7'0"balsasandwich riding impressions.

General Discussion
21

The biggest thing about preforming the skins is that you start to look at the board as a collection of components working together rather than as a single monolithic unit. On my last skins (after jjp’s break) I broke loads of test panels (scraps :wink: ) and consistently the compressed side folded and the tension side exploded (I could have this reversed). It did not matter whether the balsa side or the glass side was compressed it always folded while it always exploded under tension.

As far as Nev jumping on the board - I think its just a parlor trick. People see the board taking the abuse, but miss what is really important - how quickly the board springs back into shape.

22

lets start with that ,yep pretreatment allright.

core flexibility on the skin. think of it as a scaled down board. (low density eps works best or the boards are to stiff)

so

low density balsa for flex.(if you wanted a really thin boards you would increase balsa density and thickness) but you want it to be ruberized and impact resistant.

also you want the under glass to have good stretching cabalities.

why does bert make thinner boards?

i think because there is less variables to control.?

also it allows more compressive flex below the neautral axis, or underneath the board on the outer curve shape.

I need a term for bottom curve…(outward curve) and deck curve (inner curve).

thats why he can jump on the thinner ones

id be very suprized if it could be done on a three inch thick compsand.

and if he could .he would have figure a way that somethingthat is not be standard in his usual construction.

whether it be from using a lower density or another type of foam or some sort of treatment.

or perhaps by allowing the core to move inside the skins independently.

Dave shape is the key

the designs have to change for these boards to work to there full potential

im sure of it.

i think your right about the rails dave

berts rails look indestructable.

Dan how are yours with regards to imapct strength.

Quote:

On my last skins (after jjp’s break) I broke loads of test panels (scraps :wink: ) and consistently the compressed side folded and the tension side exploded (I could have this reversed). It did not matter whether the balsa side or the glass side was compressed it always folded while it always exploded under tension.

yep. but were the panels curved with parabolic stringers?

Quote:

The biggest thing about preforming the skins is that you start to look at the board as a collection of components working together rather than as a single monolithic unit.

yeah man thats what im talking about .

hey i gotta go keep this thread going if yas wanna

i didnt really get time to expand

23

As a side note…

why do you need wood?

the crafter and I had talked about using this on the bottom

http://www.foambymail.com/Polyethylene.html

covered by this

http://www.foambymail.com/Volara.html

Also foaming flexible epoxy or Dow sealant/glue to fasten the skins on…

then the bottom can take whatever load the top dishes to it until the foam itself blows.

better yet how about a 1/8"-1/4" sheet between two .75lb sheets of EPS as well as a sheet on the bottom along with a shaped and inverted (opposite rockered) maple or bamboo or obechi springer under the deck skin and solid rails. Then you’ve got a real double a-frame suspension system for the load.

You only need the strength right under your feet where you are applying the stress the rest of the structure needs to transform the stress into recoverable deformaties that you manipulate via shape and thickness (i,e, snap and springback).

But everyone is right based on the load tests panel tests and JJPs real life tests, the bottom need to survive alot of load deformity with recovery to prevent the snapping and buckling we’re so accustomed to.

How bert is doing this with balsa lams is the question.

Solid rails not attached at all to the bottom panel via over laps or glass laps is a possibility along with skin prefab and foaming flexible epoxy to join the skins to the core are all potentials. But only your hair stylist Bert and Josh will know for sure whether the blond is natural or not… I don’t think this is rocket scientist stuff but more a slight of hand trick in order for it to be that simple and quick for Josh to start popping them out so quickly. I bet DanB’s closest…Also deformable concave bottom would introduce more elasticity to the bottom surface area to absorb the flex load.

Lots of options maybe DanB, Silly, and Jimmy can lead the way.

Look up the threads on Basalt Glass and some other stuff Holly tossed out to Bert and Greg a while back. Holly’s thrown more stuff out for people to catch than anyone can remember I bet. Bert seemed real interested in soaking it up at the time if I remember it. There was a “springer material” that Holly got “Y” to use which may play a part as well for an under deck reinforcement. There’s also Dyneema, Spherex and a host of other carrots for the taking… Just got to scour the archives.

24
Quote:

Lots of options maybe DanB, Silly, and Jimmy can lead the way

Or I can be soooooooooo wrong, and I’m going down the wrong path! Everything I know about boards I’ve learned from sways. All I’m really good at is hacking together ideas and problem solving.

25

Paul,

Good (and interesting points). Like we agreed on another thread, probably the most common way one of these boards is gonna break (assuming and appropriate mix of materials and techniques, etc) is when compression/tension are reversed (like going over the falls). Your summary of what compression and tension failures look like are pretty accurate to me.

I have waxed lyrical on here about surf curvature and how it affects flex, stiffness and strength. Noone seemed the least bit interested. Their loss, I suppose.

