solid balsa rails -- what's your technique?

General Discussion
81

My thoughts - take them for what they are worth.

Standard composite theory (Meecrafty’s diagram in earlier post) requires that the core be attached to the skins. Without an attached core, the strength to weight advantages would be lost.

If the EPS is not attached to anything (not the top skin, not the bottom skin and not the rails) than the EPS is no longer acting as a core of a standard composite structure. With a free floating EPS, we have created a Hollow Wooden Surfboard for all intensive purposes since the EPS is now irrelevant.

Now lets consider the rails. If the rails are attached to the top and bottom skins than the rails act as the core and we still have 3 composite structures in 1. However, if the rails are not attached to the bottom skin, but only to the top skin, as many have alluded to, than we no longer have 3 composite structures in 1 and the surfboard will be much weaker. In fact the bottom skin, in this situation would become negligible in terms of contributing to surfboard strength. (Although the bottom skin would not be contributing much to the strength of the board, it would still be used for planing area, buoyancy, and directing water flow.)

I am not saying that only attaching the rails to the top skin is is wrong, I am just pointing out my simplified view of the mechanics of the situation. And if I were planning on only attaching the rails to the top skin, I would seriously question whether putting balsa on the bottom of the board is worth the time, and effort.

Note: Meecrafty has appeared to come to this conclusion long ago.

82

If the bottom skin wasn’t attached to the core…and wasn’t attached to the rails…wouldn’t it fall off? :slight_smile:

83

I said to myself i wasnt going to touch this topic again but i guess i was wrong…

meecrafty , your engineering diagram above was interesting , but could be re drawn with a whole range of different variables …

therein lies the problem Bert, way too many variables to deal with…its like a fruit tree where there are no low hangers…everything is high out of reach for most of us…getting to the top is not only difficult but very expensive. As a manufacturer, you have the luxury of lots of feedback…trial and error…how much longer would it have taken you without a steady stream of feedback? You and I both know that feedback is the key to good development. You could spend a million bucks making the most advanced surfboard in the market but until it hits the water its worthless…

i tried to start a converstaion about the neutral axis …

the bottom line is , no one had a clue what i was talking about , so couldnt even converse on the subject in regards to surfboard performance …

I beg to differ. Ever take an engineering course on Mechanics of Materials? The neutral axis is day 1…for me that was 1991…solved enough beam problems to give me joo-joo eyeballs for a week. Honolulu knows what im talking about.

regarding surflight v sunova on the issues of shear forces and how they are dealt with ???

neutral axis over the largest possible area of your board is the key …

not saying one is better than the other…my point there was of technical elightenment to others who may have not yet appreciated its basic concept or potential benefits. Even you would admit that concept is a winner…i’ve read many patents in my career and that one is a homerun…Holly agrees too…Oneula would confirm to the expertise of the individuals involved in its development…believe me those guys arent amateurs (perhaps you know some of them)…i was speaking strickly from a shear force analysis only…not about who’s construction works better in the water…which by the way is also subjective and debatable.

youve stated more than once that getting composites to ride better then poopee took you five years. Were they too stiff all those learning years? Are we amateurs just making custom balsa surftechs? In your development, was having a keen understanding of that shear force diagram key to its proper evolvement and potential solution?

Your product and discussions are usually very captivating and like many others here, I decided to take the plunge. I have no regrets (except maybe financial regrets) my boards rip but so does std eps/epoxy…

Sometimes i wonder…Silly’s lastest is perfect example…he did so many things right but still he feels its a bit too stiff. I offered some simple advice there but i dont think he took it. Maybe next time Silly.

give away hard earned information???

I know i wouldnt so i dont blame you. It does have commercial value and youve invested a lot so i agree with you. I told you privately that it would be foolish for you to sit on your technology in a small corner of the world…i may sound a bit jaded recently but the reality is im cheering you on wrt your commercial interests…for me its about more choices…no nev/surfburgers here yet…

finally as far as crumbs…im sure others will appreciate them and theyre welcome to deal with them…no more doors and hallways for me…there’s ALWAYS more than one way to skin a cat…

Regards

PS - sorry i was so tough on you Dan…but tough love is good sometimes…debates like these are common in a for profit engineering environment…looking on the bright side, there’s a lot of good information here now

84

Benny1,

you bring a smile to my face. I guess I should of been clearer when I used the word “attach”.

