On May 4, 2018 6:48:00 PM UTC, "mcrawf@nuomo.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
><<Did you actually read my post.?>>
>
> Yes. Fully.
>
> I think differences come down to two sets of assumptions.
>
>I'm assuming that the hull will indeed be overstressed while it's in the water, perhaps in ways that we aren't aware, so I'd want the most resilient core material available.

Then why not use a steel core?
One has to compromise. You want a material that meets the guestimated needs.

My point here is there has not been an assertion of an engineering reason for choosing such an expensive core over a less expensive option. Rob has admitted there is a localized economic reason for his choice if H80. Not an engineering one.

And, your statement "most resilient core material available" is factually untrue, with respect, H80 is simply one grade available. They make higher grade material that is provably more resilient.

How is H80 better than H60 or H200? Why choose H80?

I mean all the above with diplomacy. If that does not come through, that is my failing in phrasing. But the points stand.

>There are significant differences in delamination, particularly due to impact, between different core materials. The stress is a given, the amount of damage from that stress is the variable.

I disagree. Only in the case of an overstress should one expect delamination. It is obvious that the carbon fiber and fiberglass anecdotes delaminated due to repeated over stress of the core, who's properties were not known.. To suggest XPS tends to delaminate based on these anecdotes is silly.

>I'm also assuming that water will find its way into the core. XPS may indeed be waterproof (I use it in my dock float, for example), but that doesn't mean it will make for a good core material when water gets in between the sandwich skins, particularly if submerged for long periods of time and then subjected to thermal cycling. Rick's experience being a good example.

Again I disagree. Are you saying all the boats made of XPS are known to delaminate due to thermal cycling? Is Finnfoam aware of that? Because i think they would laugh at you. You know, it is known to thermal cycle in their homeland.

>But I'm a conservative guy. Many others have tested these materials for compression, tension, shear, delamination under stress, delamination under impact, and the effects of water intrusion. Including their manufacturers.. There's a lot of data out there, much of it that I couldn't reproduce through my own destructive testing.

That seems strange. These are ASTM standards, right? If you did not get the same results you probably should contact them to see how you got your test wrong, right? Unless you are suggesting there third party testing was lies. Are you suggesting that?

What grade of XPS did you destructively test?