Can we put the eps = extra float myth to rest once and for all?

General Discussion
41

One reason for the apparent corkiness myth of EPS is IMHO that most blanks out of EPS are made using a hotwire cutter. To make this board the same volume as a clark blank of the same length you would have to remove a serious amount of foam. To really make them the same volume, you would have to put them on a shaping machine to really compare.

I wonder if anyone have checked the surftechs with a caliper? I wonder if they are really the size they were intended to be. I have no clue how they shape the plugs for them to make the forms they are made in, but I can see that there could be problems with getting it accurate which may result in problems with the volume of the boards.

buoyancy = displaced water - weight. Period. Secondly, it’s POINTLESS to look at the board only unless you plan to surf it with remote control or mind bending. The system of ride and board is what counts.

regards,

Håvard

42

ah meecrafty , always has the numbers when you need them …

meecrafty …

wildy …

ozzy…

all in the ball park …

static float and displacement is one thing …

the thing that is being most overlooked is the speed with which a bouyant object rises to the surface …

the lower the density the faster it will rise out of the water …

this translates to the timing of how you exit a turn …

if you use a floaty bouyant material and use exactly the same shape , as you unweight coming out of your turn , your board will start to cork out on you and want to rise to the surface quicker than the timing of your turn …

go try it yourself …

take 2 peices of foam , some 1lb styro and some 4lb urethane , submerge both of them , notice how the urethane rises to the top slower ?? the eps just wants to jump out of the water …

2 things happening , a bigger difference in densities between each foam relative to water , and the lighter foam having less inertia can acelerate quicker to the surface with the same given force applied …

power to weight ratio …

same power(bouyant force) with less weight = faster acceleration …

more power (bigger difference in density between eps and water than urethane and water ) also = faster acceleration …

this acceleration is upward and out of the water bouyant acceleration of an object …

in both cases the overall static float and water displacement is barely measurable …

but what is incredibly noticable is the speed with which a more bouyant material will want to rise to the surface …

pinhead!!! , bouyancy and drive shouldnt be confused , neither should weight and drive …

drive comes from design , you really notice how poorly a board is designed once you take the equation of inertia away …

once the exact reason for the added feeling of bouyancy is understood , its only logical what you will need to do to design around the different characteristics …

2.8% is still 2.8% but the percentage of extra speed an object rises to the surface is proportionatly greater

if you take a 7.5 lb board and make it 5 lb for the same given volume , discounting material density in this case , it means the 5lb board will rise to the surface 33% faster , now that is one major difference when your talking about the timing of your turns and how your board responds under your feet as you unweight and go from rail to rail , or boost and look for rotation in the air …

the more radical you surf and the harder and deeper you bury your rail the greater difference you will feel in performance as opposed to the 2.8% difference in static float of a stationary object …

there are still other things involved but they are the major ones in simple terms …

team surfer comment ::::

this guy first started getting styro boards , he said when he came down off a late reo and burried the front rail on the landing it was corking out on him before he was ready …

normally he would bury the rail and as the rail was still going under he had the time to get his weight back over the board and come out of the turn on the other rail …basically going rail to rail partially submerged …

but the styro was popping out before he had his weight fully over the board , so he was not linking the turns together as the board was blowing his timing …

solving the problem was straight forward , less rail volume , but now he had a lower apex =better release , less viscous drag on the rail , less pressure drag due to a cleaner water cut off …

basically a faster more sensitive board which still was coming out of turns in harmony with the timing of his body movements …

randy offered a royalty , and in return made a mockery of the design skills and understanding of the worlds best shapers in regard to things they had never dealt with before …

you see ,for a kook, a surftech offers 2.8% difference in float which will help him …

but for a hot surfer theres a 33% difference in performance unless accounted for in design …

i had many conversations with webber a few years back , about designing within the performance characteristics of the materials …

even tho he doesnt customise in epoxy styro , his first surftechs were closer to the mark than anyones …

stretch , who is based in cali and builds custom sandwich , designed the rat boy model , again , more good reports …

it can only get better as long as we dont get sucked in by what we are lead to believe , based on our previous experiences with the design myths and superstitions surrounding p/u p/e …

so the myth???

minimal difference in float …

major difference in bouyant acceleration …

question ???

how can we overcome lack of inertia due to reduced weight???

boing boing …

we design in characteristics that help us generate speed …

but thats a whole other subject dealing with a different myth …

gota go …

regards

BERT

43

I think Bert’s explaination gives the soundest support for what I’ve witnessed in person: a friend who normally has no problems with big heavy takeoffs, who started suffering from weird unexplainable mid-face spinouts and hideous wipeouts where it appeared he turned way too early, his board “corking out” from under him, riding a popular (blue) semi-gun of a well known shaper in the same thickness as his previous poly boards. He kept trying for two years before giving up and going back to poly.

