Rapido, who has announced the release of this product, says that the purpose of the "ACR" is to reduce car weight (Rapido website), but I think it is for bulk grain transportation and increases the strength of the side structures. I think it's the same as the GN and D&RGW 12-panel boxcars.
The answer to your question is right there in the link that you cited.
Rich
Alton Junction
No undecorated.
I guess that is it. Only Accurail now reliably manufactures undecorated versions of their freight car models.
Are there any others?
-Kevin
Living the dream.
Tangent and Moloco offer undecorated kits.
“Alternating Center Rivet” (or “ACR”).
It's literally the first three words of the text on the Rapido page that was linked in the OP.
Chris van der Heide
My Algoma Central Railway Modeling Blog
I believe the OP's question wasn't what ACR stands for, but the purpose of doing the additional rivet rows. Rapido's explanation, that the car was made lighter by having thinner sidewalls, but then due to the thinner walls needed additional bracing, would seem to make sense. Rapido's folks tend to do pretty extensive research on their models.
Thanks for the follow, wjstix.
It is certainly easy to imagine weight reduction. Are there any references to it? How thick is the skin? In terms of time, I can't think of anything other than Grain Loading. The purpose of this post is to leave a mark that I made that claim. It's not about convincing everyone. See "Light Weight" in pictures below quoted from Car Builders' Cyclopedia 1953.
By the way, do you know PRR's "ARP"? It stands for "alternating rivet pattern" and was adopted by the X29 and X37. (The Penncy Modeler)