A theory of how composite boards work

General Discussion
21

a very quick perusal of the FW site makes it abundantly clear that they obviously feel pretty good about overlapping the bottom and deck skins with the rail material. In fact, this is something that they have moved TOWARDS in the evolution of their production; not AWAY from. Their initial boards; wood rails with little deck overlap and apparently no bottom overlap (though that’s not to say that there isn’t an inner layer of wood that you can’t see). Their current boards? less wood in the rails, overlapped bottom and deck skins. Much easier to make. Much less susceptible to the stresses KK is describing; way better build for longevity IMHO.

either they’re trying to make a too flexible board stiffer, or ease their method of production (could be both).

my tests show lapping/not lapping the bottom makes no difference. panel thickness, overall board thickness, and core density, on the other hand, most certainly do.

22

I’m wondering, is firewire changing from C to A or B type rails? (pic from an old thread)

Secondly, while some time ago most were saying C type will give alot more flex, now experience says that A type rails yield adequate flex(unless you’re lightweight and surf soft waves)?

regards,

Håvard

23

I think that’s right, Haarvard. I completely agree with Silly that panel stiffness & core density have 95% of what affects flex and which of those types of rail build-out you do is maybe only the other 5%.

Then again, most of mine have been A style (if balsa skins & rails) because I’m a big heavy guy who likes big heavy boards.

24

okay so here’s the expected follow up from our little corner of the world.

If you don’t do the solid balsa rails and just do a full rail wrap with only a slight over lap of the deck and bottom skins along the bottom edge of the rail like CMP had been doing for 10 years before Bert stepped in with his post…

What then?

Has CMP been ahead of the curve once again without realizing it?

(After Bert we all here thought rail wrapping balsa was totally wrong versus gluing up a solid band)

If it’s only skin thickness and core density that makes up most of the flex pattern and you just wrap the soft foam rail shouldn’t you get more flex under this theory with out the solid wood rails or is it going to be stiffer like everyone has been saying about the surftech construction method? Seems like if you thin out the profile thickness a tad and don’t use the solid heavy rails as well as taper out the thickness of your planks from center to rail you be able to create the right type of flex everyone is seeking and still provide deck strength along the centerline.

Perhaps the problem has been making the core too thick by copying the standard PU specs when duplicating the design in EPS versus really thinning it out and perhaps going wider like Bert’s showed us with his favorite personal little hot dog board he showed us in the wide tail discussion…

25

I’ve done both A and C and I think A is noticably stiffer than C. However, I’m making a set of 3 boards that are going to be similarly shaped, but I plan to 2 of them with the C approach and 1 of them with the A. I’ll let you know.

26

Hello,

Just a remark from a outsider, isn’t this a way to construct what you are looking for, sounds like what you say about firewire construction.

Deck and bottom fixed by central stringer to make I beam construction, longitudinal stiffness, a gap between deck and rail to allow suspension type movement between deck and bottom, the rail stiffening the bottom to keep its shape while still allowing flex…

Just a thought

Soul

27
Quote:

hi, tirides/les, sorry to hear you have broken a couple of your compsand boards, i counld/nt help but notice there does/nt seem to be much rail wood in the picture, how did you do your rails

Rails… The one pictured was like rail design #A pictured in one of the above posts. It was 4x1/8" balsa strips or 1/2" wide and the rails were pinched. Board thickness and thickest point (3" from rail edge) was 2 3/4" thick, probably 2 1/4" in the middle. I remember posting a question shortly after breaking this board. “Why and how can I improve on the next one…” I got plenty of suggestions, thicker balsa on the deck/bottom, thicker fiberglass, different shape. Then Bert got on and said something like - you did just fine, the board worked for what it was made to do, at some point there will just be forces too much for it. The force that was too much for this board was a wave that was overhead. The wave didn’t just gradually roll over, the lip pitched/tubed, there was a LOT of force. I wasn’t on the board, I went out the back and the force of the wave hit the deck. I don’t really need (or want) a board that will take on the full force of the Pipeline! I’d make a board much different if I did. I just need one that will last in 99.9% of the waves I (or any one that I’d sell/give one of my boards to) would ride. I think that I’ve accomplished that with the redwood rails, I just want/need to improve on it while keeping the board as light and responsive as it is now. Les

28
Quote:

Hello,

Just a remark from a outsider, isn’t this a way to construct what you are looking for, sounds like what you say about firewire construction.

