I want to start experimenting with flex. Which part of the board is it important to have flex, is it in the mid section or last ft or so of the tail? The board will be a squash or a swallow tail. Any suggestion or views are welcome.
Cheers
Seems everybody has a different idea about flex. Here’s my view (incorporated into virtually all my kneeboards since the late 60’s):
-
Progressively decreasing rocker (center and rails) along the length of the board from nose to tail, resulting in no rocker at the tail (an option only viable for a fairly short board).
-
Glass/foam/glass sandwich down the centerline to inhibit/minimize the development of rocker under the loading of the rider’s weight. Near the tail, this typically transitions to decreasing thickness of layered glass to allow some small degree of tail kick to develop under heavy loading while maneuvering (generally made stiffer for larger faster waves, more flexible for boards for smaller slower waves).
-
Glass/foam/glass sandwich from the front extending down the rails on both sides, diminishing in thickness and to tapered glass near the tail (transition distance depending again on the kind of waves to be ridden–but beginning substantially earlier than down the centerline). Multi-axis lay-ups with unidirectional glass to yield desired bending characteristics under loading. Generally not nearly as stiff as down the centerline.
The theory is that one wants minimum rocker for speed. But when the board is banked to turn, the rail involved in the turn becomes more heavily loaded (less wetted area, more load, hence greater load per unit wetted area)–especially to the rear–and develops curvature that assists in generating a carving rail turn. The primary variables to play with are the stiffness/flex of the rear portion of the rail (too little flex, and the effect is reduced; too much and the turns tend to “hook”). The flex is, of course, controlled by the sandwich (or glass) thickness, glass orientation, and length of “glass only” area (which, optionally, may be covered by a flexible, closed cell foam if more flotation is desired).
MTB
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
Can any of you guys suggest some good materials to obtain the optimal flex.
Howzit Swifty,
As a builder of boards which flex up to four inches throughout their entire length as an integral part of their design, the subject is very interesting to me.Here are a few pointers:
-
A board with a tapered profile will not flex properly throughout its length.
-
A board with a parallel profile will flex quite naturally throughout its length.
-
Flexibility throughout the length of the board is preferable to short flexible tail sections.
-
Timber is one of the best materials for flexible boards.
-
Most of the power of flexible board is lost if there is no horizontal control surface at the tail (Like a dolphin trying to swim without a tail).
-
Longboards are easier to design with functional flexibility than shortboards, because they can be made proportionally thinner
Quote:
Can any of you guys suggest some good materials to obtain the optimal flex.
As my old philosophy instructor used to say … that depends … on board length, width, outline shape, desirable floatation, how much flex is optimal, what kind of structure/construction methods and substructures you wanna use and have available, rail shapes used and more, let alone the questions of the waves you’re surfing it in and your style of surfing… it’s a matter of putting it all together after experimenting, studying, analysing, trying new materials, methods of construction . Successful flex craft have been built using fabric and air; fiberglass, resin and foam; plywood and not least of all a poly-somethingorother foam originally meant for lining shipping containers that contained optics and other instruments*. These have included longitudinally bulkheaded designs, composite tuned-flex substructures, carbon fiber sheets, rods and tubes, fiberglass I-beams, varied density foams and more that I am either ignorant of or have simply omitted through lapses of memory.
Put it this way, if you’re serious about experimenting with flex, you can have a very interesting and enlightening twenty years or more ahead of you. There are no simple answers to what is optimal flex in general, though flex can be built into any shape of any size, contrary to what some may say, it’s not limited to long boards of thin cross section, etc. You just ( ‘just’ , riiiiiight, like that’s simple ) have to think about the whole complex structural-shape-pressures system and how it’ll work together. As MTB mentioned, he’s been working on and thinking about flex for around 40 years. Plus Bert, plus definitely Dale, Greenough and several others. These are some of the most innovative thinkers in this business. It’s not a trivial problem with easy answers. It’s thinking waaay outside the box of conventional surfcraft making.
