What’s a mystery to me is why Bert or Nev haven’t passed one over to Mike Paler to bring to Big Sur for S.A. 2005.
If someone brings a saw, we could cut it up and see exactly what’s going on in there… WTF
For me its the techniques and materials involved. I like that I start off with pretty raw materials and end up with something worthwhile. I’ve always heard Bert make three claims about his boards: they were light, they were strong/durable, and it made a difference while surfing. I can attest to the first two being true. They are definantly “carry by one hand light” and I couldn’t believe the beating they received and still looked good. As far as surfability goes, I’ll be really interested hear when somebody actually rides one. but they do have looks, lightness, and durabilitity going for them while the current high end/pro boards only have one of these attributes.
Keith and Wahoo look out. I raised the point several months ago that people were getting awfully excited about boards nobody that any of us knew had ever ridden and we should buy one to pass around or take to a Sway event. I ended up being called everything from cheap skate to idiot and was suggested to change my name to Creepnon.
The diagonal wood grain seems like a good trade off. Straight vertical would give the best energy transfer down the board and twang but wouldn’t be as good for keeping the rails from twisting off. Straight horizontal would do the opposite, real good for rail twist but not so good for twang. Diagnal still transfers energy down the length of the board as well as toward the rails and would help with the rail twist off.
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The diagonal wood grain seems like a good trade off. Straight vertical would give the best energy transfer down the board and twang but wouldn’t be as good for keeping the rails from twisting off. Straight horizontal would do the opposite, real good for rail twist but not so good for twang. Diagnal still transfers energy down the length of the board as well as toward the rails and would help with the rail twist off.
I think people dramatically overestimate the role of the wood grain in stabilizing the design longitudinally or cross-wise. It is glued between two glass layers that are an order of magnitude stiffer - the orientation of the wood is cosmetic - it is sandwich material, not a structural beam support in a truss sense.
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I think people dramatically overestimate the role of the wood grain in stabilizing the design longitudinally or cross-wise. It is glued between two glass layers that are an order of magnitude stiffer - the orientation of the wood is cosmetic - it is sandwich material, not a structural beam support in a truss sense.
Overestimating, yes, but the core does contribute structurally. Not as much as the skins, but significantly none the less. Especially wood. It’s easy to test or even visualize. What if your core is made out of the lightest foam you can find, or, for example, it’s made out of steel. Those extremes demonstrate that the core can contribute structurally. Wouldn’t you agree that wood is stiffer longitudinally versus cross-grain, without any skins involved.
So it makes sense to use the wood core’s structural properties to inhibit torsion twist (diagonal placement) which doesn’t require a lot of structure in surfboards, and the skins to stiffen the board longitudinally where structure is most needed.
But like you said, the skins (and the distance separating them) offer the biggest and most efficient structural contribution. So the best core material is air, unless there are core material structural properties that you can exploit like you have with balsa.
By the way, you could get the same torsion stiffness by just adding some 2 oz. (or less) glass diagonally to the top and bottom of the sandwich without using balsa, which would seem to be more efficient, but then you wouldn’t be exploiting balsa’s other properties. What makes balsa a superior core material over foam is the fact that it has a grain that adds structurally.
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Quote:I think people dramatically overestimate the role of the wood grain in stabilizing the design longitudinally or cross-wise. It is glued between two glass layers that are an order of magnitude stiffer - the orientation of the wood is cosmetic - it is sandwich material, not a structural beam support in a truss sense.
good point.
i know you guys know all this, but just to lay out the ground rules again…
normally, the ‘core’ of a sandwich only needs to carry the shear loads between the top and bottom skins.
But this sandwich IS the skin for the overall structure.
so it is forced to carry it’s share of the tensile/compressive loads due to flexure, as well.
The relative load carried by the balsa and glass in the skin is mostly a function of their modulus and cross sectional area.
-glass modulus:approx 2.5x10^6 psi
-balsa modulus: approx .5 x 10^6 psi
-2 layers of 4oz on the deck is probabably .018" thick
-basla skin: approx .100" thick
…
the glass has 5x the stiffness of the balsa,
but the balsa has 6x the cross section area.
so, if the above numbers are close, it would appear that the balsa cores are carrying more than half of the load traditionally assigned to the glass ‘skins’ alone.
who knew?
