# Rib orientation in controlling HWS flex patterns... also, cloth orientation in glassing to control flex patterns like Gerlach's

Several Questions all wrapped into one thread:

I have seen most HWS ribs attached at a 90 degree angle to the stringer. I saw one example of Dan Hess putting his ribs back at like a 30 or 45 degree angle or something like that. I believe I read somewhere that adjusting the angle of the ribs can alter the flex patterns of a HWS. Is this true?

If so, then what is the explanation behind this?

If no, what options does one have in altering the flex pattern of a HWS?

Moreover, how can you get an accurate stringer-to-rail contour for a rib vs. the way you would do a contour for a rib straight out (90 degrees) from the stringer to the rail?

Any tried and proven methods out there?

I even saw Rich B.'s rib transfer calipers, but couldn’t get my printer to print the template out full sized.

Furthermore, can the angular direction/orientation in the weave of fiberglass cloth be laid out on a board during lamination to allow different flex patterns? I ask this because I read the fin articles in the latest Surfer’s Journal and learned that George Greenough and or Curtis Hasselgrave gave Brad Gerlach a fin panel laid up with carbon fiber. Brad’s fin was templated and cut out with the weave at a 45 degree angle, which significantly altered the flex pattern of the fin in comparison to the same fin cut out with the weave at 90 degrees.

I figured that the same thing could be done in laminating a board during the glassing process to make the entire structure flex more than it would with the status quo of pulling the cloth directly off the roll and laying it out on the board with everything being the same direction.

Am I just grasping at straws?

Has this been done?

Anyone have any input on all of these questions?

Thanks,

Dave

comparatively not very strong in compression.

do the vector analysis and figure out if a 45/45 weave is going to have more of longitudinal vector than 0/90.

I routinely lay my boards up at 45/45 if I wanna loosen them up.

Have look at how carbon is applied to snowboards (plenty of manufacturers specifiy this on their websites; further, plenty of snowboards have clear topsheets/bases that make the orientation of carbon completely obvious). Do they lay it up at an angle or longitudinally/horizontally, and to what purpose?

so…

yes.

I’d anticipate that a fin with a 45 degree weave would have more flex along the span from base to tip whereas a fin with 0/90 weave would have more fles from leading to trailing edge (ie looser tips) that would respond better to changes in flow/angles of attack.

hess may do his ribs in that manner to get better curvature control over a larger area with less material…it may well have nothing to do with flex.

an elementary book on composite construction will give you great insights into materials, how to place’em, when to use’em and what effects they’ll have…almost always available at university book stores at the end of the semester when the materials engineers are done their course for the term. cheap cheap.

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I saw one example of Dan Hess putting his ribs back at like a 30 or 45 degree angle or something like that. I believe I read somewhere that adjusting the angle of the ribs can alter the flex patterns of a HWS. Is this true?

That same thing had me guessing as well, Kawika. This is probably the photo you saw that got you thinking, right?

I asked Hess about that on the ERbb design forum, and this is what he had to say

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The picture on the website shows the perimiter frame with spacing cheaters. I use these to maintain the shape of the rail line before putting in the Internal 1lb.EPS frame. The EPS frame does look far different, and varies alot depending on the flex characteristics I am looking for and the shape.

sounds like he’s not giving up any secrets there, although I do have my own theories on what goes on under those beautiful wooden skins.

Diagonal frames and rail blocks will help the board to flex more, when compared with a board with all fore and aft timber, but the biggest factor is the thickness(max) to length ratio. . . . . that’s one reason why we use a parallel profile. . . . it reduces the maximum thickness of the board at any given volume and thus increases the flex

We get a high to medium flex with a thickness to length ratio of around 1/50 or 1/60 (using diagonal frames )

Tapered profile boards will always have less flex at any given board volume, all else being equal.

.

My understanding of the rib angle and the subsequent attachment of the deck and bottom skins, result in what is know in furniture / construction as a “Box Beam”…Maybe I’m wrong, but I don’t think that once the components are attached to each other, you’re not going to get much flex…

Or maybe I’m missing something…???..

Yes Paul, you are missing something, it’s all about thickness to length ratio. … . thinner boards flex more.

One can talk about grain orientation and timber joints all you like, and they do make a slight difference to the flex, but the main factor is the thickness of the board . … and the next most important factor is the density of the deck and botton planking.

In fact grain orientation in deck and bottom planking makes MUCH more difference than frame orientation.

I know you prefer stiff boards, so perhaps you haven’t gotten there yet

this is going to sound wrong

but one of the first things you have to learn when you building fine wrapped rail balsa compsands is how to play with your wood. If you can get good wood that is…

CMP taught us this…

and I’ve learned alot bending hardwood veneers like koa, zebra, and ebony around curved forms using vacuum bags, epoxy and veneer softeners.

But basically you pull out all your balsa 1/8", 3/16", 1/16" and you bend them along the grain sorting out the stiffer planks from the ones with the most flex. It called grading I guess…

The reason is that you need to use the most flexible of your planks along the rail line if you plan on bending and wrapping the wood completely around the rail. (old school but pretty technique if done right like CMP has mastered). You can then use the stiffer planks along the flats or on the bottom.

