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Thread: Flex

  1. #1
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    Flex

    Flex seems like one of those mysterious, psuedo-surf terms that isn't really measurable. I've experienced it in a couple different boards but someone said best on here that you feel it the most when it's not there.

    With that said, where do you feel the most flex on the board and where/how does it affect you on the wave?

  2. #2
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    I have been surfing for 40 years, and this still has me stumped. LICrew wrote an earlier post about how the board will harmonize with the wave on a vibrational level if surfed properly. For me, I can feel the flex in different fins and how this affects the board a lot more than the flex of the board itself. I have been riding old boards the last few years, except for the fish I made, and it was glassed with epoxy, so it doesn't have much flex but it still rides great for the waves I designed it for. It could be faster if it flexed more when I pump it down the line for more speed, but it is pretty darn fast as it is. I am going old school fiberglass on the hplb that was just shaped, so I can feel and play with the flex on some juicy waves on the big board. Good question bro!

  3. #3
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    Seriously though, Roy probably knows a thing or two about it.

    I feel it most when I bounce off the foam on a lip, when coming out of a real tight, but fast turn when you're right past the apex or anytime I land an air. It becomes most noticeable to me then. I only notice it on longboards when I put the board through a lot of stress, like pulling a floater on my 9'2". Last time I did that it wasn't planned, I was just surfing closed out beach break. The board almost seemed to buckle and when I got out of the water, it had actually delammed from the stress. Too much flex.

  4. #4
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    Oh yeah, one more thing.
    I have never felt what I perceive as "flex" more than on this board, bash a lip and it really does feel like it loads up and then releases energy. More so than the original Coils and definitely more than any of my poly/wood stringer boards. Could be all in my head:

  5. #5
    Flex is a very important part of surfboard performance but as you say, ClemsonSurf, it is not measurable.
    I've been playing with flex for years building a surfing boards with laminated bamboo stingers, carbon fiber stringers, stringerless, parabolics, flex tails, variable glassing layups and laps, strategically laminated areas with different flex modulus epoxy resins, even built and embedded a stinger with adjustable compression spring in the board...
    There are 2 main things I learned through all the experiments.
    1. You don't want a board that is stiff with no flex (most pop-out contructions)
    2. You don't want a board with too much flex and loose like a noodle. It plows water when flexed and bogs the board down.
    Flex should be gradual and evenly distributed along the length of the board to fit the curve of the wave at various angles. It should also serve as a "rebounding mechanism" and load up with potential energy when flexed and transferred into kinetic energy when released - providing a little "pop" out of our turns.
    Wood is a great material for natural flex patterns but most wood centerline stringers have knots in them which mess with the continuous flex, also providing a weak point in the board. Wood stringers are best as parabolic where they can twist and bend, providing a nice torsional flex, bending to the wave...
    I could go on an on but I have to go.
    ~Brian
    www.greenlightsurfsupply.com
    Shape Your Surfing Experience

  6. #6
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    Quote Originally Posted by ClemsonSurf View Post
    someone said best on here that you feel it the most when it's not there.
    definitely something that's probably unquantifiable. the quote above really sums up how i got on to the concept of flex in boards. i had a pair of hand shaped eps/epoxy boards a few years back that just felt "dead" under my feet, one was a copy of a pu/pe board that was magic for me; there was no "pop" out of turns in either of those boards, while the pu/pe seemed to almost go where i wanted it to w/out conscious thought. when discussing this sensation w/ some more knowledgeable friends, i concluded that what i was missing was the flex of the board. i've been gun-shy of boards w/ eps cores since.
    flex is something that's undeniably important in a good board, but it's hard to really explain how or why (at least for me).

  7. #7
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    This is a super complex and difficult topic to discuss… and one that everyone is not necessarily in agreement on. Like bottom contours, most of the “evidence” is anecdotal, and not empirical, so in that absence of data we can only try to apply theories to fill in the blanks. Here are a few theories I put a lot of confidence in:

    A board’s flex is determined by a combination of design elements and materials. To dial in flex, you have to have both variables in mind. For example, things like concaves, channels, and domed decks stiffen a board. Flat bottoms and flat decks increase flex.

    Thickness and foil effect flex. Thicker boards, and boxier rails, stiffen a board. Thinner boards and thinner rails allow more flex. The nose-to-tail foil of a board… the tapering at the ends (or lack of it)… determines to a large degree a board’s flex pattern.

    Flex is less important than “flex return”… the ability of a board to spring back to it’s original form when the load is released. Paper is very flexible, but has no flex return.

    All boards have a frequency… a vibrational flex/return pattern… that the rider needs to use in order to get the most performance out of a board. Materials, design, and the construction methods used to build the board alter a board’s frequency.

    None of this is my own theory. All of it comes from somewhere else, applied to surfboards. There’s TONS more to it, but these are some of the basic principles I use to achieve a desired result. Where do I feel flex the most? When pumping, in the pocket or tube, and on bottom turns (actually any hard turn). Shorter, thicker boards, like fish, don't create much leverage, so I don't feel much flex on them. Same thing with big, heavy, three stick logs... very little flex on my boards, and I don't need it there. But on a hplb or hpsb, I do like a degree of flex, and design my boards as such.
    Last edited by LBCrew; Apr 7, 2014 at 05:41 PM.

  8. #8
    you want to learn about flex, ride a soft top in some sizeable surf. Cranking off the tail you can actually see and feel the front half whipping all around. Insane.

  9. #9
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    Quote Originally Posted by zaGaffer View Post


    Seriously though, Roy probably knows a thing or two about it.

    I feel it most when I bounce off the foam on a lip, when coming out of a real tight, but fast turn when you're right past the apex or anytime I land an air. It becomes most noticeable to me then. I only notice it on longboards when I put the board through a lot of stress, like pulling a floater on my 9'2". Last time I did that it wasn't planned, I was just surfing closed out beach break. The board almost seemed to buckle and when I got out of the water, it had actually delammed from the stress. Too much flex.
    I will summon him.

    Roy Stuart or Roy Stewart (I spun around 3 times in front of the mirror in the dark while typing this.)

    I notice it more on a LB when I'm doing something wrong and have noticed it on a SB like you said at the bottom of a turn when you get that burst of speed you were talking about.

    Flex should be gradual and evenly distributed along the length of the board to fit the curve of the wave at various angles. It should also serve as a "rebounding mechanism" and load up with potential energy when flexed and transferred into kinetic energy when released - providing a little "pop" out of our turns.
    So are we talking flex like a diving board, a twisted spring or a combination of the two? I can see it two ways, sort of a torsional flex along the stringer like a twisted spring being flexed at the fins. I assume that small rebound could give the je ne sais quoi that we're talking about on a steep wave. On a fatter board I think you experience the diving board flex. Both examples seem to be at the tail 3rd of the board rather than the whole length of the board.

  10. #10
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    Imagine a full rail turn... depending upon where your feet are and how your weight is distributed, the foiled ends of the board will cause it to flex like a bow, with the ends flexing most. With one foot over the fins, and the other about 2/3 up the board, both on the stringer, means the noseward 1/3 will be flexing the most, because your feet are the fulcrum, with the area between your feet flattening. It's the flex and rocker outside of your stance that determines the radius of your turn.