one for the balsa sandwich guys

Ok, if you were going to use a deckpatch for added strength against heel dents, would you put it on top of the balsa, or below it, and why?

I’ve used one on my previous ones and I’ve always put it under the balsa (that way I know that it would be invisible). I knee paddled my 11’3" all summer and not a dent on it. I’m not doing it on my current one. Its time for me to stop overengineering my boards. However, on my future board I’m going 3 oz all the way around so I’ll use stratigic patches were ever I need them.

I put the extra patch on the outside, my reasons are that a sandwhich usually fails when one of the outer skins has pressure applied and then this glass fails under compression, the sandwhich material then breaks, then the inner glass fails as this too gets compressed. In a non failing sandwhich the glass under the balsa sandwhich will be under tension not compression when pressure is applied to the deck and glass handles tension really well. So I believe that the underneath glass will do it’s job just fine by itself. I beef up the side of the sandwhich that will be under compression as more glass will resist the begginings of sandwhich failure.

Here’s a pic from Bert’s vacumm bagging thread. On this board Bert went under.

i have been doing mine under. since i have been doing the handlayup on the outter glass putting the extra layer on the underside where i am using the wetout table ensures that the extra glass adds very little weight. also i believe that deck patches don’t do much for board breaking. they only really help with denting.

dan if you use patches of e glass it will wet out invisible on the outter layer.

ps. i haven’t seen a dent in any of the 10 boards that i have made yet… some of them are 2oz under 4oz over no patches. a huge contrast to poly boards that get heel dents the first day…

This thread has caught my attention and at the risk of sounding totally ignorant of the processes involved in building a balsa sandwich board, which I am, after reading what has been posted so far I have come up with a question that I hope someone won’t mind answering: if you are going to put a reinforcing patch under the balsa and bag it (I assume you mean vacuum bagging),since this patch will be invisible why not use carbon fiber or carbon fiber/Kevlar cloth insted of just plain fiberglass cloth under the balsa layer? Wouldn’t it give you a sandwich of considerable strenght? Both compressive and tension.Or would it be really be overdoing things?

Thanks, Rolly.

the whole theory with the balsa sandwich is flex… carbon, kevlar etc will provide strength but they are stiff materials. look up Bert’s post where he gives the results of his cloth breaking tests… carbon only flexes to a point and then SNAP!!! glass will flex further before breaking… carbon has better flex return then glass but since we have the wood to provide the return this is a property of the fabric that dosn’t really matter. beside these boards are so dam strong with “just” glass anyhow… but i would think with the carbon look on the outside you could fetch a higher price becasue people will think it is better… just like with fins.

I was certainly of the impression that deck patches were unnecessary with sandwich construction anyway.

The problem is knowing where you can cut back and where you need to beef it up. With a composite board there are so many options. At this early stage of bagging mistakes can destroy the board or provide giant leaps forward in understanding (like happened today).

Come on Dan, what exactly did happen today?

btw started my rocker table yesterday, made the steel frame, should be finished by the end of the week, will post pics when done. Cant wait to get it working for me!!

bluejuice , had the most logical comments in regard to overall sandwich structure and what usually fails first …

we also have to consider how well our sandwich medium tranfers energy or force …

while bluejuices comments were right in general , there are still exceptions to the rule …

this will be so brief it might not make sense to some …

if our sandwich medium doesnt transfer force well , then it must be protected and reinforced to help spread load …

but if our sandwich medium transferes energy well , then we have to make sure the extra tensile strength of glass is matched with the amount of force being delivered to it by outside layers …

as an example , its possible that our inner glass can break while the outer glass remains in tact …

there are no rules as to which side should have more glass , because the sandwich medium itself is the consideration …

some sandwich materials have an energy transfer bias , load isnt directed straight through but its spread out instead , as the density and energy transfer bias of the sandwich material changes the percentages of how much glass should go under or over has to change so that when failure occurs it happens at the mximum limit of all the materials combined …

in that picture dan . you have to consider what was being put on the outside as well , and where the traffic areas are …

as one facet of the structure fails , you have 2 options next time … either make one part stronger or weaker , depending on the problem and depending on the sandwich medium …

would love to elaborate …

but gota go …



the whole theory with the balsa sandwich is flex…

is it? do you mean the lack of it?

i thought the whole premise behind composite construction is strength to weight? getting good flex out of it is an entirely different ball game…and when you do get it the risk of creasing your stick triples

bb has mentioned that it took 5 years to get better performance than poopee…

have you guys tested an thin ultralight poopee for flex and then directly compared it to a compsand?