Deck and bottom fixed by central stringer to make I beam construction, longitudinal stiffness, a gap between deck and rail to allow suspension type movement between deck and bottom, the rail stiffening the bottom to keep its shape while still allowing flex…

Just a thought

Soul

I thought that center stringers were out on compsand boards? At least I haven’t used one since I started using EPS (last 17 of 19 boards).

Les

Les

29

Oneula touches on a point which I was just about to voice - the shape changes needed for compsands.

As I waffled on about earlier, I think flex can be achieved with either construction, but will result in two different shaped boards, and any number of other differences such as weight and cosmetics.

What I think would be interesting, is if variations on the “C” rail or other new ideas could allow pu/pe shapes to be valid in compsand construction.

The best shapers in the world have been incrementally refining their shapes in PU foam for decades, to the point that standard shortboards seem to barely differ from each other, pretty well optimised for the materials.

Whilst i’m very interested in new designs, and will be trying my own wide template, concave-deck boards, it would be great to be able to incorporate all the design knowledge and proven shapes/foils that have been around for years.

It seems like the main reason some people depart from these shapes is to make compsands flex.

If we can use the composite materials in a way which allows “traditional” shapes to flex, wouldn’t that be more easily accepted by your average surfer consumer?

I know the beauty of composite construction allows us amazing freedom to try new exciting designs, and i’m all for that.

But will it take us 20 years+ to get the shapes optimised to the limits of the materials?

Do we really have to re-invent the wheel to get this stuff to work?

It’d be cool if I could make my favorite 6’3 exactly the same out of more durable materials, to give me something to ride in between crazy experiments.

Whilst my last few boards have been fun, my surfing is suffering by having radically different boards each month!

Maybe it’s actually improving, but it’s weird having to surf differently all the time, as these boards do require a different style.

The long and the short of it is, I’d like to be able to make normal shapes as well as explore the limits of the materials.

I think it’s definitely possible

Kit

30

Is that a “springer”? You know, the red thing about eight miles north of the Neutral Plane.

No doug, It’s a gasket tool that I used to seperate the layers of glass/balsa to repair it. I used the tool to lift that edge of the glass/balsa/glass layer.

I’ve used a springer on two of my boards and didn’t feel any differnce so stopped using them.

Les

31

Just me rambling…

YOu don’t have to keep searching/shaping for that perfect board, you said you have or was it HAD it. Now stop, don’t go any further. Naw, that won’t work, at least not for me!

I find that the experimenting is what is so stimulating. Using the new materials with the old pu/pe designs and gradually tweeking the designs with new thought for the next, then the next, then the next board I make.

Besides, by the time we get all the bugs worked out and we perfect (ha) the balsa compsand then someone will come out with NEWER material for the next generation to experiment with.

I figure, each board that I make and have to tweek my surfing style just makes me a better surfer. Like the SUP I just finished, in one hour of practice I was able to only stand up for 10 sec., the next time out I was able to go 20 sec. without falling, yesterday I went out again and stayed up over 400 yards! Must be practice makes perfect, or at least makes ‘joe’ a better surfer.

Keep asking questions - Keep experimenting - Keep having fun!

Les

32

Regardless of what a board is made of, performance is all about shape (assuming optimal fin choice and postioning). Flex is really just a property of shape i.e. the way shape changes in response to force from wave or rider. Volume is another property of shape. Volume is really the distribution of bouyant force.

