balsa core, endgrain or not?

[sigurd]

When considering a cheap canoe hull, I am thinking of using balsa core, with longitudal hardwood and glass sheath. With the cost of all the epoxy I think pure glass will be as expensive as the hardwood veneer, for the same puncture and abrasion resistance? With the veneer I'd put 50gsm glass between it and the core, on the outside. The inside could be veneer, but light glass, 200gsm or so would probably be cheaper.

You can get endgrain balsa or planks. If I use planks, I'd lay them in the transverse direction. If I get endgrain panels, I'd have to consider strengthening the skin in the transverse direction.

But which one will be more impact resistant?

[TeddyDiver]

Endgrain..
Just curiosity, but how thick panels you are talking about??

MVH Teddy

[sigurd]

balsa: if planks, 4mm, endgrain is 6mm.

[TeddyDiver]

Have you a mold ?? You need one for endgrain sandwich. Otherwise it's easier to make stripplanked and then you get better results with spruce..

[waikikin]

Have a look for Michael Storer or Known here as boatmik , he did a nice longtitudinal balsa planked canoe. Regards from Jeff.

[sigurd]

Waikikin, I saw one on the net - could be the same canoe.
Less than 6kg it was, 7mm core with 75 alternating 150 gsm glass.
Teddy, I have been considering stripping birch, spruce or similar, as well. I think I would need a total of 3mm laminate, then. It would be much less stiff, but puncture and shock resistance should be easier to get, I think? I've never seen endgrain balsa. I'd build a mold from stringers on a frame - I assume you don't think it is necessary with a complete mold?

[robherc]

sigurd:

For abrasion resistance, glass is OUT...try Kevlar, or better yet (if you're prepared to do some vac-bagging) Dynel for the outermost layer(s) if you're wanting a surface that'll stand up to a good bit of bumping & grinding + dragging & scraping. The Kevlar adds strength similarly to e-glass, but is pretty expensive; the Dynel doesn't add much strength, but is the BEST for abrasion resistance.

As far as the balsa, end-grain is a good bit stiffer & more impact resistant, but it's also harder to work with in tight curves. You'd almost be better off cutting the endgrain into strips & strip-planking with it than anything else, IMO.

Just my $0.02(US, unfortunately), take it for what it is/isn't worth ;)

[PAR]

Dynel or for that matter Xynole (which is 2 times better then Dynel at abrasion resistance) will suck up huge amounts of resin and make for a heavy laminate. Kevlar is the fabric of choice if the ultimate in both regards is required.

I don't think a cored structure is the cheapest way to build a light canoe. Even if the core is inexpensive, the goo and fabric cost will be higher then other material choices.

Impact resistance is a pretty relative term in regard to a small, light weight canoe. A good light weight species plywood and a thin sheath is fairly hard to beat, pound for pound, dollar for dollar.

[sigurd]

PAR, I agree with your assessment of thin plywood, but to get the shapes I want, it would have to be cut up a lot I think. So in that case it might make more sense to me to laminate the plywood myself. But the stiffness of the balsa laminate is alluring, so i'm trying to find a cheap way to make it abrasion and impact resistant. To that end I was thinking of using ipe or another hard, strong wood as the outer 0.6mm sheath, 50gsm glass under it, and a thin glass sheath on the inside of the hull, the glass sheaths could be reinforced with carbon tow (also cost effective for me now, in small amounts). Not sure what to expect from such a laminate though, and using a much thinner and denser core like spruce or birch at least in the bottom seems the safer way but needs more supports.

Kevlar vs hardwood as sheathing, it would be interesting to know the differences.

[TeddyDiver]

Teddy, I have been considering stripping birch, spruce or similar, as well...
Birch is too heavy and has other issues too.. Stringer mold (for endgrain) is allmost a ready strip planked body so it's excess work.. but possible. In thin cores endgrain balsa sucks relatively lot of resin and there's hardly none if any weight benefit compared to stripplanked spruce.