44

In Bert’s example, he compares 1 lb EPS to 4 lb urethane and draws a conclusion that the EPS “just wants to jump out of the water…” Is this comparison valid?

What if it was 4 lb EPS vs 1 lb urethane? How do you compare the “core” of a hollow board? What if it were a hollow board filled with helium?

Is this about material or about density? For the sake of discussion, maybe a better comparison could be made between finished boards of equal weight and dimensions?

Using all of the implied logic so far, nothing should beat a hollow board - filled with helium if you like. Wouldn’t it have the lightest “core” of all? Of course, what it boils down to is the final weight and dimension of the finished product… even the hollow board has a shell. If it is glassed so that it’s heavier than the other boards of equal dimension, it isn’t going to float as well.

45
Quote:

In Bert’s example, he compares 1 lb EPS to 4 lb urethane and draws a conclusion that the EPS “just wants to jump out of the water…” Is this comparison valid?

I think it is, if you want to give an example of the bouyancy acceleration. But what about the shape of the object and the fluid’s ability to flow around it as it rises to the top of the fluid?

If we have 2 objects, both of equal material type and volume. Say 1 cu. ft. of eps. But one is shaped in a round sphere and one in a cube of equal sides. Wouldn’t the round one rise to the surface faster because of it’s ability to let the fluid flow easier around the shape of it, even though they both have the same buoyancy factor? Or would it? What if one was shaped like an upright surfboard?

Then would the opposite come into play when considering not only the volume but also the shape of rail when trying to bury it at the same speed with the same timing of the rider used to a heavier board like Bert was talking about? I think it would. But I’m not sure. What does everyone else think of this?

46

Me, I’m not real sure this buoyancy vs performance thing is valid and I think Ozzy is on the right track. The results/effects everybody’s citing can be interpreted as caused by greater buoyancy but… while buoyancy is the easy answer, I think it’s the wrong answer.

Lets make a few basic assumptions. For instance, when you are moving on a wave, displacement/floatation isn’t an issue.

?

Right. It’s a planing hull, skimming along the surface. It’s not floating. The board isn’t submerged like it would be at rest waiting for a wave. The amount of the board in the water, pushing on water, is directly proportional to the weight of the board-and-rider unit and the speed at which they are travelling. You see a board in use, it’s not half sunk into the water like it would be if the guy was just sitting there, right?

Okay, so what?

Well, if the board isn’t acting as a displacement hull, then buoyancy and weight goes right out of the equation. Instead, it’s the weight of that rider+board system and the area and shape of that system that’s contacting the water. It’s not about how the board floats, in other words.

Think about it. If it was about buoyancy, then every board would need the same volume for a given weight surfer. If you surfed a 9’6"x22"x2 1/2" longboard and wanted to go to something 6’6" with a narrower,gunnier shape, it’d have to be something like 7 1/2" thick to work at all. Which is silly, right? Oh, and water skis wouldn’t work at all. Or paipos, or flex kneeboards or some of the really odd things you see in the water.

The weight of the boards may vary some for urethane foam vs styrene foam, call it 25%, but the weight of the board plus rider…well, then we get into percentage differences in the low single digits. If you have, for instance, a 170 lb guy on a board that’s 12 lbs vs the same guy on a board that’s 9 lbs, it’s less than a 2% difference. That’s not much.

What shape is the board?

Let’s assume they are originally identical. Originally, but maybe they flex differently. One flexes differently under stress, well, it is gonna present a very different shape to the wave and rebound differently when the rider’s position on the board and/or the wave changes.

While this may not seem like much, well, consider how much of the board is in or on a wave when in use. A small part of it, and usually that small part isn’t symmetrical with respect to the centerline of the board. If the board can twist under that kind of asymmetric pressure, it will. And that will most definitely affect how it works.

If a board twists more, well, it’ll turn differently, need a different rider position to hold it in a certain spot and trim on a wave, lots of things. It’ll behave differently coming out of a turn, go differently on the flat, the whole ball of wax.