I meant to connect the parts in a way that ALL forces are transferred between the two parts (directional forces and Moments or twisting forces).

There are ways to connect two parts together without ALL forces being transferred between the two (think of a hinge or rope) but you wouldn’t have the advantages shown in the composite structure diagram in that situation. (My Mechanics of Materials is rusty so correct me if I am wrong.)

Also, I should clarify that I believe Meecrafty is attaching his EPS to the top skin. Its not free floating. Of course he can tell us otherwise. ;]

85

Meecrafty like Bert is well beyond the materials game…

He like Bert has been doing for some time putting his energy in the component we’re all missing…

Design…

Look at that rocker he configured from the original model… What a beautiful profile appropriately thin where you nee the flex but not too bulky anyway. A well balanced compression unloader.

I can see the built in springer and I can see the diving board CMP and I have been in search of.

Once you’ve figured out what you can get away with regarding thickness, floatation and performance you can add on the materials to “complement” the design.

Everything I’ve seen built here so far (other than the peanut) has looked from the side like Meecrafty’s “before” profile meaning we’re building boards with today’s designs using tomorrows contruction techniques thinking that materials and technique are going to make the difference. As Bert has been saying all along and what we all have learned from our Surftech experiences, is that you need to design the vehicle to maximize the best use of the materials and the technique. Doesn’t seem like any but a few have reached that point of nirvana…

By the way Meecrafty… That new rocker profile is exactly what Jim’s blue foam springer looks like under his Polypropalene shell and urethane skin you guys seem to be taking the same path just a little different technique.

I do have to stress though that these new boards will require a new technique to realize their true potential on a wave you have to learn to anticipate and use the spring versus fighting it which is the natural tendancy…

Couple questions if you are apt to disclose…

The dimensions? your 175 right?

86

I once started looking into foaming epoxies and I couldn’t find a commercial product anywhere? I read that it is a third additive that is mixed in. I would love to give it a try, even though I believe the weight reduction would be minimal. I bet a product like this would be more useful to someone like sabs who is approaching the limits of weight reduction. I still have so many other things I can cut to reduce weight.

In case you were wondering what a neutral axis was (I was) here’s how google defined it:

[*]the internal axis of a member in bending along which the strain is zero; on one side of the neutral axis the fibers are in tension, on the other side the fibers are in compression

[*]An axis of a figure, a circle or a sphere, which is indistinct from any other axis of the figure; an imaginary line in the cross section of a beam, shaft, or the like along which no stresses occur.

I wonder if the springer is used to spread the load that is put on the board by the surfer so that the axis exists in a predictable place. Without the springer does the neutral axis change?

87

Perhaps the springer - solid wood being the least elastic or compressible component of the structure - is the neutral axis? Everything above is designed for compression & everything below is designed for tension.

If that were true, then you could control deflection by changing how much of the structure were above & below the springer. For example, when you dado out the slot for the springer, you make the cut shallower in the ends so less structure is above, creating more compression in the deck skin in those places…for a heavier rider, the slot is cut deeper all along…

88

thanks Oneula but between my results and Sabs i think i’d rather ride a Sabs model…i’ve just taken information that i think is relevant to the ride and applied it using simple techniques…my background allows me to sort thru the noise thats all…

interesting comment on the surflight springer…but im not doing anything even remotely close to that construction…and i stole the general design from Bert (yup im a thief and that bugs me)…i just slapped some thicker balsa on the deck and allow for my bottom to stretch and hopefully return as well…

for every action there is an equal and opposite reaction…the diagram is depicting stresses under a load…one component in tension and the other in compression and the two summed equals the force applied…reduce or eliminate one of the stress components and F changes…pick your poison and cross your fingers

have to admit tho…the floating foam concept has been buggin me for a while but i would estimate that at the low low foam densities it doesnt matter whether it is attached or not…its just soft floppy foam…either way it would proly feel the same…but not really sure…your guess is as good as mine

on a more philosofical note: i guess after several successfull attempts at this and becoming more proficient at making composite boards in the garage, the big difference now is when i ask myself ‘HOW’ (how many times have you asked yourself that question?) i also have to ask ‘WHY’…

losos asked how to put on balsa rails and i asked ‘why’ (he gave a valid response but adding it doesnt come without sacrifice and he’s comfortable with that)…

why is glassing the outside first better?