I will make one small suggestion, though; in your initial post you mentioned that you’d use a squash tail or swallow tail, but I’d suggest going to a relatively wide rounded square tail for simplicity’s sake. Otherwise, you’ve got a relatively complex shape with some interesting water pressure/leverage/structure things going on which will make your initial efforts that much more difficult to build, understand, adjust and analyse the performance of.
Also, I’d suggest that you choose a construction method that is ( pardon the pun ) ‘flexible’ - that is, something you can add or remove material from or otherwise adjust without too much effort or major rebuilding so that you can tune the flex to your optimal characteristics.
Hope that’s of some use. Look forward to hearing about this as it comes along.
doc…
- Really. Consider Tom Morey ( as he was then) and his experiments with the original flexible boogie boards, which were meant to flex considerably. The foam was one made for shipping instrumentation in, made by ( among others ) the Packaging Industries group of Hyannis MA which was also the parent company of the BZ bodyboard and soft surfboard company. They happened to be located on that hotbed of surfcraft development Cape Cod, Massachusetts, USA, which is how I happen to know a very little about it.
Thanks guys for the help so far keep the ideas comming.
I was thinking of manking a 6 X 18.5 X 2.3 squash with a fairly wide tail. I have found a blank supplier that will make me a blank with an upside down Y stringer. As a result the last foot( I will need to calculate this still based on where I put my back foot and fin positioning but its roughly a foot or so) of the board and the deck will be parallel to the bottom in the last foot and a half. Has anyone tried this what do you think.
Doc,
I did not say (as you imply) that flex is limited to long thin boards, only that it is easier to achieve flex with a long thin board. Also, contrary to what you say, a functional flexible board is very easy to make. Some people just don’t like a simple, efficient solution. In my opinion, ignoring the flexible board innovations which I have come up with, just as if they are not there, is a sign of poverty of spirit. If those on this forum who you mention as great innovators in the field of flex can’t even make a sensible comment on the new breakthrough of flex driven horizontal fin surfaces, then they have their heads stuck firmly in the sand!
R. Stewart
Hi Roy,
Lack of response to some of your posts should not be assumed as apathy, ignorance, ambivalence, agreement or disagreement.
As for me, Im not ignoring you or your innovations, Im not aware of any “poverty of spirit”, nor is my head “stuck firmly in the sand”.
-
I look forward to your posts and photos.
-
I come from an entirely different perspective.
-
I often couldn
t disagree more... but thats o.k. -
I work a lot… usually away from PC, TV and phone.
-
I often don`t know where to begin, and what to say because of points 1 through 4.
All the best
Thanks for your reply, Dale. I certainly wasn’t criticising you, I was actually talking to Doc. I feel like someone who is watching a bunch of square wheeled cars bumping down the road, and trying to sell the idea of a round wheel. It is frustrating to be told that flex design is complicated and will in the future be worked on by a list of established design heroes, when I have some very simple and practical, well tested flex solutions. I realise that even if an idea is really good, I can’t necessarily force it, but it is my job to try. Unfortunately because I am personally presenting ideas, there are those who won’t want to hear them because of of some personal feelings or attitudes. This is a pity because the ideas belong to all of us. If I could present them as the work of George or Laird I might get a better response but it isn’t possible.
Give the Dolphin a tail!
Hello Roy,
I say… just keep on with what you`ve been sharing!
But also… consider that there are many here who are rightly satisfied and successful with their individual approaches to surfing, wave craft design and construction. I know a fair number of us come from very different vantage points.
I also reckon very few visit Swaylocks amped up for vigorous debate… fewer still are willing (or able), to physically cope with long, heavy wooden equipment such as yours. In the water or out.
Yet, I`m guessing here, but many of us are curious, eager to learn/see more, and do respect your insights and achievements… even if it is vicariously.
All the best to you.
