IMHO the stringers is there to stiffen up the board, but more importantly, to prevent buckling.
regards,
Håvard
IMHO we can both be right sometimes.
Shortboards of suitable thickness in waves of consequence can and do snap more easily without stringers.
The stringer will distribute the load fore and aft. If you land a drop on one foot, with no stringer the force is all absorbed closely around the foot. The glass pushes into the much softer foam which distributes it only a little by the time it reaches the bottom glass.
In the classic I-beam theory, we say the stringer resists shear between the upper and lower glass layers. By resisting shear, the compressive and tensile loads on the top and bottom layer are spread over a much longer distance, which reduces the strain. These are not small effects, make a standard shortboard only 2 inches thick, glass it however you like, and test snappage strength with and without stringer. Or just make test samples and try it out (this was in an old Grubby newsletter).
The interesting thing is that failure strength (of a new board) does not increase much with increases in glassing schedule. It snaps when the glass delams off the stringer, which breaks the I-beam effect. On used boards thicker glass is stronger because it flexes less with each wave, and thus ages better (lower strain cycles).
Perimeter stringers are a nice solution because snappage starts at the rail and works its way in to the stringer. If you stop it at the rail with a stringer, you save the whole board…
I make stringerless shortboards and I surf some pretty heavy waves on 'em. I agree that given two otherwise identical boards one with a stringer would take more force to snap. I think that’s fairly intuitive. But I also agree with GregTate that for shortboards you really don’t “need” a stringer. There are other ways to make a board resist snapping. EPS/epoxy materials are so light that you can really load up on the glass schedule and rail laps if you want and still be lighter than a similarly shaped PU/PE board with a stringer. And as you said, most broken boards are caused by delam. The best way I know to delay delam is to put more glass on the deck, not increase the size of the stringer.
Greg,
Do you think that the eps that Rusty refers to is a leap ahead of the 2# we are getting from Carpenter? I’m on my third 144 cu/ft block. Did have one board that buckled after being ran over by a car, but it was repairable. Dings (rare) do not seem to suck any more water than pu.
Take care,
Dave_D
…or increase the dent resistance of the soft core beneath skin…which is one of the big reasons I like EPS better than PU… a core material that resists denting takes longer to delam, and prolongs board life… And, speaking of design changes, a uniform foam is naturally more dent resistant than something with a softer inner material and an outer “crust”…
Hey Dave (cool name),
There are a couple mfgs of surfboard specific eps foam (Marko and White Hot). The main benefit is the packing and fusion of the beads. Improvements in these two areas make the foam stronger and more water resistant.
Here’s what Stewart has to say:
http://www.stewartsurfboards.com/whats_new_pages/whats_new.html
Im finishing a Marko cored project as we speak.
Craftee, I’ve wondered about the diff between insul. EPS and Marko–
can you take a pic of your blank close-up?
I would like to weigh the merits of each–my (p)lanks cost $30 and I can cut my own rockers, and I think maybe I could get heavier than 2# but I’ll have to see (and see what it looks like)
Thanks
Great thread
Nothing wrong with regular eps foam. Its just that the new stuff is an sig improvement. Generally speaking, if you are the type that buckles and breaks boards often, then you would benefit from the improved foams. If you dont, then regular is fine.
Everyone has there preferences. Some what to build boards cheap, some want convenience. I prefer to buy good materials and save on my own labor. Really, whats $40 when your gonna ride it long term? OTOH, if your a board building junkie most want cheap materials so they can satisfy their addiction without breaking the bank.
Your decision.
ps - when you look at the Marko beads closely, they are irregular shaped…adjacent beads “squash” each other flat. There’s no air gap between the beads. Regular foam has round beads and has air gaps. Simple.
Marko is a pour “molded” blank just like the PU’s
meaning the mix is poured into an expensive steel mold and expanded under pressure.
They also can adjust the air/water and temperature as well and the mix formula around the mold to create different density effects within the same blank. That’s why the beads are more tightly compacted and why it’s taken a while to get various sizes.
The steel molds are quite expensive.
It’s a way different technique and result than a factory cutting small blocks out of a master big block to sell to shapers. The blocks being bought today are just small chucks of the big pour so the quality can vary quite a bit depending on what happening in the big pour where the smaller block is cut from.
