Hello!
Could anyone help me figuring out how much volume should I have to descrease while going from PU to EPS blanks?
Some people recomended me to put 20% less on volume.
Since I surf with 6’3 x 19 1/2 x 2 1/2 (31.5l - PU), I was wondering if it would be ok if I order a 5’11 x 18 3/4 x 2 5/16 (27.5l - EPS).
What the shapers have to say about that percentage?
Thanks in advanced,
Aloha!
depends on the density of the EPS and the density of the poly
Aqua said it, it depends.
If I used PU, made small boards, and really cared about weight…
31 liters is about 1.1 cubic feet.
IF the PU was 2.0 PCF the foam weight @ 31 L is 2.2 pounds.
IF the EPS is 1.5 PCF the foam weight @ 31 L is 1.65 pounds.
Assuming same glass, resin, fins- the difference in board weight would only be .55 pounds, which is the same as .25kg which is solved by .25 liters of volume since 1 liter of foam floats 1 kg (2.2 pounds) minus its own small weight per liter.
PS Enclosing a PDF chart I found online for PU density
As others have said, it depends. But I have heard rules of thumb about 1-2 liters less for epoxy short boards.
At same weight 2 boards of same shape float the same. At same shape a lighter one float better. EPS allow to make lighter board but it’s not a real advantage because when they are make “traditionnaly” they are light but chattery, and as if not more disposable than light pupe. With some adjust in tech to take care off “stiffness feel” the only advantage for me is you can make a durable board with EPS at same weight than a standard pu. If you go to the light standard EPS don’t reduce volume too much because your board will go well in small surf where float is more an advantage, on better surf you will want more inertie no matter if board is lower volume.
Float is the displacement of water. If an EPS board is half a pound lighter, and half a pound of water is 4 ounces, then that is how much less surfboard volume would make it equal.
Foams of equal density (pounds per cubic foot, pcf) in identical shapes will occupy equal volumes. Both shapes will displace the same amount of water.
Basic High School Physics & Algebra:
Density = weight/volume
Volume = weight/density
A pound of lead weighs the same as a pound of cork but the **densities **are different.
I think all the above comments are moot because the OP is looking at a completely different board. A 6’3 x 19 1/2 x 2 1/2 is so different from a 5’11 x 18 3/4 x 2 5/16 that worrying about volume is simply playing at the edges.
I’ve gone 1/4" thinner on my stringerless EPS epoxies and all’s seemed fine. That 25% volume difference the OP quoted seems overdone.
OP wrote:
how much volume should I have to descrease while going from PU to EPS blanks?
I took this to mean using a PU blank vs. an EPS blank for the same new board.
Water weighs about 1 ounce per fluid ounce, 16 ounces to a pound.
Pint’s a pound the world around and all that jazz.