…its a long high hill my friends

“you have 2 options next time … either make one part stronger or weaker”

Maybe, maybe not… an “out of the box” thinker, when faced with just 2 options, automatically starts looking for option 3, 4, etc.

im starting to think that the more stiff it is u know the more heavily things are tied together, the less the skins can move (or sheer)… so in this case, less overall movement under tension means the board will more likely crease or give way in one point,

If everything moves together in harmony you should be able to flaten and upside down board but still have it hell stiff and springy.

i saw one picture of a board holding berts weight, if two people stood on it im sure it would have flattened without creasing. so its dialed for the riders weight and flex preference. but still skins can move independently (eliminates creasing)

hell even if ya do

2 oz 3mm balsa 4+4+4 oz deck

2 oz 2mm 4 +4 bottom

you could have a board that could be

1…very hard to ding

2 …immpossible to break

3 …could still flex and not creasing ( i think that the skins moving independently is critical sort of sliding across each other and the core)

4 …be 2 inches or less thick (more sensitivity)

5… have a shortboard that can easily float a heavy rider

6 be still at least 1/2kg lighter than a poopee

i could be way off track here but its where im at playing with blank no 5

could do with a few trade secrets by now :wink:

Maybe, maybe not… an “out of the box” thinker, when faced with just 2 options, automatically starts looking for option 3, 4, etc.

ah yes…how’bout the out of box thinker who feels options 1-4 are obsolete and writes off the current “state-of-the-art”

now this is an example of some unhelpful stuff. Several guys post opinions, but no one can, or will, really SAY WHAT WORKS. Then along comes BB, who tells us almost nothing about the actual facts of construction, and posts hints about the “qualities” of his work rather than what it is he actually DOES.

I guess it’s because most are just blowing some kinda smoke, no one really knows other than “what I did last time and it has/hasn’t broken yet”

So let’s lay it down: What are the baggers doing to reinforce, say, a 1/8" balsa deck and/or bottom skin, and/or a 1/4" and/or bottom balsa skin? Given that, what is the spacing of your internal ribs if you’re doing a HWS?

For standard polyurethane/polyester construction, this list is full of excellent information, both in real time and in the archives. But with few exceptions, it’s erratic and sporadic as hell for someone considering non-standard methods.

Hey it’s okay that there are many ways to skin a cat, but surely there is some emergence of “typical” process and materials in each of these categories…or is there?


1) but no one can, or will, really SAY WHAT WORKS

2) what I did last time and it has/hasn’t broken yet

3) What are the baggers doing to reinforce, say, a 1/8" balsa deck and/or bottom skin, and/or a 1/4" and/or bottom balsa skin?

I’ve marked 3 things that you said that I think I can answer, but at this point the answer will be of little real help.

  1. Nobody has made enough boards to really say what really works. To make it even more confusing, What works of one style of surfer will not be ideal for another. What make making composite boards so satisfying is that it offers you the chance to really dial in each aspect of the board and suit it to a persons needs. The problem is, do we really know what we need (for example, if you could put the flex exactly at any part of the boar where would you put it). These questions never came up with poly boards because it wasn’t really possible.

  2. This is the problem, but to be fair - how many people what to really push the limits of board design most likely have it end up in the trash. Its been said that you need to shape 1000’s of boards to know how to make a board that works in many varying situations. How can we have a clue when so few boards have been built. What you’ve heard so far is that people like them as much or more than the poly boards they were building.

