Hypothetical scenario…three surfboards that all have two 1/8th inch stringers. The first board has the two stringers glued to eachother. The second board has a foam t-band with the two wood stringers one inch apart. The third board has the two stringers eight inches apart. None of the boards are painted. They all have the same shape, thickness and glass job. Which board is the least likely to snap? Which is the most likely to snap? And why?
Hypothetical scenario…three surfboards that all have two 1/8th inch stringers. The first board has the two stringers glued to eachother. The second board has a foam t-band with the two wood stringers one inch apart. The third board has the two stringers eight inches apart. None of the boards are painted. They all have the same shape, thickness and glass job. Which board is the least likely to snap? Which is the most likely to snap? And why? Interesting question… I’ve heard the sales pitch about gluing two strips together with opposing grain for extra strength but if you install a box or fin plug (not indicated in original question) you will violate some of the stringer’s thickness and compromise strength at that area. With the foam t-band, adding just a little more spacing between the stringers would allow for a box installation between the wood which (IMO) doesn’t compromise the stringer integrity and increases the strength of the box installation. With the wood 8 inches apart, you have a vulnerable nose area at the tip with no stringer at all for several inches depending on the nose width. All things equal, and no fin box or plugs, I’d say the board with the 8" spacing will be most likely to snap (at the nose) and the other two pretty close with the foam t-band having the edge because of the additional glue line which might be slightly stronger. For my personal board I’ll take a wedge cut with the stringers far enough apart at the tail to allow a box to fit between.
If you assume the snapping won’t occur in the area forward or rearward of the separated stringers (and most boards snap somewere in the middle third), then OTHER THINGS BEING EQUAL, no board has an advantage. But “other things” are never equal. Though board flex prior to breaking distributes the stresses somewhat, at some point there is initiation of disaster resulting in complete failure. The question becomes: Can we identify the initiation point(s) and reinforce them adequately?
Has anyone ever documented the force of a pitching lip or the turbulence underneath a broken wave, quite often you hear of guys saying that they were just duckdiving (hanging onto the rails)and it creased or snapped, I myself have done the “starfish” at Burleigh a few times (pined to the bottom face first and cant move)Yep glass your board stronger and you decrease the crease factor but when your in the wrong spot at the wrong time, just be thankfull that it was your board and not your leg or neck. I had a board once that I surfed for probably 2 years, I surfed it every where, big or small, coped some floggings at 8’ Johanna (victoria)where I thought that it was broken for sure, but to my stoke, it just wouldn’t break. Then a mate of mine takes it out the front on a 2 foot mushburger day and snaps the f#%#%$g thing in two. WRONG PLACE, WRONG TIME If there are any studies done on this subject could you let me know KR http://groups.msn.com/MyKRSurf/krcomweb.msnw
I think the two glued up stringers would hold up the best. First of all, this helps to even out weaknesses in the grain of the wood. If you have two separete stringer with equal load and one of them fails, there will be quite a heavy load on the other one. Secondly, two stringers glued together are more torsional rigid than two seperate stringer. When the stringer are under heavy load, they want to twist. The things stopping them from twisting are the stringers anti-torsion qualities, the stringer to glass bond and the (soft) foam. If you take two seperate stringer wo foam and glass and apply load on them untill they twist and then try the same load on the same stringers glued together, I bet the later won’t twist. This means that two separete stringers would rely on glass to stringer bond at that load. PS. if you know an construction engineer, he would know the math to calculate it. regards, Håvard http://www.earthlife.net/birds/flight.html
Water weighs 62.4 pounds per cubic foot, so the falling lip can hit a board with a lot of force in a wipe out. I knew two guys that had their boards broken trying to duck dive a wave too late. One suffered back problems for years. Maybe still does. I sometimes think if a Martian came down and looked at our surfboards, that he’d be dumfounded by our lack of symmetrical strength. We’re very anal about the symmetry of our templates, shape and foil. But many of our boards aren’t glassed symmetricly. They are like an I-beam that is intentionally made weaker on the bottom even though it seems that many boards snap from a downward force. I’m not proposing that we make the bottom stronger, but maybe just equal with the top since we have to live in a universe with action/reaction laws of physics. Equal rail lap strength should be considered, too. My thought with the two stringers was that the t-band might make a better I-beam than the two stringers glued directly to eachother. Perhaps better penetration of resin into the foam in the t-band. I guess we’ll have to wait for an engineer or some testing to determine that. I like the tapered t-band to allow for the center fin box. Good one.
