Bert's take on Surface Area vs. Volume

General Discussion
1

An interesting read and I’d tend to agree with him based on my own past experiences:

https://www.facebook.com/permalink.php?story_fbid=706597229393232&id=150291551690472

 

Hi Dean

Sorry to say , its all about surface area …

These new designs have major surface area…

You only need adequate float …

More float than you need doesn’t equate to better wave catching … only equates to worse performance , and as counter intuitive as it sounds , worse wave catching …

Im taking 4 new boards to Sri Lanka , all potatoish designs …

My normal literage on a short board is 36 liters …

Formula is 1 liter for every 3 kg of body weight …

But that is only true if I have the correct surface area …

So I usually run between 2 ¼ and 2 ½ to get float right , consider my weight , 108 kg/240lb …

I could run 3 ½ thick in something with way less area , and never in a million years could I catch waves , because of the reduced surface area , even tho float would be the same …

I am running extra volume in the test boards for Sri Lanka … around 39 liters , just 10% more , plus slightly more surface area than my regular shortboard …

Why more surface area ???

Simple law of physics …

The more area , the less speed needed to plane …

The less area , the more speed needed to plane …

A surfboard only functions when it is on the plane on the surface of the water…

You can plane on your bare feet if you are going fast enough …

Look at tow in boards ? how much area do they have ??

Water skis??

Kite and wake boards ??

The surface area is relavent to the operating speed …

Low speed small waves , and you need more area …

But consider where the area is …

When you make a board shorter and wider ,you place the area in a more concentrated location under you center of gravity …

So I could have a 10’ x 12” board …

Or a 5’ x 24” board , both having similar area , of coarse the short one will plane better because the surface area is directly underneath you , so its more effective …

All these new super chunky boat designs are a total fucking myth …

I validated this one 15 years ago , with 2 identical outlines , both being the same length and width …

One at 3.5 “ thick the other at 1 ¾ thick …

The thinner one caught waves easier , was faster and more responsive …

Both boards were super wide at 6-4 x 23 …

Even tho the thin one actually had not enough volume and I sank past my chest while stationary , as soon as took a few strokes, all the surface area allowed me to be up on the plane and right back at the surface …

Why did the thin one catch waves easier and perform better ???

3 factors …

1… A thicker board naturally comes with a thicker rail , so its harder to create a defined apex where the water releases , so as you take off the thicker one has more water wrapping the rail , slowing it down , along with more rail engaged in the face holding it back …

2… the thick one , took way more effort to bury the rail especially on the first pump while attempting to get speed , so it was naturally slower to get going because it was less responsive…

3 … you completely fuck up the flex in a thick board , the thick one relied on buoyancy off the first pump , I would have to bury the rail , then wait for it to float or cork out , as it did this I could then sink the opposite rail and start to pump …

The thin one could bury the rail immediately , as well as flex into the turn , then spring out with projection and I was away at lightning speed …

Just think about what that means in terms of a quick get away , flexing an object and springing out of a turn or sinking an object and waiting for it to float to the surface…

Yes the volume of your board is important …

But the surface area is more important …

You can have not enough volume and adequate or more surface area and the board will still function …

You have adequate or more volume and not enough surface area and the board will not function …

So whats more important ???

It comes down to education …

Unfortunately , when most boards designers are uneducated, what do you think they will pass on to there customers ???

I struggle to comprehend why so many board designers are following this current trend …

I can only think of 2 scenarios …

1 they are clueless …

2 , they really do know , but just want to sell more boards to a demanding market and realize they will sell more later when crew figure it out.

Stupidity or greed , take your pick …

The hard part for me is stating the facts , while trying not to sound condescending or like a know it all …

As long as we clearly state the functionality of our designs and can back it up with simple laws of physics and scientific principles that you cant argue against…

Then we make our point and stick to our guns …

Fuck man , if the world cant get it , does that mean I will blindly ignore the laws of the universe and follow the crowd …

Been there many times in the past on other areas of design , only to be proven correct years later when the majority start to agree…

Lastly , why am I only putting 10% more volume in my small wave boards , there is a slight compromise there…

While you can go thinner if you increase surface area , its harder to convince someone if there already on the back foot and skeptical …

So , a slight increase in volume and obviously an increase in surface area and its an easier sell …

Plus the thickness increase is not enough to compromise the flex of the board or the ability to sink the rail …

So yes , even im doing it for the sake of sales , but still staying within the realms of reality, hopefully crew wake up sooner than later and we can get back to making those magic morphing sling shots…

Regards

BERT

2

Thanks for sharing!

