My personal feeling is that flex needs to be measured to really find what effect this is having. We make 4 different resins with different flex patterns and I have yet to fully understand exactly what flex is effecting as far as ride quality. I do know that very light boards generally need stiffer resin because the laminates are thinner. Without thickness the laminate isn’t providing the stiffness of a thicker/heavier laminate. In Bert’s case (sandwich construction) he does have the laminate thickness even at very light weights. We have used a more flexible resin in conjuction with cored laminates with a great deal of success. But again, with nothing measured we basicly have a crap shoot.
Greg,
Measuring is probably a good idea, but flex works brilliantly over a wide range, whether or not it is measured. What is the point in measuring laminates for flex characteristics unless you have a good working knowledge of flexible boards and their behaviour? I don’t even use a cloth/resin laminate on my boards and they flex very well. I wouldn’t describe what I am doing as a ‘crap shoot’.
It is important to realise that for functional flexibility the shape of the board is important. We are not just talking about materials, we are also talking about shape. That is one of the reasons why I cannot agree that shaping has ‘run its course’
Roy
Hey guys love this post,
Growing up on the North Eastern coast...I spend alot of my time snowboarding as well as surfing in the winter, so I understand the importance of having flex in a board. I think that with progressive surfing using a more bottom-top surfing method (what i mean is alot of off the lips, snaps, repeated bottom turns, airs)(not trying to discount the other elements of riding either) the flex of the board could be used alot more to generate more "whip" (loading and unloading the board) So I think its time for me to start shying away from exclusively polyester, fiberglass boards. After going over the pro's and con's of these boards in relation to flex...they leave much to be desired. Do you think an all Balsa wood shortboard, stringer-less, would have good characteristics? Another idea is an EPS blank, stringerless wiht epoxy. I'm angling toward stringer-less so the board can have a truer flex and would not have the stringer determine alot of the flex characteristics rather than the blank. I have never used balsa wood before so im unaware of the characteristic of it's flex. Im sure Bamboo would be one of the best materials but I've never experimented with vacuum bagging before...I'm very intrigued though I'll have to do it soon regardless of a flexy board, not sure if I have the patience or time now though. I also think that with the right horizontal axis fin..a flexxy board could be phenomenal. Any advice would be much appreciated.
Thanks.
TJ
Check these guys out…
they seem to be the most focused on snowski-like torsion
box construction in a surfboard. I like the idea having spend a good deal of time snow skiing on reverse cambered torsion boxes of various designs Atomic, Soloman, Fischer Head…
I’ve seen a bunch around my breaks an old guy with a longboard and some kids with short boards. They ride real different according to the old guy but I don;t know if that’s good or bad.
Jim Richardson and Jeff Johnston aren’t shapers to scoff at, so at least there’s some craftmanship in there somewhere.
About 6 years ago I saw a used one for $300 at Jorge Vincete’s shop, I guess there was a big Brazilian contingent using them… I couldn’t sum the courage to pick it up although now I wish I did… something like 7’2"x 18.5" which I though was too small for 200lbs. The outside is squishy like a boogie board.
As a sidenote I 've contemplating building a stringerless EPS version of this with the keel to see how it goes. Could be interesting to have a flexible version of this will the old keel attached to the bottom…
today
1972
ah…the single keel re-appears !!
Oneula, when you do the flexi with that fin, I’d LOVE to hear how it goes… two projects I have waiting on the sidelines at the moment , also ! [We can compare notes when they’re done eh ?]
… merry Christmas, everyone ! [ it’s tomorrow, for us aussies !]
ben
how did the single keel boards ride?
Hey Bert if you see this…what do u think of the solid balsa shortboard? Is that the wood of the board flexxing in the photo? If not, are there any other types of timber you could recommend, not just for a solid wood board but also for vacuum bagging…You’re expert opinion would be much appreciated.
Thx,
TJ
like turbojets i have also been following this post while relating the flex question to snowboarding. I have been snowboarding for nine years and have seen how the progression of flex has allowed the sport to grow. Can a thin wood core such as one in a snowboard be implemented into a sandwich construction? If this were possiable the technology of snowboards progressive flex is very easy to dial in exactly what sort of flex you need.
Another question is: can you change the stinger wood to adjust flex? I am not sure if people already do this but thier are many other types of wood that offer different “snap”, can the type of stringer be used as a flex variable?
Gents,
The hyperbolic shape of snowb’s and shaped skiis is the dominant element for providing flex…the tips grab, the center grabs far less, the board bends.
Surfboards have the opposite shape and thus implementing snowboard-esque flex into a surfboard is mighty difficult indeed. Making matters even more difficult is where the rider’s feet (force) are placed in relation to the desired flex characteristics, particularly in the tail of a shortboard.
