Thickness of a sandwich composite panel, and a few other related questions?

[rxcomposite]

Here is what it says about marine grade plywood.

From what I have read, Oukume is classified as structural but not marine grade. The list attached which are classified as marine grade.

 

[fallguy]

As long as you use epoxy and do a couple of neat coats of resin and epoxy primers, I'd use the wood that failed the test at 6 hours. Any exposed edges get neat coated, so when you, for example, install a coaming, you bond solid timber coaming and close the plywood edges. Then a fairing fill above and below. Never allow the edges to be exposed. This is sometimes painful, but for that boat should be simple to achieve. At the deck interface, the deck to hull must be done so no ply is exposed. There are alternatives for this joint. Rx may even have a sketch. Or I may find one. But you can always laminate timber to close the edge as well.

But you must commit to leaving no wood edges or surfaces exposed to sun or water.

I'd want to better understand how the plywood does in a tear test as well. If you epoxied a piece of timber narrower than the ply and let it cure for a couple days, does the mdf shear easily? It may not matter, but I'd like the peace of mind. If it tears like paper, I'd not use it.

 

[fallguy]

Here is a edge modification for honeycomb core. Here, no edge exposure of this plastic core material was acceptable. Your plywood can be treated same fashion if the core is exposed in any way.

 

[Tall Grass]

Hi,

I'm thinking about building a Souriceau 4.75., a smal costal cruiser designed by Eric Henseval. Since I'm located in Bangkok, it is impossible for me to locate marine grade plywood. The "marine" plywood that are used for boats here is of unknown quality, a risk I'm not ready to take.

The alternative is using a PVC foam core instead, something that are more commonly available here. The NA Eric Henseval suggest the following foam core sandwich to replace the 9 mm plywood/
fiberglass sandwich for the hull:

Outside skin lamination: Fiberglass +/-45° , total of 600 gms
Fome core: Divinycell PVC foam core 80 kg/m3 @ 15mm thickness
Inside skin lamination: Fiberglass +/-45° , total of 600 gms

Is there anyone who can help me with an estimate of how thick the finished sandwich panel will be? I'm not sure if it changes anything, but I thought I better mention that it is my intend to do a hand layup.

When changing the thickness of the sandwich, it will of cause affect the dimensions of cross halving joins between the bulkheads and the longitudinals, and I would also have to add to the edge of the deck panels where they meet the hull, so an idea of the sandwich thickness will be very helpful.

What is normal procedure when laying up the above sandwich? Should I use one layer of 600 gms cloth on each side, or two layers of 300 gms? Does it make a difference in terms of workload and the finished result?

And lastly, does anyone have any recommendations on some books I should read before jumping into this endeavour?

Is "Fiberglass Boat Building for Amateurs" by Ken Hankinson still the go to book on the subject, even though it is more than 30 years old?

Thanks,

Peter

Hi Peter,

Have you construct Soriceau 4.75 in Bangkok?