1. Fill a (big) bath.
2. Place board in bath and completely submerge.
3. Mark where water line is and remove board.
4. Take 2 litre (yes spell check: 'litre') milk carton and count how many litres needed until water level meets the mark.
... well, that's one way anyway.
I work out the volume of my blank from it's weight and density.
Then do the same thing with the foam sandwich and add the 2 together, trouble is for some reason, this seems to give me a figure that's too high.
There are some board designing programs that give you volume, but the free version I had is so old it won't do modern board shapes very well. And changing rail thickness makes no difference to what it says the volume is!
I haven't tried it, but you could make an accurate scale model and use the evil panda's displacement method.
thanks decrepit, well im going for the 11kg per mtr i know its light and less in destiny so do i make it fatter, the length is 240x50
panda
Sorry, not with you.
But if it's 11kg/m3 it would be 1.1kg for 100 litres.
.825kg and .88kg for your 75 and 80 litre volumes, but then you have to take into account the sandwich, the last board I made was around 8 litres. If yours is similar, then the core needs to weigh between .74kg and .79kg.
Trouble is you don't know this till you finish shaping, that's why, if you want it accurate, a scale model may help.
Keef , I have been modelling my board designs in 3D and the program can measure volume . I have modelled six boards now and with every one I have had to make adjustments to reach my desired volume .
I think your question is really valid and I would be interested in knowing how board makers accurately predict volume without the aid of CAD systems .
I guess trial and error ?
Keef, if you are ready for it, have a look at
en.wikipedia.org/wiki/Ellipsoid
You'll see some nice mathematical formulas (not the boards) that should make it close for your volume.
Good luck.
It's ok for production companies they cam make a pile of boards, measure them,and then give that figure in the specs, (as rider says, it doesn't seem many actually do this with any accuracy).
It's much harder if you're only making 1 board and want to get it fairly close first time.
I guess there's a very approximate guide, average width X average thickness X length.
Just depends how well you can calculate/judge/guess the average.
Ah, before you make. I guess as others have suggested you'll have to guesstimate/estimate.
Now I've never, ever made anything before outside of a computer, but here's how I'd do it:
1. It's going to be mostly core/cell. Using bathtub method calculate how much volume 1kg of the cell material displaces. When you've finished shaping the core/cell weigh it again and multiply by your calculated volume/kg.
2a. Repeat for your other materials, subtracting wieght of you core/cell each time.
or
2b guestimate the rest.
I recall reading somewhere on these forums someone who was lodging their production slalom board for racing and the volume was way out, around 10%.
Like Mr Love said above, do it in 3D if you can. I modeled my board in Autodesk Maya and calculated the volume at 102litres. There is a free learning version you can download from here:
www.autodesk.com/ here
agree the software is the way to go.
for a guestimate, i was told that 1cm additional thickness to a board 2.4mx.6m equates to around 10 litres.
I'll go along with that, my ~8litres for the sandwich is based on 3mm top and 5mm bottom
Nice looking software, I'll give it as go and see how it agrees with my weight/density method
thank's for the link shear tip, but i'm dislestic il'l have a look and it from front to back,or left to right thanks for helping thats why im here you guys are a great help
Select to expand quotevando said...Dont ya just love 3D
Dont ya just love 3D[
it aint easy when your A,D,D vando
but i'm listening to ya buddy
Maya Sheer Tip !!! High end . I expect nothing less than full animations of the board in action .Maybe we,ll see Shrek Windsurfing soon?
I,m modelling in Alias .
The beauty of Computer modelling is you can quickly do variations on a theme . After doing a few now I can pump them out really quickly and the volume tool is bloody awesome . You do have to build a complete model to get an acurate figure , but it certainly beats building a real board before you find out that your 100 litre slalom is really 87 litres .
I,ll post some images next week , I don't have any of the recent stuff on my home computer .
Keep up the good work .
Cad modelling is the way to go for designing but if you want to measure the volume of an existing board it will be easier to do it by displacement. Pete Somlo's method is really simple. It works on measuring the uplift on a submerged board. (Remember Archimedes).
