Hey everyone, I just built a new shortboard and it works, just not quite how I wanted.
Basically, when you get your foot all the way over the thruster fin, it pivots on a dime and feels loose and free, with an ultra-tight turning radius (especially for how “medium” the rocker is). But if you put it on the front of the pad, it barely turns at all and feels stiff.
In short, it feels like I’m surfing a rocker that is shaped more like a candy cane than a smooth curve. But I’m not entirely sure which rocker is causing that feeling, rail or centerline.
I staged the rocker on this board, modelling it on a board I like already (CI Fishbeard) but kicking up the tail an 1/8" and adding more concave in front of the fins. I’ll put the centerline rocker numbers below with concave for reference.
Board: 6’3" x 20 1/2" x 2 3/4"
Rocker numbers as follows:
T 0" — 2 1/8" — Concave: 0
T 6" — 1 3/8" — Concave: 1/16"
T 12" — 7/8" — Concave: 1/8"
T 18" — 1/2" — Concave: 5/32"
T 24" — 1/4" — Concave: 5/32"
Center — 0" — Concave: 1/8"
The board doesn’t surf bad. It’s actually kind of fun when you get your feet in the right place. It’s just twitchier than what I was going for and I’m trying to figure out why. My Fishbeard is considerable smoother, even though the centerline numbers are the same between T-12" and Board Center.
Ironically, I’ve only tested it in overhead waves. It definitely likes a steeper wave though. Will definitely keep trying it in these conditions though!
Compare fins numbers, that have way more influence on turning properties than concave… A bit less of toe-in and your board can feel stiffer to turn with foot in front place, and so easier to trim accuratly in barrel and long turn… That’s what i do for Hossegor barrel board, low toe-in low cant and even more quad option for ultimate speed and control down the line with front stance but full rocker to manage late drop and turn with back foot on pad. I put single with double in now to have curve of concave more on rail, like a camber, so more rail grip in wave face and stronger bottom skin.
Since the board itself is kind of a done deal, I’d say the key in getting it dialed in will be the fins. Relatively minor changes in fin sizing and fore/aft spread can make big differences in board behavior. Are there any differences in the fin set-up between your new one and the C.I.?
It’s set up as a standard thruster (fin base ~4 1/2"), rear dot set at 11" for the front fins (toed in 1/4") and 3 1/2" for the thruster. The CI is actually a twin fin, with the rear dot set at 9 1/2" (toed in 1/8").
I’m definitely playing around with fins to get it dialed in. But the reason I’m asking this is to understand the design principles and get a better sense for what I’m actually feeling and why (and because I never know whether it’s rail or center rocker shapers are referring to when they say “rocker”).
The CI is definitely curvier through the middle in the rail, but has less flip in the last 12" of the tail (rail and center rocker) than mine. And I feel like these differences seem to indicate that the rail rocker has more of an effect on how a board performs (i.e. “feels”) than the center rocker?
Also — if I wanted to get my board design closer to how my CI feels, I could reduce the concave (raise the rail rocker) at the T 18" and T 24" marks back to 1/8" (which is what the CI is)?
The C.I. in question likely feels so different because of the fin differences. I could be wrong but 1/8" tail rocker doesn’t seem as critical as the thruster vs twinny differences.
Hey everyone, I ended up doing a little experimenting and made a second board that’s identical, but with a different rail line rocker (i.e. changed up the concaves). Wanted to share what I found in case anyone was interested.
I did both of these boards on Shape3d, so they’re completely identical with that one change (my CNC shop cuts to 0.02" accuracy, and I used the exact same fin placements and fins). All I did was change the concaves by raising the rail line rocker at the tail by 1/16th to add some vee in the last 6". The rail curve is exactly the same, just higher relative to the other board’s rail rocker.
Centerline rocker numbers/concave as follows:
T 0" — 2 1/8" — Vee: 1/16th"
T 6" — 1 3/8" — Concave/Vee: 0"
T 12" — 7/8" — Concave: <3/32"
T 18" — 1/2" — Concave: <1/8"
T 24" — 1/4" — Concave: 1/8"
Center — 0" — Concave: 1/8"
WOW. I can’t believe the difference between the two boards. It’s night and day. The second board is so loose you can laydown swooping carves from the middle of the board just by tipping it on rail. Again, not what I was going for, but really fun in the right conditions.
This more or less says to me that what you’re predominantly feeling performance-wise on a shortboard with concaves is actually the rail rocker, not the center. And maybe even more specifically, the curve between the board midpoint and fins.
Now I’m really curious what happens when you change the radius of that curve…
Very interesting! A guy here, Mark Miller (everysurfer) has done some experimenting with specific rocker radii. I think he actually plotted out the curves on his driveway. You might give him a shout(?)
The poster is onto it. There is stringer rocker and rail rocker.
Stringer rocker is about paddling speed and running flat. Rail rocker is about the turn when carving. Concave or convex is the byproduct of those two curves.
I draw mine out on the computer, send the drawing to the blueprints, spray 77 the paper onto plywood, and cut out a rocker template.
Then you get into where are you putting the different radii in the rocker.
Flattest part in the middle for a groveler?
Flattest part between the fins for a step up? It’s all about the experiment
Sounds like I’m on the right track. Totally know this is all a subjective thing, just trying to understand what controls what. Thanks for the confirmation!
A good starting point is to take existing boards that you like for different waves.
Then with a straight edge anx measuring shims, see which part of the board has which rocker. Meaning with a 2 foot straight edge, slide a nickel under each end of the straight edge, and slide them towards the center of the straight edge. See where both nickles and the straight edge all touch the board. That is one radius area. Then slide the straight edge and nickles along the stringer. Does the curve stay the same, get curvier or flatter? Save those numbers to use on the boards you make.
Are you saying run the straight edge with the nickels under it along the rail, down the length of the board (and stringer too)? Or laterally?
I’ve been getting my rail line measurements from boards I like using centerline rocker + concaves (with a rocker bar, straight edge, and feeler gauges).