and backward. I like the idea of being able to move them in both directions to loosen or create drive when necessary. In that case I’ll put the fin in the middle of the box and measure from there.