Aloha Swifty - here’s something else to ponder which in the quick skim back on the other replies, I didn’t see mentioned (sorry if it was). There’s about 3 guys that I can think of off the top of my head that are playing around with the… let’s call it “disappearing stringer”. Can’t think of what they call it at the moment. That would be Rich/Toby Pavel, and thus his protoge Manny (of the Mandala fish), and I believe Rusty. Don’t know where to see any of the Pavel shapes, but you can see some of Manny’s on his website, and I’ve seen one of Rusty’s several times in magazine ads. I’m afraid I don’t know all the technicalities of it, but Manny has a picture and description on his website of one of his… Calls it a “stringerless flextail”. Haven’t checked Rusty’s website, but he might have an example there as well… As far as I know, it looks like the only difference is the lack of stringer in the tail section of the board. No differences in thickness/foil/planshape… but that’s only conjecture from looking at pictures and not having seen one in person… Just more ideas to chew on…
roy’s pretty much onto it…ive never found a composite that can offer what wood can…
when you look at celulose , its nothing more than a microscopic spring…
any composite will reflect the qualities of its smallest units…
the best part about using timber as a composite…
it never fatigues,
a tree can stand in the wind and be blown around for 1000 years , but still springs back to its original position…
no man made composite could do a 1/100th of that…
while ive covered alot of ground on flex …
somehow i always end up back with wood …
roy i just want to look a little closer at some of your quoted comments below…
1) A board with a tapered profile will not flex properly throughout its length.
-
A board with a parallel profile will flex quite naturally throughout its length.
-
Flexibility throughout the length of the board is preferable to short flexible tail sections.
-
Timber is one of the best materials for flexible boards.
-
Most of the power of flexible board is lost if there is no horizontal control surface at the tail (Like a dolphin trying to swim without a tail).
-
Longboards are easier to design with functional flexibility than shortboards, because they can be made proportionally thinner
in point 1 and 2 , are you saying that a finely foiled tapered board has something missing but a crude box of wood will out perform it???
in point 3 i agree with you , to add tho, you can still dial in a little more or less flex , in certain areas to suit your needs …as the tail is the area that your on while doing critical manouvers , its the area youll notice the biggest gains if you start there…
point 4 …timber is the best… make a conventional board with out a stringer… yuk…
timber adds life…
i met this guy a few months back , he noticed the boards in my car and came over to have a look , we talked for a while , he was pretty stoked with my work…said he was making wooden boards before foam came in …
he said when they made the transition from wood to foam …the boards felt dead…
but because it was the latest thing , everybody wanted it …he built them , and made money , but his heart was still with wood…
he was pretty old i reckon 75 at least , said he was making boards over 50 years ago stopped making them 30 years ago…
said he had one of the biggest board productions in australia…
he introduced himself as gordon woods, i said " not the gordon from gordon and smith" he says " no "
he must have been before my time…
is that name familiar to anyone…?
point 5 , you wouldnt be trying to insinuate a dolphins tail is more effective than a sharks tail…
point 6 , yes and no , yes a longboard will flex easier , coz its thinner proportionately… but no , its not easier to design with functional flexibility…if you get it wrong , the board can be ugly, get it wrong on a shorty and its not as critical…
roy i just thought id throw another comment in , i had a 7’-8" that could flex 12" over its length, to this day my best board for sucky 6 to 8 foot surf…
ill see if i can find a board around with extreme flex , i will try and get a photo of a few people standing on it , so you can see what i mean…
serious question ???
can you give us a breakdown on the new breakthrough of the flexible driven horizontal fin…
im intrigued to the benifits of such an idea…
what style of surfer , or types of conditions would it favour???
hey roy i read something on another thread…
you wouldnt be related to any rabbits would you???
i found a place on the south coast down here as well , it needs a little work but it might suit you…heaps of room for the kids as well…
enjoy…
regards
BERT
Hi Bert, thanks for your time!
In answer to your comments on those flex points:
Your question: “in point 1 and 2 , are you saying that a finely foiled tapered board has something missing but a crude box of wood will out perform it???”
Answer: No I am not really saying that, but in discussing the difference between a parallel profile board and a tapered profile board, please allow me first to remove the value judgements in your statement and concentrate on the physical differences between the two types of profile. Your description of a ‘finely tapered’ board in comparison to a ‘crude box’ is to presuppose that one kind of profile is better than another. If we could leave that sticky question just for a moment, then we can look at the differences in flex between the two profiles.
