Surfboard volumes/weight and buoyancy?

I am curious and want to get a serious discussion going about surfboard volumes and buoyancy. 


In the past surfers have gauged the buoyancy of a surfboard roughly by its length, weight, and thickness (assuming a similar distribution of thickness in any surfboard), as well as the classic “hold under the arm test.”  With more and more surf companies posting the volumes of their boards (Sunova, surftech, firewire, Coil, CI), it is becoming an increasing important aspect of surfboard construction.  Surfers like knowing that a board has similar flotation to what they are used to, as their is no worse feeling than buying a board only to realize its too small for you. 


Now we all know that volume has a direct relationship to the buoyancy of the surfboard, but I believe the grey area here is the weight of the surfboard (density).


For example:

Sunova’s use a .7 lb per cu ft EPS foam in their surfboards, and are in general lighter than normal PU boards.  So does this mean they are more buoyant?  and if so (which i believe is true) by how much? 


Is the lb per cu ft of the actual foam of the surfboard the greatest determining factor (aside from volume) of its buoyancy? 


How much more buoyant will a board made of 1 lb per cu ft foam be than a 3 lb per cu ft board?  Assuming equal volumes?

Yikes… here we go again.

#uK!  I'm a scientist!  I've got the answer here somewhere????   If I can't find it in my slide rule somewhere maybe SammyA or Coil Mike etc. can help you.   There's plenty of "eggheads" here that should be able to help you

get some different density foams and shape some boards. Report back your findings.


Never heard of Archimedes and pulling out a calculator?





Yeah!  I think about that $#!t everytime I scrub out a 6'2 for some 250 lb. fat-ass.

The thread njsurfer referenced is a good one, but there's others also. Search and you can find...

But to summarize, the volume and weight of the structure are the sole determinants of static bouyancy. So if two boards have identical volume, but differ in weight, the lighter one will float slightly higher. Core density by itself does not have an effect, it's the weight of the total structure that matters.

We've been putting volume #s on the boards since 2006, well before everyone else (save Dave at Diverse, who's been doing it since 2004). I predicted a while ago that it would become commonplace in the industry. It's been fun watching the rest ''discover'' volume.

Volume is a very useful measurement. Many of our customers will attest to the benefits when working across a quiver, etc. But there's so much personal preference in volume that you have to be careful about ''guidelines'' or ''rules''. Some guys like to float and others like to swim.... So you have to get a feel for where you are on that scale before you can really use the #s.

Good assessment.

If we just want to know how high your ‘cork’ floats when you are sitting there waiting for a wave (“static”) then the volume is fairly easy to reference and make comparisons to. 

The tricky part is how the actual board planes when you are paddling for a wave. There are SO many variables that come into play in the scenario that is is difficult (if not impossible) to get a constant. 

For example, if you took two identical boards EXCEPT one was a tri fin and another was a single fin, you would find a difference in the drop in rate from the second you “caught the wave” to the time you hit the bottom. 

Or in another scenario, you might find that a thinner board actually catches waves easier than the blob next to it because the thinner board lifts more once you start paddling it. I had a thin board just like this, and guys couldn’t believe I was catching waves ‘so early’ for my size compared to the length and thickness of the board.  I like what we generally call ‘flyers’, and the thin tapered rail the board had w/other components made this board just jump up easily on a plane.

I have seen some very poor paddling corks in my day.

Going back to sailboards. We did have a mathematical formula for determing volume in the sense of total liters. The molded boards back then were rated in liters and the system was based upon how much water was displaced when the particular board was submerged in a water tank. Even this would have to be clarified if using salt water or freshwater.

Some oceans/seas are saltier than others.

As far as buoyancy, I seem to recall that 1.0 lb EPS in 1982 displaced 60 to 62 lbs per cubic foot. This was before EDRO/IDRO machines were capable of superfusion. 

Epoxies also vary depending upon the amount of solids that are in them.

In other words, lotsa variables… including your body weight from day to day, hour to hour.

Good luck on your quest.

There was a time that windsurfboards where characterised by the length.

Thats about 15 years ago.

Now all windsurfboards are charaterised by the volume and the length is become a less important measurement.


It is easy to see a parallel with compsands here. Some shapers say they invented compsands, but actually they where the first to apply it to regular surfboards. It started in the windsurfing industry and now 95% of the windsurf boards are compsands: wood, honeycomb, double sandwich, hollow, … I’ve seen it all passing by. Yes there was a time PU/PE was used, but I windsurf for 16 years now and I’ve never seen anybody surf one in my life.


If we take the parallel back to volume measurements:

More manufacturers will include volume measures on their boards. It is an important measure, but 90% of todays surfboard shapers will never use it. And they will tell you that volume is not important.