DanB,

Tension failure will be evidenced by a rupturing apart (a shower of splinters with wood), typically the compression surface will simply fold or crack neatly. Compression failures are usually evidenced by a lifting/delamination of the surface layer and overlapping layers, with the tension surface usually hinging neatly.

26
Quote:

berts rails look indestructable.

Dan how are yours with regards to imapct strength.

So far they are doing great - 4 oz on the rails doesn’t seem like it should be enough but I think woods natural ability to absorb impact helps out. Thats why I don’t think that you would want to have too much epoxy absorb into the rails. I think that were Bert is so far ahead is his understanding of how the rails and springer interact. Bert has described his boards as stiffer than most until they are put under load. There is no way that I would describe my stringerless board as stiffer than most. I’m learning that a stiff board is great until your actually on the wave (chip should love that line). Thinned out rails seem to allow the board to perform more hooky turns but they don’t store energy so you don’t project out of the turns as much. A stringer stores some of the energy from the flex and gives it back as the board straightens out. If the stringer is too strong it hinders the natural flex the thin rails gave you. This means that you should design the stringer to overpower the rails were you want the board stiffer and … you get the idea. This is what I think Bert means when he says that he can design around issues people have with his boards.

27

cosmetics aside

wood can handle thousands of cyles without fatigue

look at a 150 year old oregon yacht mast.

its has high strength to weight ratio and compressive strength

glue sticks to it

its a renewable resource

its cheapest

and most importantly

it can be plasticized witout adding very much weight

onelula i dont think the glue used is what is important, cuz the foam fails first anyway

its more about how to disperse that energy into the core .

so the bottom skin has to move in unison with the core.

but because the deck is stiff(desirable characteristic for positive flex return)it means everyhing is moving at different degrees.

i recall bert saying jjp,s board was most likely unbalanced .

does this ring any bells for you guys.

just a side note on foaming epoxys etc.

i do see potential there to use them as a treatment to the foam at the surface to improve peel strength.

ie. if the resin is not to dense and penetrates into the foam core say about an inch .

that would be an effective way to prevent delams.

but unfortunately would stiffen up the core .

so it kind of goes against its purpose. of keeping everything moving/flexible at the same amount

Quote:

have waxed lyrical on here about surf curvature and how it affects flex, stiffness and strength. Noone seemed the least bit interested. Their loss, I suppose.

hey doug

pinheads post on 80s rockers

i think pinhead and bert are interested !

berts flattened his rockers for a start

why?

how does curvature affect springback?

and less curvature allows a board to flex more.

therfore less curvature equals more strength

dan

Quote:

Thats why I don’t think that you would want to have too much epoxy absorb into the rails.

why?

surely if the balsa was fully saturated with a flexible resin they would be more durable

im sure if the board im building now was say 1/2 inch thinner it would be majic.

but then it wouldnt float me so it would suck

when your using thicker cores u need to compensate to make the board more flexible

when you use thinner cores u need to compensate by using thicker skins and concave decks.

and the answers right there in our faces .

thinner skin isnt the answer cuz you loose your flex return.

it has to be something to do with the core

lighter foam may do it 7 kg density

or multi densitys

i was thinking to slice the core the whole length of the board at the bottom about 3/4 inch in from the bottom

that way there is movement between the deck side of the core and botom side of the core.

allowing the bottom skin to stretch more in unison with the core

this i imagine would give it a lot more flex/and absorb compressive forces.

there other possible ways as well, Meecrafty as per your recent discoveries

28

i garuntee rocker curvature has something to do with flex but i can’t do research,i need a vaccum bagging set up.

29

Paul, All and sundry,

Yep, wood’s the stuff strength comes from :slight_smile: Everyone understands that wood is weaker in tension than compression? We fix that by the glass we put on the outside of the skins (blessed composite construction!).

If people ARE interested we could start discussing here :slight_smile: Lets start with a basic facts. The diagram below shows some cross-sections of a bend object, force is centred in the top with the ends supported. So the “deck” is in compression (blue) and the “bottom” in tension (red). This is a static example, obviously.

As we can see a rectangular cross-section disperses the forces involved evenly and can, thus abosorb more force before it fails. The less rectangular in cross-section the more the forces are focussed into the outermost curved area (the crown). So a completely circular cross-section absorbs far less force before it fails.

Think about it for a moment and you’ll understand that a rectangular cross-section flexes more easily that a round one. And flexes further before it breaks. Also meaning that it returns from further. And a rounder cross-section is stiffer to bend.

Does this help us see concave decks a bit differently?

So surface curvature patterns have an effect on flex characteristics. They most assuredly aren’t the only component, but they are a component:)

Well, that’s a start. It goes a lot further than that (there are other curves at work here - these things are more complex than people think).

30

Oh you are definately right.

For one thing the more extreme the rocker is the more your board will resist flex, all else being equal.

