What about carbon fibre? And if I recall correctly Murray Burton of Pipedreams glassing diagonally. Any thoughts on these?
carbon fiber is expensive and hard to get
and difficult to work with
but i can definitely see its value in composite surfboards
but the general public wont wear the cost
I’m probably going to get written off for this but the best board for hollow closeout beach break is a sponge. take off late, get way deep and the only thing that will ever break is you ribs. easily the most versatile, strongest boards on the market.
cheers
oops; wasnt really disagreeing as much as adding to the mix of failure modes.
I should clear my last post up…
I guess we’re talking about weakest links…
yes, laminate/foam bonds play a role, especially on pupe, but you can have a great bond on a very weak adherend and still have easy failures. To answer your rhetorical question, eps is far weaker in tensile than pu. However, it is accepted that wrt strength to weight, eps/epoxy is stronger more snap resistant than pu/pe. So what’s going there? Obviously, eps/epox has more ‘weight’ where it counts, in the laminate, lucky for us, it just so happens that the laminate is made partially of fiberglass, an incredibly tensile strong and light mat’l. It wants to buckle less, boards are stiffer, bonds are great.
However as pointed out, skin buckling/compression is a board’s weakest link. Upon compression, the skin wants to buckle away towards the path of least resistance, thats away from the foam. Thats why the core’s tensile strength is important. This affect gets even weaker with thin flexible deck skin. Having said this, you are correct Mike, this stuff happens when a board over-flexes, which is easily solved by thickening the board.
Ive often pulled laminates off boards (pupe and epoxy) and in most cases, the foam is still attached to the laminate, meaning the bond isnt the weak link wrt to this ‘peel’ test, a measure of the bond/core tensile strength.
Just to add to the discussion, one can also thicken a laminate making it more buckle resistant. Looking at a 6/6/6 stiff epoxy deck eps, the eps is weak in tension yes, but the laminate wants to buckle far less. Replace the middle 6 and add in thin balsa and Bingo, compsand. Lucky for us, thicker stronger laminates like 6/6/6 also has a significant board stiffening affect, similar to thickening the board slightly, but at a heavier price. But, you also get the benefit of dent/damage resistance which we’ve agree also impacts snapping. Didnt even mention all thaty glass on the rails.
I’d be willing to bet that the GregL guys in your neck of the woods would agree on the 6/6/6 and 6/6 game plan, stringerless.
I agree with Silly’s take on balance in compsand. Simply put; some things are better built than others. Over the years, Bert has mentioned many times that ST’s are brittle.
In the end, mother nature is gonna have her way, no matter the build.
Just my $0.02. Enjoyed it.
I’ll stand by my statement that thickness is the ultimate stiffener.
Load bearing capability can be read as “break strength”. It doesn’t
refer to any “wall” applications, sorry for the confusion.
bizgravy is probably going to build himself a “conventional” board,
I’m just trying to help him make it as strong as he can, and help folks
understand the mechanics of “conventional” boards breaking.
I agree with your comments on flex for the most part; it can do some
wonderful things for both the load bearing capability and more importantly
the RIDE. We both have the same goals, just different ways of getting
there…
And I don’t advocate PU/PE for America’s Cup! LOL.
Gotta go to work, maybe more later.
Mike
Good choice of words on the “weakest link”. Thats exactly what we’re talking
about. And the ocean will have it’s way, and find that weakest link, every time.
I’m not sure that it’s “accepted” that hand laminated eps/epx is more "snap
resistant" than pu/pe. As I said, I could find people to argue both sides. Only
objective testing would resolve this. If hand lam eps/epx is stronger, it’s not
by much… back to the weakest link, etc. But it is stronger than pu/pe in other
measures.
I’m enjoying this discussion but I gotta go shape a few, maybe more later…
Mike
Sandy closeout barrels??? I’d say leave the board on the beach, grab a pair of swim fins, and enjoy the view
Quote:
I’ll stand by my statement that thickness is the ultimate stiffener.
…and i’ll agree with it. a linear increase in thickness yields a geometric increase in breaking point.
Wow, this is great stuff. Thanks for the discussion. I’m sure that I’m not the only one getting something out of it. What about eps stringerless vs. with a stringer? Would no stringer actually be better because it would be allowed to flex more? Does it just depend on the situation/stress being applied whether or not the stringer would help or hinder? Yes this would be made by me in and would be for the most part, pretty conventional/standard hand shaped, hand layup.
Ok, so now i’m thinking eps/epoxy (to cut down on weight a bit) with or without a stringer i’m not sure…and maybe a bit thicker/shorter would be a good call to help combat the potential of snappage?
Thanks again for the in depth stuff here…
yeah mike
i agree its “the” stiffener
but its not necessarily gunna make the board a great deal more snap resistant
especially if the board is “brittle” as craftee put it
hey bisgravy
if i wanted tough and not a compsand
id be looking at a 1.5 pound perimeter stringer marko eps blank
with a satan deck (6/6/6)
and a 6/6 bottom
epoxy resin
Quote:
However as pointed out, skin buckling/compression is a board’s weakest link. Upon compression, the skin wants to buckle away towards the path of least resistance, thats away from the foam.