[sigurd]

How much resin?

[sigurd]

http://www.powerandsailmarinesurveyors.com/Serv%2005%20end_grain_balsa_core.htm
Pre-coat one side of the end grain balsa sheet with laminating resin just prior to installation. The average amount of resin to wet out a LamPrep® surface is 1.5oz (40-grams) per sq.ft. An AL600/10® coated surface uses 0.70-oz (20-grams) per sq.ft. The resin is generally hand applied with a short nap length or foam covered roller.

That is a lot of epoxy. How much does spruce need then?

[TeddyDiver]

That is a lot of epoxy. How much does spruce need then?
To make a quess maybe 1/4 compared to endgrain balsa but it greatly depends of the quality, density and humidity% of the timber (balsa and spruce or any timber) and the viscosity and ambient temperature among other things so only a test will tell.

[robherc]

Kevlar vs hardwood as sheathing, it would be interesting to know the differences.

Kevlar:
Strengthening is encapsulated in resin, and is a waterproof fiber...so as long as the Kevlar is still at all in-tact, there is no danger of rot.

Hardwood:
Covered in Epoxy for waterproofing, and (depending on the wood) can be water & rot resistant, though not to the degree of Kevlar. Thicker than Kevlar fabric laminate, so can last through more long-term abuse before "wearing through" and needing replaced (probably easier replacing the whole boat).

This is by no means an exhaustive comparison, but I think it'll give you an idea of the balance here. Waterproof/rotproof vs. Longer-life, lower-cost. ;)

(You can, however, extend the life of the Kevlar with very little weight added by using 2-3 layers of Kevlar...drawback: higher cost)

[sigurd]

Wonder if norway spruce is a good strip material?

[TeddyDiver]

Wonder if norway spruce is a good strip material?

For sure.. I'm using it.. or actually finnish spruce but..anyways most of strip planked constructions in Scandinavia are local spuce..

[PAR]

The basic problem with balsa or most core materials for that mater, is they are selected for their compressive qualities and typically by their nature, have limited if any useful longitudinal stiffness. This requires the laminate or additional structure to be employed to carry these longitudinal loads, which can be fairly high in a canoe. The thicker laminate thickness and/or additional structure make for a more costly build, that also requires more effort to produce. This is one of the reasons inherently stiff materials like plywood, solid lumber and to some degree, metals are so popular.

If you want complex shapes, then molding or strip planking will be the more cost effective methods. If you employ the Lord method strip planking, you'll have higher laminate costs, but a lighter and stiffer hull then just about another technique.

[robherc]

If you decide on plywood, I'd look into CM ("cylinder" molding). It limits your shapes a little, but it's a quick/easy way to throw a boat together, and it turns out nice & strong by overlapping the ply panels.

[PAR]

You could conically or cylindrically develop some pretty fancy shapes with plywood panels. If you introduce some torture into the panels, even more "shape" can be admitted. I've bent 3mm (1/8") ply into some fairly hard curves.

You also could use a strip planked turn of the bilge and transition to a conically developed plywood panel for the remainder of the hull.

[sigurd]

Thanks for the tips. What is special about the Lord method?

Here is what I'm thinking now: I have costed some super dense and some normal density 0.6mm ply for the outer skin - cheaper and I think probably better than 400gsm or so glass. Because of the abrasion resistance on the bottom I would like them to have longitudal fiber orientation there, at least.

The 3mm spruce I would then like to lay diagonally, as shown.
veneer: 0.6mm thickness x 1.2 density is 720 gsm
3mm x 0.36 is 1080 gsm

I know it is usual to use the core in the lengthwise direction, but I am not sure it is the best way, always. The way I would do, is to use a strong keel plank, and a floor with reinforced edges, about where the hull sides starts becoming vertical. This becomes a stiff triangular beam, when held apart by the diagonal strips and longi veneer. It is also stiffened by the gunwale.
So, contrary to the normal philosophy as I understand it, the lengthwise strength is concentrated in 4 or 5 logs instead of along the skin, which, being stronger vertically than normal, is a perfect shear web between them.
With the logs being placed as far away from the neutral axes as possible, this looks to me like an efficient structure. I also think the panels will be locally stiffer than it would have been with purely longitudal core.