31

yeah. a concave deck brings stiffness out to the rails cuz there is domes there.

but what about the parabolic curve or the concave part

you havent included an example of that.

.

my goal is

1 to maintain flex while increasing core thickness !( i want a three inch board that flexes)

2 and allow the bottom of the board better resistance to compressive forces

3 have really ding resistant rails

4 have good spring back

things to address for point 1

reducing rocker?

reduce skin thickness?(this reduces goal 4)

lower density skin and core(mildy reduces goal 4)

dont dome the deck?

split/modify the core to allow more movement(multi foams)

shit im starting to think there may be more to berts springer concept

things to address for point 2

split the core to allow more movement(multi foams)

use less glass on inside and a more flexible resin

use less glass on the outside (pretreatment allows less glass)

use a glue that is more flexible and or penetratres into the core.

dont wrap the bottom skin over stringers?

dont use rigid fin systems

point 3

saturate balsa on rails with resin and use aramid fibres(may contradict point 1 by increasing board stiffnes)

use a material on the rails that has more springback (ie flexible resin)

point 4

use denser thicker skin material on the deck

use a springer

use a top hat

all these things are possible solutions to the prob

shape has a lot to do with it. but at the risk of performance

32

a heavily rockered pupe would feel more “alive” in flex

a heavily rockered compsand would be stiffer .

tommorow i got some 4 ft to 6 ft clean waves hopefully so i get to try the new board out

so i can let you guys know how it goes

It is a stiffy, but seems to be kind of springy

i actually havent built one that feels like it before, so im kinda excited.

33

I said it was start, didn’t I :slight_smile: Gotta start with basics and build from there.

Yep, concaves bring stiffness out to the rails because of the domes (crowns). But there’s a trade-off. Those crowns concentrate compression, so we have to be careful to build in a way that allows for more compression there. There’s also (potentially) a bit more to it than that in compsand boards.

On to the next things. BTW I don’t understand everything here perfectly, so don’t just buy it piecemeal. Debate. Discuss. That’s the Sways way!

We started with cross-section curves.

Rocker curve (aka side view curves). More rocker will mean that the board flexes in normal compression easier. But this means it will also resist flex when compression/tension is reversed (i.e., turn the board upside down and jump on it). It’s always easier to bend something in the direction it’s already bent (IF pre-tensioning is not a factor). And harder to bend it in the other direction. Plus, a structure that is used to a given compression/tension pattern fails considerably easier when the compression/tension pattern is reversed. So we build for that for durability, amongst other things.

Profile curves (aka top view curves). Take a 1/2"x1/2"x2’ bit of slat. Steam a curve into it. Now:

(a) bend an identical straight slat.

(b) compare this to bending the curved slat “with” the curve.

(c) compare to trying to bend the same slat against the curve.

(d) compare to trying to bend the curved slate from the side.

You’ll find that difficulty increases from top to bottom, but for different reasons. There won’t be a huge amount of difference between A and B, but B is slightly “pre-tensioned” and will be a little more difficult than if it’s straight. Our little C is explained above in Rocker curve. But D, D isn’t directly resisting with compression/tension. It’s trying to snake back to its original shape and twist in your hands. If you can secure it somehow to prevent torque you’ll find it can be rather stiff in its own right. Because it’s resisting in two planes. Our perimeter stringers! The greater the curve there the more it’ll resist, all else being equal.

Note A and B are a bit different when we are dealing with just “plain foam”, because foam doesn’t have those funky wood fibres running its length. So pre-tensioning isn’t as significant a factor with foam.

I think we do need to be aware of all the components, what they do in isolation and how they behave together.

On to your goals.

Point 1.

Yep, I think those are all possibilities. Your concave deck is still domed, tho. It’s just “split domed”. Looking at the depth of the concave (with a view to reducing your crowns) is a possibility. The perimeter stringers are going to be a big factor, so the more you wrap skins over the rail the stiffer it’s going to be. Also, the wider they are the stiffer it’s going to be (so 3 x 5mm is stiffer than 2 x 5mm).

Yeah, I think the springer’s a fairly important concept.

Point 2.

Yeah, I think minimising wrapping and using pre-treatment will be useful here. I also thing we need “strong enough” without too strong. Because there’s going to be a trade-off with increasing bottom compression resistance (it’ll also impact the bottoms tension properties).

Point 3.

I think the outermost layer of the rails is the one that has the primary responsibility for ding resistance. If we pre-treat that and go with less “thick” rails we should be able to improve ding resistance without sacrificing flex characteristics. Dunno about the glass over the outer layer. That’ll improve ding resistance, but if it’s overdone it’ll counter flex. Again, we need enough without using too much.

Point 4.

Denser, thicker deck material will reduce flex by having increased compression resistance. That’ll improve recovery (spring back), but at a cost to flexibility. I am really convinced that the springer is very important to recovery/spring back (hence it’s name).