This makes perfect sense hydrodynamically.

3

Science is our friend …

4

Interesting, Really interesting.

It makes sense since we need more surface area at low speed.

And with decreased thickness, you get more sensitivity and your CG is lower too.

 

5

Thanks for sharing. I learnt a lot.

Bert does not mention paddling out. When you are flat water paddling, volume can be your friend. When you are duck diving the extra volume is a pain.

There is a point at which area becomes counter productive. Somewhere around 24" wide in a 6’ board you end up with a pig to paddle and little return in lift. You’re pushing this disk along.  I’ve found  by taking width down to 22 or so, consequently reducing area, but making the rails more parallel I can overcome most of the pig effects. Not that most of you are ever likely to get into the 6’ x 24" realm, but the principle is worth noting.

6

Good points.  I tried something like that, in an experimental shape, and ‘pushing the disc’ is a good description - I didn’t like it, it wasn’t at all what I had expected.  Floaty (“corky”) but hard to catch waves nonetheless.

7

I certainly agree. Through the years I’ve found that I need about 38 to 40 liters and about 7.5 sqft of area and I can ride any shape that is not too wide. I weigh 168 and am about 5-9. 

This formula has worked for me for years with boards by G Loehr, Mike Daniel at Coil and George Gall at PlusOne. And the ones I build for myself. Everyone should know their numbers before buying or building. And it is pretty easy to figure out your numbers using boards you have had success with and boards that were not successful for you. I always start with those two numbers before building for someone, unless of course it is a longboard. 

Of course, thinner boards are more subject to snapping. 

8

Some pretty strongly held opinions there. It’s good to be passionate. Anyway, here’s some less strongly held opinions from me… My experience has always been that if I shape two boards with the same outline the thicker one seems to catch waves better. This could be due to my expectations. I dunno, I guess I could be tripping. In regards to wider boards, I agree that they seem to catch waves better than narrow boards of the same volume.
I would, however, dispute your thick board = boxy rails theory. I can make a three inch thick board with the same rails as a two and a half inch thick board. It’s just a matter of the thicker board having more of a dome in the deck.
Your flex theory had got me thinking as well. Thickness must surely affect flex. I agree, however is the change in flex that comes with a thicker board necessarily a bad thing? I’ve noticed that my thicker shapes surf differently, sometimes worse, sometimes better. How much of this can be put down to flex? There are so many other variables that it’s hard to say how much flex is contributing the difference.

My apologies if I missed something from your post. I’m quite happy to be educated on this.

9

Because bottom surface is curved by rocker, effective planing area is also function of rocker too.
Flex perception of boards while surfing come from vibration, recoil after turn is mostly negligible because deformation are really low: boards are stiff and when surfing forces (foot and water) are opposed whit small distance so there is too low flexural momentum to really deform the board.

10

It seems like 3G (possibly as high as 4G?) could significantly affect flex:

(Force = Mass x Acceleration)

centrifugal/centripetal acceleration is

a = \frac{v^2}{r} \, ,  where a = acceleration, v = velocity and r = radius

Earth’s gravitational acceleration is 32 ft/second per second.  Times 3 = 96.  So if my calculations are correct, a turn/cutback with a fixed radius of 10 feet at 21 mph will produce centrifugal/centripetal acceleration of 96 feet/second per second.  Apparent rider and/or board weight will be 3 times greater than stationary (gravitational) weight.

Is flex a function of length and thickness?  Is strength directly proportional to the cube of thickness?

Could too much flex create “bogging” or plowing (i.e. increase drag)?

[quote="$1"]

 3G is realistic.  In the late 80’s I used calibrated clay rods called PlastiGage

under a sheet of plastic, went out and spiked a solid bottom turn and came in.  The amount of PlastiGage 

deformation resulted in a loading of about 4G or just under. 