A board will flex more easily if it is thinner. A tapered board will flex less where it is thicker, in the middle, than it will at the ends. A board with a parallel profile will flex more easily throughout its length, because it has no stiffer sections due to taper.
Regarding the question as to whether or not a parallel profile board will ‘outperform’ a tapered board, I offer the following ideas. ‘Performance’ is relative to a percieved goal. However a parallel profile board has two main advantages over a tapered profile board. The first is a lower centre of gravity via a thinner midsection . This is not a significant advantage for shortboards, where the difference in thickness will be small or nonexistent, but it is a major advantage for longboards, particularly longboards with a lot of rocker. If we compare two twelve footers, my parallel profile board can be built down to 2 inches thick, whereas a tapered 12 foot board is usually between three and five inches thick. This makes the tapered board less easy to control. The second advantage is the continuous flex factor mentioned above.
There are of course reasons why you use a tapered profile, and I am sure that they are valid also, but I notice that thinner, more ‘performance’ longboards have less taper.
Your comment: "in point 3 i agree with you , to add tho, you can still dial in a little more or less flex , in certain areas to suit your needs …as the tail is the area that your on while doing critical manouvers , its the area youll notice the biggest gains if you start there… "
Answer: Your performance goals are slightly different from mine, being more concerned with critical tail based maneuvers, so no doubt that is why you want your flex mainly in the last part of the tail. What happens when the board flexes throughout its length is that the rider experiences ‘gains’ through flexiblity all the time, as the board is constantly responding to weight changes by flexing and springing. As the tail sections on my flexible foil boards start at 30% back from the nose, some of my boards have tails 10 feet long, so to get the entire tail to ‘twang’ I have to have a parallel profile.
Your question: “you wouldnt be trying to insinuate a dolphins tail is more effective than a sharks tail… ?”
Answer: No I wouldn’t. The reason that I refer to the dolphin rather than the shark is because the dolphin has a horizontal tail rather than a vertical one, and it drives the tail using an up and down motion, which is the kind of motion which is available to us through board flex. To drive a vertical tail like the shark has using board flex, the board would have to flex side to side, which is obviously very difficult to achieve.
Regarding the flexible board driven horizontal fin breakthrough, and what conditions and surfing styles it might favour, I can really only report what I have done with the idea. I think, however, that it has the potential to be applied to many different boards and surfing styles, just as the conventional vertical fin is.
If you want to experience the radical thrust given by a horizontal board flex driven foil, then perhaps you could put a star fin on a very flexible board for a quick taste of what it feels like. I would be really stoked to find out how you like the feeling! A tunnel is better, I think, and easy to make, but if you happen to have a star fin then give it a go and then I won’t have to carry the full burden of being the ‘Expert’ in this field.
Perhaps Gordon Woods is the man from ‘Atlas Woods’ surfboards. Wayne Parkes is now reviving that label (he shaped for Atlas Woods during the sixties). The latest ‘Slide’ magazine has an article on Wayne and the AW brand, I will go and dig it out.
Er . .nice bus, when can I move in? I am ignoring the other comment, children are a blessing from God, and I was an only child. .our clan needs building up . . . I am starting a Dynasty!
Wood is good!
Regards, Roy
yea he did mention new zealand, and the atlas woods label , that would be him…
roy i see your point about the horizontal fin …the funny thing is , the only way it could function effectively is with a flexible board…
the flex you decribe with a paralell profile , would flex proportionately more through the centre, flex has a component of leverage , the lever gets shorter as we get closer to the ends, so if we want consistent flex we need to increase flexibility as we get closer to the ends, so the board has a more even flex throughout…
im wondering how short a board you could go with the horizontal fin conecpt, yet still be functional …
i can see how it would drive …but it would mean a complete different approach…
that approach , i feel could be accomplished with relativly simple body movements…
to cover a wider range of manouvers i reckon conventional side fins would add to the package…
…
hey roy check these pics…
i just learnt how to use the self timer on my camera…
its sunday and im the only one here…
i put a block of foam with 1" increments marked on it so you can see scale…
placed camera on the ground took a snap , then with timer set clicked, ran over and jumped on …the board is 8’ …
ive had 2 people on this board before , it bottoms out on the ground dead flat ,if i trampoline on it , i can get it to almost bottom out , but i couldnt do it for a photo and get timing right,
you can see in this photo with 100 kgs on it it bends about 3 inches , that means if turned over it would bend 3 the other way…
so 100 kgs gets this board to bend over a range of 6 inches under these conditions…
but under g forces out surfing that range could potentially be doubled, add another g and you have 200 kilo load…
ive been twanged out of bottom turns so fast in the past my legs collapsed under my own body weight , coz i couldnt even hold my own weight under extra g’s…
you reckon this type of flex would propel a horizontal fin???