In my opinion molded EPS blanks are the future especially molded blanks using MDI like homegrown.
Richard L’s foam might be another pathway down the road as well but everyone will need to get the manufacturing costs down in order to match the other not as good options without going out of business.
Hm. Thanks guys.
Oneula and I played with several of Marko’s original blanks a couple of years ago. Last year we went to the local distributor and saw new stuff that they were working on. It had smaller, tighter beads, and a variety of densities. We also saw finished boards made for Andy Irons that were feather light. These blanks can be machined if you slow down the router speed.
This is the way to go if you want good EPS blanks. If you just want the cheapest thing, buying the big blocks and cutting blanks yourself is hard to beat. If you are buying blanks cut from big blocks, you may be better off with the molded blanks.
My total infantile experience in construction of boards amounts to a whopping 3 years, all of which is in Kiteboards. So if I sound like I don’t know what I’m talking about then it’s because I don’t, but I’ve found that I’m a good guesser.
Non-the-less I’m a firm believer in the theory that “if it is going to break then it’s going to break”. When your dealing with the power of a wave and the shape and size of surfboard if the board gets into a bad position then it will break. Yes a comparison of epoxy to polyester and stringer thickness to other materials can make a difference but I feel that it is negligible.
So for me it boils down to producing a board that lasts for a reasonable amount of time, paddles well and has good riding characteristics. To try and concentrate on making the board indestructible is getting away from the original intent of actually shaping the board in the first place.
In kiteboard construction you don’t need to paddle the board and you don’t need to pump the board to make speed so you can concentrate on more important characteristics like flex. Right now in the Kiteboard market the current emphasis is flex, not just flexi but just the right amount.
After using materials like Kevlar, Carbon, Corecell, biax glass, etc. these past years I can’t wait to give some of these materials a go on something different. The EPS makes this a reality for me. My angle is that you now have a lighter core material for the paddling that allows for stronger possibly better performing skin layup. The perimeter stringer blanks are even more intriguing. Now if I want to add a sheet of Corecell to the deck I won’t have to screw around with the stringer, won’t have to wrap the rails. From a performance standpoint the in line center stringer never really seemed like a great idea, just a convenient one. Looks like Marko will be offering these blanks sooner than later. I can’t wait to get my hands on one.
Now if I can get them to make a variable density blank then that would be really cool. Maybe 1lb bottoms with 4 lb decks.
go with segway composites, they already have parabolic stringer blanks in production. they are really nice to, i have shaped one.
Quote:
Now if I can get them to make a variable density blank then that would be really cool. Maybe 1lb bottoms with 4 lb decks.</blockquote></div>Wonder if that would work. Stringerless, with some kind of glass/adhesive layer in a dual density foam sandwich?
Too me it makes sense. Lighter density on the bottom to allow flexion and the higher density on the deck to resist compression.
How’s this, one of the snow board co’s are inserting some kind of anti-vibration dampener into the sandwich of the board. The material is made out of rubber to dampen the chatter yet still allow for controlled flex.
I know this is getting off track but too much coffee makes my mind wander.
snowboards arn’t very thick they are really thin like a blade a surfboards squishy foam core would act much like the rubber dampener when you think about it. snowboard and surfboard are like oranges and skis
You know what you are probably completely correct. I warned you I had too much coffee.
Quote:
How’s this, one of the snow board co’s are inserting some kind of anti-vibration dampener into the sandwich of the board. The material is made out of rubber to dampen the chatter yet still allow for controlled flex.
Some, like www.donek.com are argueing that you need less dampening than many others are using as it deadens/cushions the ride too much. The vibration occures due to the high speed and unsmooth surface and partly because the flex and sidecut are not working in unison ie. the sidecut want to make one turning radius while the flex wants another one. You can see this with surfboard too, watch a few shortboard surf vid in slow motion and see how much the boards bounce around even in perfectly clean surf(I’m surprised the surfers stay on their feet, but these are pros after all). I’m wild guessing that the rocker want to turn in one radius while the fins want to turn in another radius.
regards,
Håvard
there was a wave of slater and it is oiled glass and his board has speed wobbles. I am trying to remember the video. And remember if you dampen the feel of a board, you will create a limp noodle that doesn’t respond to the finest of touches.