…HINT:  it’s not the downstroke but the return stroke that matters.

Best regards,

George

[/quote]

 

11

Here’s my strong opinion - Bull shit!  When it comes to the entire surfing experience, and there are factors that can be tweaked - my 4.5" board has sub 2" rails in the middle, blah blah blah…

Carry on - have a laugh and forget it. 

12

Shapers in many ways are like preachers, absolutely convinced of the righteousness of their particular religion.

And because all religons are faith based, they each have great arguments to explain the ‘righteous truths’ that rationalize and justify their particular faith.

When you take off deep and critical, gotta have faith.

So choose your faith wisely…

 

 

 

 

13

Normally the Sways sht fight doesn’t start until the second or third page. This is way more efficient. 

14

I thought the piggish/slug nature of short fatties had to do with too much bottom (hull) that could be ruled out with a bit of concavity?

Also thought that volume up front was a paddler’s friend?   I get how fatter rails can be corky and limit responsiveness in a carve and that a fat board will not give rail to rail quickness as a narrow board, but I am stuck on understanding how increased volume  and a 24" width correlates with pig paddling qualities.

I did have a 6’2" x 22" that was a pig because it had too much bottom and pushed water so I got rid of it after a dozen surfs, but it was more of a riding problem than a paddling problem.  Only time I dumped a board due to subpar performance.

I had a thick 6’4" x 21" with deep concaves shaped that paddles and is fast, but can be a bit corky when the rail pops out at the end of a carve.

Curious about the idea of paddling being hindered by the volume and width, because I have spoken to a home shaper and a pro who are doing a lot of quads in the 5’8" - 6’0" x 23"- 24" range and they love them for paddling, but do declaim the boards tendency to slide the tail rather than carve a turn at the arc’s apex.

The garage shaper was doing displacement bottoms on his, while the pro is doing subtle single to double barrel concaves.  They are not egg shapes, but do have rounded (disky) outlines with fatter noses and tails than what I consider a classic egg.

 

On the other front (flex).  It does seem like the thinner boards and logs have some pop (vibration) or liveliness that isn’t as apparent with fatter rails.  I thought thinner boards have some quantifiable flex, but it looks like there are couple of differing schools of thought on that one.

15

“Normally the Sways sht fight doesn’t start until the second or third page. This is way more efficient.”

Classic Greg - I almost spit my lunch on the screen…

Gotta say - in the spirt of the Sway Sht fight/fest…  I’m with lcc on this one.  Over the years there has been incredible science about boards/waves interaction, but, to me, the most respectable purveyors of science has conseded the full science is very, very, if not too, complicated to put forth a whole formula.  And then throw in personl preference to wave riding approach, waves, conditions, etc.

Still fun though - and it’s not getting personal…

OK - I reread the first thing.  I’ll say, I am right, plenty of pure shit.  Sorry Bert.

TaylorO

16

Many variables combined with many opinions …

Science?

17

I think I’ve said this before but I reckon the most important design feature of a surfboard is that it has enough volume to be able to be paddled. Pretty much everything else you can get used to and adjust your surfing accordingly. I once made identical boards, one with concave and one flat bottomed. I couldn’t tell the difference in how they rode. I suppose either I’m not a good enough shaper, not a good enough surfer, or a combination of those two!
That said, it is fun talking about complicated design issues. Better than watching TV anyway.

18

I liked the analysis.  Very insightful.

With more planing area, bottom contours take on a more significant role.  A single concave will produce more lift on a wider board.  I suspect subtle changes in concave depth will manifest in interesting ways.  In addition, these lower aspect ratio boards will naturally make rail design even more important.  Do we go with more smaller fins or less larger ones?

I, for one, am excited to play with the variables on my next boards.

19

I don’t know enough to comment but Berts construction is so different to PU/PE and PU/epoxy, volume and floatation of materials must aid paddling in some way??  Because I’ve got a 6’3’’ Professional modle Sunova, it’s an incredible performance board but it doesn’t paddle so well compared to a PU blank of the same dimensions??

 

PlusoneShaper wrote some good info on his take a few years back : http://www.swaylocks.com/forums/board-rider-flotation-effect-steeper-waves

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Sunova metawaii keg

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