I read online today that 1 cubic foot of EPS will displace 66 pounds of water. Does if matter if the cubic foot is comprised of 1lb, 2lb, 1.5lb, 3lb foam? Does anyone know what foam density is being used in Boardcad, Akushaper for calculating board volumes in those programs?
I ask b/c I saw a thread on the erBB where a shaper (Mike D.) wrote .94 cu. ft. on a board with dimensions of 6’5 x 19 x 2 1/2. I have a couple of Aku boards with those dimensions (very close) and the volume is more like 32.2 liters, which would give you 1.137 cu ft and it’s not computing to me. Someone from that discussion said that Mike is weighing the shaped blank and multiplying the weight by the density to arrive at the displacement. If you have 2 identical shapes, one shaped from 1lb foam and another shaped from 3lb foam, are the boards going to have different displacements?
okay i just answered part of my own question and i’m a dumbshit for not seeing it earlier - 2 identical shapes, shaped from different density foam are going to have different weights…
Weight does not equal displacement. The reason Mike can find a displacement figure by weighing one of his finished blanks is because he knows the weight factor for the foam density he’s using.
The reason his density factors are coming in different from your’s is probably due to his foils. You can add or remove a lot of displacement by changing the shapes of the foils, decks and rails.
Thanks for chiming in Mike. I guess I should have added that I’m not trying to be critical or imply that I think there’s anything wrong with the volume #s you’re putting on boards. I’m curious about the impact of foam density on displacement. It appears that you’re putting out a great product and if I were going to buy a board from anyone (I’m into making my own stuff right now) it would most likely be you.
In the most literal sense, density doesn't have anything to do with displacement. Read up on Archimedes Principle, etc. But if you're talking about bouyancy, the density of the foam affects the bouyant force of a submerged surfboard by the amount of increased weight incurred by the heavier foam (if everything else is constant).
Good Mike - I didn’t finish my post saying something similar: Displacement is displacement; it’s based on the volume of the object. Buoyancy is something else, but as you point out, the two end up going together when it comes to us on the board.
water is 62.4 lbs per cubic foot of volume...so if you have 1 cubic foot of 1lb density eps is should weigh 1lb. 2lb eps would then be 2 pound per cubic foot etc. long story short its not going to make that much of a difference. 2lb eps would be 1/64th more water displaced than 1lb eps...fractions of an inch more in water displacement. its confusing math but I hope that helps.
finsider
EDIT: thats only talking if you have a 1 foot cube of eps. a surfboards displacement will be variable with shape, etc as mentioned by others.