why is panel flex and spring better?

why is a morph bottom better?

is my surfing experience suffering from not having these elusive features?

is it worth the effort and expense to chase these things?

are these things truly better or is the grass just greener over there?

not making judgements here…just asking some real basic and fundamental questions…

maybe its just easier to buy one…

89
Quote:
With a free floating EPS, we have created a Hollow Wooden Surfboard for all intensive purposes since the EPS is now irrelevant.

Funny you should say this. Yesterday I was thinking about how to remove the foam all together, and finally figured it out. In fact been thinking about this on and off for some time. About 1-1.5 years ago there was a wachy thread on desolving the foam out after the board was complete…

In the past Bert has elluded to and others have discussed… core vs skins and that maybe with composites the core (eps) is just there for framing the skins vs convention where the glass skins are there to protect the core.

With the conventional construction you have 1 composite/sandwich structure: glass core glass. With the balsa sandwich you have 3 composites. 2 skins made up of glass/balsa/glass and then the thicker composite/sandwich of skin/core(eps)/skin.

Now it seems the concensus is that the 3 composite approach is too strong/stiff… What would happen if the eps core was removed and the sandwich was skin/rail/skin? (like Bart pointed out) I’ve got the construction process worked out but don’t understand the engineering impact on design/performance of removing the eps core. In this approach one can manage flex (to some extent) by using different thicknesses of deck skin vs bottom skin to manage compression vs tension. Even thought about how an internal springer could be used in the hollow balsa sandwich.

So interested on thoughts of how this design consideration would impact performance. If people feel that my idea on the construction process of how the hollow balsa sandwich (no internal frame like HWS) would impact performance I can add that later. Sorry for the late post (falling behind the thread, but have to ration myself due to work).

90

i dont believe ill really get something great for a while yet but thats okay .

im building boards that are at least as good as what i can buy so im happy.

even if i could make them to professional standard .i wouldnt sell them because it would be giving away a competetive edge,in a crowded lineup.

I have a vague understanding of the engineering principles, but putting that to words without sounding like a moron, keeps me pretty quiet.

What ive discovered though,through practical applications and extremes in design and testing has been valuble >

Dave ive listened very closely to what you have shown and have applied many of you ideas to what im doing. Its just im getting bogged down with simple problems which dont really relate to the engineering of a balsa sandwhich but more to my inexperience as a glasser and shaper.

I love the way my last blank felt,In fact, i knew it was right.

basically i just put to much glass on the rails>which didnt happen on my last board and the rider of it is 15 kg heavier than i am so it flexes nicely for him…

ill know for sure on the weekend when i surf it .

its kinda funny but i can build a board thats

1 kg lighter

wont pressure dent

twice as strong

and thats still NOT ENOUGH???

sh!t i have to make them surf better as well???

91

Not a far off idea 4est…

Benny and I have been brainstorming around with the same idea.

I’ve envisioned build my skins one side at a time by vacuuming them over a plug or mold namely my Surftech Al Merrick Flyer. Vacuum the whole thing; inside glass, wood or corecell and exterior glass to one side of the mold over lapping the rail and then doing the same for the other side.

You can pull heavy vac pressures since there’s no EPS foam core to worry about.

In the end you end up with two prefabbed skins that have overlapping edges… Dremel cut the edges to overlap a tad.

The problem is what to do about the insides…

Not sure whether I go the Soloman route and build stantions(?) to support the shells or implant longitudinal stringers of blue foam (who cares about the delams you need water proofing) for support. You could even envision sculpting out some glassed on balsa bracing (Tophat ?) fastened to one side and the other like building a guitar back and face along with the foam support piers. The questions is what has more floatation? Air or foam?

CMP’s idea want to insert rubber baffles inside that you could inflate or deflate from a plug to stiffen or soften the board as needed. An 80% inflated bag core would be neat.