[robherc]

Sigurd:

With ply, the grain is alternated at 90* angles each layer. That means that when you turn your 3mm ply at a 45* angle, you're creating a double-bias effect (2 veneer plies at 45*, and 1 at 135*). There's nothing wrong with this approach to my knowledge, just wanted you to be aware of it. When someone builds in ply with the facing layers longitudinal-grained, they're counting on the middle layer (grain facing athwartships) to hold everything together (well, that AND the glass/epoxy shell).
Your way might be better, or the more-standard way might be better. I'm guessing that either will works, but it'll be interesting to see if you find any special properties your way. :)

[sigurd]

Now I ordered the ply! 0.6mm, ipe for the bottom, makore for the rest of the outside, and kingwood for the cockpit!

[sigurd]

I would like to try preservatives like tar and linseed oil, instead of coating with epoxy (Then I will be certain it can not collect water and rot). How could I glue the veneer to the 50gsm glass without getting a lot of glue on the outside? If I make thick epoxy bog, can I vacuum clamp the veneer?

Anybody tried beeswax as wood preservative?

[sailor2]

When considering a cheap canoe hull, I am thinking of using balsa core, with longitudal hardwood and glass sheath.
...
But which one will be more impact resistant?
I read the thread, but it doesn't seem to answer if you are making white water canoe or something for calm waters instead. A major difference in suitable materials and how to dimension them.
Are you asking impact resistance for a given panel weight or for a given material cost or given thickness or ???
The correct answer depend a lot on what of those question is assumed here.
None of the discussion so far seem to give any hints what so ever on this.

[TeddyDiver]

I would like to try preservatives like tar and linseed oil, instead of coating with epoxy (Then I will be certain it can not collect water and rot). How could I glue the veneer to the 50gsm glass without getting a lot of glue on the outside? If I make thick epoxy bog, can I vacuum clamp the veneer?

Anybody tried beeswax as wood preservative?

You are now making your project a bit more complicated than it's necessary. Just put the glass (roven) and epoxy on top of the veneer and save tar and linseed oil for lapstrake hulls..

[robherc]

If you're worried about penetrating the wood with waterproofing, try using an ultra-low viscosity (with NO thinners) like MAS Infusion 3-part @ 100-150cps. The thinner epoxy will absorb deeply into the wood. this will increase the weight of the wood (and decrease its flotation) somewhat, but it'll give you the long-lasting waterproofing you're looking for from you linseed/flax oils! (just a thought)

NOTE: If you use a super-low-viscosity epoxy, you need/have to vac-bag or vac-infuse the parts to keep from having runny epoxy get all over everywhere & leave terrible runs on your project that would require extreme amounts of sanding.

[sigurd]

sailor2, It is a kite boat, so pretty severe use. Difficult to answer your question - has to be as strong as possible for as little as possible money and weight. :P The puncture and abrasion resistance is necessary for ice and beaching and a long life in general.

[robherc]

The puncture and abrasion resistance is necessary for ice and beaching and a long life in general.
Hmmm...how about 3 layers of 11.1g/m^2 satin-stitch kevlar 49 then (or maybe you should actually look at K29 (ballistics grade Kevlar)...rofl :D

[sailor2]

If you're worried about penetrating the wood with waterproofing, try using an ultra-low viscosity (with NO thinners) like MAS Infusion 3-part @ 100-150cps. The thinner epoxy will absorb deeply into the wood. this will increase the weight of the wood (and decrease its flotation) somewhat, but it'll give you the long-lasting waterproofing you're looking for from you linseed/flax oils! (just a thought)

NOTE: If you use a super-low-viscosity epoxy, you need/have to vac-bag or vac-infuse the parts to keep from having runny epoxy get all over everywhere & leave terrible runs on your project that would require extreme amounts of sanding.
If the low viscosity epoxy is applied while the plywood is flat on the table, the issues you mention should not cause problems. The panels can be bent into shape to form the canoe after that process. And then join the pieces by laminating over. Would make it easier.

