<<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.  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'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.

  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.

  So I'm happy to spend $88,000 on a proa to benefit from that R&D, rather than spend $80,000 and wonder about delamination and water intrusion.

  Of course, that's a subjective choice.

---

  The question, as I mentioned in my first response, is:  how much do you need to save in order to risk the safety of your family on the open ocean?

  Everyone has an answer to that question, and they clearly are all equally valid.

  Personally, I'm most comfortable looking at time-tested core materials and picking the one that best suits my goals.  I'll spend a bit more, and tolerate a bit more weight, to get the most resilient core I can.

  Someone else who cares about every gram would make a different choice.  As would someone who wants to shave down that last 10% of the boat cost.

        - Mike

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