  3. This is a poly way of thinking. I think that when all is said and done that building a composite board that MarlboroSlim would like (and yes it is possible) would be built very differently that something that Meecrafty would surf (even if they were both the same shape). But until people start branching out this won’t happen.

Unfortunately, at this point I think it boils down to “I don’t know yet” not “I don’t know so obviously it can’t be done”

I have been bouncing this around my head and I wonder what people would think of this idea. I think all of us have seen enough pictures of balsa boards. Theres only so many times that you can say that its beautiful, but how does it surf (even though every one that I’ve seen has been beautiful). What I think would be most benificial is to start posting step-by-step pictures of how we build the boards and what we were trying to achieve, and if it worked. Each of us is essentialy running it solo without much idea of how others are doing it. You wouldn’t need to include EVERY step but just the highlights (kind of like Bert did on the original composite thread). I’m building this board very differently than any other board I’ve build and I’ve discovered some new insight. Bert tried to do something like this in regards to design on this thread . Its the best design thread I’ve seen because it actually give me insite to why he shapes the way he does (I ran a lot of the longboard photos through aps3000 and looked for where he tweaked the shape to fit the specific situation). I would also be interested in seeing more content and less ideology on Swaylocks and this seems like a good way to do it (you get to show off your work and people become more informed. Is anybody else interested in doing this?

hey charlie dont know what the majic formula is but if you want my honest opinion i think most compsand guys are simply making nicer looking custom surftechs…the recipe for making a surftech is well known but is that what you want to ride? thus, i’ve gone in a different direction now but i still feel that my majic vac bag board is true majic…an erroneous result which yielded the best board i’ve ridden in years…stringerless #1.5 eps with a 1/8 balsa/dcell combination deck…nothing fancy and quite easy and fun to make if youve got a vac bag system

Uh, yeah. What he said. :slight_smile:

My biggest problem is one that’s fairly hard to publicly admit. My best composite skin board is the first one I ever made. Blind luck trumps knowledge & skil & technology.

I had no vac bag or pump, so I epoxied balsa strips to my EPS blank with the pressure of ziplock bags full of water.

I had no sense of the strength of sandwich skins, so my balsa is almost 1/4" thick.

I had no idea how much the board would ‘grow’ by adding skins, and it came out 3.5" thick, with rails you can hardly wrap your hand around.

I was worried it might not be strong enough, so its all 6 oz S glass.

I laminated it & hotcoated it with blushing epoxy in a 55* garage.

But you know what? The damn thing surfs as fine as any board I’ve ever had. I’m not blowing smoke. Even friends say to me that they’ve never seen me & a board looking so fluid together. Size & shape put me right where I want to be, every time.

Since then, I’ve built 5 more composite-skin boards. All with the help of the vac bag. Yeah, some of them have been wild experiments in shape and others have tried alternative skin core materials like d-cell. The shapes are smoother & smoother. But not one surfs like that first one.

Its not an emotional thing. I’d built boards before. I’m even able to part with personal masterpieces without too much separation anxiety.

What I really need to do is go back to the basics of that first board, but apply what I now know about glass weight, balsa thickness, and epoxy curing. See what happens.

But there’s no possible way I could make a meaningful comment on where to stick a piece of extra glass to add strength or flex.

Moral of the story: Don’t overthink. Trust your intuition. Trust your hands & your eyes, & ignore your brain when it goes off tangentially. If you think your board would benefit from a deckpatch, slap that sucker on there and don’t look back. Dive right in & make something, because it might just turn out magic. And then refine what worked rather than trying new stuff that may or may not work.

I don’t remember who said it first, but if we knew the results we’d get, it wouldn’t be called experimenting.

Edit: Allright, after reading Dan & Meecrafty’s posts again, lets see a show of hands on how many of our most ‘magic’ boards involved a traumatic error in construction execution…

isnt it interesting…two guys on opposite coasts…two seperate independent f_ckups and we both get majical results…theres a moral there…keep it real simple stupid