EPS Design Theories

Hey Resinhead…I was wondering about your board experiement. Didnt you put just one layer of glass on the bottom and three on top? I was a little concerned about that. Nevertheless, looks like youre a convert.

Janklow, look at the Stewart 9’5S blank…thats a good reference. I think the 8’10S is similar.

Toes, you dont need supercomputers and aerospace degrees…as much as people want to over-complicate things, surfboards are incredibly simple things. The proof is in the water, a computer simulation wont tell you anything about feel.

I agree with Bernie’s sentiments.

soul, some questions for you regarding xps:

what density are you using? what is the lowest density you’ve used and what the lowest available?

xps in europe is blown with air or co2 is it really gasing? do really need holes?

one of my plans is to built xps sandwich or sandwich on top only. i like the idea not to stop surfing if you have a small damage.

what’s your glass schedule and achieved weight?

thanks for the info


hey souly

i find your input quite refreshing

not sure i agree with your use of carbon

but who knows unless you experiment right?

ive been playing with carbopn a bit lately

----In reply to------------------------

i kinda disagree

i feel that the components should have similar characteristics

(ie deck and bottomskins should have similar scheduals)

that way

every thing moves together in harmony

and no component is stressed anymore than any other

I’m kind of a nobody (not nearly as much experience)…but I disagree with your disagreement. When a board is flexing in a turn the top and bottom are not in harmony, but rather in complete disagreement :slight_smile: That is, the bottom is under tension and the top compression.

Greg can correct me if I’m wrong, but I believe I read somewhere that he recommends RR2000 on the deck for compression resistance and a higher breaking point…and RR 2020 on the bottom for more flex.

Toesidereefer- never thought about the concaves resisting flex but your argument makes sense. Kind of funny how so many hi-perf boards have concaves in the tail, right where I imagine you’d want alot of flex. Makes me wonder about the bonzer5 I’m going to make- double concaves, fin box, two sets of runners each side…I can’t see much flex going on there. I wonder if I should shape it in (adding tail rocker)?

Onuela- I love this stuff too, but it also can get discouraging for someone like me who gets to make one board a year (and for sure can’t be spending tens of thousands). I know it would be easier to go to a master and shell out the bucks for a product that’s been tested and proven. But where would be the fun in that? I’ve fallen in love with this whole board building business again (I made a lot of boards back in high school…20+ years ago). Guess I’ll just ask a lot of questions and avail myself of the expertise floating around this site. There was nothing like it 20 years ago. I remember I didn’t even shape off the crust of my first blank! How bad was that? No template either. I just went at it by eye…but then again I remember I sold that board and made some money. HA HA.

http://www.vectorply.com/lamdesign/vectorlam_sw.htm There ya go.

Hi Uzzi

I use the densities I can get, first I used the blue Roofmate, I think it is 35kg/m3. I bended and glued 3 layers together under a lot of pressure to get the rockerline. For stringer I use 4mm (1/6") maple. Bending the foam pressurized the bubbles in the deck. This caused delam problems in tropical conditions when pressure dings started forming.

Last summer I tried a different approach using blocks and gluing them together in 2 or 3 pieces to fit the rocker. This time I used BASF green foam with a bit lower density, because it was the only kind I could get in this thickness (8cm, 3+"). With this foam I get pressure dings easier, but there is no pressure in the gas, so no bumps. The boards haven’t been used in hot conditions yet, only once in a hot car, but no problems, maybe also because I leave the pinholes in the deck now.

I glass with 3 top 2 bottom 160gr/m3 (about 4oz) “keper”, that’s a weave where the wire goes over two wires and than under two, not over one than under one as usual. I don’t have vaccuum jet, still in doubt if it can help enough with this method.

The weight is around 2.5 to 2.75 kg with a lot of finboxes (check superturtle in resourses).

Love to get some feedback, enjoy shaping and glassing


Hi Silly,

The properties of carbon are important for its use. Compression strenght and reaction time and the way it gets back to its original shape. But it is weak in tensile strength, so be carefull using it in that way.This makes carbon very interesting to use as a “spring” to load up in a turn and to quickly give its energy back coming out of it.

For windsurfing masts it is still material no 1. As opposed to glass which has slower reaction time and swings more and dissipates more energy flexing back.

I like the idea from Toes of using kevlar in the bottom, wish I could get it that thin here. Kevlar has good tensile strength but not that good reaction speed and flex characteristics, maybe combined with carbon this gets better.


Mahalo to all for the great posts!!!

I’ve been gone over the weekend, and it has been great to come back to find that this thread now has a life of its own!

Lots of good info here.

I’ve got more Questions:

Parabolic stringers in eps construction –

Traditionally the stiffest part of the board (pupe with single wood stringer down the middle) was right under your feet, so vibration – “feel” of the wave was translated to the rider through the most rigid part of the structure. By moving the stiffest part of the board to the rails and placing the rider over vibration dampening foam, do you loose “feel”?

By applying parabolic stringers to the rails it seems that you drastically increase the overall torsional stiffness of the board (without drastically changing the “1 dimensional” flex). How does this translate into turns – especially hard fast turns where forces are greater? Is one stringer setup more advantageous for big surf and one more so for small waves?




Mahalo for the input and for all of the great posts in the past.

Do you attribute your eps tail rocker design to address more the increase in stiffness or buoyancy of eps?




http://www.vectorply.com/…ign/vectorlam_sw.htm There ya go.