-bill
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Quote:I think people dramatically overestimate the role of the wood grain in stabilizing the design longitudinally or cross-wise. It is glued between two glass layers that are an order of magnitude stiffer - the orientation of the wood is cosmetic - it is sandwich material, not a structural beam support in a truss sense.Overestimating, yes, but the core does contribute structurally. Not as much as the skins, but significantly none the less. Especially wood. It’s easy to test or even visualize. What if your core is made out of the lightest foam you can find, or, for example, it’s made out of steel.
A red herring. You’d never make a sandwich composite with a skin structurally weaker than the core…
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Those extremes demonstrate that the core can contribute structurally. Wouldn't you agree that wood is stiffer longitudinally versus cross-grain, without any skins involved.
Wood is strong in tension and compression in the direction of the grain, and weak in shear in the same direction. So, although one might think that one could maximize strength by aligning the grain with the bending or stress axis, you would infact be minimizing the strength of the sandwich by doing that - because the main mechanical benefit of the sandwich material is its ability to withstand shear.
If you really wanna good sandwich, you use end-grain balsa, but I suspect that doesn’t work as well wrt cost-benefit and aesthetic quality.
The glass is 200-500 times stiffer, and the small changes in shear or tensile or compressive strength by manipulating grain just don’t matter that much. But if you want “the best” sandwich, use end-grain to maximize shear strength and stiffness.
Blakestah
Yes agree 100% the idea of a sandwich is to separate the skins with a product that has good compresive strength
Of interest my boat is made using dura core which is 25mm endgrain balsa sandwiched between two 3mm hard wood veneers each with the grain running lengthways the boat is strip planked (the strips are only so you can build round shapes otherwise flat sections use sheets) this is then glassed on both sides with a single layer of 800 gram triaxual glass
That gives a light strong and flexable ( ie flexable to with stand pounding loads where ridgard hull forms will crack on bulkheads) hull form
So as you can imagine it has the best of both worlds longitudinal strength and compressive strength
You can use end grain on surfboards but its difficult to shape end grain on the rails interface (chips off) and unless you glass upside down on the outer surface will absorb lots resin
In most sandwichs you change the flex either by varying the skin laminate or the thickness of the core or both
The advantage of balsa over dcell i see is that balsa has a better compression recovery cycle, even across the grain in the way we are using it in surfboards
Mike
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If you really wanna good sandwich, you use end-grain balsa,
You might be right about that. It’s worth looking into.
It’s all about surface area, amigos. Surface area can run horizontally AND vertically! There’s more to it than the diagonal balsa pretties deck mumbo jumbo. Bert is using infusion to make balsa into a flex wood - catered to flex required. He IS a friggen genius. I hope he can talk about it some more before they go public, cause once that happens, mums the word.
We’ve been thinking - pull the cloth off the roll. He’s been thinking - what is the CELL STRUCTURE and PHYSICAL PROPERTIES of this and this combined and yada, yada, ya…
Origami anyone?
daddio,
I reckon you are on the right track there. I think he’s also made refinements on the timber use that other’s haven’t twigged to yet (and if he hasn’t it’s just a matter of time until someone does). For example - wood experiences sheer only on its very surface. And when you laminate three thin slices together only the top and bottom layer experience the stress of bending… But it is possible to cause each join surface to take its own load of sheer!
You might all prefer to work on a different part of your game… Or think I am not even in the same ballpark ;D
-doug
interesting…but how many guys have noticed bert uses A-cut balsa…we novices been using mostly c-cut…i realized a while back that bert is more of an advanced wood worker than foam shaper…he proly spends 60% of his time processing wood…the rest mostly resin/glassing…next to nothing dealing with foam
very interesting posts here…until some one else puts out a flexible springy craft im going KISS
I told Bert how nice his balsa looked and he told me its just C grade stuff (the stuff model builders don’t want to use. I remember reading somewhere that the wood picks up its color when the tap root goes too deep and starts picking up minerals. Heres a board that he built for one of his team riders (and thetemplate for my new super light board).
The graining of the C grade is what makes it look nice!
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interesting…but how many guys have noticed bert uses A-cut balsa…we novices been using mostly c-cut…i realized a while back that bert is more of an advanced wood worker than foam shaper…he proly spends 60% of his time processing wood…the rest mostly resin/glassing…next to nothing dealing with foam
very interesting posts here…until some one else puts out a flexible springy craft im going KISS
Mostly, you get what you get, and sometimes you get lucky. In the end, they’re only surfboards. It’s more importantly the surfer that counts. Are you really going faster in those Florida waves?
Bert has reached Sainthood.