So basically you’re saying that we don’t know what makes a board a good wave catcher?  Like if someone comes to you and says, “I want a board that catches waves easily…”  what do you do?  Flatten the rocker and bump up the volume?


I read through the thread he linked, as well as many of your comments.  I am so glad I have a board shaped by you as it represents (along with the forums) a shaper interested in how boards are made the way the are, and how they can be made better.



I will be honest that I have fallen in love with swaylocks, as it seeks to address WHY we make surfboards the way we do.  Rather than just randomly trying a new shape and seeing if it works or not, we try to figure out WHAT makes a shape work.  What effect does flex have on performance?  Rocker? Rail thickness? Tail shapes? etc. etc.  These conversations allow for shapers and surfers to get together and examine how each aspect of surfboard construction work together to make the perfect boards suited to an individual’s style of surfing.



Sway on!

I have been keeping a database of my customers in a custom built filemaker database for three years now. I include customer age, surfing frequency and years of experience, along with board size volume and several other key components. My wish would be the coil guys and others who have seen the benefit of putting it on their boards, biolas, hymen etc could one day share the data to create a super list of knowledge and experience…

Always felt volume was as important as any other measurement.  EPS gave us the chance to measure volume easily with hand shaped boards.  Urethane always was difficult because of all the variables.  If everyone was EPS it wouldn’t be any big deal to post a volume on the boards.  Most of the machines figure that now so even urethane can be easily figured.


What is the difference in measuring it for EPS compared to PU? Putting it on a scale, because the density can be asumed constant in the foam? But that only works if the board is stringerless. Or am I overlooking something more obvious here?

Mcding can ya do a 6' 2" for a 240 pound guy ? Width and thickness not important but must be able to knee padle ! What do you imagine the thickness will need to be ? Oh, by the way it will be used for riding sunset at 10 foot plus so keep that in mind on the shape!

Hello Delacroix, when I saw the title of this thread my reaction was similar to some of the others - there has been much written on volume preferences for catching waves. On that subject it became apparent to me from reading many posts and ultimately my own experience that Mike Daniel’s is right and some people will get on better with lower volume ratios and some with higher when it comes to wave catching and there is no simple way of saying how volume and length helps us catch waves. A short thick board is the good wavecatching combo for me - at least in waves up to about 1 1/2 head ht. My personal reasons are that I like float for flat water paddling and a board needs to be short enough for me to get an effective leg kick on takeoff - my leg kicking is better than my arm paddling.

However, you are not actually asking about the role of buoyancy alone, but rather the role of density or another way of putting it considering both volume and weight and its effect on performance

  • you have one of Mike Daniel’s boards - I’ve never seen or ridden a Coil, but I have owned and borrowed a number of different build types including the following - Tufflite (stiff sandwich), TL2 (light sandwich from surftech), SLX (stringered EPS/epoxy from GSI), Josh Dowling sandwich, and of course PU/PE. They all have quite a different “feel” to the way they ride. So based on those eperiences, I can’t imagine that a Coil would feel the same as a comparable shape in  PU/PE? So I guess you have noted the different feel and wondering if the key to the difference is density? The difference in feel I am talking about is “responsiveness” and “dampening”.

However, based on weighing and measuring the stiffness of different boards I don’t believe the significant unquantified ingredient is density - instead I think the significant ingredient is stiffness.

 I am currently enthralled with the feel of my Diverse Dynocore and I now realise that stiffness and weight is not the complete answer - I think there is also stiffness distribution coz the dynocore reinforces specific regions of the board and there might also be “resiliency”, but I don’t know about that latter quality or how to measure it.

Volume is a great thing to have measured and written on the board - its not the complete answer to how well the board will say catch waves, but I can at least look at a shapes specifications and together with volume get an idea of how it will paddle on flat water and catch waves.

Surfers are getting more educated, myself included. There was a time when litres wouldn’t have meant much to me, but I have got a better grasp of that measurement in recent years. What BASE surfboards are doing and I think is great is giving their boards an entry and exit rocker rating, I have been doing this with a rocker stick after purchase and compiling my own ratings for better understanding as in the pic below, however it would be nice to look at a catalog and get an idea before purchase and not everyone can be bothered with rocker sticks anyway.

The Dynocore has customisable flex - both the amount of reinforcement and the length it travels up the rail can be varied - for boards like this I think the measurement of the future will be flex rating. However I think every manufacturer will have to have their own rating scale due to different flex distributions and the different way boards of similar stiffness will feel

[img_assist|nid=1059387|title=rocker to front foot emphasis comparison|desc=|link=none|align=left|width=640|height=464].