Solid rails aren’t just (even?) about flex. With compands with solid rails you get a bit more control over bouyant force at the rails. Materials with lower density resurface much quicker after submersion so bouyant force at the rails has big effect on the way a board feels. Although you don’t use much wood, you are still looking at a material 10 - 15 times denser than the core.

I’m pretty sure the density of your cores (both skin cores and EPS core) is the biggest factor governing flex - solid rails are about changing the way the rail responds in turns - particularly for super light boards. That’s why we see it in Greg Loehr’s Segway EPS blanks and the light weight XTR boards from Lost.

33
Quote:

Solid rails aren’t just (even?) about flex. With compands with solid rails you get a bit more control over bouyant force at the rails. Materials with lower density resurface much quicker after submersion so bouyant force at the rails has big effect on the way a board feels. Although you don’t use much wood, you are still looking at a material 10 - 15 times denser than the core.

I’m pretty sure the density of your cores (both skin cores and EPS core) is the biggest factor governing flex - solid rails are about changing the way the rail responds in turns - particularly for super light boards. That’s why we see it in Greg Loehr’s Segway EPS blanks and the light weight XTR boards from Lost.

http://www.segwaycomposites.com/ParabolicSystem.html

Don’t forget that the parabolic stringers also are about reducing torsion/twist as well which should increase rail bite and possibly increase drive.

regards,

Håvard

34
Quote:

But will it take us 20 years+ to get the shapes optimised to the limits of the materials?

Do we really have to re-invent the wheel to get this stuff to work?

It’d be cool if I could make my favorite 6’3 exactly the same out of more durable materials, to give me something to ride in between crazy experiments.

no

you can build it the same dimensions

thats fine!

and it will be a stronger lighter board

that feels like a new one for an indefinate period no matter how hard you thrash it

(what more do you want?)

thing that could be changed would be subtle, such as

foil distribution and concaves.

Quote:

Hello,

Just a remark from a outsider, isn’t this a way to construct what you are looking for, sounds like what you say about firewire construction.

Deck and bottom fixed by central stringer to make I beam construction, longitudinal stiffness, a gap between deck and rail to allow suspension type movement between deck and bottom, the rail stiffening the bottom to keep its shape while still allowing flex…

Just a thought

Soul

i can only say forget about the centre stringer!

most of the points so far raised in this thread are based on practical experience

Quote:

Has CMP been ahead of the curve once again without realizing it?

(After Bert we all here thought rail wrapping balsa was totally wrong versus gluing up a solid band)

If it’s only skin thickness and core density that makes up most of the flex pattern and you just wrap the soft foam rail shouldn’t you get more flex under this theory with out the solid wood rails or is it going to be stiffer like everyone has been saying about the surftech construction method? Seems like if you thin out the profile thickness a tad and don’t use the solid heavy rails as well as taper out the thickness of your planks from center to rail you be able to create the right type of flex everyone is seeking and still provide deck strength along the centerline.

hi Bernie

yes and no

what works for cmp is based on his style of surfing in certain types of waves

surftechs work for heaps of people as well !

but there not compsands imo.

compsand is a buzz word tech term that has come from the developement of berts/mikes and a few other initial developers

thanks for cmp and his influence as an original developer. but i feel weve moved in new directions .

imo wrapping the rails is not the answer for an even distribution of shear forces

in the case of a wrapped rail it will always fail at the weakest point or the point taking most of the load

high density rail material allows the board to flex further without failing across the rail apex.

also its a great impact resistant, water barrier.

(and thats just from the durability aspect.add in a rail that feels better as well and your laughing)

35

I’ve been thinking about this don’t connect deck and bottom as it looks up shear thing that bert said. But still you connect the deck and bottom at the rail one way or the other since we wrap the board in glass, so maybe it’s just about minimizing shear forces. One thing that Bert seems to be consistant about is really thin rails. This allows for a consistant flex throughout the range of shapes and length, ehich in turn makes it easier to tune the flex with a springer. But it keeps shear forces to a minimum where the deck and bottom is connected as shear increases with thickness when the board flexes.