Still I think the quest is worth pursuing…
i agree the sidecut has some to do with flex but not much. The side cut allows you to snap in and out of turns but has little to do with the pop of the board and its ability to flex over differnt surfaces. The way the core is laminated is the factor that adjusts the flexibilty of the board. Thats why i was wondering if a thin laminated core can be used. the different stance is a good point but if a thin core was able to be used I think that it could also be adjusted to take this into account.
The hyperbolic shape of snowboards and skiis are used to increase the amount of effictive edge proportional to the amount of flex…the more the board flexes during a turn the more of the edge will be in contact with the snow. In surfing a hyperbolic shape is not practical for a number of reasons…Surfers use different techniques to carve and turn(weight displacement is completely different) either a surfer puts most of his weight on his back foot to turn or he uses his front foot for drive and his back foot for control. A snowboarded uses his edges, his weight is balanced most of the time. A hyperbolic shape needs a great amount of flex to be effective, it probably never will be used on surfbaords bc that much flex is never needed. My ideas are to use flex to increase the speed out of turns, if you’ve ever had an arcing turn that seems to shoot you out then you know what i mean and what I want to do. Todays surfboard’s literally get destroyed when they flex too much, the foam cannot take the stress nor the fiberglass. My experience’s snowboarding that im applying to surfing is “loading” up on board during a turning and the sensation of the board “unloading”, which generates a substantial amount of speed. I think a flexier board would benefit most high performance surfers on a high performance wave (chest- a couple feet over head). Too big a wave and the flex would be too much and your legs would buckle, on too small a wave theres not enough speed for you to be able to dig that much rail and not stall.
Meecrafty, I definately agree with you thats it’s easier for a snowboard to flex, but thats not the question we are pursuing. Surfboards should never flex as much as snowboards do there is no need…however you can’t deny that they do flex, and if you have snowboarded for awhile then you know how big a deal flex is to a board’s characteristics. Surfboards do flex…very little…and when they do too much it’s bad news for the board. However if we could develop a board that flexes the appropriate amount needed for effective surfing we just might be on to somehting that could raise the bar a little higher…
Turbojets …
yea your onto it …
i had one board that loaded so hard in double head surf , that my legs wouldnt hold under the g forces as it onloaded and sprang me out of bottom turns …
what your talking about is something ive been able to explore for quite a while now because of my different construction techniques …
having flex dialed in allows way less dependance on static shape characteristics …
i had a customer make a comment the other day about on of his favourite boards …
he said
" just looking at the board the curves are so average it doesnt look like anything special , but the thing just goes off and no one can figure out why"
i said " its all about spring and the speed at which the flex will return …"
im not sure if you were asking about the photos i posted above or another flexing solid balsa board ???
the flexing board in the photo is vacumn formed balsa/epoxy/glass/urethane over eps core …
most timber will work in the flex department …
its such a natural part of its everyday job … trees will stand for hundreds of years blowing back and forth in the wind , when the load comes off , it springs back to its original posistion , it can do it time and time again without fatiguing …
while all other composites eventually break down and become lifeless from fatigue , timber keeps on performing …
blending the flex characteristics , is real important …
look at a board and consider where your placing most of the load in various circumstances , then increase or decrease the spring in those areas …
its probably way easier to get an understanding of how the flex affects performance if you ride longboards as well …
a longboard is more sensitive to flex adjustments , also being easier to tell whats going on …
most of my major flex breakthroughs were made on longboards first …
for me doing longboards and working in this area , definatly made the biggest difference to overall performance …
99% of longboards in general are still in the dark ages design wise , so decent static design combined with controlled flex and you have a huge gulf in perfromance …
the question about flex in regard to different stringer options on conventional boards…
yep that makes a big difference …
to the point that ive seen guys chasing there tail around trying to copy the performance of a particular board , because they ignored the stringer type and flex patterns of the board …
i find it quite amusing that flex has become quite a buzzword lately …
with the change to different constructions comes a rewriting of all the traditionally excepted cliches regarding weight , which affects flex …
traditional construction was bound by certain flex characteristics , which meant you couldnt go to thin or to light without getting an unresponsive flopper …
i dont know how many times ive heard the argument " o yea , they dont go any good if there to light "…
my first thought was just another lost soul of the p/u p/e mass …
that reasoning is so flawed …
the deal is they dont go any good if there to floppy …
positive flex return is the key …
unless you go to vacumn forming and sandwich construction …
most flex experiments will end up being quite limited …
once you start pressing layers of different materials together , a whole new world of options becomes available …
even to the point where materials once considered of no value to the performance of a surfboard , become completly different when combined or fused with other materials and impregnated with resin under vacumn …
i could go on indefinatly on this subject …
so ill leave it there …
regards
BERT
i agreed with how you summarised snowboard flex turbojet …ive only just figured out that flex/ outline / rocker thing just recently because of sandboarding alot …
for double enders and trick boards the snowboard designs definatly work best …
Hey Bert, I was wondering do you contribute most of the board’s ability to flex to the wood rails or the laminates?..I’m doing an XTR blank right now and I wanted to laminate the balsa wood between the foam, since I’m going to have to use something to adhese the two pieces together anyhow. I surf on Long Island so I’ll use it until it gets warm… I want to go with the wood rails also but I’m not sure to how to go about it…There are two ways I can think of:
A) Use thin strips and epoxy them parallel with the side cut, then epox additonal strips to increase the volume of the wood so you can shape the rails.