[sailor2]

sailor2, It is a kite boat, so pretty severe use. Difficult to answer your question - has to be as strong as possible for as little as possible money and weight. :P The puncture and abrasion resistance is necessary for ice and beaching and a long life in general.
So you are making a sailing canoe with free flying kite. That would be very far from severy use conserning impact strength compared to whitewater use where you would be smashed against rocks while going down "river" Therefore all mentioned methods can easily give you enough impact strength for such a small vessel.

For the abrasion, only the outer surface matters, not what's below it. You could have used even the balsa with grain not perpendicular to surface.
What matters for surface is the thickness of laminate. For best abrasion resistance go for a solid thick aramid laminate with no core or wood for light & strong. No other way gives you same or beter abrasion resistance with less cost than that except using metals. Including wood core gives you more weight & cost for same outside laminate, or with less outside laminate you get less abrasion resistance and somewhat reduced puncture resistance ; less so with high density woods and more so with light density woods or foam core.

[sigurd]

You are probably right about "severe"! Sometimes there is ice though.

Putting glass outside the wood, sure, it would protect the wood, until it is breached, then the veneer will get waterlogged, heavy and rotten. The glass is only 50gsm so it won't stand the abuse that the veneer can, I think. Besides, if the veneer is breached, no harm done as long as the glass is still there - plenty of time to glue a piece of veneer there, without getting waterlogged in the meantime. Guess I'll try to glue a sample piece and see if I change my mind about it.

Kevlar is too expensive - more than 40 dollar per meter. Would be nice to try it though.

Beeswax is a solid (I think), unlike tar and oils, so it stays within the leather without getting washed out as fast. Having tried both tar-based, silicon based and many other shoe waxes, I have come to the conclusion that snoseal, which is beeswax, is the best for shoes. Therefore I think it is probably also best for boats? With heat, it would probably saturate the veneer. Noone uses it for wood finishing?

[apex1]

Beeswax is a solid (I think), unlike tar and oils, so it stays within the leather without getting washed out as fast. Having tried both tar-based, silicon based and many other shoe waxes, I have come to the conclusion that snoseal, which is beeswax, is the best for shoes. Therefore I think it is probably also best for boats? With heat, it would probably saturate the veneer. Noone uses it for wood finishing?

Use some common sense ! :!: Does your wax harden your shoes ?:?: Does it keep ALL moisture out ? :?:
You ask high tech questions and after receiving some high knowledge advice you go back to linseed and wax ???:( :mad: :confused:
Regards
Richard
BTW: I would buil it in a simple, classical, cheap and strong strip planked Epoxy glassed way.

[robherc]

Kevlar is too expensive - more than 40 dollar per meter. Would be nice to try it though.
How about $13.57/yd @ 38" width (0.91m X 0.96m width), Would that make the Kevlar seem like a better idea to you?
That price list is from: www.fiberglasssupply.com
Also, for your canoe, you could probably get away with 12" (0.3m) tape, or cut the standard width kevlar fabric in thirds lengthwise. If you used 3 layers that way, it'd be almost bulletproof (or at least HIGHLY rock & ice resistant)!

[sigurd]

"Does your wax harden your shoes ?:?: "

no

" Does it keep ALL moisture out ? :?:"

yes

"You ask high tech questions and after receiving some high knowledge advice you go back to linseed and wax ???:( :mad: :confused:"

don't be mad. I thought I had made an argument for why. I didn't mention the UV problem with epoxy, ofcourse not applicable under water.

"BTW: I would buil it in a simple, classical, cheap and strong strip planked Epoxy glassed way."

