I have a 1/4" Paulonia stringered 1.75lb EPS core that will be bagged and glassed something like 2x 6oz top and bottom. It will come out around 6lb.
(I’ve had about 8 snappages in stringerless, bamboo veneer top decks, 2x4 bottom 1x4 top, so I want to beef the lam schedule up a bit)
I’m considering 1/4" corcell inserts in the top deck to limit denting.
My question is, will a bamboo veneer on the bottom deck help strength? How should I adjust the glass schedule if I do this?
I’m not worried overly by weight, and think stiffness is good, but I want the board to last.
Here’s my take. Corecell deck w/ out a stringer will flex more than a stringered. It will develope buckling dimples under your back foot, not at the corecell, but on the rail where the corecell meets the uncovered deck.
Stringerless corecell needs extra cloth on the rail, not on the flat. Either two layers of carbon on the rails, or about 6 layers of fiberglass.
Don’t see how fiberglass at an angle will help with buckling, but that’s just me.
Take a look at the modern laminates thread. There is a good tip I got from a mechanical engineer about shear.
For snapage problems, you should perhaps try multi axis cloth (x-glass). Or rotate the orientation of one layer of your cloth from 0/90 degrees to 45 degrees. Lots of stuff in the archives on this. Graphite Master sells it in 6 oz which is a little heavy for multi layer stacks but you aren't concerned about weight. I am no expert but have built several stringerless boards with X and they are truly tough in the materials sense and they will not snap. Let me know if you laminating tips.
i got 3.8 sabs got 3.6 with balsa build . boards could be jumped on upside down and a shortboard is virtually imposible to snap. wrt strength to weight, these builds aka bert burger are still superior to anything posted lately on swaylocks. all the new fibers and materials are gimicky and for people that dont understand the basics of sandwich construction and like flushing money down the bog
top and bottom should be the same. corecell is average core. . simple bert build with paulownia both sides will be lighter and stronger than anything posted here lately. try 4 pounds
Snappage came from eps breackage because of shear caused by buckling of thin compress skin.
Stringer and /or rail reinforcement increase overall stiffness, that increase fatigue resistance and massive buckling resistance, but not really local buckling.
Thickening of skin, more fiber or sandwich, increase overall stiffness too and increase local buckling resistance, the best way to build strong surfboards, like said Paul it’s possible to build ultra strong ultra light compsand boards but harder to make well.
From my experiment : most time carbon in surfboards is shit because of too high stiffness, Sglass is a far better investment (with good resin). Xglass only work with something that take lentghwise strengh. Exotic plastic fiber don’t like UV and are in general poor in compression and adhesion, they can be an improvement when they are well used in vacuum bag sandwich…
Bamboo venner on the bottom will not significantly increase buckling strength, it doesn’t have a real high tensile strength compared to glass. Veneer is good for impact resistance (when backed with 1.5 oz or 4 oz. cloth) but don’t count on it for preventing buckles.
nice board btw wouter. im with lemat and greenlight !! anything ive ever done with pvc skins are a compromise . also sucks resin increasing weight. veneers ie. timberflex are good for blown eps that has good integral strength . lightweight cores require thicker skins. wood is the best fiber for skin cores. highest strength to weight ratios and flexural strength. as lemat says buckling and snap is skin failure/delam and rail failure . the rail is the key for preventing snaping. rail rail rail… wood is the best for rails for snappage. cores have enough strength for boards under 6 foot you can make compromises for the sake of style and cosmetics. over 7 foot then the rail should be built like a longbow. multple laminations. it needs flex. types of woods and grain orientation influence overlal stifness. rails should be strong and flexible with longbow type stiffness. cores and skins should be light and have good shear properties like 1pound eps … if you want the strong board to flex you create a board that is thin and bulk out the volume on the outside of the composite AKA cork or epp. high performance soft tops are the futre
That’s why in think carbon on rail isn’t good: ultra stiff and brittle. I make some and repair much, when carbon fail its’ quiet impossible to repair correctly. I’m not abale to shape correctly wood rails (and full compsand either) so i stay with eps and have good results with Sglass UD reinforcement around those rails: strong and still flexible, add a lot of ding resistance too, and it’s relly important for eps core, i often repair eps/epoxy boards with dings on rails. I do an egg without, only 3x4oz on rails (wood deck and my omega laminate springers), the guy surf in crowded spot, he ding rails 2 time quickly, never have one of the glass rail reinforced board returns for rails dings… only snap boards LOL. I work on it but hossegor and around beachbreak are very hard this year !
Paul do you test epp ? I only find some with big cells like shit ultra light eps. I don’t really like wood look and find cork so ugly, so i still search a good “flexible” (and white) material for deck sandwich…
We’re struggling to find x-glass over 2oz down under. Any leads would be appreciated.
We’ve tried laying conventional cloth at an angle, but the laps are a bitch because the angle of the weave doesn’t help when you’re trying to pull the lap tight. Prepreg does not help, either. Any hints on how to get this right would be great.
I’m humbled by the extent and depth of the feedback in this thread from luminaries in the field.
My take on the answers is:
Don't bother with corcell for strength, but it may have some place for impact resistance, or just use bamboo top decks, as we've been doing.
Bamboo bottoms don't help much for strength.
Get enough glass on the rails. I remember a minimum of 18oz from one of the threads.
Did I get that right?
Some specific comments:
**Everysurfer **- much respect. We’re testing sourcing and testing Cerex and other matted cloth thanks to that thread. Until we can get infusion happening, it seems like these will be interesting avenues to check on puncture resistance and adhesion to cores.
**Paul **- We’re still inspired by Bert’s build method and trying to get there, but trying to get from blank to board in one step. By the way, I just finished a XPS board using the rocker numbers you threw out a while back 2.5" tail; 1" at 18 and 18 back, 4.5" nose. Struggled to hit the numbers, but got close and the board flies - thanks.
Wouter, I surf a range of waves, but there is a bit of power down here in VIC, and some size. I ride kneeboards which means lots of seriously late takeoffs (because I can) and tubes. It also means that the fulcrum is a line across the deck where the knees go, so pressures are probably substantially different to standup boards. I use 10mm foam pads on the board to protect my knees. Even with bamboo laminates and pads the board gets heavily dented. I have moderate doming and concave bottoms, but only 2 1/4" thick.
**Greenlight **- I hear ya. Bamboo on top if at all.
**Lemat **- thanks for your insightful technical posts. Yup, we’ve gone back to stringers and are doing pre-preg, bagging. This has reduced the resin loading and so weight, and potentially improved flex (50/50 resin/cloth ratios) without compromising strength/weight. I think that the layers of cloth should be separated by some sort of filler in order to exploit the cube function from separation of layers. This might be where mat comes in, but then how to keep the resin weight down in the separating layer and how to ensure good bond between the filling and the inner and outer skins? Paul’s composites is the best we have now, but how to do complex skins in one step? Infusion I think is the way, but that’s a whole different core ballgame.
I saw “we” in this post because I’m working with a really experienced laminator who is crazy enough to accompany me in this quest for one perfect board (just one, that’s all I want!)
Red, for a durable and still flexible shortboard i’ll go with 1.9# eps stringerless, wrap rails with 8oz UD Glass (sglass if you find), about 2 inch on the bottom and 1 inch on top, then 2x4oz warp under, 45° 3oz flat wave glass under 2mm corecell and 4oz Sglass over cut lap to the edge. Still a simple build, and a nice weight/durability ratio for me. I do some like that with 1.5mm balsa instead of corecell that was very durable but a bit stiff for me.
