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[Bernhardt]

As I look at my 1/4"-1/8" cedar and paulownia boards I've been making it's got me wondering about something....

Has anyone ever prebuilt out their skins maybe 3/16"-1/4" thick and then just "attached" them only to the rail and not to the foam at all? Kind of live building a 100% delammed board that's just skin and rails with a foam filler? Might need to attch the tail for the fins though..

Rails wound be glass and bound to the foam core while the preglassed  skins would just be attach to the rails using glass tape.

If you laid a piece of poly over the foam you could vacuum on the deck and bottom skins using glass under and glassover the "preform" the skins prior to attaching them to the rails. I've done this withe thin veneer skins and veneer softener to form the stiff wood before lamming it.

The sandwich would actually at this point just be the thicker wood skin between layers of high pressured applied glass and be like a HWS but instead of wood ribs you'd have and "unattached" foam core for support.

Anyway we just might give this a go using blue for the center before we stop.

I guess our new board logo should say somewhere..
Just fooling around here folks..


Okay and now for a reality check from the crew..
what are we missing here...
  

[Jarrod]

I think it would work as far as assembly, but I wouldn't see any benefit to not tying the skins to the core.    It would allow way more flex, but it would severely weaken the whole thing.   

I've thought about this myself, and I blew it off after some thought experiments.

Mentally take three layers of balsa wood and just stack them together, no glue.  Flex them, puncture them, and karate-chop them until they break.   Now do the same thing with a stack of balsa that is glued together.  Much tougher.   A more accurate experiment would be to use some eps as the meat in the sandwich.   

It seems like without the skins tied to the core you could literally put a foot right through the board.   Without the I-beam effect of everything being tied together, it is just a stack of individually fairly weak materials.

[RCC]

Hey folks,
   This site (and sways) is great!  Thanks to all contributors.  Just got started on my first compsand build.  8' long, top layer 1lb EPS, bottom layer 1.3lb EPP (yes, RR epoxy does stick to EPP, and 3M super 77 works well too).  More on that project when I've made more progress.

Along the lines of this topic...  here's an idea of perhaps another way to increase flex without reducing strength much:

What if, instead of skipping the attachment of the skins as mentioned, build a Home Depot style blank such that the two layers of foam are only glued together on a few inches around the rail all the way around the board?  The rest of the construction would then follow "standard" compsand procedures.

Predicted result: The top and bottom skins would still have similar compression strength compared to a regular compsand, and the rails would behave similarly as well, but the shear force in the core while flexing the board would be less, providing a way to build a board with more flex for a given thickness.  If it worked, it could open the door to thicker boards that flex, or boards with thicker wood that still flex, possibly with a faster spring rate. 

One could take it a step further and plane out a little on the inside sides of the foam sheets where they're not going to be glued together, making a little bit of an air cavity down the middle of the core(might want a vent!), so that when the board flexes and compresses the core it compresses more easily in the middle, possibly creating a temporary concave bottom while turning.  Okay, okay... I'd better stop there

Thoughts?  Thanks!

Bernie,
   Seems to me like your idea would work well with thicker skins, as you mentioned, as long as you're okay with the added weight of the wood.  Would probably be a little safer if the deck skin were made of two or three layers of wood to get that plywood effect.  I was thinking of building a hollow balsa board so I epoxied 4 pieces of 1/8" x 18" x 4" balsa with 4oz S-glass between each layer, as well as on the top and bottom surfaces.  It had a slight arc in it, like a domed deck.  I could stand on it (170lb) without it flexing flat, and I could bounce up and down on it.  A few minutes of that eventually showed a compression fracture forming on the top near the middle.  I wanted to use 3-layers of 1/8" so the fracture with 4 of them was a little discouraging.  I concluded (with some guessing) that a completely hollow board might take too much wood to keep it light, and that a foam or wood-rib core would allow the skins to be more reasonable in thickness.  Once I realized I'd want some sort of core to keep it light, I realized I should just go compsand.  But, I'm pretty sure your idea would work with a 3 x 1/8" thick deck, and maybe even less.  Actually, I'd probably make the top layer of wood a little thinner and saturate it with epoxy for compression strength.  Anyways, I'd be a little concerned that the added thickness of wood would stiffen the board some and take away from the gains of the detached skins.  But... I haven't even finished my first compsand, so what do i know? 

