we were on a post on s glass and the shear question came up in regards to surftechs…i didnt have time to reply but i did agree with you …
basically for a board to snap you obviously get shear …i think the surftechs dont tolerate as much shear ,the first place to fail is the rail join…
its my opinion that a board with more flex is less likely to snap,the board needs to tolerate bending so it can absorb impact …but at the same time you dont want a floppy board with no spring and drive …the old stringerless boards wernt that weak, they just didnt ride as well as a stringered version…because of response time from the timber…
because i use parabolic stringers the board can bend along way but still spring back and has good stiffness when not under extreme load…
have you ever got a stringer and bent it to mimick the load of snapping it wants to buckle side ways, its stiffer then suddenly fails and starts a chain reaction…
the stringers in my boards are about 1/2" thick (on each rail)and roughly 1 1/4 deep
a normal stringer would be 1/8 to 1/2 and 3" deep
given the same load and degree of bending it has to fail earlier…
interested to hear your thoughts …or anyone else who wants to comment…
I agree with your assessment on the flex issue. In sailboards we found that wrapping the rails with the core material (as Surftech does) made the board break worse because it focused the entire load (shear) on the seam. When we brought the core to the bottom edge and inlayed the deck, it allowed force to be distributed over the entire rail. Later we used biaxial cloth to re-enforce the rail which helped even more. In fact I think I put myself out of business in sailboards because nothing could happen to them. 15 years later those things are still floating around out there. This was also a theory of Gary Efferding’s. Also in Hawaii at that time the board builders there started using twist weave cloth on polyester sailboards to give the boards a bit more flex, which helped with breakage.
By the way, since your appearance here I have been experimenting again with parabolic stringers. I’m getting great feedback. I’ve never used them in surfboards, only in sailboards and cored inside the stringers building what amounts to a torsion box with rails.
Am I understanding right that your stringers are inlayed and don’t go all the way through the blank and are you coring both the deck and bottom. This would be very close to those sailboards we built years ago. The possibilities of what could be done using this type of technology is pretty far reaching in terms of controlling flex patterns and buoyancy characteristics within the blank itself. The materials available for deck and bottom re-enforcment are much broader than 15 years ago and epoxies with different flex patterns make the applications broader still.
Also I remember reading in the Aussie mags years ago about timber decks. Was that you? We made a number of them at Ocean Ave. and were quite pleased with the outcome. Unfortunately, the market at the time was completely price driven and we stopped making them. I see things as different now.
Well Greg, I managed to snap my white board in Hawaii, it took 10 foot Sunset to do it, but it was a learning curve even from that. The resin bonded so well with the 1.25 beaded foam that the break was clean, with no cloth ripped off the top or bottom. The bottom did have a secondary snap about 3 inches away from the break, with a inward buckle leading from the secondary snap. On one small day as I was bellying in across the inside from Val’s to the drain pipe, I could feel an incredible amount of deflection that one would not feel while standing, it felt like about 4" of flexing. The two stringers showed a slight sideways deflection that occurred during the breakage, but minimal.
Otherwise, I am already working on my next one, thanks for all your hard work and help. Jim Phillips
yea the timber decks were the precursors they started in 87 and opened the door …it was pretty much me and cutloose who did them ,cutloose did way more advertising so it was probably theres that you saw…i actually reckon theres looked better than mine i dono who did there inlays but the guy was a talented craftsmen…o yea i forgot i was doing a run of norwest guns and we ran a couple of full page adds in surfing mag i think? they looked pretty kool with aboriginal style graffix where the timber finished on the rail…under the label wild…
as for my stringers basically as they got closer and closer to the rail the board went better and lasted longer …to the point now the whole rail is solid wood …
it does alot …gives the board structual integrity lengthways…allows it to flex further before breaking …gives brilliant side impact resistance…and stops your rail line from flexing off so you get sick drive out of turns…there are more benifits as well but they depend on what other contruction technique you combine them with…
So Bert, it was you who made Wild. I often wondered, as I used Wild as well, because it’s my name. However I was never a private entity, I always worked for others, mainly down Phillip Island, where I originally met Paul Donda. Greg.