So, how much glass would you use, inside and outside, for a 3mm spruce core?

[sigurd]

robherc, 13.57 is for 150yd, but the prices are still good! thanks!

[robherc]

I build multi-hulls...they use a LOT more fabric for abrasion-resistance...go figure. ;)

[sigurd]

Well, mine is much like a multihull too, except it has only one hull...

[eponodyne]

And here's another though: Instead of balsa, which has all the rot resistance of bumwad (Dunnyfodder), has anyone considered the use of cork as a core material? Sheets made from granulated cork, with a polyurethane binder (thus necessitating a PU resin for layup, I'd guess?) are readily available at about $4US/sq. ft ($40/SqM) in thicknesses of 1/2" (13mm) at a density of about 16 lb/cu.ft (~250 kg/SqM). Cork is quite rot-resistant, I know, but I also have no idea how it would hold up in shear strength.

Just a thought.

[sigurd]

All I know is it's comfortable and funny! It would add great impact resistance as a deck surface at least... Is it really that rot resistant?

What is better, makore or sapele veneer? Somebody commented on the great rot resistance of sapele.

[robherc]

Cork has nearly 0 shear strength, has little compressive strength, and is not at all stiff. At best, the cork would act as a sponge, and absorb 10x its weight in resin. Then the resin would act as a core material and give a very stiff, strong, and HEAVY laminate (kinda like using 1/2" of cast fiberglass/resin, but cheaper).
Good idea on the rot resistance side, completely unusable for anything but flotation material in the end, though.

sigurd-
Yes, so you only have to protect the bottom of one hull, in a cat I'll be using twice as much Kevlar (2 hulls), and with a trimaran, depending on the sizes of each hull, maybe up to 3 times as much... at which point I might as well buy the roll & save the leftovers for the next boat. ;)

[sigurd]

some are very happy with cork as a deck material. Some of them are mixed with rubber. Sounds very nice.

[sigurd]

What about aramid mat. I reckon it skould be about as puncture and shock resistant, in a laminate, as woven aramid? You think?

[robherc]

I don't think the mat will be as ABRASION resistant as the woven aramid. I'm quite sure it'll still be better than e-glass, though, whether woven, or mat. So, if you can find the mat for significantly less, it may be just the ticket for you...all depends on where your price/durability trade-off makes you the happiest. As far as puncture/shock resistance, I think any decent-weight glass OR aramid cloth should fare pretty well there; they do NOT tear easily...especially not when they're encased in a couple coats of good, strong epoxy.

[sigurd]

Someone said "starspan" is based on aramid. it is 40gsm mat and 3.75 UK quid per m2. That is comparable to the 50gsm woven glass I can get here. It is going under the outer ply so only puncture and shock resistance is important.

The other places I have found aramid mat:
up to 32gsm, no price http://www.hollingsworth-vose.com/products/afn/applications/composite_roll.htm
up to .4oz, expensive: http://www.acp-composites.com/home.php?cat=252

I think it is used in electrical insulation films and such.

So far, this is the cheapest woven aramid I have found: http://www.discountcomposite.com/

[robherc]

I think that as long as you're putting it underneath the plywood, fiberglass "woven roving" will give you the best puncture & shock resistance per quid...kevlar will be a good bit lighter, but a LOT more expensive too. I actually found some 18oz "woven roving" on http://www.fiberglasssupply.com for cheaper than any of their other fiberglass, as low as $2.19(US)/yard (100yd roll)!

The main reason I was recommending Kevlar earlier is for ABRASION resistance. If that's not important, and you can afford a little more weight, then I think glass will offer you substantial money savings, and I remember that was your big catch with the Kevlar at the beginning.

[sigurd]

yeah it was, but it went from 40usd/m2 to 12usd (woven) or 3.75 ukp (mat) with some searching...

So with that in mind I am interested in assessing the suitability of the materials. I am quite hung up on weight but also robustness. If I can prevent the spruce core from ever soaking, I think the veneer can easily be patched when damaged.

