Taking a poll of sorts as there’s a lot of EPS/epoxy experience here and I have none. Making a short 5’3" X 20-1/2, approx 2-1/2" thck, stand up fish. I’m 5’3" and weigh 130-135 pounds.
Using 2 pound EPS w/ no stringer. Plan to dish deck a little. Using all 4 oz cloth. Was thinking 3 layers bottom, 4 layers on deck. But then I started thinking some more… I want it to flex but I don’t want it to break. Any suggestions gratefully accepted. 3X4 in the ball park? Too light???
(200 pound X 6’2" Greg Loehr said he used 3 X 6 oz on sailboards for himself)
If you’re after flex, there’s no good way to get it without compromising strength in the glass sched. I’d go single 4oz bottom, double deck with a small patch for under your back foot and another for under your front foot, that goes all the way to but not around the rail.
Also, ask Greg about the 2020 or 2040 resins. They have more flex than the 2000. That’s what I’d tweak… the resin and the shape, more than the glass sched.
I did ask and got the 2020 as he suggested. He thought the 2040 might end up being too soft. I’m thinking your suggested glass might be too light, remember no stringer!
Are you proposing 16oz of glass on deck and 12oz on bottom?
I am currently riding a 2.5lb eps stringerless. It was glassed double 6 (total 12) top and double six (12) bottom. It is solid as a rock. It does not flex noticeably… it feels like my pu pe boards and is stiffer than my firewire.
I’d go light on the glass. I think NJ is spot on. Light glass, flexy resin, post cure gets my vote—BUT, I am an amatuer with limited experience. Maybe 6/4 top and 4 oz bottom would be a nice compromise.
With all the glass you’re talking–stringer on no will not be relevant in my opinion and limited experience.
You guys must have really light feet when you surf. Anything lighter than 2x6 on the deck will leave you with a bunch of heal dents. I would recommend 6,6 top with a 4 oz stomp. and a 6,4 bottom. It’s still going to weigh 6 lbs.
It’s the rail lamination where you get the flex or stiffness. Also the type of cloth, Impact, warp, S, or E cloth? If you want a stiff board do full wraps, if you want to keep it flexy then only wrap the one layer of 6 on the top, and one layer on the bottom, do the rest as inlay cuts.
2 lb EPS is pretty buttery stuff, you need to put glass on it or it’s going to pressure ding really fast. remember the strength is in the rails.
Loehr told me pe resin shrinks 8% or did he say 6? and epoxy only 2% so not much warp risk. Tricky business, true the flex is in the rail glassing but so is the strength/break resistance. 1/2 way somehow somewhere…
Couple years ago had Mandala flex tail fish (stringer stopped 18 inches up). As I remember it had 2 X 6oz on bottom and 2 X 6 oz plus 6 oz patch on deck. (pu/pe)
Deck will be dished out in center in back half a bit to make for more twisty flex, if tail tips displace by an inch under max load that would be mighty fine I think.
Stringers really don’t do much for strength… I’m using pvc foam stringers…there’s not much structural integrity in foam!
I agree that the rails give the board snap-resistance. That’s why I suggest wrapping the rails with lighter glass, but using deck patches for dent resistance.
Either way, the more she flexes, the more stress and strain, and the quicker she’ll expire… No getting around that.
Structurally, the stiffness of a board (other things equal) lies in the distance of the glass from the neutral axis. Put simply, thick boards are stiff; thicker boards are (much) stiffer. And the stringer does help, perhaps more than you think, because it’s held in place by all the other material around it. And, of course, it’s nice to have a stiff blank rather than a noodle when you’re shaping.
RAILS DO NOT GIVE A BOARD SNAP RESISTANCE. Rail glass is closest to the neutral axis and thus contributes the least to stiffness or “strength”. Rail glass does play a role in shear transfer. Think of rail glass as the web of an I-beam.
With respect to snap, I get the feeling you don’t seem to have the picture quite right - I know for many years I didn’t either. The school analogy is to bend a deck of cards. The outer card on one side wants to compress, the outer card on the other side wants to stretch. All cards are supported at the thickness of the whole deck. A single card bends easily; a single card not supported by the others will also buckle easily. Think about bending an aluminum can. Anyone can crumple the can, but what if it was filled with a low density material that helped the skin maintain its shape, but didn’t contribute much to the bending stiffness? That’s what is going on in surfboards.
The initial failure of a board about to snap is that the glass ON THE COMPRESSION SIDE shears from the foam - it loses bond and “slides” in the plane of the surface. Once that happens, shear transfer is lost, and the glass crumples outwards, forming a ridge or buckle line. If the failure progresses, the board folds in half since one glass surface now has negligible strength and the foam can’t take much bending stress. ONLY THEN does the board snap. ('scuse my caps, I want to add emphasis where I think it needs to be).
I agree that thickness plays a significant role in stiffness.
I disagree that stringers, especially foam stringers in EPS blanks, add significantly to snap resistance. The ones I use are pretty much aesthetic and/or a point of reference for the rider (whether we’re conscious of it or not). I tape them off and use different shades of glazing to make them look like grained wood. Beautiful. But that’s another thread…
I don’t understand your theory about how rails play no role in snap resistance. If that was so, lap-railed boards and zippered (non-lapped) railed boards would have the same amount of flex, and would snap with equal amounts of stress. This is not so. Lapping the rails adds rigidity, which increases snap resistance.
Imagine the outermost, “vertical” surface of a rail that’s perpendicular to the stringer. Then take two peices of the same material and imagine that this material is that vertical surface - one long and thin that would be a single layer of glass; one long and thick that would be a double layer of glass. (And let’s assume that you only had one layer of glass on both the deck and the bottom.) Flex them both and you’d find that the long thin one would flex the most, leading to the theory that more glass on the rail adds stiffness.
I know this is an oversimplification, but to say the rails add no snap resistance is, I believe, inaccurate.
The main point to my earlier post is that you can’t increase flex without decreasing snap resistance without using different materials. Lightening the glass schedule for flex necessarily decreases snap resistance. Other than changing thickness, you’ve got to change the materials you use - including core material, cloth, resin…
How about this, though… You are dead on about the deck delam leading to snap. So what if we made a thin board, and didn’t seal (or minimally sealed) the deck foam, allowing the resin to penetrate the foam a bit more deeply. Would the migrating resin increase the lam bond to the foam, resisiting delam? What about vac bagging?
2 1/2" is pretty thin for a stringerless w/o a triple six - triple six. I don’t think the weight diff of the surfer is that significant.
In my opinion, you want a balanced panel, the same top and bottom. I’d go triple six. Greg’s only built a million of those things.
I’ve seen a lot of Clyde Beatty’s boards, and they do snap. Go heavy on the glass or you will be shaping another on as soon as that lip hits it when you a caught inside.
3 X 6oz = 18 oz; 4 X 4oz = 16 oz------of cloth. Using 4 oz you get a bit more cloth per amount of resin which should increase strength a bit (no?) and maybe also increase flexability. Add a deck patch. Seems plausible to me. All the boards I’ve ever had break for sure broke on the compression side in just that way. Nice description. Clear, makes sense. Flexspoon KB has no foam in back and none in middle. Tail ends up w/ 3 or 4 layers of 4 oz gradually thickening glass as go forward. Where they buckle tends to be up a ways, front of fin or where knees are; point loaded areas more or less…thinking out loud…