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

General Discussion
21

You have described the effects I have been thinking about Mee, especially relative to the weighting and disweighting.

The lighter board does not actually help you weight or disweight, that’s all in the persons control, skill, fitness and experience.

The lighter board will however react much faster to the riders input, allowing the disweighting to be more effective. And that lack of board weight needs less pressure to keep it up against the riders feet during that disweight, particularly on whitewater where there is less bouyancy.

The flex component then comes into play when the rider applies weight or pressure, again a complex combination of board manufacturing and rider skill and weight.

It seems pretty obvious to me that the combinations of strength and weight of composite/balsa sandwich boards is why they can be so much thinner and still work so well.

The experience and fitness of the rider is still a very big factor when it comes to getting the most out of any board.

22

Well…

Some things to consider -

Quote:

I unweight when hitting whitewater on my PU board too so that aint it. my compsand board has a different feel for sure - it seems to fly over sections and I come down a lot lighter and with more speed. You are right, I can’t discount different flex patterns as a cause for the difference but the board is about a kilo lighter than the Pu board it has replaced, so I can’t discount that factor either.

Also, might just be that you have gotten a bit better at it?

There may be a little less inertia to the lighter board, true. Tradeoffs are there, certainly. But about the only thing happening is that if you unweight the board totally then the board alone will take about a third less force to push it up against your feet. But nobody ever totally unweights a board. If they did, well, they need to hang onto it, lest they fall off. You do see exactly that in certain air moves.

Quote:

Regarding the so called myth of bouyancy I’m really not sure what you guys are on about. If you take two boards of equal volume, the one with the lighter core will weigh less and therefore will be more bouyant ie it will take more force to submerge it - which means it will take more weight to sink the rail or stall the tail, you will notice the difference just as sure as you will notice a flat deck or a thicker nose.

Well, will you? If you’re talking about balsa vs redwood, foam vs balsa, maybe. In the case of two boards with a volume of two cubic feet ( lets make the numbers easy ) you got board that displace around 128 lbs of seawater. One ( 3.7 lbs/cu ft ) polyurethane Clark foam will weigh in at 3.4 lbs more than an otherwise identical board made of 2 lbs/cu ft polystyrene foam. That’s around 3% of the total buoyancy.

When you’re talking about a board and rider as a unit, when planing, that’s also not gonna make a helluva lot of difference.

Now, tow in boards. Again, a very different scene. You have boards built heavy, yes. Typically, they are operating in considerable chop, at least relative to what we’d be dealing with on an overhead day in decent surfable conditions. And they want to stay in contact with the water, cos otherwise they are losing control - if no edges are in there, they can get sideways and life gets real ugly, real fast. Adding weight to the boards is the only way to do it, 'cos you don’t want to put on, say, a weighted vest. Getting back up is problem enough without adding 10 kg of lead.

We are also talking about boards where the weight may be what, 20+ lbs to start with, what with lots of heavy glass, heavy foam and so on. Adding another 20 lbs - well, good. We’re talking about a major difference, not the very small difference of polyurethane vs polystyrene foams.

To those guys, buoyancy doesn’t matter one little bit, so long as the board can float itself. Remember, they are towing in to those waves. They are not paddling with it at speed, hell, they could get away with water skis or something that thin. It’s all about planing area and inertia of the board, so that it doesn’t bounce around in the chop. Not buoyancy at all.

hope that’s of use

doc…

23

yup Wildy…

Shwuz, here’s a little experiement…

fill a balloon with water and take all the air out (or just assume)…the balloon will suspend neither rising or sinking…

now to that same water filled balloon, add a few BBs or a small steel ball inside…the balloon will sink very slowly

take the steel ball out and put in an air bubble…the balloon will rise very slowly

its not just the volume but also the density differential between the object and the water and between floating objects…both boards will rise but one rises faster (and perhaps higher too)

freebody diagrams are used to graphically/mathematically explain this but i dont do them anymore so the analogy/experiment hopefully works to make the point…

if not, just try a surftech of equal volume and you’ll be a believer too…just make sure you measure the weight of the two boards…mathematically the diff may seem small but in practical use it really isnt…i roughly estimate that between a 5 pounder and a 7 pounder, it represents about 3/8 inches in thickness to get similar float…

the really nice thing is that the 5 pounder also does everything else better if youre a progressive surfer…mainly response and accelleration…thats why i call the other one’s poopees :wink:

24

Two balloons of equal size. One filled with air, one filled with helium.

