Once upon a time I was surfing on swaylocks until the end of the night and I remembered reading someone explained how to calculate rail rocker with stringer rocker and concave measures. It was looking super obvious to me at this time until today where I tried to find out how to do it. After making sketchs of rail and stringer and board and aluminium bar and ruler and etc etc I find myself really confused. So I tried to find the post I’ve read few weeks ago and I can’t. Did I really read it? Can someone help me please?
I would just figure what my stringer (rocker) would look like prior to adding any concaves through the middle, and that would be what I would rough shape to, then I would shape in the concaves, channels, V, whatever. I don’t consider rail rocker separately and independently, as I would never try to shape the rails first then work my way in to the middle of the board, always the other way around.
I was wondering how to calculate the rail rocker of a surfboard that you want to duplicate when you just have the measures of the stringer rocker and the measures of the concaves. I took those measures on a surfboard that I wanted to duplicate, I took them at nose, 1’from nose, 2’from nose, center, 2’from tail, 1’from tail and tail. I also duplicate the stringer rocker with a rocker bar I made (see the picture).
I found many dicsussions on how to duplicate the rail rocker on Sway but after giving the board back to his owner. I know that it’s not just a question of measures but also a question of curves, so I took many photos with my camera to have an idea. I also spend a lot of time looking at the board picturing it in my mind. Hope it will be enough.
If you have your stringer measurements - run a straight edge from rail to rail - measure the depth of concave - subtract it from your stringer measurement - that’s your rail.
With measurements every 6” just connect the dots smoothly and your good to go.
With that rocker bar - adjust the areas that you have concave and it should give you a perfect curve for your rail rocker.
I was wondering if you plotted out some marks parallel to the stringer - say every couple of inches towards the rails - in nose and tail area, could you line up your rocker tool at each position and get a good idea?
Tell me if I’m wrong but you have to substract the center concave and add the concave at the desired point . For example if you are flat on the tail, you have 1cm concave on the center and a 12cm stringer rocker, the rail rocker is going to be 13cm I think.
Just curious, why is this so critical? If you have the plan shape, the rocker, and the general rail and bottom configuration, you should be able to build a good board that works well. I mean, it’s not rocket science is it? What am I missing?
With all due respect, even with eye development and expertise there are reasons why most pro shapers and team riders are dialing in their rockers with computers and templates. At current levels of surfing and shaping, eyeballing just isn’t accurate enough anymore… especially when trying to reproduce a given shape except for miniscule adjustments. For most of us, not a huge deal but for pros - yes.
Exactly. Dialing in. So they have a basic, successful shape, and they dial in or tweak the variables, for different conditions, on the hundred or so boards they go through each year (Koa Rothman’s vlog shows him ordering 30 boards a pop). But rocker, plan shape, rail and bottom are a good starting point for a basic successful shape. So no need to pretend like a few thousandths of an inch variation in “rail rocker” is going to make or break a basic shape, when you already know the rest of the variables are good. I mean, how much variation in rail rocker is even possible, if you stick to the stringer rocker and bottom / rail shape?? Not much. Everyone’s entitled to their own opinion, and mine is, computer technology might be helpful in tweaking, and mass producing boards, but lets not pretend we need machinist grade precision to make a basic, successful shape. Just sayin’.
In my early days computer designing I would measure boards.
I’d get the rocker off a tool like yours. And top rocker, too.
Then I’d put a straight edge from rail to rail and take measures every 50mm or so, and every 100mm along the stringer line, ending up with lines of measures parallel to the stringer and an width measure at each 100mm. Vee was a bit tricky to measure. I’d do a similar thing for deck roll and use a carpenter profile measure to measure the rails.
A trick in those days was to put the board through a sash window to get thickness measures.
I was never that successful at dupicating a board, but it gave me a starting point. My boards improved dramatically when I tossed the detailed measures and designed my own from scratch.
In those early days there was lots of talk about scanning boards for measures. The trick was, and still is, in setting up the design so that the machine cutting path ends up close to what you want. Same thing in trying to hit numbers by hand. A few passes different with coarse paper and the concaves are different to the original.
I think that the scanning wave of learning has passed. Now good shapes are digitised and the tweaks happen from there.
My boards improved dramatically when I tossed the detailed measures and designed my own from scratch.
I hope it will do the same for me! The last surfboard I’ve made with more complicated bottom contour are looking realy nice (in my opinion) but are not working as good as what I’m searching.
Sort of. Consider: ‘’…more complicated bottom, not doing as well.‘’ I call it ‘‘busy bottom syndrom.’’ The water doesn’t know your theory of what you want it to do. Keep the bottom simple, and smooth. Speed is your friend, even in small waves. By the time I’d made and ridden about thirty boards, I had things pretty well figured out as to what made a surfboard work the way I wanted it to. You’ll probably have a similar experience. Just keep at it, and pay attention to what happens, when you change something. Don’t be guilty of over thinking the process.
Just asking, I cut my blanks from eps and to copy a rocker we put the original board 90 degree on the side and trace the bottom with a pencil. The result is an overall rocker curve and I add contours from there.
