Can some one explain why the typical
polyurethane-foam/polyester-resin surfboard has anywhere from 50-60% of its weight in its core?
Wouldn’t it be prudent to move most, if not all the structural mass to the outer shell where it really counts?
Wouldn’t it be better to have an easy to shape ultra-lightweight core and super strong shell, yielding a much lighter and stronger product?
Why the heck not?
PS - air is not an easy to shape core
Possibly incompatitbility of bonding super lightweight weak core to the strong, thin, almost brittle outer core?
Then superlightweight cores tend to expand and contract, and skin just doesn’t like to give, keeping it’s bond.
Eggshells, are they better than easily punctured, but possibly giving softer shell, with a waterproof core?
Eggs are a prime example of natures work, and tend to need care almost constantly.
Can you give a surfboard than much care and attention?
Yea and verily my friend, LeeDD - god made the egg to be broken out of - a flexible or non-breakable membrane would be the joke of the devil himself on the next generation of peepers. hmmmm… air is hard to shape? What if the structure was a hard unbreakable slighty flexible material like (Don’t they protect their employees down at the Quickie Mart with something clear?) but you had an adjustable air bladder type of thingie inside to control thickness/dome thereby controlling flex? Hey meecrafty instead of using the plexi for half the vacuum bag it becomes the board skin, now you’re talking. Now where’s that post by Dale on how to make “air bladders”?
Need adjustable pressure membranes, with a pump to increase pressure and a valve to release pressure.
Seems plexi in a thin, light structure is not stiff enough, but I of course DON’T KNOW!
I was thinking removable tailblock slide in a different maybe inflatable - maybe solid for longitudinal stability, then slide in bag(s) with features (you said) affix the tailblock and inflate bags with pump! When can we start?
"Possibly incompatitbility of bonding super lightweight weak core to the strong, thin, almost brittle outer core?
Then superlightweight cores tend to expand and contract, and skin just doesn’t like to give, keeping it’s bond"
Lee, what if the skin to core bond didn’t matter? The core shape is just a process means to the end.
Daddio, interesting idea. But Im just not on the board flex bandwagon…flex is just a variable I dont want to deal with…give me super-ridgid-responsive anyday…in most sport speed/racing applications strutural flex is a no no. Flex gives control…but I think you can get control from other sources like the static shape/fins itself. Flex has a place with longboards but I dont ride them.
unless you get the outer skin/shell hard, rigid and thick enough (heavy) the shell flexs without the support of the core and thus cracks. That is part of why over shapped blanks (resulting in low density cores) are more prone to dings than say classic weight blanks.
That said, your comments are consistant with both Hollow board design and sandwich construction. As for hollows and keeping the weight down, the Pope Bisect is an example. With strong/light frames you could follow the Jensen hollow method and get similar results and keep the weight down. But still sandwich is probably the easiest way to achieve just what you are talking about.
As a first step towards that direction, I’m trying 1#eps core with 6x6 bottom and 6x6x6 deck. vac bagging the lam in effort to improve glass/epoxy ratio. In this case the core is really just to provide shape and interier mold the glass. It really is not expected to provide much strength.
Hi Dave,
I’ve always thought that rotational moulding would be a suitable method for producing a nice hard shell for surfboard. A super light expanding foam could be injected after the moulding if required. The vast of majority of rotational moulding is done with polyethylene however other plastics can be (and would probably have to be) used. If excuted correctly, a ladder type frame arrangement could be placed in the mould and then overmoulded conventionally for greater structural integrity.
One of the main problems I see with anything that uses a mould is the lack of, or difficulty in customising the shape.
For a hand shaped, customisable approach, I think Bert’s stuff is pretty much as good as it gets at this point in time. Or were you mainly discussing polyurethane/polyester construction?
Kind Regards,
Matt.
Dave,
Actually, when you mention “for the masses”, what sort of customising would you deem necessary?
Kind Regards,
Matt.
I’ve used lighter cores for years, EPS. Expansion and contraction isn’t a problem. Here are some truths regarding all foam. First, the lighter a foam is the more it tends to leak. A 2# density EPS leaks very little while 1# leaks quite a bit. Same with urethane. Ultra lights leak much worse than a green.
The lighter the foam the softer it is. This makes buckling more of a problem for lighter weight blanks than for heavier ones. This is, almost, regardless of the glass job on top. The glass and foam are connected and share load. The less load the foam is capable of taking the more the load shifts to the glass.
The lighter the foam the more memory it has. Cell walls are thinner and more flexible and will come back to shape easily. There are advantages and disadvantages to this.
Having said all this IMHO the standard surfboard carries too much weight in it’s core. I prefer a lighter core. I think it rides better, at least for me.
And one more thing, multiple density cores and sandwich construction change all the rules above significantly and need to be judged seprately from uni-density (a new word?) blanks.