I tend to prefer the stringers on both sides of the fin box as Starfins are always weakening that area. Poobah, nice idea about the equal glassing on top and bottom. Perhaps the standard thinking of deck strength vs. weigth is overlooking something more basic. Does it take aliens to see this??? What’s the Koa/Channin Compositech T-band stringer made of (besides the wood)? I have one of those and with S-glass it handles a regular bashing of rocks and barnicles with only occasional minor dings. What about PVC stringers? I remember Greg Loehr saying something about them. (And that wood and water don’t mix well). Rob Olliges
Hypothetical scenario…three surfboards that all have two 1/8th inch stringers. The first board has the two stringers glued to each other. The second board has a foam t-band with the two wood stringers one inch apart. The third board has the two stringers eight inches apart. None of the boards are painted. They all have the same shape, thickness and glass job. Which board is the least likely to snap? Which is the most likely to snap? And why? This will have a lot to do with the board’s length, surfer’s weight, wood species’ etc. Wood stringers with a thickness of 1/8” can have significantly less structural integrity, even if glued to another 1/8” part. In my opinion, you need at least 3/16”, 0r ¼” glued together for an increase in structure. As far as your specific question goes I’ll say the foam tband w/ 1/8” offsets.
Hypothetical scenario…three surfboards that all have two 1/8th inch stringers. The first board has the two stringers glued to eachother. The second board has a foam t-band with the two wood stringers one inch apart. The third board has the two stringers eight inches apart. None of the boards are painted. They all have the same shape, thickness and glass job. Which board is the least likely to snap? Which is the most likely to snap? And why? My belief is that the purpose of the stringer is to provide some measure of a shell for the glass. The glass is the ultimate strength, not the stringer. The purpose of multiple stringers in not adding in stringer strength, but in providing a more complete outline for the glass to adhere to. I’d say one inch apart. The rationale is that glass is MUCH MUCH stronger than the stringer, in isolation, and that the glass will fail before the stringer does, because it is much less compliant. The stringer just keeps the glass on the shell. Without it, every heel press will be more likely to dent foam, leading to delam, and delam weakens the structural integrity substantially. The issues with delams are concentrated around where the feet are placed, which is near the center. But each stringer will have en effect for a few inches on either side, so having them glued together will sort of minimize the area over which they help prevent delams. I’ve often wonderer why the stringer theory wasn’t followed up with a more complete system. You could envision a pair of circular pads that go under the front foot, and have little beams running through the foam (like two disks and a bed of nails between them, but plastic, not steel). This should do much more against heel dents than an extra 4 oz layer of glass, and wouldn’t weigh too much.
The only thing that matters with a stringer in the width and depth, all other things being equal (material type, material strength, etc). And of the two, depth is far more important. But I’m confident that both are much much less important than a good glass job that is well bonded to the foam. The glass and foam, well-bonded, form a box beam. Consider the flex in an unglassed blank compared to the glassed board. I think stringers look good and provide some function as a navigation reference in shapping. But not much more from a strength standpoint.