Would the helium balloon be more buoyant?

25

yep

26

What about when they are both completely submerged under saltwater?

27

like most things in physics, it all boils down to a final, definite number. within any given medium, all things positively buoyant will float, and those that are negatively buoyant will sink. buoyancy for the medium, in our case, saltwater, is zero. while the balloon filled with air and the balloon filled with helium are both positively buoyant, and will both float…the helium-filled balloon will yield a higher coefficient than the air-filled balloon. it will take a greater amount of force to displace the helium-filled balloon than the air-filled balloon.

28

So wouldn’t that suggest that MeeCrafty is on to something? That there are other things to consider than just Archimedes Principle?

Does that lend validity that in eps/epoxy boards, which has a combination of core materials, eps foam and a little air, that would bend the displacement theory into something we could call the Buoyancy Theory?

Therefore, would it be defined, and the myth proven?

{Edit} Grammer corrections {/ediT}

29

there’s more to it than just AP, and there’s more to AP than just the little intro that was previously stated.

i typed out a detailed response, but then i mistakenly hit the “back” button on my keyboard and lost it…argh!

and so, i’m gonna go get a haircut…and then try and find a rideable wave to surf.

then it’s back to blank shopping…time to make a trip up to the clark warehouse (like a little kid in a candy store)

30

It boils down to equal dimensions and equal weights of the compared objects. If one is lighter, it doesn’t matter if it’s hollow, EPS, XPS, urethane, cork, compressed horseshit or whatever… it will float better but you’re comparing apples to oranges at that point.

What if it’s 2.5 lb EPS vs 2 lb urethane? Glassed the same, the urethane will weigh less and float better. That isn’t the point.

Sounds made by fingernail tapping against the shell, chatter when riding over chop or various other factors (like flex) may create the illusion of better “flotation” but the reality stays the same.

Try it yourself… make up some identically sized blocks of different materials (ANY materials) and glass 'em so they weigh exactly the same. Put 'em in a tank and add weight until they go under. It’s all been done before but if that’s what it takes…

31

Those were simply questions I posed to everyone for discussion.

In my personal opinion, Archimedes Principle covers all the bases.

Archimedes Principle: Any object, wholly or partly immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.

IMO, Archimedes Principle IS the buoyancy theory.

The myth is a myth. But that is just my opinion.

32

i think the point people have been trying to address relates to the standard construction of a poly board (say, clark supergreen) vs. EPS (say, 2#). even if the shapes are identical, once the boards are completed, the EPS board will generally weigh less. so…if you’re looking to maximize float from a specific type of shape…wouldn’t EPS/epoxy accomplish that? i’m pretty sure that’s the point people were trying to make when this whole “myth” began to evolve. sure…identical size, identical shape, identical WEIGHT will react the same…but when does that ACTUALLY happen if shaping 2 boards from different materials (unless, of course, that is your goal)?

33

…in several countries, rescue boards are made with styro…and I dont think that the flex is important cause some boards ´got lot of fiberg layers…they re kind of rigid…

34
Quote:

You have described the effects I have been thinking about Mee, especially relative to the weighting and disweighting.

The lighter board does not actually help you weight or disweight, that’s all in the persons control, skill, fitness and experience.

The lighter board will however react much faster to the riders input, allowing the disweighting to be more effective. And that lack of board weight needs less pressure to keep it up against the riders feet during that disweight, particularly on whitewater where there is less bouyancy.

The flex component then comes into play when the rider applies weight or pressure, again a complex combination of board manufacturing and rider skill and weight.

It seems pretty obvious to me that the combinations of strength and weight of composite/balsa sandwich boards is why they can be so much thinner and still work so well.

The experience and fitness of the rider is still a very big factor when it comes to getting the most out of any board.

and , am I the ONLY lightweight person on this forum who doesn’t like very lightweight boards for that very reason ??

…ie: because I am lightweight , and the board is lightweight / oversensitive , I find it hard to keep momentum, and keep the board in the face .