I never really appreciated what Greg, Bert, Michael Jones, Sabs, Surftech, etc have been getting at. My initial experience with Surftech was less than satisfactory and I kind of wrote the concept off. After reading this article that was posted here a couple of days ago, I think it’s starting to make sense. In a nutshell, Greg, Bert and the others are right.
thanks for mentioning me John. i’ve been busy building, but taking lots of pics which i will unload here when i’ve finished my latest. i started off building 2 more sandwiches. One closely following the other. I finished them but they aren’t to my satisfaction, so i’m most of the way thru another one now which i’m very excited about. Of all the ppl on swaylocks you’ve influenced my recent shaping the most, specifically the way you combine 2 rail theories into 1 inseperable package has been the most easy to understand explanation i’ve been able to follow so far.
anyway back to the sandwich, i’m interested to know what were the negative aspects of your surftech experience and would a customized version solved the problems or was it something quite fundamental that you didn’t like?
good link john …
i love it when big dollar companies can back up there technology with basic enginering priciples and information collected from years of research , and it backs up what ive been doing for years …
surftechs problems in a nutshell , there low density core is turned into something more closely resembling a higher density core by resin penatration , combined with cored skins which add stiffness and you get something to stiff , with no shear movement …
without shear movment , you have no flex …
now while the link on sandwich construction was more to do with structural applications …
flex is a must if your creating something that has to flow and manouver within a moving changing medium like a breaking wave …
meecrafty …
control by static design …
that goes against everything a wave is not …
control by engineered flex and we have something that can handle a wider range of scenarios in a changing enviroment as well as having static design to fall back on …
you get more with less …
win win …
regards
BERT
Im interested in #1 EPS without a stringer…
so according to guru GregL there are two main issues:
1.leakage (Im assuming from dings)
…so in dealing with #2…
rail channels (possibly top and bottom) with more glass in the channel…and/or full or partial deck sandwich material
opinions comments?
Bert, you would hate it here…conditions suck 90% of the time.
In addition, Im just a garage board builder making boards for just one customer so I apologize if I have a serious bias against flex.
…in most sport speed/racing applications strutural flex is a no no. Flex gives control…but I think you can get control from other sources like the static shape/fins itself. Flex has a place with longboards but I dont ride them.
Even in static structural engineering applications you have flex. You cannot get away from flex. It is a matter of reaching a point where the amount of flex is balanced with the amount of stress imposed on the material for that given amount of flex or deformation. The key is engineering for a point where the stress on the board over time (fatigue) is reasonable. ie. That you’re not buying surfboards once a month. Also to keep in mind is toughness. Just because something is “strong” doesnt mean it is tough. The harder and stronger a material is, the more brittle… the more catastrophic the failure… pop!
Flex is a way to dissapate energy. An example of this would be race cars… there is flex built in to the chassis. Tack welds hold everthing together… the cars dont have full welds on each and every joint… if they did, you would inevitably end up with major cracks all over the place.
Flex in a surfboard turns the kinetic energy of a turn at the high engergy point of the turn into potential energy (spring energy). At the low energy point of the turn… it returns it into kinetic by springing back… An analogy would be a Sector 9 thin deck longboard when bombing a hill… we all know those work quite well.
use hessian fabric , dont let the gaps fill with resin , when it sets sweegee on a coat of qcells to fill the weave , sand back then reglass with a layer of 2 oz for a good seal and finish …
now you will have a thicker glass job almost resembling a sandwich but not quite over 1# eps at a reasonable price …
like greg said the lighter eps folds easier , you need a thicker outer skin to compensate for that …
if its not a sandwich , then you need another way of making the outer skin thicker but not to heavy …that will give an even feel to the board …
super light eps doesnt respond well to re - inforcing locally , with stringers and things to strengthen the board unless you can get a decent thickness outer skin on …
you can really still get a big variety of results without having to get to technical …
core mat is a little more expensive , but that will give a sandwich feel to a hand layup …
theres 2 options for 1 # eps …
regards
BERT
hey meecrafty once you get into 1# eps flex becomes a factor you have to start dealing with …
flex is your friend if you treat her right …
Thanks Bert that approach makes a lot of sense. My local supplier has 1.5oz cloth but its $7/yard…ouch!
I’ve made a #1 blank…b4 any shaping the thing weighs only 1.25lb so Im planning to use a “heavy” lam using s-glass…4+4 bottom and 6+6 deck. I was thinking about doing something similar to your horizontal stringer to keep things from moving too much.
In the end I want to end up with a small wave shortie (6’3) under 6lb…used mostly for avg non-critical surf…without V-bags and expensive sandwich materials…but maybe Im just chasing rainbows. I enjoy making my boards cheaply…plus all this new stuff is challenging.
“use hessian fabric , dont let the gaps fill with resin”
what about just using the 2oz cloth wetted seperately, then applying it to an acrylic sealed blank?
I’m not sure about the fabric, but Bert pretty much describes what Michael (MrJ) did with a 6’ something asymetrical thruster I saw at Plaskett Creek. Michael’s board weighed not more than 3 lbs, was tough, dent proof but stiff (and ugly as all get out). I saw the future right there…
Seems to me that volume distribution will have to be changed substantially from what it used in poly boards. I can’t imagine that they will have the same “feel” in the water like a poly. So you’d have to get used to that.
Which begs the question: Is there such a thing as a surfboard that is too light?
Hey Meecrafty, have you thought about three fours on the deck instead of two sixes. Layed up tight separately you could save some weight without sacrificing any strength.