Discountcomposite has a lot of different stuff, spectra fabric for instance... Wonder how it compares to kevlar for this application. It is stronger in tension per weight than kev, but stretches less I think.

From this to that: Is it true that the inside of the cored skin will be in tension only, so that any compression strength there will be useless?

In another thread some people recommended corecell for a whitewater kayak. I have checked the price, it is not completely insane, almost a possibility for this project. A550 would make the boat quite a bit lighter, if it is not very resin hungry. Granted, I'd then have to add some transverse fibers, no big deal I think. But, will the panel be as tough as with the spruce core? It seems unlikely to me, since its density is 1/4 of spruce.

[robherc]

The strength of the end-result panel for sandwich core depends more on the stiffness, thickness, and shear-strength of your core material. With that in mind, the spruce will have higher shear-strength, but the corecell is pretty comparable everywhere else, I think. If your main goal is lightweight, then go corecell...if it's cheap, or extreme durability, then spruce may win.
As far as compression or tension; the CORE material needs high compression strength, but the important part for BOTH skins is the TENSION strength.fiberglass/kevlar/carbon-fiber do nothing to increase the compression strength of epoxy/polyester, but they do a LOT to increase the tensile strength. Since tensile strength is all that matters most in the skins, they're great. ;)
If you're happy with the pricing, I think I'd go with the Kevlar woven cloth, because it allows you to have a higher ratio of fiber to resin. That way you're adding less weight in epoxy/polyester to your finished boat (ESPECIALLY weight per strength).

[sigurd]

It is the first time I have heard kevlar gives a better fiber to resin ratio. It is funny that you mentioned it now and I just five seconds ago wrote a question about that in the ganja reinforcement thread.

I am going to have to ponder what you said about compression. When you look at an I beam in bending, one of the flanges (skins) are compressed, the other tensioned.

EDIT: If resin ratio is tied to fiber density, and skins only need tension, spectra should be spectacular skin material (Don't play with puns!)?

re. aramid, it seems some people are concerned it will soak water. Any views on that?

I found a great price for 9mm A550, could be split with hotwire to 4.5mm?

[robherc]

I didn't mean Kevlar gives better fiber to resin ratio...I meant that WOVEN fabric gives better fiber to resin than MAT...because of the way the strands lie...the more uniform & flat the strands lie, the less space there is to be taken up by resin (thus unidirectional "fabric" can be the best for fiber to resin ratio).

In an "I" beam, the flange under compression always fails first...BUT that eventuality is slowed by the height of the center, connecting portion. This happens because steel has a much higher tensile strength than compression strength. If you were to replace the central portion of the beam with a material that had a higher COMPRESSION strength, then you could significantly increase the strength of the "I" beam, because now you'd be taking more advantage of the TENSILE strength of the flanges (though only one at a time, mind you).


....I hope I made sense there...the ganja might be clouding my judgment....... :P

[sigurd]

Here is a drawing of one of the things that is befuddling me.
It tries to illustrate how the outside skin can be tensioned or compressed, depending on a lot of factors.

Shear strength for sitka spruce parallell to grain is 2.6 MPa, A550 is 1.1.
However, I haven't found the shear values in the *transverse* direction for spruce, which I imagine are the important values as a shear web for the 0.6mm ply skin.

Along the grain the bending stiffness and strength of the spruce would be the baseline for a calculation of the transverse fibers that would have to be added with foam.

It appears that spectra unsurprisingly has some issues with bonding as well as the previously mentioned lack of compression strength (apparently lower than resin alone!)

[robherc]

If you ignore the red "compressed skin" line in those drawings, all of the rest will make sense to you.
If you think about it realistically, if your core is stiff & has good compressions strength, then all of the energy that is applied that WOULD compress the near-skin, the core transports the energy directly to the outer skin as TENSION force. This way, the tensile strength of each skin can be used to make up for the poor compression strength of the other. Basically, in plain english, you're using the core as a lever to allow one skin to see a strain as a "tension" load so the other doesn't need compression strength.