timber , natures spring…
regards
BERT
Hello Bert,
Actually a parallel profile board will not necessarily flex more through the centre because the board is wider in the middle which makes the flex get a bit tighter towards the middle. Your flexible board in the picture is certainly thin, and isn’t that far a way from a parallel profile in terms of the way it will flex. Your tapered profile in this case differs from my boards more in terms of the rail line in the ends, than in terms of flex. I know what you mean about those g forces, the timber will load up a lot of force, and then release it as soon as you relax your legs slightly. Because your legs are relaxing anyway, the twang as the board releases will tend to collapse your legs. If you think that it is rad with just the flex, with a horizontal fin as well, the board will load up more and release faster, only as well as more g’s, you get flung backwards as the board squirts forwards. When this happens on a bottom turn, if you wind up squarely over the foil it is like you have hit a patch of ball bearings, and the water feels hard, like concrete under your feet.
That board in the pics flexes heaps, it will do the deed alright. It is a lot flexier than any board I have right now ( my two favourite flex machines are no longer with me).
By the way the tunnel works very well without a flexy board, but a flexy board is heaps better for it. If the board is rigid your body has to flex more to make it work. With a flexy board like the one you have, with a foil on it you will find that it will leap and twang even with subtle weight changes or if you hit a bump in the wave.
Rergards, Roy
Hi,
Go to search for, enter in “re: KR might know” check out the thread by Murray Bourton, manufacturer of Pipe dreams surfboards.
Mr T
you can see in the pic tho , the board still supports my weight…im 100 kg and its holding me up…
ive stepped onto polyester boards and they just flex easier and snap on the way down…
my boards are actually stiffer , but will bend way further under load before they break…
that stiffness combined with flex is the key to boosting off nothing, getting heaps of squirt out of tight turns , and anything else your body lets you do on a wave…
also timber has the fastest memory of any flexible composite…
try bending a wooden and a plastic ruler over a desk…
which one springs back faster???
that translates to a sensitive board …
also no energy is lost through timber, as an example with some composites , you put 100 grams of force in you get 80 back out …with wood it has the ability to store all the energy you put in and give it back…
that board in the picture is 9 years old and its still in my quiver…
at one stage over a 4 or 5 year period i did that to the board about 4 or 5 times a day , it was the demo i gave every customer interested in a new board…
no other composite would stand that sort of abuse ,its a careful blend of timber , foam , glass and epoxy…using different constuction techniques…
i know some crew will think this is uncool …
but i still make the claim , that these are the worlds lightest strongest boards …the board im standing on is an 8’ mal and it weighs 7.5 lbs or 3.4 kilo…
and it didnt even cost me 12 million to do it…id like to see a blue board stand that sort of punishment…
mr t i tried that search . it kept coming up with your post on this thread…
have fun …
regards
BERT
ps
couldnt resist gettin a shot in …( roy , not you in case your wondering)
Hi Bert, I remember reversing my 2100kg Dodge ambulance over my twelve foot solid balsa. It was sitting deck up and I drove up it like it was a ramp, the only damage was a small section of the pintail which broke off (when the vehicle fell off the tail), and the fibreglass split because the board bent so much. The timber under the glass was fine.
Regards, Roy
Try “Zane Harrison” then check out Murray’s reply
MrT