Also, I've seen many posts suggesting that the deck of a compsand be attached as usual, but the bottom skin is left unattached.  Perhaps if anyone has actually tried this, they could tell you half the story of what to expect.  If they didn't get fractures while duck diving, that's score 1 for detached skins.

[Jarrod]

My idea was just a thought experiment to illustrate the difference between a multi-layered structure with the layers tied together and one with the layers simply stacked.   

I wasn't actually proposing to make a balsa ply structure, you'd be better off with thin traditional ply if you were going to do that.   the point was that the skins should be attached to the core somehow.

[Ian]

Hi Bernie,
I think Rio did some thing like the delammed board idea.He just used a little S glue pattern on the foam.
The end result was not good.
I think he reglued the top skin and changed the rocker.
I think you would make a big bubble.To much lost with more weight.
Just my 2c, let us know how it goes.

[Bernhardt]

Thanks everyone!

be interesting to find out everyones interpretation of the following,,,

1. what is the purpose of the core?
i,e, why is it there and what is it supposed to contribute to the construct?

2. what is the purpose of the skins?
i,e, what are they supposed to do and why?

3. what is the purpose of the solid or higher density perimeter rail
i,e, what is it supposed to do and why?

4. since water is not a solid how does increased flex not contribute to more drag since the water will want to give way to any flexing solid sitting on it's surface? ie can you really flex a board in the water like you can on land with having alot of length for support? Won't the board just sink where ever you apply pressure?

these are kind of simple but extremely fundamental questions that I don think anyone has really addressed on any forum from a technical/engineering standpoint. Be interesting to see if there are some real baselines that we can be set for all of us to work from...

sorry if i'm scaring anyone..

let'r rip!

[Benny]

I'd honestly say in a lightweight shorty, the core is only there as an easier way to make a hollow board.  A stay-in-place male mold.  With cheaper tooling 

I've tried to make logs like that, though, and the knee paddling kills 'em.  Plus, they just don't settle into the curl right on the dreamy waist-to-shoulder & glassy waves I want   

Surfed a 30 lb board the other day.  Came away thinking that Tom Wegener & Roy Stewart might be on to something after all. 

Sorry to veer off road, but a lot of the uber-licht stuff here just simply doesn't apply to those of us who surf the 60% of boards sold worldwide.     Compsands are also spectacular for performance & durability in shapes not ever intended to bash lips! 

Although...I suspect you know that already, Bernie 

[Bernhardt]

The path Tom and Roy are currently on is all about trim speed and length of ride. They seem to  understand the importance of the rail versus the fin and how shape/outline contributes to control and release in respect to rail/bottom surfing.

My brother is so amped after seeing those videos of tom carroll and the wegner video he's planning out his own 1-2 inch thick alaia from some wiliwili (hawaiian balsa) logs he has access to.

part of what I suspect from what little I know about wood sandwiches is that they are doing the same thing regarding the importance of the impact of the rail in surfing dynamics but are also throwing in a couple other aspects like weight and flex into the equation.  I think if you understand what doing what to these various components I mentioned before then it will help a builder piece them all togethor along with shape to get the most of a design.. But we need to understand the basics which is the same for any board design.. Greg Griffin teaching legacy to me was that all the pieces of a board have to be designed to work togethor as a single unit if you want any form of control on the outcome/performance.

But you did bring in another important component though and that is weight and weight distribution/foil in regards to momentum.

I'm sure you all can write the book on this stuff anyway..   