I’ve been puzzled by the reports that the non overlapping bottom skin boards flex more. It didn’t make any sense. But maybe it creates a hinge around the rails which allows the bottom to flex rail to rail and squeese into the foam to form a concave when the board flexes, the bottom skin is like a string from nose to tail that want’s to flatten. This may be further exagerated by the deck concaves Bert uses as he showed in the paper bending trick. Also, it allows the bottom skin to form into a concave when you push hard against the board wo causing much change in the rocker and spring back creating a extra boost thrugh turns. Greg called this the trampoline effect. If you put the bottom skin on top of the rails you stiffen up the rail to rail flex and limit the above effects, however you may get a stronger, stiffer board. These effect are probably most noticable if you use 1 lbs foam, if you use 2lbs you might as well put the skins on top of the rails(or maybe since you are using 2lbs, you are a big, heavy, powerful surfer who manage to get plenty flex and trampoline effect out of 2lbs foam with the skins on top of the rails.)

I think if you want to use a springer you really need to consider the shape and material of it, and preload it to give it adequate flex. How much does the board flex without the springer, does it add one inch or five to the rocker during a turn? To be able to even notice the effect of a springer it need to provide a significant amount of spring while only bending a few inches. Secondly, I wonder if you put a stringer off the neutral axis, even connecting it between bottom and deck, you could control the amount of maximum flex while having a very flexible board. Ie. if you attach a string between the bottom at the center and the deck at the tail, but keep some slack in it then the board could easily flex untill there is no more slack, then the rocker would be set at that point and not flex any further. By using a springer instead of a string you can control the flex so there is no sudden stop in the flex yet make sure the rocker moves no furter.

regards,

Håvard

36

First off, I come across sounding much more passionate about this than I mean to. I think its an operational hazard of being a teacher.

I agree with what tridries says about them just breaking. I think one of Bert’s ideas is that with his custom boards you actually needed a quiver. A small wave board should have a better chance of breaker if its taken out in giant surf because it was made to flex easier. In reality (at least for me) I surf the board that happened to make it to the beach that day - sometimes is the best choice and others its not.

Kit, in most cases I don’t think the shapes need to be wildly different. I think the key is to not stick to something just because its always been done that way. Bert’s big design goal was speed and I’ve carried a lot of those biases into my single fin design where they might not be appropriate, but the definitely apply to my performance longboard.

Steve (pinhead), I think that you are exactly right about the job of the rails. I think the deck skin transfers energy to the rails to beef them up and turn better. I also agree about the density of the cores. I just happen to think that the way they’re put together makes a difference. Take making cookies as an example - you could just throw all of the ingredients into a big bowl and turn on the blender. What you would end up with is a cookie like thing. However, all cookie recipes seem to want you to mix the sugar, butter, and egg first then add the dry stuff. There’s a reason you bake this way and I think there’s a reason Bert put his boards together the way he did.

Paul (silly), you’re right about us agreeing on about 90% of how the board works. I think longboards exaggerate design differences so they make highlight things that might be too subtle to feel on a short board. I remember taking off on a wave on one of the twins. As the wave closed out I turned to shore and hit some chop and I saw over a foot of movement in the nose of my board - it looked like one of those earthquake film clips.

Haavard, I think the difference is joining the bottom skin plays up the panel effect of the board - it is in effect one composite piece. I think not attaching the bottom skin to the rails breaks the board up into two distinct composite pieces.

37

I think the major difference in flex, as has been said before, is panel stiffness.

If you wrap the rails, like CMP, you get a very stiff panel (skin) because of the compound curve you’ve introduced be wrapping it around the rail. Don’t forget, that in that case, there’s glass both in side & outside the skin, all the way around the rail. You can get the same panel stiffness with things like heavy deck dome or concave, the inside-the-rail channels (on the deck) that some use for stringerless EPS, etc. Its all about putting the complete skin through some serious curves.