And yeah, I agree. Shape is important. It can be used to increase or reduce both flex and recovery. So can (should?) most, if not all, of the other components we are using.

Putting a 3d lattice over our boards could/would provide an enlightening view of the various curves in action and how they interact, I think.

Look forward to hearing how your board goes! And seeing how this discussion shapes up!

34

ha ha

i used a dremel with diamond circular saw and cut the bottom skin of one of my stiffest boards

the board is 2 inces thick with a concave deck .the bottom skin overlapped the rails .

the stringers are still in place

this board buckeld in the middle when i jumped on it upside down

right where the balsa but joins on the sheet.

heres a apic

wanna know a secret

before i pulled off the skin

i cut into the glass and stringer all around the apex of the rails to test if it would effect flex.

guess what

it hardly made any difference

then i cut off the bottom skin leaving the stringer on

it was quite difficult to pull off actually.

all of a sudden the board can be flattened

the stringers dont really seem to make much difference at all

also they are delammed from the core in places.

i alway thought it was the deck skin and stringers that affect stiffness the most

but in fact its the relationship of both skins with the stringers as the binder !

the skin is where its at for flex .

i am really sure now that stringers are a water barrier and prevent twisting

heres a pic of the skin

see how where the resin soaked in more was around the seams of the balsa

it must tend to pool there if its not sanded flat or something.

buckling and then rebuilding a board is teaching me a lot

i will do the same planshape as the one i just finished but it will be alot thinner with out bottom concave

35

silly man!

Interesting stuff!

your helping me and others out a lot doing what your doing, thanks for posting.

I’m gonna go lighter core,lighter interior glass,thinner bottom skins…keep my 3mm decks for springback, Am I right or way off you think??

thanks alot

Was out today after a storm overnight,face still bumpy but some waves were really nice.

size at head-headhalf. my 7’0" balsa really came alive in these conditions(size).

could feel some really nice projections out of turns and was able to hit the lip really hard.

I also had those adrenaline rushes from going superfast.

but still tuned wrong for me if we’re talking “bert standards” I guess. but still lot’s of fun!

Jimmy yoshio shibata.

36
Quote:

I like the fins , too , Yoshio !

…what wood did you use ?

cheers !

ben

37

no yoshio IMHO, i think your right on the money.

with changing to lighter foam and innerglass.

especially for a small wave board

i think the stiffer boards work better when its big.

like at overhead.

and the lighter flexi ones in smaller conditions.

i think you will be very pleased with the result.

try one and let me know

honestly i think the hardest part of making compsands is taking the extra thickness off when your shaping.

my boards are always 3 to 5 mm to thick.

the latest one i took out this morning in fat 1 ft 20 knot offshore

it was fast and loose but kind of boaty .

i sure this is a combination of too much volume in the rails too much tuck.

i managed to link a few turns but the waves were slow and sectioning so its hard to judge

maybe it went really well cuz my other board prolly would have sank.

ill take it out again today cuz the surfs picking up.

does anybody know

is there a improved compressive strength from a cloth like Dynel.?>

i was thinking of trying it on the inner skin on the bottom.

also dont put your balsa butt joints in the middle of the board at the rails.

when you stagger sheets you want a nice long piece out at the rails

thats why im using diagonal on the bottom at the tail and my the nose sheets extend down past midpoint

there is a deffinate weakness in the butt joints so placement is important.

38

the latest one i took out this morning in fat 1 ft 20 knot offshore

it was fast and loose but kind of boaty .

i sure this is a combination of too much volume in the rails too much tuck.

i managed to link a few turns but the waves were slow and sectioning so its hard to judge

maybe it went really well cuz my other board prolly would have sank.

oh yeah youll need more time on it…

got one just like that and it goes really well in small tight fast pockets…where your turn rhythm is quicker…but it sucks in larger choppier surf (too boaty lacks control).

im making a larger choppy surf board sometime this year…I already have one made (panel flex is so trippy) but its a wee bit heavy…i’ll likely break some serious conventional rules with it.

Hey Jimmy,

You can break that board in quicker by supporting the ends on blocks and placing a heavy weight in the middle…set that up in a place where you can push down on it so it wiggles up and down…maybe next to your computer…adding the weight makes the board oscilate like a diving board…after a couple thousand oscilations it may ride and feel better. Or you can just surf on it a lot and wait a few months.

39

sorry ben, forgot you asked me BEFORE.

They’re made of 9mm ply. Total of three layers of 4oz when finally on board, feels flexy which I like.

Think the wood of the ply is lauan and something else combined.

Jimmy yoshio shibata.

40

Ha Ha! Next to the computer…Wish I could do as much surfing as much I’m doing the computer!

Think I’ll just surf it til it feels better.

Jimmy yoshio shibata.