I’ve noticed heavier guys like my mate big Daz can push down better on the board when making late drops for instance , and their cutbacks are more rail engaged right the way through the turn . When I try their boards , however, I find I need to take extra paddles to get in , and really try to PUSH down with my front foot when doing cutties , for instance , in order that the nose stays in the water .

just my .02 , and the reason why I don’t go apeshit over lighter boards.

ben

35

Chip,

Have you tried a compsand board made to the Burger recipe? I tip the scales at 65kg and I like mine alot.

That said, it does only have average drive - it should drive better given it has a low rocker and a fair bit of straight rail ahead of the fins. This may be a fin problem - the side fins are a bit small. I’m putting in bigger sides for my next session, if that doesn’t make much difference then I’d be prepared to say the lack of drive is down to the lightness and it’s something you have to design around.

36

g’day pinny !

you’re the same weight as me .

I sent you a pm asking a few more questions .

What is a compsand exactly …the ones you make …are they balsa veneer ? or vacuum bagged divinicell stuff , or what exactly ?

I’ve certainly seen variety here since berts vacuum bagging thread opened the floodgates to creativity . But apart from having a go on a sunova a mate had a year ago , I haven’t had any such board of my own .

When we last heard from “Gray Murdoch” , he was thinking about going the styrofoam vacuum bag route.

‘Bluejuice’ ?

have you done this ?

…if so , I would be really keen to hear from you , and if possible see and try one of those boards …have you made any like that ? If you weren’t happy with me trying one out , I’d love to see you surf one . [Nothing like watching something in action , that’s the best way I LEARN !]

cheers !

 ben
37

? How many of you surf 4 or more times a week consistently? thinking way too much and not surfing is not good floatation.

38

Ben,

“Compsand” is composite sandwich and is a term I’ve seen used on Sways to describe the Bert Burger recipe boards. Mine has balsa rails and Core-cell skins check: http://www.swaylocks.com/forum/gforum.cgi?post=228607#228607 for details and pics. Most people here are doing balsa skins, but I think Core-cell, Airex or Rohacell would probably work as well for shortboards.

Divinycell or klegecell are more brittle cross linked PVC foams. You could use them but the foams mentioned above have better flex properties.

39

I thought “Compsand” was a brand ,thanks for clearing that up.

I suck as a performance/competition surfer…But I surf 3 times a week minimum,2 hours per session…some times more…Some weeks I surf every day. Night shift is great!!

Here’s my theory

The less time you spend in the water the more time you think about surfing…

It’s a good thing

Let the debate continue !

I’m having fun

Stingray

P.s. Did you ever notice that Rhino’s avatar is identical to the logo on all those killer Shipman Surfboards???

40
Quote:

I’ve always followed that logic myself, but kept quiet about it :slight_smile:

I think Surftechs corkiness is attributed to greater bouyancy because so few surfers really know how flex works. When you try to kick stall a Surftech board - sink the tail - it squirts around under your foot but won’t submerge the way a pu/pe will. Its widely assumed that this is due to increased bouyancy, but I think its due to extreme stiffness. Same thing with laying out a turn & trying to bury a rail. A pu/pe (or a properly engineered epoxy) will bend & conform to the shape of the wave a bit, while the Surftech will stay straight as a board & give the feeling of staying on top of the water. Corky.

Surftechs are also sold & talked about as ‘paddling machines’ or ‘lineup equalizers’ (trading on the insecurities of weak paddlers). But I think they paddle so well because you’re not losing any energy to flex. What’s more efficient to ride up hill, a rigid road bike with 1" wide tires or a full-suspension mountain bike with 2.2" tires? Assume you’re in a tough gear - 42/16 or so and out of the saddle. The road bike will transfer nearly all your leg energy into forward progress while the mountain bike eats up half that energy in compressing the suspension, mushing the tires, rolling resistance…you get the idea.

I think the bouyancy thing is a smokescreen to cover other, truer concepts which are much harder to quantify & understand.

The proof, to me, is my d-cell covered surfboard. Anyone remember what I said about it? “All the weight of a pu/pe and all the corkiness of a Surftech.” No Flex. Explains it all.

Edit: I liberally use “Surftech” but also, of course, mean Boardworks, South Point, etc…as well as a couple of my own flexless failures at sandwich boards which ended up surfing just exactly as well as waterlogged Surftechs with not so nice a finish :slight_smile: Others - the wood ones, really - surf just like I hoped they would…

It’s funny how you can take a longboard Surftech board turn it upside down and stand on it and it flexes, but doesn’t break. Try that with a Polyboard.