The core in a sandwhich doesn't need to be super strong. 

Maybe the fiberglass reinforcements you want to make aren't needed?

You said to replace stringers. How about just choosing a thicker core?

On Sat, Jul 7, 2018, 16:42 StoneTool owly@ttc-cmc.net [harryproa] <harryproa@yahoogroups.com.au> wrote:

 

Doug:
    This is not about strip planking at all.  The wrapped planks, or planks with just glass along the edges, would be assembled into a flat panel on the table top just like solid sheet foam.  The difference is that between each pair "planks" would be a two ply glass rib running the entire length of the panel.  This rib joins the two surfaces of the sandwich like little the web on an I beam.  Think of those I joists used in the construction industry
or aluminum truck decking      The strong tie between the two surfaces would greatly enhance the strength and stiffness of the panel compared to having just foam as the shear web.   The failure modes of foam sandwich virtually always involves separation of the face from the core, or shearing of the core. 

    Something like this might be too stiff to bend much longitudinally once infused.   That's good as far as eliminating the need for stringers, or for compensating for the lack of stringers by thickness of the core or surface plies, but it might require the table to be curved longitudinally during the layup and infusion process, but it should twist fairly easily.   MDF is not especially flexible, but it is flexible enough to be able to shim the table supports  enough to match the longitudinal curvature of a long narrow hull catamaran or proa hull.  The real beauty of this is that the plank width and number of plies along the edges  could be varied based on the load in a particular area.  Areas subject to water pressure and impact would have narrower planks, possibly with more plies or heavier fabric between them.  The function of the foam then becomes much less critical. 

    Bjorn suggested angled slices in the foam creating a sort of honeycomb.  The problem I see with this is that it would allow resin penetration, but resin though it would create some stiffness, has no real structural strength.  It would not physically join the two surfaces with a structural material.  I don't see a way to produce something of that nature with real useful properties.   The planks would be fairly easy to do and pretty versatile,  Once you start breaking things up more than that, it quickly becomes impractical.....

    Anybody who has not read it, should read marine surveyor David Pascoe's piece on foam core boat building and it's problems.   It is worth keeping in mind that the construction techniques used in these boats left a great deal to be desired.  Gel coat sprayed into a mold, then layers of hand laid glass, then the foam pressed into the mold with bonding paste, followed by more glass, so they really are not comparable to what we are talking about on the HP group, but the failure modes when it does fail, will be the same.  With infusion however we should start with a far superior bond, a much better product.     http://www.yachtsurvey.com/core_materials.htm


                                                                                                                              H.W.


On 07/06/2018 09:25 PM, doha720@yahoo.co.uk [harryproa] wrote:

 

Sounds like y'all are catching the invent a new way of doing things bug.

It is good mental exercise, but no doubt common sense should prevail as eruttan said.

I have done couple ply on stringer and frame boats then i did the HP El in strip planked kiri.

The shapes were completely different. Hard chine with flat panels for thd ply boats and round smooth curves and oval like cross sections for HP. These round shapes add to the overall strength, so no stringers needed in the strp planked HP. Not so sure how different the new flat, straight designs are for strenght, but the old HP lw hulls were very strong looking and feeling.

Doug