And I think that’s where the performance differences are coming from.

doc…

47

You know Bert’s example of his team rider parallels the surfing mag review of surftech vs salomon vs pu . . . Rob Machado, Ben Bourgeois, and Pancho Sullivan. From what the pros said of the handling characteristics of the non pu boards . . . Rob kept saying the boards wanted to go free and fly when he was hitting the lip, Ben B said they were loose and good in small surf, but it would randomly loose control. Pancho didn’t seem to have any problems except the non pu ones needed sharper rails . . .

Interesting . . . you have to adjust physical characteristics to new materials, but also surfers have to adjust how you surf it.

48

if paddling and float wasnt an issue, i’d be riding boards as thin as wakeboards…a thinner eps gets me closer to that dream…rode my two inch thick eps today…just sitting on it and feeling the rails inspires confidence…its just one of those things you have to try rather than figure out by abstract conversation…Bert’s got the insight again…didnt really analyze it the way he described it but part of the bouyancy acceleration to me AGAIN equalls better response…there’s just less delay with lighter boards…more things are possible to the avg surfer

John M is right too…the focus should be on the total weight or specific gravity of the board…not necesseraly on what its made of…OTOH, it just so happens that eps is much lower weight than poly…hollow helium would be epic if you had to volume just right

the debate ends and the myth dies once you actually ride one…

49

Bouyancy acceleration! yep my compsand has the same float as the PU board it replaced, but when I come up from a deep duckdive ,I bob up to the surface noticebly faster
50

“it just so happens that eps is much lower weight than poly”

Do you hear that sound? I’m smacking myself with my shoe.

Thanks for the bone but this is another generalization that doesn’t hold water… Don’t they make EPS in different densities? Aren’t some of those exactly the same (or even heavier) than some urethanes? They also make urethanes in different densities. No matter… if it’s 2lb per cu. ft., it’s 2 lbs per cu. ft. and two chunks of foam, each 12" X 12" X 12" EPS or urethane will weigh the same… 2 lbs.

51
Quote:

you really notice how poorly a board is designed once you take the equation of inertia away …

Duh! there is one important issue I’ve overlooked - my compsand semi-fish doesn’t have any concave in the bottom - it’s dead flat. I thought I’d leave out the concave and see what the difference would be - maybe average drive is the difference. Also, the cluster is quite tight, I might spread it a little. Still waiting on my bigger side fins, might try that while I’m waiting.

52

If you have a block of wood and a block of lead both of the same size and dimensions don’t they both displace the same amount of water? But which one floats better?

53

HA!

hope that shoe your smakin your head with is made of eps!

right john, 2 pounds is 2 pounds no matter what its made of…

my additional point is that GENERALLY speaking, eps is lower density and thus makes lighter boards…

Clark foam poly is higher density and therefore heavier…ive discussed this in other threads…my #2 shapes are about 2.5lb with stringers, a same clark blue is 3.75 pounds…i’ve been using mostly 1.5eps from a billet i bought…finished shapes at 1.75lb…#1eps about one pound…

there isnt any clark foam option to satisfy these weights…nowhere close

even so, its the finished board weight that matters most…a simple Loehr style #2 finishes 15-20% lighter, with better durability. Loehrs apprentice Sam often rides #1’s that are 1.75 inches thick…proly about 5 pounds finished board…maybe less

#2eps is the cost effective limit…#3 can be made but it is incredibly more difficult/expensive to make and there’s a limited market for it…i know it can be bought tho

so i’ll stick to my earlier generalities about the lower weight of popular eps vs popular poly-u

54

Update to this older thread… When comparing foams, it might help if we mention densities of each. I realize that Clark densities are somewhat variable, as are EPS densities, but trying to compare EPS or XTR to urethane on a bouyancy

standpoint is pretty meaningless without knowing at least the approximate densities. With EPS densities up to 4 lb/cu ft now and 1 lb, 1 1/2 lb and 2 lb densities being commonly used, generalizations can be misleading.

Insulfoam is also, right now, introducing foams of higher density as well. All the way up to 4#. So, if you want a superlight weight blank in EPS that’s a 2.5# density. If you’d like a supergreen, that’s 3#. If you’d like a classic weight, that’s 3.5# and for tow boards and heavy longboards you have 4#.