[robherc]

In the second picture, the core was too soft, and/or the impacted skin wasn't bonded well enough/didn't have enough tension strength, or the impact was simply more energy in a smaller area than the panel was designed for (ex. if you shoot a .50 Barrett at a rowboat, it'll penetrate because there was no reason to design for that load). (all three explanations work, just depends on how you want to look at it)

[sigurd]

robherc, I think you are wrong, that the outside skin experience compression. Look here if in doubt.

http://www.oneoceankayaks.com/Sandcore.htm

[robherc]

I wasn't trying to tell you that the skin never experiences compression, what I was trying to illustrate to you is that a core with good compression and shear strength can work with the tensile strength of the opposite skin to "make up for" the lack of compression strength on the compressed skin. If the goal were to make skins with the highest possible COMPRESSION strength, we would NEVER use reinforcing fibers in the skins, as they're almost exclusively useful for their TENSILE strength, at the expense of compression strength.
You could build a laminate with high-compression strength and low tensile strength skins if you want...just use wood instead of fiber-reinforced laminates. Wood has more compression strength than it has tensile strength, so this would work; I think the reason it's not used is that the tensile strength of fiber-reinforced laminates is FAR SUPERIOR to the compression strength of the wood (at least on a strength to weight measurement).
By using cored construction, we are able to take advantage of whichever strength (tensile or compression) of our skins is the best, and have one skin's strength "cover for" the other skin's weakness when stress is applied to the panel.

...If you wanted to build an "ideal panel" for laboratory conditions where all stresses would come from the same direction (i.e. inside skin, or outside skin), you could achieve some pretty amazing results by using a wood veneer for the compression-side skin, and a fiber-reinforced laminate for the tension-side skin. The problem with this panel would be that it would have comparatively almost NO strength it the stresses were reversed as the fiber laminate has VERY little compression strength, and the wood has little tension strength...so the panel would fail VERY early that way.

[sailor2]

Wood has more compression strength than it has tensile strength,

The problem with this panel would be that it would have comparatively almost NO strength it the stresses were reversed as the fiber laminate has VERY little compression strength, and the wood has little tension strength...so the panel would fail VERY early that way.
In dry laboratory conditions most spruce samples have ultimate tension strength more than twise of their compression strength along grain. But the strength for extended time periods is substantially lower than instantionous strength for all wood both in compression & tension. Any higher moisture content decreases all strength properties of wood, and stiffness more so making it easier to bend without breaking it.

For the laminate the same applyes, they are stronger in tension but the strength in compression is still 10...20 times stronger than resin alone. If it were not so, composite masts would not contain max fiber to resin ratios for max compression strength. The important part when long & thin sample is in compression is to make sure the laminate is not going to fail by buckling mode long before max compression strength is accheaved. This requires correct sequence of orientations of fibres as well as excellent bond of fibres to resin around it.

Shear failure in wood results almost always grain being slided with respect to other grain. Never grain breaking in shear. As a result wood like spruce has 2 different shear values depending orientation of shearload. When the wood is still growing in the forest, the tangential direction is 60%...100% stronger than radial direction regarding shear load. This means laminated veneer lumber has same difference in shear properties. Plase the grain running in x-direction and apply load vertically along y-direction and the beam is strongest when glue joining the plys has thinnest dimension (<0.05mm) in z-orientation.
In tension the tangential direction can be upto 10 times stronger than radial. along the grain is of course the strongest.
In case of plywood there is always some plys where this weakest radial direction is aligned with one of the edges. One of those plys will always break first when whole plywood is under enough shear loading to cause shear breakage. Tension or comression breakage can of course be the limiting one instead of shear.

[sigurd]

If I read you correctly, an axe shaft should have the stripes from the season rings going parallell to the axe head (true, from experience), but if you laminate the shaft, the stripes from the glue line should be 90' to the axe head. Is this what you ment?