yea originally it was george huttons label in the early eighties …we linked up in 89 and all his boards came through my factory ,we handled all his glassing and timber decks…eventually in about 94 i brought the label off him and all his production equipment and templates …i was trying to run about 4 labels side by side …different styles of boards under different labels …(not including the different contract labels which came through),i had mel redman running wild on her shortys from 95 to 98 on the ct ,after a while i couldnt see the point with all the different labels ,from a printing and advertizing perspective it wasnt cost effective …so i let them drift…
Bert, you say you are making wood rails? Are you using balsa? how much of the rail are you making out of wood? Are you making long boards or short boards like this? One more are these styrofoam boards? TK for any information you can give. You have caused me to rethink my supper blue/ light glass /epoxy board. Now I’m trying to work out a EPS longboard. Balsa rails sounds like a good ticket.
Yes, it was Wild Surfboards I saw. I can see how running the stringer on the rail would give you better performance especially in better surf. One of the things we’ve found is that in small waves we preferred to have the boards centrally weighted so they would plane quicker and all the weight under your feet made it more lively. As waves get better, bigger, more powerful, we tend to begin to like the weighting to be more around the perimeter. This offers more drive and momentum. At the very beginnings of the epoxy era, 20 years ago, Rusty once said to me of epoxy /polystyrene boards, they ride so good in small surf it’s scary. At the time we didn’t know it but this had to do with the boards being more centrally weighted. I feel that this realization, along with a better understanding of controlled flex, is key to the next generation of performance boards. In a recent interview Tom Curren stated that the future surfboard will go after and be more responsive. Controlled flex and weight distribution will undoubtedly be part of that equation.
its funny you should make those comments …coz i found in my early eps boards they felt ugly in bigger surf ,its almost like the flex was outa sync with the timing of your turns…but the small wave performance was bullistic…which made me realise it was something worth chasing…
ive basically got em to work real well in up to solid 10 foot ,they will take 15 if its clean ,but once it starts pushing 15 to 20 i dont have the confidence to take out an epoxy eps …i had this magic p/u 9’-9" for years full gun like 10" tail…anyway i made a few similar eps guns but couldnt get a decent one ,so i ended up copying this old favourite to the last mm ,
it felt almost indentical in 8 foot ( just gettin a feel for it) when i rode it in 15 ft it felt every bump and chop ,even tho i glassed it real heavy coz i thought it was a weight issue with chop…now im actually thinking its a flex thing ,a standard p/u board has a real dead flex and is not as lively ,so i reckon in big stuff ,its kinda acting like a shock absorber ,coz its not transfering the energy as efficiently…
but its exactly that which makes p/u feel lifeless in small waves…but the epoxy eps transfers energy so well ,its like you raise an eyebrow and the board responds …you can feel every ripple under your feet…
…i ended up selling the 9’-9" …some days you role up and its 20 ft and scary …most crew are standing around saying " id go out if i had a bigger board ,whats your excuse bert"…
these days if i cant paddle in on a 9’-2" its to big…
That’s exactly the same conclusion I’ve found in the windsurfing industry.
Epoxy styro is best in light load applications, but when it matters, poly glass with wood stringers seem to match the flex of human bone and is more comfortable and predictable.
Funny…my board #2 in 1968 was a 9’6"x19 with a 9" pintail, and originally about 3.5" thick, thinned to 2.75 after I found it works only in 14’+ (I can barely handle paddling out that size). So thinner, it worked like a hot dogger in 10’ surf, flexing more, more feel, snappier and lighter of course.
I see lots of Mav’s guns of that size at 18lbs., 3.35" thick, wider of course, and foiled lots.
more on your comment about flex …im claiming rail stringers on eps give the board more range and get it into the 10 ft range …but still go off in small stuff…
Greg have you ever thought about a principal to do with the neutral axis???
its basically where when something is flexing theres a particular point where nothing happens ,no shear no twist no flex…usually around the centre.
im not saying this as fact .but a theory still in process ,the stringer down the middle of a conventional board gives a focal point to the neutral axis…
where as the parabolic stringers on eps mean the whole board can twist and flex and the neutral axis moves with you so you can control a greater variety of moves from different parts of the board depending on where your weight is…
i was also gonna post about energy transfer through different mediums and the sensitivity or lack of it of different foams but with that last comment about the axis ,something will get missed .so i will leave it on one subject…
Hi Greg, are you saying that a sandwich board fails at the bond between the outer and inner foam when the board is bent/stressed? Does this occure with or without a stringer? Does the outer high density foam help with ding resistance? Is it possible to make a lighter board by this method while maintaining the same strength?
