It struck me that an EPS board should not be that much more likely to break with the same lamination schedule as a poly board. Yet it is reported that the extra lams are clearly needed. But then it occurred to me that less weight and the resulting increase in bouncy would interact with the fall of a wave with exponential increases in force-- not linier: physics rather than simple math. An EPS board would not be experiencing just a 20% increase in energy as it may be 20% lighter – but may be many times that force. Notice this equation for the energy of a wave. 
Crunching these numbers is a little out of my league, but if we have some Caltech types that could come up with something, it would be interesting. I am thinking that EPS boards, particularly long boards may need to be even lower volume than we are making them currently to compensate for bouncy and the corresponding higher results of energy in wave impacts. We are in the hunt, but maybe chasing the wrong rabbit?
Too much time on our hands , not enough surf , right ?
but …
isn’t it WINTER where you are ?
when’s the next swell due mate ?
cheers !
ben
…my solution, however, is… I’ve made a mal ?! [“longboard”]
Shine,
Has someone done the simple test by taking two pieces of foam? One is EPS #2 and one is PU Ultra Lite. Make them both 2" X 4" X 12" shape. Snap both of them and see which one gives first. Dose one flex more then the other as it goes in to buckled state before it snaps. Does one flex less and then snaps cleanly. Things that have more flex will need certain conditions for them to snap because the flex and return to shape. Rigid things will snap once the force is reached. From my little knowledge of the materials with the exception of the last month of shaping two boards. I fell the independent beads that make up EPS have fracture points built in to the foam. PU foam is one complete material from the start to finish. Again I am not an expert or do I have enough experience to know what I am talking about. I am only putting in my 49 years of life experience and working with other materials outside of the surfboard industry.
Timmmyyy
The foam has little to do with the board’s snapping strength.
There’s a great little article in the book Essential Surfing that was taken from a Grubby newsletter. In a single stringer surfboard, snapping strength is a function of
-
stringer thickness
-
adhesion of glass to stringer (which is linearly related to stringer width)
The same things apply with foam/glass EPS boards, although it gets a little more complicated with sandwich boards or perimeter stringer boards.
The use of more glass typically gives the board more weight and more resistance to dent dings. The best way to make a board more snap-proof is to make the stringer thicker.
What Gordon said was, even thickening up the stringer on thin boards won’t prevent breakage, the real strength factor was, thicker boards
May explain why my 1.75" stringerless broke! Ha! tO
Lets just put ultra-lite steel stringers in the boards
Blackstah
I read the article in “Essential Surfing” with the explanation of the breaking points of various lay-ups with the stringer. The I beam being the best. I know the foam has no strength by its self. It is the encasement of this foam by the laminate layer that gives the board its strength. Most boards are built with flex in mind. PU foams flex a lot before they are laminated and continue to do so as required by some surfers. I feel the EPS boards do not have the same flex and will break/fracture along the bonds between the beads. In fact the other night a friend of mine put two pieces of foam in some red colored water to see what the absorption was. One was EPS#2. The other was Clark Ultra Lite. What struck me besides the EPS absorbing the water to the mid point on a 1 X 1-1/2" X 2 after 24 hours. The Clark foam didn’t absorb more then a 1/4". He snapped the EPS between his two hands. He had top cut the Clark foam with a knife after trying to snap it with his hands. The test in the Essential Surfing was only done on PU foams if I am correct. I wonder if the same test were done on EPS, how would it turn out. I still feel the boards are as strong as all of its parts and the persons ability to put them together right. Just my point of view though it may be wrong.
Timmmyyy
Did he weigh them before and after? Penetration to a certain level around the beads for eps, saturation to a certain point with the poly? Just wondering, we did something similar.
AKA,
He did weigh them on a previous time over night. I will get the details tonight and post it.
Timmmyyy
This has all been gone over before(archives…) a poly blank glassed with poly resin is more prone to breakage than a similarly glassed EPS epoxy. You only need extra glass if it is stringerless.Otherwise the epoxy board is stronger,lighter, has better flex and return…I am just a garage grunt but the info is in the archives…check it out…have fun…
Clark had done assorbtion tests, with his poly foam having less than 1/2 of one percent assorbtion in 30 days of being submerged.
With the bead foam, fusion of the beads makes a big difference, flotation block doesn’t seem to take in much water, while some foam is so pourous that the suction of the shaping machine can’t hold them down I also think that a sealed board is affected by atmospheric pressures, with it being placed into water, causing the air inside to contract, thusly making it want to inhale if punctured. I would like to get some gills that would be left open until ready for a surf, closed, then opened when finished to stabilize the inside pressure ? Hey what do I know, I’m winging it too
I would like to get some gills that would be left open until ready for a surf, closed, then opened when finished to stabilize the inside pressure?
What about Goretex vents? Anyone tried one? Are they really waterproof? How big would the Goretex have to be, to be effective for a short board?
It sure would be nice not to have to worry about opening and closing vents.
AKA,
I think the best way to see what happens is to cut two blocks of foam up. Weigh them and put them both in the same water with color dye in them. If you can put three or four of each type in at the same time you can break or cut one pair open every couple of hours. You will need a good digital scale to do the weighing of the foam before and after each time interval. The other choice is to read the archives and believe what you read there. I feel the test will tell you more about the absorption rate then the archives. My friends test showed the water wicked up around the beads. Buy a Easter egg coloring kit and test it out. We always have scrap foam around when we shape boards. Good luck.
Timmmyyy
Gents… read the archives. This has been beat to death. But it’s late and I’ve nothing else to do…
Foam does not directly contribute to bending resistance, it DOES matter for shear transfer.
Y’all should realize that the initial failure in a breaking board is a shear failure - where a “buckle” line shows up across the board ON THE COMPRESSION SIDE. This is where the bond between the foam and glass has failed IN SHEAR. That’s right… in shear. Not in tension or compression. I seem to recall Grubby mentioned this once, and sadly I’ve seen it on one or two of my own. Once again: the initial failure is in shear, on the compression side.
Once you lose the bond between foam and glass, and there’s a buckle line, that cross section is basically a hinge - it has very little further resistance to bending, and the board is gone.
As for the stringer, it will stiffen the board, but since we’re mostly using quite thin stringers, the bond between the glass and stringer is limited to a very narrow strip. The stringer is in the most efficient place, the thickest part of the board, which is good. What is bad is that it’s so narrow.
Basic mechanics of materials (CE 370 at University of Hawaii) tells us, should we listen, that the bending strength goes up as the third power of thickness. So a board twice as thick will be eight times as resistant to bending.
The problem with EPS is that (as Bert Burger has said) it’s lousy for shear transfer. Haven’t done EPS yet myself, but I suggest this lack of shear transfer capability is why EPS boards can require additional layers of glass.
Well, hope this lights a match, or better, in someone’s cranium.