Dud, sorry bout the sweden thing I ment Norway, dam!
Lexan, great stuff, maybe have GM build some like the car door panels (saturns), then when we go to resale them they still look good but the value is gone.
The original fin box fins were made of this, as the bases.
Grew up surfing beach break closeouts in sand, and loved the rock reefs of san diego sunset cliffs to trestles, now hawaiian reefs and these are the meanest for hamburger on the feet let alone the board dings/broken noses kooks etc…
Lexan. I had a Saturn, managed to ding the door panels fairly well. Traded it for a vehicle made from real, thick steel. Heavy but hardy. Motto: I can ding any board for $39.95.
Strong skin, weak core…must mean strength in the skin, so ding resistant, eh?
Moderate skin, moderate core…must mean it dings easier, but since the whole structure is semi even in strength, might be stronger against breakage…
Weak skin, strong core…eminently dentable, soft riding and mushy feeling, will look like cancer after a while, but good for slow response and ease when it hits you…
I’ve been thinking about it and I’m not sure I’m buying it. For the sake of argument, if you glassed steel with a thin layer of glass(2oz) would this glass shatter easier if you hit it with a hammer then say a 3x4oz layer of glass over EPS or conventional PU foam? Doesn’t help anyway untill we put it into context with weight so we get a strength to weight ratio. However, if you keep a constant weight it would be interesting to see a foam weight to glass weight curve for strength. regards, Håvard
Have another read of my post above. You really need to get to grips with the term “strength”. Engineers often refer to a term called “failure mode”, all this means is how does the object break or what is the weak point? The idea is then to choose the best material or combination to prevent failure.
There are so many material properties that can be classed as strength. For example lets take two non-surfboard materials, stainless steel A and stainless steel B. A is a stronger material than B in most respects except that the amount it stretches before it breaks is very small, say 5%, B can stretch 15%.
Now we make a nut and bolt out of these materials, identical in size. The bolt made from A might break under a one off load of 10 tonnes, while B might break at 6 tonnes. But our bolt is going to be loaded on and off repeatedly to just 5 tonnes. We now find that bolt A can be loaded one million times before it breaks, and bolt B five million times.
it’s interesting that you bring this up. I’m fully aware that there are several kind of strength, however I do believe that a generalization is in order, especially regarding the the topic of this thread. As far as I see it, there are mainly to kind of ‘strengths’ for a surfboard, impact strength and ‘breakage’ stregth(forgive me for possibly not using the correct terms, but English is not my primary language). IMHO if we increase impact strength with the construction we are using we are likely to also increase breaking strength and to some extent visa versa. Sure, there are exceptions to this rule, like increasing the thickness of the board and width of the stringer which affects breaking strength only. Other then that all kinds of stregths are largely interconnected and depend on each another. But I digress…
The (simlified) formula for breaking strength/stiffness seem to be generally well know. What I would like to know is if there is a mathematical formula for impact strength of a sandwish panel(guessing it depends largly by the flextural properties of the materials used and the thickness?). Surely someone must know?
That’s why composites is such a black art, or could I say, it’s in a very grey area when it comes to perfectly reproducable test results.
Similar test results will prevail if the manufacturing situation is fully controlled. But the experience of the hands makes a big difference in the end product.
Vacuuming levels the playing feild a bit, but not fully. Again, personal techniques used with exactly the same materials will still get different results.
Yeah, that’s why I hit the same coral head at the same tide in the same wave situation to take as many variables out of the ding proof equation.
My personal epoxy boards I use are so much stronger than the polyester resin board in the ding department. I think there is no comparison(surftech and other pop out epoxy boards excluded)
Take one of CMP’s or Bert Burger’s Epoxy wood sandwich over EPS boards…
Then cover the whole thing top and bottom with a skin of about 4"-6" inches of boogie board material and external skin
Pretty 'ding" proof and definitely strong.
Wouldnt want to ride it especially with the soft stuff on the deck.
But I bet you could drop it, bang it against something, scratch it, have it fly off your roof racks on the freeway with little damage to the core epoxy wood board although getting run over by a semi or a pipe barrel could snap it at will like anything else… Dale’s softy would pop too under the wheels of a semi or smashing into a razor sharp coral reef head… Spongies slam their boards all the time on the ground to bide time waiting for their bus rides home… Never seen one break yet on the sidewalk.
If all you want to do is increase the impact resistance of a conventional surfboard without changeing the flex charecteristics I’d suggest useing Kevlar/epoxy. Just remember that Kevlar is less dense that glass so for a given cloth weight will give you a thicker laminate and assuming your resin ratios are reasonably constant this will also be a bit heavier. If you want to go big time try a structure ala BertBurger, but remember this will radically alter the response of the board to the rider.
Unfortunatly it very dangerous to generalise when it comes structural analysis (which is a big part of what I do for a living).
I don’t think it would hurt that much to generalize about it as long as we stay within the subject of surfboard design because A)no one knows a damn thing about it anyway and B)If the sturcture fails, nobody dies. regards, Håvard
I’ve built over 100 boards using Xynole polyester fabric. Excellent ding resistance and easy to work with. White on color and cuts with regular scissors. Use with a more flexible epoxy as most epoxies don’t have enough elongation for this product (RR 2020 works great). Polyester resins don’t work at all. Available from Defender Marine in NY, NY. Use 1.5 EPS and one layer of xyenol on each side covered with a layer of 6 oz. glass.