[paul cannon]

hey RCC
i dig that idea and often thought about doing it
Sabs suggested it to me ages ago
i was thinking if the core is layered like you suggest
the flex may be better
but it also may alleviate the need for vents
as the core will possibly balloon in the middle
and stay attached to the skins

gday bernie
maybe we should break those points up into a few discussion to make it easier to follow

[Bernhardt]

Actually this brings up another idea I haven't had the time to do.

But all we've pretty much built these past two years have been homedepot/lowes wood sandwich boards. so basically we're bending in the rocker we want into a couple flat sheets we glue togethor to get the thickness we want to start with.

To "lock in" the rocker we've been using a "horizontal stringer" that basically uses the offcuts of the same woven bamboo material we've been using as exterior skins. We've learned to plane out a 1/16" gully in the bottom slab in the shape of the horizontal stringer so the two sheets glue up flush togethor(We had delams while shaping when we didn't). We also lam on the bottom skin as we bend in the rocker to speed up the build process and help siupport the rocker during deck and rail shaping

I guess if we use a thicker bottom skin as well as a rocker table instead of using a surfboard as a rocker table then we could get rid of this horizontal springer(which also supports the fin boxes routed in later) and replace it with a thicker piece of polypropylene foam. I think a thick enough sheet of polypropylene foam inset and glued in between the two sheets of flat EPS foam might act as a foam lubricant to enhance on the dampening of the shear caused by the bending and torquing of the board under stress..    I've alway been looking at putting it on the outside of the bottom but maybe it needs to go on the inside..

better yet if anyone can get one of Richard Landingham's foam blanks (which supposidly can be bent over 180 degrees without breaking) and then wood laminate that I'd like to see how those perform. I just haven't found any way to get one of those blanks eventhough others have tried to make normal (non wood skinned) boards using those blanks.

Benny
do you have any info on those polypropylene blanks?

[Benny]

Simon Jennings did a couple interviews with Richard for worldsurfradio and got really excited about matching us up for some experimenting.

Unfortunately, Richard went on Sways and came off as a real kook.  I didn't respond - didn't want to have anything to do with those threads, really. 

But then when I emailed a couple times & even called once, I introduced myself & mentioned Simon, and got no response back whatsoever.  Now his website says the blanks aren't available outside - just completed boards made from them.  I don't know if it was his poor experience with Sways-type builders (many of whom did petty crap like criticize his spelling) or his own arrogance (obvious from post #1)  that made him change direction, but I'm not sure there's much hope there right now. 

I like your polypro springer idea.  I think it would definitely help lubricate the flex motion within the core.  I just wonder if it would also dampen responsiveness too much.  Maybe the right thing is as simple as a piece of plastic sheeting in between your EPS slices - no volume to affect materials characteristics, but certainly a lubricant for allowing motion...  I guess it might wrinkle in there eventually unless the edges were tacked or glued, but it would be interesting anyway. 

[Jarrod]

When I got foam from home depot, one side was already backed with plastic, and I had to peel it off before gluing up my blank...  Why not just leave that on and put it towards the inside?  Would certainly be an interesting experiment, that's for sure.

[RCC]

Thanks Paul.   I hadn't thought about the idea that not adhering the layers
of the core (except around the edges) might allow one to skip the vent... enticing  

I've now started over from square one because I accidentally adhered my blank to my
rocker table (aka longboard) while vacuuming on the rails (whoops!!!) and I had to
destroy about 3 feet of the blank to detach it.  Not what I hoped for, but in the process
of breaking it, I learned some things about the strengths and weaknesses of the way I
did my rails, so I should be better equipped for next time. 

