I’m looking forward to shape my first own shortboard for waves from waist to overhead height. I first started with a single concave and quickly thought that I could make it end with a double for smaller waves with less speed . This is where things got really complicated. I thus ended up with two versions; one with a single concave, as I thought my imperfection would have less impact, and one with a single to slight double that left me with a lot of questions that I couldn’t answer searching on internet.
In both case, I can’t really tell if the depth and transition between concaves is in the right place so I could use some help.
Both boards have almost exactly the same dimensions and rocker, and even if the concave type is different, both have the deepest concave (almost 0.26") point slightly behind the middle.
Here’s images so you can see all the specs. (the red line shows where the sections are made and the blue line shows the concave evolution)
Okay, what I do for this kind of board know is a single start at one foot from nose finish at front of back fin max depth at two feet+ from tail where I start a double barrel concave up to tail. I work it to make lot of angle at rail, harder to put fins but good feeling on wave.
So I moved the deepest point of the single concave to approximatively 2.3 foot from the tail where it switches progressively to a double concave with the deepest point between the front fins. I also readjusted the angle of the double concave that is now dominant at the rails and flatter in the center. (image below)
Does the rail profile and angle with the concave looks alright and do you think the concaves are deep enough? (3/32 inch (almost 0.1 inch) for the deepest double concave point and 0.235 inch for the deepest single concave point).
One last thing, do you think I should make the angle of the rail less sharp and more open? They almost seem a little too pointy even if the section is down around the front fins
I am a hand shaper so I don’t be used to look at those kind of pictures… Double profile look good for me but at that point it’s insert in the single. So overall deepness is more for me in general for short boards.
On most single to double boards I’ve seen the “spine” of the double is above the rail line. So like lemat said, you basically make the single, then carve the double into the single. If you have a local surf shop nearby take a straight edge in with you and ask them if you can just lay it over a few boards. That will give you a really good idea of concave depth as well as rail profile and where the concave starts. I have a couple boards that carry about an inch of flat inboard of the rails before the concave starts. It never occurred to me until I put the straight edge on them. A lot of boards also finish with a V in the last 3-6" where the center/stringer is the lowest part.
I did a single to double on my first board and it definitely complicates things. I think fin box placement is a little tougher and it’s important to make sure your template/router is level on the board for the cuts (I used Futures) and that the depth is just right or you’ll have half the box under 1/8" of resin and the other half sticking out. I levelled the board and then levelled the template and it worked ok. Sanding is also much more complicated because you either have to be a master power sander or hand sand the double concave. Resin is going to pool in your concaves so you may need to tilt the board a little more to get it to run off or you’re left with a heavy sanding project to keep the depth of the concaves. I’m still thinking of how I’d solve this last one, but I think I’d raise the tail significanlty and make sure I still fill the tail dam, but let the rest run off the nose.
When you’re straight edging boards also notice where the apex of the rail is as it moves back toward the tail. Your drawing is probably a little more squared off than most on your rear slice. Most of my purchased boards have rails that go out to the apex and then come back in 1/8" or so before the sharp edge. They do eventually go pretty vertical but not until around the rear fin, sometimes further back. Good luck!
unfortunatly, as you mentionned, it’s hard to work with single to double. To not mess around the board too much on shape3d, I kept it mostly single but added a slight double profil that is at it’s maximum between the front fins and flattens completely as it approaches the tail. But as you can see on this new pic, the “spine” of the double isn’t above the rail line and quite far from it.
Do you know if this will still add some little benefits of a double concave in the single or will I just loose the benefit of both types and create a shitty hybrid?
Good observations on your part. You have really trained your eye. You’ve done it by looking at other people’s boards and taking notes. You are well on your way to becoming an excellent shaper. Now you will need to spend time on technique and training your hands to bring your observations to reality. That part of the shaping process takes time and familiarity with tools and techniques. Practice, practice, practice. Lowel
I’m assuming by your comment you’re having it cut on a CNC machine and have already sent the file. Unless you’ve already laminated it, why not just make adjustments by hand? From my (extremely limited) experience it’s easy to remove a lot of foam quickly so you should have no problem using a straight edge and some sand paper to deepen the double if you want. Create a sanding block from some foam or wood in the shape of your concave or just use your hand/palm. Go slowly and measure often. Slide your straight edge down the board to make sure your depth is consistent or changes how you want it to. Even with the CNC machine it takes a little “art” to get it the way you really want it. Someone on here spoke about how a board’s curves feels is often more important than how they look or measure. Run your hands all over it until they’re happy.
