| 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.