Question(s) On Foam & Floation

[Califoilia]

Reading another thread wrt figuring the number of liters of foam per weight got me thinking about a board that I currently have had in production with a local shaper for about ever (for another time and thread), and since it's still in its raw CNC'd form I went over to way it just for shits and giggles...or so I thought.

The foam blank (6'0x28x4.75) weighed in at 3.13 lbs, and using this chart for the 1 lb foam it was cut from...

...I come up with 3.13*30.24 = 94.65 liters. Only problem, the computer/CNC program spits out 116.4 liters which I need...94.65 liters is about 15-20 liters shy of what I have had float me when I never knew the blanks weights in the past.

Thus my question: Is "weight to volume" in liters, the same as the amount of weight needed to displace "X" amount of liters of water? Or is "weight to volume of liters" the same as the weight required to displace a particular amount of volume of water in liters?

Hope that makes some semblance of sense in what I'm confused and concerned about wrt this new weight number of a board that the "numbers" say won't float me. 

[jrandy]

The true weight of the foam might be less than 1 PCF.
If the shape is accurate for liters and the scale was accurate for the machined blank, you should be able to calculate actual density of foam.
94.65 L corrected for .88 PCF= 107.65 L
94.65 L corrected for .82 PCF=116 L
Or so it would seem if I did the math right...

[surfcowboy]

Jrandy is the Shoe Shack mvp lately.

[Califoilia]

Ugh, I'm not understanding the the "true weight" not being 1 PCF (not even getting what "PCF means for that matter)...and admittedly even more confused where the "corrected for" numbers (.88 and .82) came from to get the 107 and 116 L respectively.

But in the meantime, I did rethink things a little more, and it was possibly more operator/reader error wrt the scale's readout than a numbers problem or discrepancy. When it read as I remember (this was a couple weeks ago already) it showed "3.13.35" - but more than likely in hindsight, it probably read "3:13.35" - which instead of instead of being "3.13 lbs"...would have been 3 lbs, 13.35 oz giving me a much different volume value.

So 16oz/lb. and thus 3 lb being 48 oz, and the additional 13.35 giving us a total of 61.35 oz of foam on the scale. With 1 oz of foam equaling 1.89 L (30.24 ÷ 16), and multiplying that by the 61.35 oz of board weight = 115.96 L of foam....or awfully darn close to the 116.4 the computer tossed out there.

At least my mind is a little more at ease than's been running around my head for the past couple of weeks thinking I might have a sinker on my hands. Phew!!

[surfcowboy]

PCF = pounds per cubic foot I think. Most foam wouldn’t be exactly perfect so this was assuming there might be some variation in the density which there has to be depending on a million factors dr9m temp to humidity to whatever else could go wrong that day.

But glad you sorted that. That’s likely what happened as you explained.

[jondrums]

what's the planned layup for 1PCF foam on a 115L board?  Are you going with a sandwich?

[blackeye]

"...it probably read "3:13.35" - which instead of instead of being "3.13 lbs"...would have been 3 lbs, 13.35 oz giving me a much different volume value."

This is a pretty good argument to just keep everything Metric.

"So 16oz/lb. and thus 3 lb being 48 oz, and the additional 13.35 giving us a total of 61.35 oz of foam on the scale. With 1 oz of foam equaling 1.89 L (30.24 ÷ 16), and multiplying that by the 61.35 oz of board weight = 115.96 L of foam....or awfully darn close to the 116.4 the computer tossed out there."

Yup, Metric is the answer.

Commencing Metric binge...