Another idea is instead of foam stantions or stringers, to build out solid wood or corecell rail bands on the sides and using it to secure the top and bottom shells in a vacuum kind of like a low ball Kolstoff, HydroEpic or Aviso.

You then secure the rails to the railbands using kevlar tape for its strength and flex ratio attaching strips of CF where you want to stiffen it up.

Pop in a relief valve and you have your poor man hollow sandwich skin board using an existing board as your mold.

The cores can vary from 1/8 strip or endgrain balsa to 1/2" corecell or fancy pants 1/4" aluminum honeycomb (Kolstoff/Hydroepic).

Off course you’d either glass on fins or glue on wood/foam box inserts on the bottom skin for boxes although I think glass-ons would provide a more interesting result

Now if you just had the extra time on your hands…

92

{reply}Not a far off idea 4est…

Benny and I have been brainstorming around with the same idea. {/reply}

well it is an obvious thing to think about; hopefully someone with materials/structure background can comment on wether it is worth exploring from a performance standpoint. I’ll be exploring from a novalty standpoint eventually.

{reply}Kolstoff{/reply}

looking at, feeling, and hearing how the Kolstoff is made helped complete the construction process for me, along with this thread to push the incubated thought to the forefront of thought…

{reply}vacuuming them over a plug or mold namely my Surftech Al Merrick Flyer{/reply}

Your existing board will creat too large of an interier mold, IMHO. A hollow will be more buoyant so you’ll want to go thinner. Also as discussed already the foil/profile is likely to want to change inorder to adjust flex.

{reply}The questions is what has more floatation? Air or foam?{/reply}

Air. Also as you reduce weight you have displacement with less weight and thus will feel like it is more buoyant (corky).

OK so here is my construction idea…

Hot wire an eps blank, template and rough shape. Trim back the template shape to account for adding balsa rails. Wrap the eps core in a plastic that the epoxy won’t bond too (painters plastic maybe, something with stretch so you can do it without creases or at least minimal creases). Add the 2 strips for balsa rails to the edge of the plastic wrapped eps (using your favorite method, many discussed here and in the archives (had to say that)), shape the partial rails with the idea that the deck skin will cover the rails. vacuum bag the deck skin on so that bonds to the rails but will not bond to the core (wrapped in plastic). remove the core and using the bottom cut off as a rocker table vacuum on the bottom skin. Use contour mats and such to produce the desired bottom contours. Trim back the skins to be flush with the balsa rails and attach the remaining strips to complete the balsa rails and finish shape. Glass the exterior as normal.

Rail build up… I’m thinking about 1" for longboard with 1/2 attached to the skins, between 1/2" and 3/4" for shorty with 50-70% attached to skins. Most of the strength will come from the balsa rails and the compound curves. Hoping that the rail skin bond will be strong enough to not delam. That seems to be the week point in the design, but Ken seems to have solved that part with the Kolstoff.

As for out side glassing… this should work with pre-made pannels or with traditionally lammed exteriors.

As I said, I will pursue this but it may be a while. Would love to hear thoughts on the design principals of removing the center core. Like Benny said, am intrigued by the whole process. I just wish sending a spacecraft to Mars did not take so much time then I could study up on the subject, I don’t have time to study a $200 book :).

Also open to ideas on the construction process, but don’t want to highjack the tread. At least I talked about rail attachment :slight_smile:

93

Hey Bert!

First, just let me say that my question wasn’t directed at you specifically. I fully understand your position on this and greatly appreciate what you have shared with us. More than I can articulate throught this medium. In my mind you have done more than anyone has any right to expect.

Second, I doubt I am in a position to fully appreciate all the answers you could doubtless share. Perhaps after a couple hundred boards. But for now I am focussing on board one.

Third, I am really enjoying exploring ideas. On here and in small scale practise. And looking forward to applying these to #001. Greatly anticipating it!

All that said any crumbs that fall from the table will be eagerly gobbled up. Assuming I can digest them!

Cheers!

-doug

94

Just as I would look to Bert as the composite man I would look towards Airframe (Ken) as the man for advice on building hollow boards. He’s way ahead of the game. I toured his shop and hes really got a grasp of whats going on. However, I definantly got the impression that hollow isn’t something that you can just dabble with. You have to be extremely committed.

