Subject: Re: [harryproa] polyisocyanurate
From: "=?UTF-8?B?QmrDtnJu?= bjornmail@gmail.com [harryproa]" <harryproa@yahoogroups.com.au>
Date: 10/25/2018, 3:00 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Neat find. How did you get to this? 
 
It was while searching for americas cup and kg/m2 and different combinations. At some point google found this line from that document:
"Water absorption [Kg/m2 ] (1 week immersion in salt water) " 
So it was more or less by accident.

Finally, this is a shitty spec. It is what is called a proscriptive spec, as opposed to a descriptive spec.  

I think I agree. Probably they copied the specs from a PVC foam they had experience with. But at least it's gives a reference to what other people think is necessary. An the PIR/XPS where not miles away.

One interesting point is the modulus of elasticity. That is something I was missing in the simple calculations of sandwich panels which I made. The core thickness and shear modulus has to be somehow linked to the compressive/tensile modulus and thickness of the skins, right? I think that during bending, ideally, the elongation of the skins at failure should align with the shear deformation of the core at failure. If not, either of the materials will not be fully utilized.



On Thu, Oct 25, 2018 at 6:49 AM '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
 



| To get back to the subject of foam core, this document has some
| guidelines:
| http://www.irclass.org/media/1850/hsc_rules_july_2016.pdf

Neat find. How did you get to this?

And also, I object.

This seems to be a spec for high powered fast boats and hovercraft, so not sure how it applies to sailboats.

I will note that chapter 3 part 4.5 says
"Other core materials such as honeycombs, etc., will
be individually considered. Expanded polystyrene
foam is attacked by the styrene in the polyester resin
and is not recommended for use as core."

Which strongly suggests these guys are used to polyester fiberglass things, and have no clue about performance epoxy. So, really, why listen to them?

Finally, this is a shitty spec. It is what is called a proscriptive spec, as opposed to a descriptive spec.

Here is a random google on the topic. Not saying is a good one.

http://www.traunerconsulting.com/prescriptive-vs-performance-specifications-in-construction/

To state a proscriptive spec in this (boatbuilding) case is to invite disaster, IMHO. Easy to meet spec and have a boat that kills people.

So, as a practical example, Stonetools 30' length proscriptive spec is very different and difficult than, say his, "need to carry 2 us tonne and have an open layout like a condomaran" descriptive spec.

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