Doh!, Their name registration has lapsed. Is it possible to add the excell file as an attachment?

Torsion Affect

I’m noticing on my board that I’ve lost torsion response. The result being I’ve never been able to slide the tail as much as I can now. This is cool when rebounding off the foam, not so cool taking a late drop and doing a slide at the bottom unable to engage the turn.

My tail rocker design creates more drive. I did a lot of tests on rocker using Bondo to alter aspects which could be easily changed. Found out how to create more drive.

There are only four significant changes in the last 40 years which have contributed to all the other design changes since the inception of the shortboard. Those four have to do with drive and that horse power you get from the bottom turn. 1. the flat bottomed shortboard 2. the down rail 3. multiple fins 4. the concave These four led to all the other aspects of the boards design. Each of these created the horse power nessasary to change design to faster and more manuverable. Through the years the athletic requirement to push a modern surfboard to it’s potenial has risen which in turn has lead to the diverity of design we see today because most consumers lack that ability. Ability to create speed through that bottom turn is what it’s all about in design and ability. The rest is just details.

Because of EPS’s light weight this material allows us the oppritunity to add a fifth drive component internally into the boards construction and that’s what’s happening today. Perimeter stringers and Firewire constuction are the first two which make use of construction components to add horse power. Added horse power will lead to other design changes. If history remains constant boards will go smaller which will lead to better manueverability and quickness in a lighter board while still being able to create needed speed through drive. The ability to ride such an animal will fall to the young and in just a few years we’ll be seeing “chip” boards being refered to as retro. Compsand will be the new status quo because it allows for the best aspects of construction component power to be brought forward.

hi Greg , welcome back !

I was wondering …

how much of this is covered in your EPS shaping video ?

it would be great to see it !



Speaking of drive and how EPS/Epoxy will affect it.

I’ve been surfing short boards since the late 60’s. I got a Greg Griffin 6’ 5-fin fish last year that has been the most incredible thing I’ve ridden in a very long time.

It has tremendous drive and every turn creates speed, not just the bottom turn. Make a hard cutback on that board and you’ll be surprised at where you can go.

Funny thing is that this is a PU/PE board. My brother has a 6’0 Firewire fish, it may have been the first one on Oahu. I tried it several times and it doesn’t come close to what the Griffin 5 fin does. I used both boards on the same day at the same beach, so I know that there’s a big difference.

If you haven’t had the chance to ride Griffin’s multiple fin boards, you should. They are formula one racers. They build up lift in the tail and when you push down to turn that lift becomes acceleration. They have incredible bite for short wide tailed designs. These boards are very loose, very fast, don’t spin out, and you don’t have to pump them from rail to rail to keep them going.

I emailed Firewire and told them to work with the guy because he’s found some magic in the whole board concept. I hope they do.

I am a proponent of new technology like EPS and epoxy, but I also have tremendous respect for the work of master craftsmen. It would be great if the two were combined to make the best of the best.

To me the good side to the boards Surftech or Firewire makes would be in having them available for renting all over the world. Once you find your magic board, you can go all over the world and just rent the board instead of taking your boards with you. I’m surprised that hasn’t become a big thing.

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Hey Craftee,

The EPS board was 2x6 oz impact top with a single 6 bottom. The bottom is the area of consistent failure. The top after the pressure dings has stayed a consistent bullet proof lamination. The next go round will have the same material but an added 4 oz deck patch and the bottom will be 4 & 6, or maybe 6 & 6…but I don’t want to kill the majic, for me if the board last 4 months thats fine, I’ll just make another one.

If I was going durable, 6,6,4 top 6,6, bottom, and you could drag it to the beach behind the car. Oh yeah it all out of #2 EPS, PVC stringer too. Pretty basic stuff, but mind blowing in the performance leap…At least with me and my friends surfing.

I used the Segway EPS Loher 8’0 and took the length out of the nose by 2 inches, Kept the tail rocker ;)…pushed the tail rocker.

Give Ken a call. The rockers with the Loher blanks are all worked out surf great.


Jay, you talkin’ about the 8-0 millenium? The millenium boards Greg built years ago absolutley rip. 2 lb EPS with 6/6 top and 6 bottom. One of the things that really makes it work is the way Greg clustered the fins. It has a thin tail, which even I can feel the flex in (on a big bottom turn). PM me if you want some pics.

I ignored them for a long time until a friend gave me his old 8-6. If I could only duck dive it. I’m building a 8-0 variation now with quad fins.

“My tail rocker design creates more drive. I did a lot of tests on rocker using Bondo to alter aspects which could be easily changed. Found out how to create more drive.”

I recall picking up a board from you and seeing the red bondo on the tail of one of your experimental boards. Gee, a 100 years ago it seems. Would you share some thoughts on that and how your tail rocker created the drive? thx

Are you spackling your EPS? Someone also recommended going stringerless with EPS but this is probably a matter of density/preference. And is it EPS? (Not XPS).

I’d like to see pics of GT’s great board, I’d like to check out some Loehr boards, I’d like a link to Loehr blanks, I’d like to know if Bondo wouldn’t signif alter flex characteristics of a thin tail…


Yes man,

You caught me, using XPS, so I dont need spackle. I build my boards traditional, no sandwich, maple stringer in the middle.

Thinking about EPS, but fear of water penetration keeps me from that. Basically the same material, only XPS has closed cells, so a bit more pressure resistance.

There are also ultra light versions of XPS, maybe a watertight alternative to EPS.