95

Quote:

{reply}The questions is what has more floatation? Air or foam?{/reply}

Air. Also as you reduce weight you have displacement with less weight and thus will feel like it is more buoyant (corky).

Maybe I’m wrong, but floatation is directly related to the amount of water displaced. You’re splitting hairs here talking about the weight difference between a hollow and a foam cored board. I weigh ~ 150 lbs. Do you really think a lb of difference in the weight of the board will make any difference in the flotation of the board while in use? (Together we may weigh 154 rather than 155… big deal). Surface area is the key. Lighter boards will turn/respond faster and that’s where the value of lightness comes in.

96

All,

Forgive me for going back to bow making experiences again :slight_smile:

We should also think about how “thick” the “neutral plane” is.

Tension and compression are at a peak on the surface areas. In normal wooden bows, for example, these forces are at work primarily on the very surface.

There are things we can do to make the tension and compression run deeper into the structure. And it sounds to me as though the springer COULD be used to do that.

Now, does it matter? Instinct tells me yes, but I could easily be wrong. I’d love to heard thoughts on it!

-doug

97

Quote:

Greg have you ever thought about a principal to do with the neutral axis??? its basically where when something is flexing theres a particular point where nothing happens ,no shear no twist no flex…usually around the centre. im not saying this as fact .but a theory still in process ,the stringer down the middle of a conventional board gives a focal point to the neutral axis…

Quote:

ive eliminated the centre stringer and just run the rail stringers…

that way the neutral axis of the flex is free to move with the rider and his position on the board…

Quote:

the horizontal free floating stringer allows the board to really flex and twist , but gives added spring

the bar works harder the more load you put on it

the closer it is to the neutral axis the better it works

I’ve been trying to learn what I can about neutral axis and its gotten me really confused. Here are three times that Bert has talked about the neutral axis. It sounds like you should place the horizontal stringer just in the point of the board where nothings going on. Could this be because the neutral axis doesn’t come into play until the board is heavily stressed. In effect, the board is stringerless until the board is stressed enough that the neutral axis no longer exists.
98

I believe the springer is used to change the “shape” of the neutral plane (sounds weird, maybe “neutral layer” is better) and, perhaps, to adjust how deeply tension/compression penetrate. A springer thats closer to the surface will move the neutral plane, witout being the neutral plane.

I noticed a broken/cut board of Berts had the sringer on, or at least very close to, the neutral layer.

The rest of your thoughts sound kinda right to me… Not that I take any notice of anything I say. :smiley:

-doug

99

So the question other than how to contsruct them is this…

What else can we make rails out of and still get a good result…

Bert showed us Divy and balsa

Benny showed us Divy

I haven’t seen corecell but I have a 4’x8’ sheet of 1/2" just begging to be cut into rail bands…

With 1" all you need is two slices and you’re done…

But is it the same?

Do you go solid woods?

You can by short planks of Pawlonia from the US distributor for testing but I haven’t heard of anyone using pawlonia for rail bands.

What about blue xps?

Jim’s using it as an internal springer haven’t heard anyone using it for rails cause delam’s are supposed to be a problem but Jim using it successfully as a core in his surflights.

Other woods?..

Eucalyptus?

Pine?

End Grain Balsa?

Last-a-foam?

1/4" acrylic plastic sheets"

Haven’t seen alot of options thrown out other than build to build them with thin strips of balsa…

Greg and Ken’s doing thin perimeter’s with a high density external band not all wood like the rest…

What happened to this concept?

PlusOneShaper made a nice one with his inset side fins and all…

Can a thin (1mm) perimeter be all that’s really required? as that concept seems to have come and gone by the wayside as we’ve ventured into building solid rails of fibrous cellulose.

What about just cutting off the rails and putting them back on with a strip of CF or kevlar in between wouldn’t it work the same and be lighter and easier to do?

Life is a bowl of cereal…

100

I’ve also been trying to find some Pawlonia wood. When I ask for it I get the strangest looks.

For the horizontal stringer I bet that a wood like yew or ash would be good. I’ve heard that its good for returning to shape.

I’ve heard that the kevlar rails wouldn’t have the desired flex, but who knows until its tried.