Method:
1) Remove fin and footstraps
2) Place board upside down in swimming pool.
3) Place plastic garbage bin on board (held steady by a beautiful helper)
4) Fill bin with water from garden hose until board is fully submerged but none of the bin is submerged. (It may help to place a couple of sticks as low volume spacers between the board and the bin )
5) Mark the level of the water on the bin then tip it out.
6) Weigh the board, and the bin refilled to the mark.
7) The volume of the board in litres is the total weight in kilos.
I hear you saying "That's all right for a 70 litre board but where am I going to find a beautiful helper who can handle a 120 litre bin?". Well all the weight doesn't have to be water. Some of it can be bricks, rocks, scrap iron, concrete, whatever.
Materials required - beer, pool, bin, hose, scales, board and beautiful helper.
To model it accurately on cad you first need the program and know how to drive it. Then you have to make lots of careful measurements. Then you have to draw the model. Thats like comparing 5 hours of nerdy dweebing with 1 hour of beer fuelled frolics in the pool with your chosen honey. I know what I'd choose.
Keef , You are really asking about "floatation" rather than volume . A boards volume is purely related to it,s dimensions where as the "floatation" is related to both the volume and to the weight and density of the materials used to build it .Also the width is a factor as wider boards with their increased stability always seem a bit floatier than narrow boards of the same volume .
I think your best starting point is to measure a board with the dimensions you are after . Make sure you look at the deck shape carefully as the thickness of the rails and the amount of dome or flatness in the deck can have a big impact on the volume as I have discovered when modelling boards .
I would guess that using a lower density foam would increase the " float " and give the impression of a bit more volume , so if you are intending to build a really light board you can maybe go a touch smaller .
thanks for the tip its great im getting some answers,the blank has been paid for but not cut as im a bit concerned about shapeing the foam for e,g the balls could come apart while sanding, so maybe i should get the 13.5, if anyone has worked with the 11kgs/mt could you let me know, im looking for a really light board because i only sail flat water
It doesn't matter what density ! I use 15 kg and the little balls still rip out, sharp tools help, I use 1st an electric plane, then a surform which only gets used on foam nothing else. then 40 grit sand paper, then 80 then a flyscreen like mesh sandpaper of 120 this mesh is used under a square sponge like what you would wash your car with.
Volume is so over rated. It only needs to be a rough guide ideally I think width is more important. Years ago we used to use width for a persons weight, then the UK magazines had a great idea
to use volume and started quoting volume in their tests (they have a lot of influence)so then the manufacturers started using volume. Now I recently saw an article in a UK mag that they think width is a good idea with the newer shorter shapes.
Don't bother filling the core, wet out your glass on a table, squeeze out the resin as you would water out of a dish cloth, unfold it lay it on the blank, put on the div then in the bag, there will be enough resin on the glass to stick to the div and the foam( you'll save 200 to 300gm each side easy).
Floatation = Volume - weight of board, so if you know two of them you can work out the third.
If your bath isn't big enough you could always use Evil Panda's method (post 2) in 2 stages. Dunk it in sideways to the centreline, assume symmetry, and multiply by two or if you have a deep narrow tank draw a half way line amidships and dunk the nose to the line, refill and repeat with the tail. The smaller the water surface in the tank the less the error.
But if your board is finished and tough enough to dunk why bother? Just take it for a spin.
When you're making a board and carving off the bits of the blank that don't look like a board (I've never done this, is that how it's done?) you'd be able to keep track with the cardboard cross section templates your using to make sure port mirrors starboard?
If shapers don't use templates you or your kids, who are good cutter outers, would have carefully fit them to shape. Make sure they're at equal intervals along the board. Work out the area of each cross section by laying them over metric graph paper and counting squares > 50%.
The smaller the squares on the graph paper and the more templates ( a dozen?), you use the more accurate your answer should be. Average the area of the templates and multiply by the length. Use metric units and add or subtract zeros until it looks like it's in litres.
Never done this only a suggestion.
