<<I have not seen a reference supporting delamination being related to tensile strength. Would you mind sharing? Typically delamination is related to over stressing the part afaik.>>

DELAMINATION, TENSILE STRENGTH, A

  After a section of a laminated panel is compressed via impact or heavy weight, the skin needs to pop back up while remaining connected to the core material.

  This requires two things: 

    - A core that will allow itself to be compressed non-destructively, so it can go back to its original shape.

    - A core with enough tensile strength to stay connected to the skin as it springs back, and also to not separate internally, inside the core, as it gets pulled into shape.

  That's why aluminum honeycomb is a poor choice for a surface that could experience impact (walking, jumping, dropping a battery, hitting a log, grounding, whatever).  Once compressed, the core does not recover even if the skin in the area does spring back into shape after an impact.  The core just fom the skin and remains crumpled.  

  HexWeb ACG core is almost three times stronger in compression than many polypropylene cores, but it's not recommended for areas that could experience impact because it deforms permanently when crushed.


DELAMINATION, TENSILE STRENGTH, B

  Sometimes sections of the core are in tension as hulls experience combined wracking and wave forces while sailing.  Torsion on a complex structure is a strange beast.


<<many different home built aircraft have been flying for going on 50 years... Delamination is unheard of. Unless builder error. Or violent accident.>>

  True.  But aircraft rarely experience impact or point loading other than on structures designed for it.   The landing gear might be very strong, but the wing surfaces are not.

  A boat's hull, on the other hand, has masts falling on it. logs hitting it, grounding loads, kids jumping up and down, wrenches dropping and 35 kg batteries falling over, and so forth.

  The standard treatment of an offshore boat might, in fact, qualify as a violent accident for an airplane.

  If that composite airplane's wing hit a log, the manufacturer would probably insist on an x-ray, and/or rebuilding the entire section.

  They'd look at me as if I were crazy if I were to say "Ahh, I'll just patch it with a sticky rubber sheet, or some underwater epoxy, and later use some penetrating epoxy and some extra cloth on it once I get to an airport with service hangar".


<<Many of these have been known to be stored, outdoors, in northern costal states, for their entire lives, with the freezing rain, snow, sleet, and hail>>

  Yes.  And so do many houses with shingle roofs.

  Yet both would fair differently if subjected to substantial forces while submerged, and then left submerged for days, weeks, or months. 

  If you look at the IP waterproof-ness ratings, IPX6 (resistant to heavy water jets,) is a lower rating than IPX7 (often specified as immersion in 1 meter for 30 minutes), which is a lower rating than IPX8 (often specified to as 2 meters for 30 minutes, but actually refers to a specific pressure and duration).

  The big water ingress question involves standing water, or being submerged under water, for long periods of time. 

  Then, since this is a boat, stressing the panel with sailing loads, impacts, or abrasion that breaks the integrity of the coating.

  And then leaving it submerged during and after the stress.


<<XPS has given years of service to some. It serves in some pretty tough environments.>>

  Definitely.  And many would say it's a great material for airplanes. 

  But airplanes aren't boats.  Boats regularly experience stresses, impacts, immersion, and abrasion that you wold not see on aircraft.

        - Mike

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