The point is wood is that it’s pretty obvious that wood will bend or flex most easily along the grain versus against it. And in most cases the grain runs longitudinally along the length of the board.

This being said the natural flex pattern of boards laid fore to aft would be along the length versus across the width. So by laying an angled pattern of boards in the tail the flex pattern should be along the grain which should produce more snappiness along the length and perpendicular to the action of the fins. By doing this along the bottom skin versus the top skin you should build greater flex tendancies on that side of your boards versus the other which is good based on the dynamics of where the surfer stands, the fins are mounted and the water is flowing against.

I’m assuming the grain pattern of the ribs run longitudinally along the length like in a flat plank so in a sense I’m assuming that you’d be somewhat strengthening the flex along the length versus a perpendicular alignment while also producing some forward reaction towards the nose from the rebound of the natural flex. Hydroepic uses the same angled pattern in it’s hollows as well. But they are arranged on the skin more like the barcing in a guitar or violin than the ribs of a standard HWS.

The angling of fiberglass is an old technique to manipulate the stiffness of the skin layer while managing the flex as well. The classic arrangement would be the tri or quad pattern arrangement that Roy uses in his five layer as well as in some of the special glass weaves used for aerospace or high performance composites. Most high performance composite structure have different layerings of glass at different points in the object to create the desired flex effect to the end product…

Daniel uses a combination of foam and wood to build his skeletons so I believe the pattern is to gian strength with less components (ribs) than to lose it with more flex… He definietly has less ribs than a typical Jensen or Grain design… And he uses custom jigs to build them…

But then I don’t really know anything about surfboard manufacturing this is just all personal experience and observation from playing with wood all the time.

But if you really want to to go big then go find some Russian Basalt Glass and build one with that stuff…

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The point is wood is that it’s pretty obvious that wood will bend or flex most easily along the grain versus against it.

Hi Oneula Actually the reverse is true ( if I am reading you correctly), wood bends much more easily across the grain because it compresses across the grain more easily Thus a board which has planks running fore and aft is stiffer than one which has planks running diagonally across the board. We use this fact often, to allow very thick panels to bend when laminating to the rocker curve ( for example a diagonal one inch thick panel will bend to an extreme rocker curve, whereas a panel of the same thickness with grain running fore and aft will not )

There is a type of carbon fiber cloth that is a bias weave, something like 80 or 90% of the fibers run in one direction only. It has a really substantially different flex oriented parallel to the weave compare to across the weave. Like, almost no strength across the weave, super strong parallel to the weave. It could certainly be used to create anisotropic flex patterns in fins if used creatively. But you have to layup with a high modulus epoxy!

Substantial changes in flex using normal E or S cloth will be difficult, there is a mild effect, but nothing to write home about.

As to Danny’s beam construction, I know he started using Paul Jensen’s techniques, he told me the switch to EPS was principally for weight concerns, the flex is controlled largely by the combined actions of the rail construction (also from Paul Jensen) and the skins. He’s somewhat torn between the environmentalist within, and the market which will be MUCH greater for more weight comparable boards. I’m pretty sure it is almost all EPS ribs now, although he can sure do wood too.

Danny is a top-notch ripper and surfs >200 times a year, so he has good feet for feedback.

But perhaps he will chime in with more if he is listening.

yeah Roy I think I was trying to say the same thing.

In other words

you will have more success wrapping balsa around the curve of a rail if the balsa boards are going fore and aft than trying to wrap skin planks that are oriented diagonally or side to side. Although with a jig and extremely hot steam you might be able to bend something in such an arc across the grain.

Let say I take a 6"x12" sheet of 1/42 veneer of exotic hardwood like zebrawood, koa. sapele or ebony.

lay that sheet with the long grain running horizontal following the top of a curved jewelry box top and try and bend it over a curve similar to the curve of a round rail on a surfboard and no matter how much “veneer softener” you soak it with before vacuum bagging it, the sheet will crack, snap and leave bubbles along the flats of the top of the box. I’ve lost so many projects and expensive veneer trying to bend wood in this direction(to save sheets) versus cutting sheets in half, taping them up and bending them with the grain running perpendular to the side curves with a seam down the middle of the box’s top (which I hate even though it’s matched). I guess it’s pretty much wood 101 for guys like Richard, Paul and Danny…

I would say glass orientation other than a density difference like warp glass(like what Blakestah talked about) would have a similar flex pattern.