Doug, is there any reading materials on surface area and shear in regards to wood, or did you fold swords in an earlier life?
epac, we don’t mean to canonize Bert. The only throne he sits on is porcelain and flushes, just like all of us’n. It’s the simple fact that we, as creative people, learn more from our failures. MUCH more. If we make materials conform to our mental expectations, with a particular goal in mind, we will sacrifice in other areas. I’m sure Bert has pondered the boards that come back for repair - more so than the pretties that go out the showroom door.
You gotta get rid of the box. This ain’t no science class, don’t dissect anymore dolphins. It’s dynamic, dude! Snap that towel, a kiss for your sweetie (or a tree) and bow your head in respect to the other creatures that surf with us…
Or grab your balls and dance like a sick little monkey. Have I got a surfboard for you!
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Bert is using infusion to make balsa into a flex wood
Who knows what he is really doing with his “treatment”. The end product he uses in his sandwhich core might not act that much like balsa as we know it. Possibly it becomes a much more significant part of the strength of the sandwhich and grain direction is important. Or it has a lot more compression strength than normal balsa (more like end grain) yet also has the longitudinal lex characteristics.
I’m warning you Epac, don’t mess with The Burger Cult. They’ll burn you on a balsa perimeter cross.
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epac, we don’t mean to canonize Bert. The only throne he sits on is porcelain and flushes, just like all of us’n. It’s the simple fact that we, as creative people, learn more from our failures. MUCH more. If we make materials conform to our mental expectations, with a particular goal in mind, we will sacrifice in other areas. I’m sure Bert has pondered the boards that come back for repair - more so than the pretties that go out the showroom door.
You gotta get rid of the box. This ain’t no science class, don’t dissect anymore dolphins. It’s dynamic, dude! Snap that towel, a kiss for your sweetie (or a tree) and bow your head in respect to the other creatures that surf with us…
Or grab your balls and dance like a sick little monkey. Have I got a surfboard for you!
I think all of your analogies are understood. I’m also impressed outside the box, but you guys haven’t even ridden the boards yet, to prove or dispel the function of the shapes.
It’s Christmas eve, did you leave cookies and milk for Santa Clause?
good one ePac!
Wonder why no one here can get their hands on one?
Money’s no object for you guys right?
Maybe a lurker can set us all straight about how they actually ride…
You’re right Epac it’s just a surfboard and there’s so much more going on out there…
14 more young dead heroes today in Iraq
the Princess Bernice Pauahi’s will to solely educate her youth over turned in court…
Tiger Espere’s funeral on Sat
Auwe my heart is filled with sadness and I mourn these losses with deep regret…
I’m stoked that construction technology appears to be advancing. Lighter, stronger, higher performance surfboards can only be good.
Bert has taken the time to post detailed threads outlining what he was doing 15 years ago. He’s also answered tons of questions from many on this site. I don’t mean to take one shred of credit away from Bert and I hope his new venture with Nev works out. I also hope that all the hobbyists aboard take their building skills to another level using his hints as a guide.
For anyone interested, there is another guy who has been at this for quite awhile. Read his story and realize that he has been using similar stuff for a long time and has developed a number of innovations himself… note adjustable rocker table, UV cure vacuum chamber, discussion on longitudinal & rail-to-rail flex, etc.
“[=1][=Black][ 2]I am learning[/][/]
how to determine that flex by blank thickness, deck dome,
number of layers and direction of fiber orientation within the
bamboo/epoxy laminate.”
[/]
http://www.groundswellsociety.org/pdf/07_TGS_Equipment-Gary_Young.pdf
As a fellow parent it’s quite obvious who Santa do am be…
And that makes us men of experience. Knowledge gained is knowledge earned.
If your kids cut open all the toys the next morning to learn what’s inside, it seems to me they’ll be on the path to becoming a surgeon, which might be a better career choice anyway, or a mechanic or repair person. If you are substituting materials you are an innovator. You have to feel this in your heart AND mind. For this to be a cult situation, we would have to be blind followers of a particular technique provided by some old guys that said how it was gonna be so they could keep the status quo to their liking and sell ya the same old same old so you would be happy sniffing model glue while they kept on giving you the same old model in a new improved and repackaged box. Sound familiar? This is the first thing that is different to come down the chute in a long time, and I for one (of many) am interested. Is it the end product? Not unless you’re used to getting in the waiting line for a pretty package from only ONE Santa…
I put the effort into getting my hands on one… the world didn’t stop spinning. But Glenn and I want to make one ourselves, now more than ever.