I have to disagree that the stringer doesn’t give much strength to a board. Consider some principles about the nature of wood: One: Two pieces of wood glued together are many times stronger than the same two pieces side-by-side. Bent laminated chairs and tables would not be successful otherwise. A 3/8" T-band using three pieces of wood 1/8" thick will be much stronger than three 1/8" stringers set apart. Two: Wood usually bonds better to resin than the foam does, making a stronger adhesion between the polyester shell and a material that resists flexing. A “good” bond between resin and foam is still only as strong as the foam. Also, the stringers are set into the board on edge, like a roof rafter. That way the wood has the most resistance to flex. And, in addition, the stringer is completely contained on all sides, making it even stiffer. Stringers are much more than something to look at, or to orient to when shaping: they do give strength to a board. Doug
One: Two pieces of wood glued together are many times stronger than the same two pieces side-by-side. Bent laminated chairs and tables would not be successful otherwise. A 3/8" T-band using three pieces of wood 1/8" thick will be much stronger than three 1/8" stringers set apart. I think 1/8" is too thin in a Tband. My call would be two 3/16" pieces glued together, rather than three 1/8" pieces. With 1/8" pieces, some woods grain gets pretty insignificant. 3/16" and above is cool, but what do I know?
easternpacific - don’t forget that even though the stringers are set apart, they are still connected - by the glass. In essance you still have a composite, there’s just some layers of foam in there as well. Regardless - you still have an I-beam… two layers of glass held together with wood.
Clyde Beatey has been successfully making stringerless boards for years (in addition to boards with stringers). If the board is thick enough, I see no purpose for a stringer. If you look at some of the “tip tweak” blanks, there is so much rocker in the nose that the wood grain in the stringer runs the short way and thus they tend break noses easily. The stringers add a lot of weight as they get thicker, so on a short and thick board going without a stringer would yield a lighter product. My next fish will be about 3" thick with no stringer. Just be sure to wrap the rails generously or the board will be weak.
By the way, one of the reason those “Fluf-tite” boards are lighter is because they have no stringer.
Stringers are an essential factor determining boards strength. If they wern’t, then we wouldn’t see them used in big wave guns to the amount that we do. I can just see Greg paddleing out on his stringerless Mavricks gun. I wonder how long that would last? I bet not long enough for Flea and the boys to pick up on the hot new trend. Stringer depth and width combined with the amount of glass on top and bottom of a board, plus how much is wrapped around the rails, determines a boards strength. The best way of seeing this is looking at buckled boards. Often times you’ll find that the stringer hasn’t even broken. The entire composite stucture, the stringer and the glass working together creating an “I” beam effect is the big picture here. Yes you can have a board with no stringer, but is it as strong as a board with one? With the same glass job on both boards. No. With more glass on the one without the stringer, maybe… but is it heavier? As for the orginal question, I would say that both stringers in the center of the board is the strongest, simply because the stringers have more depth in the center. (not true on flat decked boards hehe) but You also have the grain structures of the two pieces working together to help splint any weaknesses in either’s grain structure. Carl
Bruce Jones has some information about the strength of stringers on http://www.brucejones.com/strength.htm regards, Håvard http://www.earthlife.net/birds/flight.html
I’ve done many tests on stringers of all different kinds. What most fail to realize is that stringers weigh a lot. Given that an 1/4" stringer weighs (with glue) 1/2 lb. (at least), then that is the same weight as one layer of 4 oz glass put on the board wherever you like. So here’s the question, is a stringless blank with a 6 oz bottom and a 4 and 6 oz deck stronger? Or is a strung blank with a 4 oz. bottom and a double 4 deck stronger? In every test we’ve ever done, the former is stronger every time. And you get impact strength as well. Greg Tate is an engineer. As such, he looks at things for what they are. In this case that means strength to weight. He’s right. But there is no doubt that a strung blank is stronger. It’s just also heavier.
Glass will of course beat a stringer in a strength test of newly manufactured boards, in the Loehr example. But, ride each board for a year, and then test the strength…Wood has great elastic deformation characteristics that make it well used for repetitive loading situations. Glass and PU foam alone are not so good in fatigue. A piece of PU with glass gets delammed too easily. A lot of guys at Mavericks run double stringers and double 6 OZ top and bottom, and boards still break. Thickness is a key factor though - the thicker ones definitely are tougher to break. Jeff Clark shaped Mavericks boards are all over 3 inches thick.
Mavericks will break any board. A 6 foot thick lip hitting the center of a board from 35 feet up is going to break the board. But you don’t need a stringer in a short and thick board for smaller surf. And if you had a stringer on a delaminated board, it is time for a new board anyhow.