Some things about Adjustable Flex

General Discussion
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1)You can’t add flex to a board by adding something to the board.  You can only add stiffness to a board.

2)When you add stiffness to a board, the recoil rate becomes faster.  Chances are that your board is not responding to you because your board is already too stiff and the recoil rate is already too fast for the human body  ~5 Hz.  So adding something to your board would actually worsen the problem.

3)The only proper way to have adjustable flex, is to start the board out as too flexible.  Then add something to the board that stiffens it.  That way, the rider can stiffen it until it hits the ideal stiffness/recoil rate.   Hydoflex has kinda this…though quite frankly I’m skeptical how well they have done it.

http://www2.swaylocks.com/forums/hydroflex-supercharger-technology

4)It’s not difficult to add stiffness/ increase the recoil rate.  Try this for $1 per board.

 

Take some heavy fiberglass reinforced adhesive tape, put it on the bottom of your board.  Done.

http://www.csnstores.com/Universal�-UNV16048-ULG1347.html

 

My friend wanted me to build him a super flexy board.  I ended up making it too flexible.  3Hz at 4.5ft.  So I put two pieces of this fiberglass tape on the bottom, and then it oscillated at 3.3Hz at 4.5ft.  (see the link below to understand the numbers).  Still it’s a little too flexible, but it will work well in clean conditions…more predictable waves can be ridden with more flexible boards.  Less predictable waves, you need something like 3.7Hz or 4Hz at 4.5ft to be optimal.

http://www2.swaylocks.com/forums/hard-numbers-flex-demystify-flex-patterns

 

There’s another easy/cheap way to adjust flex, I’ll post it a month or so.

Cheers!

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One piece of tape can hold 600lbs!

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That one kinda tickles the imagination.  For instance, the first thing that comes to mind is that you can move the tape around and use different patterns, like a single piece down the middle with a couple pieces on either side running out to the rails at 45*.   Deck patches and springers.  Parabolics following the shape of the template.  Etc… 

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What aboud shaping Stringerless with more rocker than desired.  Force the rocker flatter with a rocker table/ vaccuum bag.  Apply your tape.

The tape would post tension the board.  Sort of like a coiled spring.  Greater strength, and quicker spring back.  I wonder if anyone else has already thought of this, and is keeping it secret? 

It has been done for decades with structural concrete and post tensioning the rebar.  Nothing new, just a different application.

 

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[quote="$1"]

1)You can't add flex to a board by adding something to the board.  You can only add stiffness to a board.

[/quote]

This is true, which is why I laugh when I see those trendy little ''flex enhancing'' heel and toe patches on the tails of 4oz PU boards.

 

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Yes! this can be done.  However, you can’t put the tape in a curved pattern.  It can only go straight.  You’ll see this when you handle it.

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Yes this could also work for those who know what they are doing.  For people who don’t understand how post tensioning works, they could potentially weaken the board.  You are shifting the neutral axis.  Some people may shift it the wrong way.

I am sure someone has already thought of this.  There’s probably some rediculous patent on it too.

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Hi Ben,

There has been at least one posting here on Swaylock’s by Bert of Sunova showing all his different widths of cloth,  some were pretty narrow. 

Ever notice how an older board doesn’t perform as well as a newer one?  Ever notice what happens to a string instrument that hasn’t been tuned in a while?

They both go slack.

I’m betting that some premium stringerless board makers (not Surftech for sure!) are doing this.  I’ve got my eye on a stringerless build later this summer.  Might just give it a try myself.

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Hi Benjamin,

Just saw this, great fix btw! 10 years ago I worked with a resin inventor (urethane resin called

DHP/AST) and built a board that was way too flexible, it surfed like shit, too dead and like a wet

noodle.  I glassed some 1" carbon tape in an "X" pattern from the fins to the water entry zone,

and viola, it worked really well.

 

So I can vouch for your ingenious taped-on flex adjusters! ha ha.