B) Use a piece of wood that is the size of the tail to the rail plus a few inches, while also being the size of the nose to the widest part of the rail plus a few inches to shape. Then you would have to glue up the pieces like plywood.
I think the plywood method would be alittle more natural to flex, but I might have to use more layers of wood, which means more epoxying, more weight…
Thx,
TJ
its a combination of the 2 , plus the core set up , where youve put resin and glass in your core , and how much resin youve put into your core via your skin attachment , and what other little secret ingriedients you might have snuck in there …
no advice on how to put the wood on …
im just the ideas man its up to you to figure it out …
regards
BERT
No need to use epoxy to lay on the layers of the wood rails. It would be awfully expensive, hard to shape, and a nightmare to keep mixing up little batches all day. Just use yellow glue and bend the strips on one by one and hold them with tape.
These last two posts were just the information I was looking for. Now I understand how to shape the rails without have to use loads of balsa. Its funny how a picture and a few words can “turn the lights on” in ones brain.
Trying to understand the basics of flex, I can envision the desire to have the tail flex so that it will, well for the lack of a better word- snap back when you snap (ect), in experimenting would you suggest leaving the tail rocker as is on a stiffer board and try to increase flex or decreasing tail rocker then working on flex?
Thanks
Joe~
Interesting thread, but as a few people don’t really seem to justify their philosophies I’d like to make a few really simple comments:
To understand the impact that controlling the flex characteristics of a surfboard it’s necessary to understand what causes flex. The surfboard acts as beam (like in a building) supporting the surfer pushing down and the dynamic lift pushing up. When the board is turned this is made more complicated by forces acting on the fins creating torsion, which as a the water flow will rarely be straight along the stringer means a board will be subject to both bending and torsion at the same time. The effect of flex in a surfboard is to change it’s three dimensional shape and to absorb/store/dissipate energy. In designing flex properties one would want to match the 3D shape as much as possible to the situation, presumably flat for trimming and curvy for turning.
The stiffness of the board at any point along its length is a combination of the materials used and the second moment of inertia. By far the biggest factor influencing stiffness at any point will be the thickness of the board, a board 2x as thick will be 16x as stiff assuming the materials are the same, while 2x width is 2x stiffness.
Now assuming you wouldn’t want to mess with the thickness too much you can play with the materials. There’s three main ways you can alter the stiffness (but remember these will also affect strength). One way is to change the materials, glass, carbon, Kevlar, wood, the resin system, and all the different flavours of each will have different stiffness, shown as E or Young’s modulus on data sheets, the bigger the number the stiffer the material. Another way is to vary the construction method, hollow framed, sandwich skins, or just plain old monolithic. The third way is to use the anisotropic nature of these materials, change the direction of the tows and you change the stiffness profile of the board.
To make sense of any changes it’s important that to really understand the effect of anything you must only change one thing at a time. It would also be a really good idea to measure the stiffness accurately out of the water. Objectivity is everything.
cant agree more about rocker…
mtb made some good points…
tail flex is what makes the most difference to enhance performance on a short board…
for conventional construction, stuff like thickness, choice of foam density,stringer thickness, stringer type(different woods),glassing, lap size and shape all can be tweaked to affect flex…
for sandwich boards theres other things as well as those mentioned above, thickness of your skin core, skin core material,internal bonds affecting shear movement,moving stringers relative to the centreline,changing the sandwich structure by putting more or less glass either side of the skin, changing the stiffness in certain areas by allowing more resin to penatrate the foam,putting extra glass or other materials in certain areas under the skins,changing the foam it self as it moves along the length of the board , using different sections of varying core material,building composite foam sandwich inner cores with multiple layers, changing the arrangement and thickness of those layers,removing layers and replacing them with different materials, changing
the thickness of your skin cores as they move along the board…
you could build the perfect shape and spend another decade just dialing in flex…
those are some of the areas you could start…
regards
BERT
Back in Black
Quote:
Bert?
You know this stuff.
You need to write some books. I will buy one. Or two.
Thanks.
Thats about all my brain can say after reading your posts.