This is why I’ve been experimenting at building my hollow skeleton ribs out of blue dow EPS that has been skinned with this 1mm cross woven bamboo weave laminate because the 1mm cross woven bamboo oriented on edge(vertically) provides incredible strength to the super light and 100% waterproof blue dow once it has been applied under vacuum on the outside of the XPS with 1-2oz glass and epoxy. You can apply 2 sheets of 4x8" the bamboo weave on each side of a 1"-.5" thick 4’x8’ sheet of blue down and then cut out all your ribs and stringers from this home made SIP panel to build your skeleton from and apply your wood plank skins over this like a normal HWS. I’m kind of using my 1mm cross woven bamboo sheet as some type of a 45 degree and 45 degree oriented “super glass”. I’m also playing around uisng these stiff light ribs attached to flexing wood center stringer to keep some flex in the structure. Also with the Blue Dow you don’t have to drill all those stupid holes to save weight in the skeleton. Just one or two to let water pass through for drainage.

But then again I don’t know what I’m doing in the first place…

I was just getting tired of cracking and snapping all my ribs trying to drill or scroll saw all those stupid holes in them and the stringer…

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This is why I've been experimenting at building my hollow skeleton ribs out of blue dow EPS that has been skinned with this 1mm cross woven bamboo weave laminate because the 1mm cross woven bamboo oriented on edge(vertically) provides incredible strength to the super light and 100% waterproof blue dow once it has been applied under vacuum on the outside of the XPS with 1-2oz glass and epoxy. You can apply 2 sheets of 4x8" the bamboo weave on each side of a 1"-.5" thick 4'x8' sheet of blue down and then cut out all your ribs and stringers from this home made SIP panel to build your skeleton from and apply your wood plank skins over this like a normal HWS. I'm kind of using my 1mm cross woven bamboo sheet as some type of a 45 degree and 45 degree oriented "super glass". I'm also playing around uisng these stiff light ribs attached to flexing wood center stringer to keep some flex in the structure. Also with the Blue Dow you don't have to drill all those stupid holes to save weight in the skeleton. Just one or two to let water pass through for drainage.

Damn Oneula, that’s some outside of the box thinking there! Always impressed with your experimentation and stretching the evelope. I keep looking at that sheet of bamboo you sent me, and I’ve decided the next boards I do will be in keeping with the spirit of exploration you infused it with, kind of lost my momentum with just shaping pretty boards the same ol’ way. Great stuff! I’m very tempted to do a real hollow, but just having a hard time with the time/return possiblities.

Yes orienting the glass weave affects flex.

BUT…

If your HWS structure is heavy duty, with light glassing; glass weave orientation wont change much (likely scenario).

OTOH, if your HWS structure is very light duty and significantly reinforced with glass laminate, then the weave orientation will affect flex (unlikely scenario).

This core/laminate relationship holds true for any construction. There are balances to consider and everything is inter-related.

One of the reasons why pupe has been so popular for so long (in addition to ease of mfg) is balance of contruction materials. It is this balance that gives it the “proper feel”. Not that this feel cant be duplicated or exceeded with different construction methods, its just that other methods require more work…like orienting your weave 45.

Onward…

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There is a type of carbon fiber cloth that is a bias weave, something like 80 or 90% of the fibers run in one direction only. It has a really substantially different flex oriented parallel to the weave compare to across the weave. Like, almost no strength across the weave, super strong parallel to the weave. It could certainly be used to create anisotropic flex patterns in fins if used creatively. But you have to layup with a high modulus epoxy!

``````  Hi Blakestah,    We have been using that bias weave carbon fiber for our bulb tipped flex fin upstands, the fiber running from base to tip   The long bulb has tremendous leverage and twangs at least 2 inches each side, the thin (5mm thick) upstand twists to allow this but has almost no side to side flex.   Needless to say, the setup is a success, but not a Hess         ;)     <a href="http://www.olosurfer.com/D11-9.wmv" class="bb-url">www.olosurfer.com/D11-9.wmv</a>    <img src="http://www.olosurfer.com/bulbflex.jpg" alt="" class="bb-image" />       .
``````

This is great stuff. I’ve made the offer in the past and repeat it here (sorry if it bores y’all), I have the kit to give you figures if you want. tell me the lay-ups you want flex comparisons for and I’ll produce scientific results if I have the glass or carbon available.

Better still send me some materials and I’ll post results…

Fibre orientation does affect stiffness and strength, it is predicting load paths that is difficult. Before I did a kevlar and glass board I made some test samples to see how much difference there was if I placed the kevlar on the outside or inside of the laminate stack. The results made me alter the stack (and the bugger still creased in a big wave, but that was due to compression failure of the deck, a different problem!).

Kevlar is weak under compression

If it’s ok I will send a couple of different lay ups for comparison.

Yeah, that would be great, no worries…

So I beefed-up the deck with some carbon uni’ I had lying around. Did the job beautifully.

As to rib orientation in a HWS built ala P Jensen, I would agree with his assesment. If the skin attaches to the ribs, you have built a box-beam whether the ribs are diagonal or perpendicular to the stringer I don’t think you would see any discernable variance in stiffness. As to a Roy construct, I would defer to his anaylsis…

7/10

Looks like something from The Jetsons : )

After going to all the effort of making a flexible HWS, it’s a good idea to use the flex effectively

Behold the ultimate fin pattern gor a flexible HWS !