 

Re: Hydroflex.  I was of the same thought as you, "How can this really work?" but by luck I've been

doing work for a top assym shaper who has started testing Hydroflex on his designs.  Granted, the

hull shape has a lot to do with performance, but from what I gathered, the flex (or a related "feel") is

being affected.  I want to also say they are glassing them with hardly any glass at this point as the

positive pressure seems to reduce crushing of the decks... 

I was reminded of another friend who builds inflatable SUP's and instead of stringers he tied the top

and bottom skins together.  Adding pressure does make a board rigid (but Nat Freq??) as can be

seen here:

http://www.youtube.com/watch?v=ZjUxlfMbdhs  (check at 00:45, turn off the bad music, ha ha)

 

The point is load can be suspended in an inflated structure IF the top/bottom skins are engaged

somehow...   ...well I found out that the skins are just that on the Hydroflex (or at least semi-attached.)

(those clever Germans...ha)

 

They are adding something but not more glass, just more gas, ha ha!

Anyways, guys were being sent out on the shapes at 9 psi, then asked to air them down until they

rode the best.  Most all surfers liked around 3 or 4 psi.  I was amazed at how sensitive to pressure

the changes in feel were:

http://hydrodynamica.blogspot.com/2011/02/more-goofy-asymmetry-from-ekstrom-burch.html

 

This is the goof-foot version I got in my shop right now, I hope to get the regular this week to ride

myself so I can figure out what is changing. (the guys riding the boards mostly had no idea why

the feel changes with pressure, but they all noticed a pretty drastic change)  There is a longer

version of this vid that is also at Rincon and they are changing the pressure, you can see the

difference, the boards go from struggling for speed then start to really accelerate much better

as the ideal pressures were reached.

 

Perhaps there is a combination of things that can make a board "adjustable" in flex (or response?)

This is good stuff, keep it up Benjamin!

George

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Hi George,

regarding hydroflex:

I have no doubt that the boards flex change when pressure is added  (even though I used to doubt it…see why at bottom**).  I am very skeptical that this is the best way to do it and I also doubt that the primary changes that the surfers feel is the flex.

As a first order calculation/demonstration, how much surface area would feet of a 150lb person need to be supported by 9psi? 

150/9= 17 sq inches.   I would guess that the average 150lb person has about 24 sq inches of possible contact foot area.  So at 9psi, you wouldn’t need the entire foot connected to support the load. Contact area is a critical part of surfing, as you told me a year ago, I doubted, then learned months later how right you were.

Cut the pressure in half-4.5psi and you need twice as much surface area to support the load.  Of course that goes beyond the surface area that the foot can provide, so what happens is that the foam below the skin engages and you have regions of foot pressure that are much higher than 4.5psi.  Still! At lower pressures, you get better contact area.

The critical thing to understand is that foot connectivity matters most when you are less-weighted or unweighted on the board.  As you unweight a pressurized board, it pops out to its original shape, and now you have very little contact are.  As you load a balloon with your fingers, the contact area increases.  You can hold the balloon with one hand and do what you want with it.  As you slowly unload your fingers, the contact area decreases, the balloon loosens from your grips, and then it just bounces away.  Now you have no control on the balloon.

This is an exageration of what would happen with a pressurized surfboard.  Contact area will decrease dramatically as you unweight the board.  At these moments, you will have very little control over the surfboard.  So ideally you have permanent foot wells in your board that maintain fairly constant contact area regardless of how much you have weighted your board.

The hull is changing shape, maybe only slightly

Flex is changed.

 

So the problem is that three variables are changing simultaneously.  In no way are they necesarily changing together for the better.  You may need to stiffen the board, and then contact area is at a loss.  Or you may want to increase contact area, but then the board is too flexible.  And who knows how the foil is being affected for better or worse in any of these scenarios…however minute it is.

 

Still that being said I would love to try one these boards, especially if George and Ekstrom are involved!

