Copying a magic PU board in EPS What would you change?

OK - Think out loud for me.

If you were askes to copy a mates “magic” PU in EPS (so its lighter) what would you change so it rode the same? Im sure its a question that has been asked by everyone involved with CAD and machine shaped boards.

I dont want details of construction methods or material changes that people would choose, I am interested in basic 3D design. ie- thickness,foil, rocker,rails. template, fin placement, widepoints and fin setup. (and anything else that you would alter.)

The fundemental question I guess is. If a board becomes lighter what dimensions would you change so the ride was the same. All, None or some and not others!

Do it for any type of board, just specify what your dealing with . Long, short, fish etc

What would you do?

use 3 lb foam and don’t change a thing

i (cough, hack) argree with otay

Thanks Otay, I’ve done that and I agree, it is a good replacement for a PU, just not a great weight saving, My question was intended to generate discussion as to what infulence board weight has with regard to board design and performance.

I have been experimenting with foil and rail volume but am interested in the idea of altering the decks to reduce volume but maintain rail shape.

Was keen to remove the compsands and Flex solutions and see what basic design changes if any people considered.

I hear it’s pretty hard to make a single “magic” board, much less a duplicate. Things like stringer wood and how a PU rocker is adjusted during glue-up might change a few things like springiness that may be hard to replicate.

A common complaint is that lighter boards tend to feel more corky, have less drive and are maybe harder to sink the rail.

Maybe try adding some base to the fins, pinch the rail a tad and reduce the nose rocker by 1/4"-1/2"?

Adding a bit (3/16"-1/4") of belly in the front third might help smooth things out as lighter density foams feel (or sound) somewhat more chattery in chop. Try tapping various boards in a local shop with your fingernail and imagine how the hollow sound might translate in actual use. Light core EPS boards sound hollow in comparison to PU.

Thanks John.

Everything you said makes sense to me

i agree about the making and copying of a “magic” board, i threw that in to help explain what I was asking rather that as a real situation.

My feeling is that rails are one of the key changes needed to maintain the feel when turning. Lighter boards seem to skip and release in turns.

When you say pinch the rail I assume you mean thinning it out but maintaining its character eg: 60/40.

What do you think about raising the rail in order to increase stickability? All the EPS lighties I have ridden have very sharp untucked down rails from the widepoint.

Bellying out the rocker is something i hadn’t thought of.

Assuming other design variables constant, reduced board thickness and rail volume will get you closer but it still wont ride ‘the same’. Feel, sensitivity and response time is different. Different could be better or worse, depends on the surfer and/or waves.

Copying the rails tip to tail down to the finest of details will also help. The bottom radius, corners, edges have to be near exact. Minor changes go a long way there. Bottom contour near the rail also plays a key role.

Sharp untucked down rails from the wp seems pretty extreme…tried that myself and its very unforgiving to the point of near uselessness. Untucked to around the front fins works, beyond that not for me.

Btw, I realize for the sake of simplicity you dont want to discuss structural, but ignoring this is futile. A magic pupe not only has the design, but also flex response too. Generally speaking, eps/epoxy flex is shorter quicker. This is very dependent on glassing materials/schedule/approach. There are tricks out there to minimize the feel gap but that’s another story.

I think you have to change a lot of things if you want 2lb foam or lighter.

My experience has been you can compensate for some of the “corky” feel of a duplicate in EPS by (1) decreasing volume by 1/8 inch for a standard shortboard, and (2) softening the edges. Same rail profile, (scaled down slightly, due to a decrease in thickness) but with softened edges.

I totally agree about the flex. It will be different. Epoxy isn’t poly, and it never will be. It’s SUPPOSED to be different. People are always trying to make it feel like poly. If that’s what you want, stick with poly.

Also…remember boyancy is displacement… so you do have a decrease in boyancy with reduced volume. This will effect paddling (make it harder) and duckdiving (make it easier). It will also allow you to push the tail into the wave more on a hard turn, so you have to increase tail width to make it feel the same.

If it aint’ broke…don’t fix it. It’s already magic. What’s more magic than magic?


One clarification, one can achieve the same result in different ways. Softening the rails while keeping rail volume similar is one way, lower rail volume keeping geometry similar is another…similar end results. Both work.

But really, its a very inexact ‘science’…how can you quantify ‘feel’ or ‘magic’.

The best we can hope for is for similar results and with any luck, better results.

For years, many, including well funded pros, have tried to close this gap. Not saying its impossible, just too many variables to contend with…CAD/CAM shaping is one thing, materials and glassing is quite another…foam blanks can vary quite a lot even from the same lot of mfg.

Here’s something fresh…foam to glass/resin weight ratios of finished surfboards. There is good stuff in there if you look but not easy to wrap your head around…again, lots of variables.

The good news is that most surfboards work just fine.

The fundemental question I guess is. If a board becomes lighter what dimensions would you change so the ride was the same. All, None or some and not others!

I would try to make it the same with exception of being slightly thinner. As stated earlier maybe 1/8". Keep everything else as close to the original as possible.

I don’t think being lighter is going to affect the ride as much as being more bouyant or as they say floaty. That’s been my biggest criticism of the plain EPS/epoxy boards I’ve used. The boards with dims I’m used to seem to be too bouyant and that affected the turns and glide. I had to push down harder to get it to work the same.