Given that the deck has rocker and is under compression, why would it suddenly try to curve the other way(unless you have an extreme s-deck). Take a plastic pipe and bend it to the point of breakage, Won’t it buckle inwards on the compression side? A few stringerless lightweight EPS boards that have been posted on sways show this failure mode. While the stringer stiffens the board it will also prevent the deck skin to buckle into the foam.
Haavard, you’re on to the other function of the stringer, which is to keep the
two skins an equal distance apart. The only way a sandwich can bend (given
that the two skins stay an equal distance apart) is for one skin to lengthen
and the other to compress. The skins have to change lengths, or the core has
to change thickness, for the structure to bend.
This is the reason that increasing stringer width doesn’t really do alot to increase
load bearing capability; the standard 1/8" stringer is perfectly capable of keeping
the two skins an equal distance apart until the point of bond or shear failure. This
one is hard for most people to swallow.
As I said, new construction methods are introducing new modes of failure. The core
failure asociated with the inward buckle is one of those modes.
Mike
Good point Havaard. Field test results would clarify things quite a bit I would suspect.
Hopefully Bill B can chime in here.
Quote:
Wow, this is great stuff. Thanks for the discussion. I’m sure that I’m not the only one getting something out of it. What about eps stringerless vs. with a stringer? Would no stringer actually be better because it would be allowed to flex more? Does it just depend on the situation/stress being applied whether or not the stringer would help or hinder? Yes this would be made by me in and would be for the most part, pretty conventional/standard hand shaped, hand layup.
Ok, so now i’m thinking eps/epoxy (to cut down on weight a bit) with or without a stringer i’m not sure…and maybe a bit thicker/shorter would be a good call to help combat the potential of snappage?
Thanks again for the in depth stuff here…
First off, going thicker and shorter IS going to help a lot (no matter what your materials).
Boards are exposed to a variety of stress scenarios, and you are correct in assuming that different construction
techniques will show their strengths(or weaknesses) in different ways. Go to the North Shore if you want to see all
the different ways to break a board!
To stringer or not to stringer? In a hand laminated eps I’d advise keeping the stringer and reinforcing the bond, unless
you go up to 3" or more in thickness, where you might be able to shed the wood. Note Haavard’s post on the failure
mode of stringerless, what happens is the “crush” strength of the foam becomes the “weakest link”. Use the hardest
eps you can find.
Glad you’ve enjoyed this thread. Classic sways; ask a simple question, spark an international debate…
Mike
Quote:
The only way a sandwich can bend (given
that the two skins stay an equal distance apart) is for one skin to lengthen
and the other to compress. The skins have to change lengths, or the core has
to change thickness, for the structure to bend.
That’s why sandwich theory does not apply to surfboards as the core is so soft that the skins do not stay an equal distance apart(at least for those flexible compsands).
Sandwich theory still applies because it’s still a sandwich. You just get a
different mode of failure.
Sandwich theory does not apply(directly) to hollow or solid boards, but any
cored and skinned structure is by definition a sandwich.
Any board that is flexing due to a significant deflection of the core is flexing
way too much, IMHO. Boards that flex too much don’t ride very well. Thats
why balsa(VERY strong in compression end-grain oriented) works so good as a
skin core, it limits the flex to a reasonable degree. When the compsand guys go
to foam skin cores, they have to go thicker or add reinforcement, a la the “springer”.
Mike
Quote:
Any board that is flexing due to a significant deflection of the core is flexing
way too much
Quote:
it limits the flex to a reasonable degree
I agree!
except, significant deflection capability of the core is a good thing in a compsand (in mine at least)
With compsand, it is beneficial to have a core that doesn’t restrict flex.
The flex limiters and therefore providers of flex return are the skins (composition of and separation of the glass layers), the thickness of the board/foil (dictates the magnitude of the stresses on the skins through their separation), and the perimeter stringers.
So I want a core that does deform when the board flexes, and interferes as little as possible.
But has properties that allow it to deform and return over many flex cycles with little fatigue.
Gaining flex characteristics by virtue of the foam is the realm of PU…
Kit
Edit: to stay on topic - for the same weight, a compsand will be vastly stronger for both snaps and impact. Getting it to flex and feel good to ride at that “heavy” weight is another story
I think we just have a different perception of what " significant" is.
I totally understand how a little deflection enables your compsand
to bend, and you have a good grasp, and explanation, of the other
factors that control that flex. I was just pointing out the ways that
you keep them from flexing too much, and it’s obvious that the ones
that over-flex are having a greater deflection of the core(usually).
Too much deflection and flex WILL fatigue the core and all the bonds that tie
your structural components together.
This thread is about breaking boards. We’ll move over some time and
talk about flex characteristics. I play with that a lot.
Mike
dont wear a leash
Quote:
Sandwich theory still applies because it’s still a sandwich. You just get a
different mode of failure.
Everything in sandwich theory is about a stiff panel where the skins are always an equal distance apart. When a surfboard flex even the distance between the panels change, in addition the force that keep the skins apart change (the core act as a spring). While you could essentially apply sandwich theory to this as well it make it a hell of a lot more complex as the thickness is now a function of flex instead of a constant and may vary along the length and thickness of the board(three dimensional function), the force holding the skins apart are dependent of flex thus is a function of flex. It gets rather complex. Sandwich textbooks don’t deal with these issues, they usually deal with a flat panels that is considered to be stiff.