 

**Originally I doubted the fact that they could change the stiffness of the board.  Then I learned that they are building their boards with .75lb density foam or 1lb.  This is really critical because now foot deflections play a significant role in the stiffness of the board.  This is a second order behaviour in 99% of boards, and doesn’t need to be accounted for.   However, with this unique construction technique, foot deflections need to be considered as first order behaviour in assessing structural properties.

 

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Actually that was the first thing I thought, "Is the board feel they are getting at their feet (micro scale)

or the entire board (macro)?"

I'm reminded of the Disney movie "Son of Flubber" ha ha...

I agree the first order calcs show affected area quite well, am also wondering about riders with boney

feet, high arches, or like Slater, flat feet-  contact patch once again.

 

Another reference frame is the immediacy of water load hitting the bottom of the board and being

sensed by the rider/feet on the other side.  I know that higher pressure internally will give more "ping"

or rigidity (and I don't mean linear bending of the entire board but a direct load path from the centroid

of the "water footprint" at that very moment, to the rider's feet.)

 

Another consideration is the varied fiber orientation that can better distribute a point load, (I'm starting

to see a single, saggy layer of deck glass (ala Hydroflex, but unpressurized,) as not having good

feedback as a multi-layer, multi-directional schedule.)   Am starting to see that as surfing a marshmallow

with a hard bottom = delayed/poor feedback, vs. a semi-delayed feedback vs. a super-rigid structure.  

That spectrum suggests an optimum within the range.  I can imagine a board that is super rigid in this

primary load path as being too quick for the rider to react, so the ride would be unpleasant. 

 

Perhaps a little "give" in the deck will allow the rider to apply their "body english" to the board

more effectively???  (visualizing a rider start to drive down-the-line, doing mini "standing broad

jumps"...   ...a "good" deck would allow that little leap forward to become optimized...)

 

(sorry Benjamin, I'm really trying not to overthink this, but it is quite intriguing...)

 

I'll keep you posted on the assym board tests, I should be able to ride one starting this week. 

You can come by the shop and check the one we got, plus the pumps and gauges etc. 

We are repairing one right now and the foam core looks to be about 1.0 or maybe 1.2 lb/ft3

but very poorly fused (unlike the super-fused all the EPS blankmakers are striving for,

ha ha.)  I noticed the one board we damaged (large finbox tear-out) that when we pumped

the Schrader valve, the gauge would show NO holding pressure (so this particular EPS

breathes quite freely.)  Normally when Carl would pump up a board, a single pump was

a little more than 1 psi, with 9 being the max allowable.  The distance from the valve to

the open ding is almost 4 feet, I was surprised how much and how easily it was equalizing.

 

Talk soon, keep at it, there's more to discover- also fins, their rake and structural tie-in...

George

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Hey George,

So, the pressure of the air sort of blocks the heels from crushing the deck?

That is cool.

Did you ride one of the boards yet?

Wouter

 

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Lovin the post tensioned idea. Wonder if you could do it with a routed channel through the blank and set up a duct and cable with a screw on the tail to actually adjust flex, and maybe even subtle changes in rocker! The mind boggles!

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Truss Rod.

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Hey Ben
For reference could you post your build schedule prior to the fiberglass tape. I have built one that was soft on the flex, hard to sync in weak waves, frontside ok in clean powerful surf, backside was smooth and easy in same surf.

Thanks
CJ

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Hi Wouter!

How have you been?  Yes there is a lot less denting even with a single layer of cloth on the deck.

Max allowable pressure is 9 psi (? kPa, I'm too lazy to convert rt now,) and they surf at 3 or 4 psi.

Seems to me you could store your board at 9 psi or so and dents would level, plus any dings or

water intrusion could be somewhat reversed.

I think Bufo just went back to Germany, he surfs the North Sea like you guys do, just further east

I think...

I'm supposed to see Carl tomorrow I think, he is supposed to have the Regular Foot 5'8" he shaped.

Then I just need waves, ha ha...

George