In case my failure can help someone else, here's what I learned: 
I used 3/16" and 3/8" balsa for the rails, depending on the amount of curvature.  As I was only making the rails 9/16" thick, using 3/8" balsa was a mistake because there wasn't enough reinforcement where the 3/8" balsa joints were.  Next time I'm gonna use 4 layers of 1/8" instead so that the joints don't create such weak spots.  Also, I used 3M super 77 to glue the rails, which made the process easier, but might have not been the best choice strength wise.  When I first took it out of the bag the joints were reasonably strong, but after sitting out in the sun a couple days some of the joints began to separate, so the longevity of the rails would've likely been less than if using a titebond III or epoxy.  ( I had to leave a titebond III wood joint under water for a month before it started to weaken. Also, I read a woodworker magazine article testing glues in which titebond III and epoxy outperformed other options, especially foaming PU)

I think I'll try leaving the center of the core detached on my next board
unless someone talks me out of it.  I wasn't planning on it because I figured
that since I'm using 30mm 1.3lb EPP for the bottom layer, which is
considerably less rigid than the EPS, the shear forces wouldn't be as
much of an issue as using all EPS.  But I suppose it might help a little,
and not needing a vent would be nice.  Plus, if we really wanna split hairs,
less adhesive = less weight.  I wonder if that was any part of Sabs'
motivation, apparently being the king of lightweight.

Has anyone tried the EPP bottom?  Just curious. 
When I ordered the EPP, I planned on doing the whole board with it, but decided it might not be rigid enough for the deck, at least unless I were to use thicker balsa.   I made a test piece about 1.5" wide, 18" long, and 2.25" thick EPP with 1/16" balsa skins and 2oz glass inside and 4oz glass outside, using RR 2020.  If I stood on it with my heel (170lb) it compressed about an inch, which seemed like too much to me.  The cool thing about EPP though, is that it springs back to its original form, with no dents.  The 2lb EPP might work well, but I didn't want anything that heavy.  It's also cool stuff cause it's less affected by water and it is quite recyclable.  However, it's less rigid and a bit more spongy than EPS, so that has to be considered.  At some point I'd like to try an all EPP board with a thicker deck skin, but I may wait till I can find a good nearby source for the 1.0lb EPP.  Because of the decreased shear, this might have results similar to the desired results of the original post on this thread.

If anyone wants to play around with EPP, I got mine from http://rcskyflyer.com/ (near LA)
and they had excellent customer service.  It comes in 3' x 4' sheets, which I had no problem gluing into
a blank home-depot style using RR epoxy and microbubbles with a vac.  Formed a bond stronger than
the foam too, in spite of the fact that many things don't stick to EPP.  If you're somewhere far from LA,
I might know of a supplier closer to you because I came across several while looking for one that was
close enough for cheap shipping.

[paul cannon]

sounds awsome mate
been wanting to do a one in epp for ages as well xps
i think it should work great
how does it shape??

id did a few tests with epp and its pretty hard to get stuff to stick to it
my best result was to rough up the surface so it was really rough and with little holes
then bond the preglassed peice of balsa with urethane glue

im planning a hybrid type rail next
with perhaps half  pvc half cedar or paulownia
i do think 5 min epoxy to be  really suitable to glue up rails

with water in the core it will migrate into the rail wood
so and extra barrier of pvc should get that issue sorted

[RCC]

Yeah, I forgot to mention that when I tested the EPP with RR epoxy I first sanded it with 100 grit on a random orbit sander to get it kind of "fuzzy."  Because of EPP's compressible nature, you can press pretty hard while sanding on it without cutting into it.

As for shaping EPP, it's not the easiest.  It is doable with a power planer if you go slow, but doesn't come out as smooth as PU or even EPS.  I figure with the wood skins over top it's not so much of an issue, but a standard glass job on EPP might not look so good.  However, if one were doing normal glassing, they'd likely use denser EPP, which would likely shape easier.

Has anyone ever made a hotwire-based planer?  Basically like a power planer, but with a hotwire instead of a blade.  I have thought this would be nice cause it would cut down on dust, and might work better for foams that don't plane smoothly.  (One would definitely want to consider a respirator for the fumes though)