Surfboard thickness and volume

General Discussion
1

Hi Swaylockers, 

i’ve just finished shaping my first board with great help from this site and past forums.  I’m onto my second shape now and I’m curious as to whether a surfboards thickness is measured with or without glassing? Secondly is there a way of calculating volume from the shaped blanks weight? I understand stringer thickness and material would effect it but ball park would be good enough for me. 

2

I have seen this posted on craigslist but never tried it.

https://play.google.com/store/apps/details?id=com.examp_derived.surfboardvolumecalc

http://sfbay.craigslist.org/scz/spo/5189650601.html

3

Well you understand wrong. :stuck_out_tongue:

You are mixing up volume,density and bouyancy. Volume doesn’t change with the materials used.

You could take the detailed dims of your board and put the figures into BoardCAD.

OR

I reckon you could do this pretty accurately using only a set of digital bathroom scales

(plus a couple of volunteers and a body of still water… say a pool or big trough).

  1. using the scales, weigh the board in kilos.
  2. weigh the bathroom scales! (also in kilos)
  3. you, the board, your volunteers and the scales get into the still water.
  4. stand the board on it's rail in the water (get your helpers to keep it vertical without pushing on it). You will see how far the board will sink under its own weight.
  5. put the scales on the upper rail at the mid point. You will see how far the added weight of the scales sinks the board.
  6. push down on the scales until the board is submerged to the centre stringer and note the reading on the scale.
  7. do the math(s). Add the reading + weight of the board + weight of the scales, this will give you the weight of water that is displaced by half the board. 
    So double that figure to give the total displacement of the board in kilos.

The board's volume (in litres) is the displacement (kg) divided by the specific gravity of the liquid in the pool

(fresh water = 1, salt water = 1.025).</li>
4

“I’m curious as to whether a surfboards thickness is measured with or without glassing?” - Either way.  If it’s in the shaping room unglassed, measure it that way.

“Secondly is there a way of calculating volume from the shaped blanks weight?” - Yes… if you have a scrap of the foam, you can shape it to a block and measure the size and weight.  You now have what you need to calculate the density of the foam.  With the weight of the blank and the density of the foam, it is easy math from there.  

You say ‘ballpark’ - a good thing because some foam density will change from outside to inside the blank.  As you’ve mentioned, the stringer (and glue) will be a different density as well.  

 

5

Thanks for the tips and comments everyone.  I’m going to take the density route for now and then learn how to draw my board on boardcad.  I also found this formula under a the forum topic 'Calculating Board Volume for Dumies"  that gives a ball park to volume amount.  1/2 height x width x thickness +(10x every inch over 6’0) / 60.02 which gives a final litre value.

Cheers   

6

Why all this silly fussing over volume? It isa the least meaningful number in how a board will ride or proform.  You can have two boards of the exsact volume one will float you paddle better and ride better then the Other why? It’s displacement! It is how it displaces water and how water moves across the shape.  Vulum is little more then a marketing tool a number to make you think it has some magic power to makea board work better for you.  

 

 

7

Volume is way better suited to compare boards than length.

Indeed don’t expect to use it like the Reynolds number in fluidum mechanics, but it’s far superior to length.

If you think volume is a marketing thing, please also stop writing the length on you boards.

(same is true for fin surface area vs depth)

8

I agree that volume is a great tool for board comparison. Using the rough calc I worked out my new shorter and wider shape actually carries around 4.5 more litres than my previous boards which is quite significant and would make a huge impact to boyancy and handling. So now I know that I can lose some more thickness throughout the shape to bring the total foam volume closer to my typical amount.    

9

If you are doing a custom a true custom then the shaper can only guess at " Volume. Lenght is only one number the best way is to take Lenth center wide point. nose and tail. That gives you the shape.  As I said volume isa marketing tool by the machine shapers to get the unknowing to think they really do Know something.  By the way diffrent programes will give you diffrent numbers on volume. 

 

10

True what artz says and if you been surf’n awhile you don’t need to know a board’s volume. You can just pick it up and have a look to tell whether it has too much or not enough.  How volume is foiled and distributed are the most important variables, anyway, ie, the shape and what it’s being ridden in.  Mike