On the skins that stop with a gap spanned by built-out rails, the panels (skins) aren’t nearly as stiff. And there’s no glass between the foam & the rail material. So the flex isn’t really due to the choice of rail material or construction, its that the panel is flatter and therefore more flexible. The rail material just fills a gap - you could spray in Great Stuff foam and shape that and it would probably be fine. :slight_smile:

38

Bert always made the point to add what you need and remove what you don’t. It seems to me that with a free floating bottom skin putting a strip of kevlar tape over the seam between the rail and the bottom panel would take care of cloth ripping problems in that area. It just seems to me that there are too many benefits to that free floating bottom to just bind it up effectively making your board a piece of wood with foam inside, instead of multiple panels free to move how they need to.

First in terms of panels. The fact that the deck connects to the rails is a huge benefit, response is instantaneous. What my feet do is tranferred to the rail with no loss of energy. Insane drive. You also want something supporting the deck. If the deck free floats you will feel serious lag because your movements will be dampened by light eps foam, maybe good for beginner boards because it could be very forgiving, and they’re not to hard on the deck anyway (That design drawn in the post above with a center stringer would be great for a beginner, something supporting the deck, but their wobbly movements won’t be transferred to the rails as much). On the bottom, however,we want exactly the opposite, we want the bottom to conform freely to the shape of the wave as much as we can, that’s why mats are so fast (just to paint a picture, not THAT much movement going on in a compsand). To achieve this it has to move as freely as possible and it DEFINITELY can’t be tied to the rails and deck, which serve an entirely different purpose.

Remember Bert told us that the deck goes over the rails and later he was kickin himself cause he may’ve let a bit too much out of the bag. There’s a reason for that - The experienced rider gains so much by having his movements translate to the rail as fast as possible, so that is a must. He gains nothing by having every little bump on the water translate through his bottom, to his rail, to his deck, to his feet when he could have a bottom that automatically handles these bumps for him.

Second in terms of entire board. So as far as controlling full on tip to tail flex we must look back to the deck and rails. I would guess that since the majority of the flexing that goes on is caused by what the rider is doing that the deck will be a key player in how much board flex we get and flex return, next comes the rails because they’re tied to the deck and most significant rocker changes happen on rail, last is the bottom it is free floating but outer glass ties it into the rest of the structure. So achieving different board flex can be achieved by different thickness, resin usage and glassing schedule in the rails and deck skin, just depends on the wave type.

I’m thinking something like:

pre-fabbed skins with high pressure to pull resin into the wood.

bottom: 2oz.-1/16balsa-2oz. with 2040 or 2020

deck: 4oz.-1/8balsa-4oz. with 2000 resin

core- .75-1 lb

rails - not sure, but was thinking of tapering down the PS towards the tail to get a more progressive flex out the back. Glass tape with 2020 resin to lam the rails. Kevlar on the seem between the bottom and rail.

39

A few thoughts about making a board with flex…

Make the skins first, and make them strong but flexible. Then laminate them onto a preshaped core but don’t overlap the rails. Use high density foam like blue dow for the rails. Glass the rails.

Gary Young makes his boards this way. I would think his boards have quite a bit of flex, but are strong because of the special layered skins.

He’s been doing composite boards for about 30 years, so he should know a thing or two about them. If anyone has mastered building compsands, it would be Gary Young.

I personally like a solid feeling board. I get distracted when I notice the board feeling soft under my feet. It took me a while to get used to riding my brother’s surflite. I think the flexing should be subtle.

40

Håvard,

When you don’t wrap the skins over the rail they are separate structures. So your board has three components - deck, rail and bottom.

Not enough epoxy soaks into the joint to cause them to be truly bonded, when you have pre-wet the glass 1:1.

When you wrap the skins over the rail they are being intentionally bonded to the rail. Now the deck, rails and bottom have become one monocoqual structure. That means that every single curve resists efforts to bend across it and that resistance is backed up by the whole monocoque structure.

Have a good read of the 7’0"balsasandwich riding impressions. thread.

Make any sense?