Sorry bout all the questions, pondering buildin a sandwich board since a friend bought a vacuum pump. Looking to build a lighter smallwave board that can take some punishment. Not worried about the thing breaking in half, not a big chance of that kind of surf here. Just not sure if it’s worth the effort.
the basic discussion in place here is ,on a sandwich board without a stringer down the middle there is way more shear movement as the deck and bottom slide past each other as the board is bent …but putting a stringer in them joins the bottom to the deck via the stringer ,so its resists the shear forces but becomes stiffer and unable to deal with heavy sudden loads in the sense that it wont bend as far without failing somewhere…whereas without a stringer it can bend alot further thus helping to absorb sudden impact…
ill give you some figures haavard ,before i started riding only sandwich boards i snapped 27 boards in 10 years and went through on average 4 boards a year ,the lightest board i could make myself, (needing a bigger board coz of my size ,)was 3.2 kilo or 7 pounds…
now for last ten years ive ridden exclusively sandwich boards and nothing else ,ive snapped 3 in the last ten years 2 longboards and 1 shorty ,my current shorty has lasted me 5 years and still not a dent in the bottom(in that same time i woulda gone through 20 poly’s)and it weighs 2.3 kilo which is 5 pounds
so with sandwich contruction you can get a board stronger than the heaviest glassed board ,but still be 30% lighter than even what the pros are riding in disposable polyesters …
could you go into a little more detail how you build your boards? Are they are ‘stringerless’ in the normal sense, with highdensity foam on the deck and bottom and balsa rails? How do you attatch/shape the rails?
i actually use balsa all over ,in the sense that i use the balsa as the sandwich material,but you can use heaps of different stuff for the sandwich…
probably while your getting clued in with vac bagging a pvc will be fine ,its alot simpler …how i attach the rails is one of those trade secrets ,but im sure anyone with a little intelect would figure it out…
i would suggest starting with pvc rails its way easier to bend…
ultimatly i use wood all over coz it peforms better ,but its definatly harder to work with ,in the sense of consistency coz every peice varies a bit in density and weight ,
rather than trying to bend 3 mm pvc around the rail ,its easier to do it on the flats and use a 12mm piece against a square rail ,then shape your rail into the pvc,it ends up giving a stronger rail with more insulation against dings…
regards
BERT
ps if you really wanna save some weight ,use a wet out table …
dont glass onto the pvc or the eps ,they both drink resin ,using a wet out table means you can wet your cloth then take it to the job and stick things together…
I think I got a good picture of what I need to do. Do you have any suggestion for layup for a shortboard with pvc sandwich? What kind of density would you use for the PVC/EPS?
the basic discussion in place here is ,on a sandwich board without a stringer down the middle there is way more shear movement as the deck and bottom slide past each other as the board is bent ..but putting a stringer in them joins the bottom to the deck via the stringer ,so its resists the shear forces but becomes stiffer and unable to deal with heavy sudden loads in the sense that it wont bend as far without failing somewhere...whereas without a stringer it can bend alot further thus helping to absorb sudden impact....
In the composites world, we would never put a single stringer in a sandwich construction, unless we wanted torsion twisting. It would be great if they would twist in the right direction, but they don’t, they twist away from the wave. Stringerless boards give a non-twisting flex.
If you don’t want your board to flex at all, then it makes sense to use stringers. But you have to use more than one. Other options to reduce flex are thicker cores or stiffer skins…either thicker or stiffer materials like carbon fiber.
Like Bert said, boards with a stringer will break first because of the twisting putting all the pressure on the 1/4" thick stringer. Whereas with a stringerless board the pressure is on the whole board equally.