XPS 100lb As Structural Core - Pros Cons

[Chotu]

[QUOTE=zstine;3265679]

Originally Posted by Chotu

thanks again. good info. I've read through many of your posts regarding your build. sorry that you have become allergic to epoxy, that certainly puts a damper on your project. I appreciate that you have kept an 'out of the box' thinking to keeping your cost down... electric winch alternative to buying a powered Harken/Lewmar off the shelf, buying a used rig, etc... good stuff! And good luck!

This 24ft boat is a prototype that I only need to sail for a few years, but even then, given the info you provided I will avoid XPS in the hull and deck. Hard points for load bearing, noted. I like to use GPO3 (cheap) for backing plates and may use it for 'core' under winches, cleats, etc. The boat is a Tri, but flying a paraglider wing or possibly a hang glider for power. Amas will be quite small as there will be no overturning moment. I intend to get it foiling, especially since the comfort on a boat without the inertia of a standing rig and sails will be like bull riding.

I have a mechanical engineering degree and a basic understanding of aero/hydrodynamics. While I'm no naval Achy, I've sailed for 30 years and have always been interested in boat building, worked at Electric boat for a decade, so I have some knowledge... enough to get me in trouble!

Wing or kite and foiling????

Sounds awesome! I hope you share the build with the community. I’d love to see that.

I had thought about getting mine foiling but in my case it’s going to be too heavy with all the liveaboard stuff.

But between you and me I’m going to experiment with some foil assist later on after the boat is “done “

[clockwork orange]

For anyone who may be interested, the pioneering catamaran design office of CSK designed a 24ft bridgedeck cat aptly named Foamy,which was built out of Styrofoam back in the 1960s and raced successfully in the Newport to Ensenada race. I don't know what resin they used.
For Chotu, you can make very lightweight cabinetry out of phenolic impregnated craft paper honeycomb skinned with just about anything. Its quite cheap but of course shipping is still expensive but if you buy enough at one time its not so bad. The same is true for all sheet goods of course but its tough to swallow with foam and honeycomb because you are paying to ship air. I have used PP honeycomb to make cored panels which of course you can use with polyester but the core is about 6lbs/ft3 so much heavier than the craft paper.

[clockwork orange]

Chotu, have you contacted John Guzzwell re the adhesive he uses, as he became sensitized to epoxy years ago and switched to something from Borden i think for cold molded wood construction

[psk125]

To get back to the original question... have you looked at balsa core? 4'x8'x 1/2" would be $86 at Jamestown Distributors, instead of $155 for the divinycel you quoted. Others may have it for less. Balsa's compression strength is 1842psi vs the 120 you mention for the foam...
The Gougeon brothers seem to have liked it for their boats.

[psk125]

with your foiling & kite propulsion ideas you may also be interested in looking at this:

https://www.youtube.com/watch?v=1tEw...ature=emb_logo

They provide background on their kite and foil research first. The result becomes apparent at about 3min30. French engineering students....

[Chotu]

Originally Posted by clockwork orange

Chotu, have you contacted John Guzzwell re the adhesive he uses, as he became sensitized to epoxy years ago and switched to something from Borden i think for cold molded wood construction

I googled this guy. I think he’s dead.

[clockwork orange]

Originally Posted by Chotu

I googled this guy. I think he’s dead.

Could be, he would be about 90, you may still be able to find the adhesive he switched to though as there were a few articles in various places, maybe Wooden Boat magazine. He built several boats with it.

[Mauro47]

The purpose of inserting a core between layers of composite laminates is to increase the thickness of the laminate without paying a substantial penalty in structural strength (section modulus), mass and material cost.
The core does not directly resist the principal stresses but it must support the shear stress developed within the section when one skin is in tension and the other is in compression. As such a good core material will be light, bond well with the resin and have high shear strength.
XPS is not very strong in shear and therefore is not a very good core material for critical structural applications subject high stress or fatigue like hull construction. In other, less critical applications like cabinetry, seating, small hatch covers, etc, the cost savings obtained by using XPS might make it a very attractive choice as core material.

[zstine]

I was looking into other core options as Divinicell H60 is quite pricey around $150 per 4x8 sheet. I found NidaCore at 1/3rd the price, $50/sheet. It is higher in compression strength (188 vs 131psi), slightly lower in shear (72.5 vs 99psi), but vs much lower modulus... so (2.2 vs 10.2 ksi compression) that tells me it must be stretchy... Another plus is it is made from recycled milk jugs.



Anyway, was wondering if anyone has boat building experience with it? The price is hard to pass up.

[Westcliffe01]

Just go to a decent source for foam. Plenty of rip off artists. There is no point in throwing all the cost of the epoxy, laminate, your time + finishing out (several times the cost of the hull usually) all based on sub standard core material.



https://www.carbon-core.com/product/...l-foam-sheets/

• Plain sheets measure 45.5″ X 96.5″
• Scored sheets measure 45.5″ X 48.25″
• All sheets have density of 4 lb/ft3 or 60 kg/m3

They show 1/2" sheet (plenty thick for hull, deck, interior structure) as being $78.63/sheet (qty 1). You get a better price if you buy by the case, which anyway would be needed for a hull. You will need to ask them how many sheets to a box (I see that if you buy by the box you get a choice of foam density too). They unfortunately left out a simple table showing how many sheets fit in a box based on the core thickness.

Originally Posted by zstine

I was looking into other core options as Divinicell H60 is quite pricey around $150 per 4x8 sheet. I found NidaCore at 1/3rd the price, $50/sheet. It is higher in compression strength (188 vs 131psi), slightly lower in shear (72.5 vs 99psi), but vs much lower modulus... so (2.2 vs 10.2 ksi compression) that tells me it must be stretchy... Another plus is it is made from recycled milk jugs.



Anyway, was wondering if anyone has boat building experience with it? The price is hard to pass up.

[Chotu]

Originally Posted by zstine

I was looking into other core options as Divinicell H60 is quite pricey around $150 per 4x8 sheet. I found NidaCore at 1/3rd the price, $50/sheet. It is higher in compression strength (188 vs 131psi), slightly lower in shear (72.5 vs 99psi), but vs much lower modulus... so (2.2 vs 10.2 ksi compression) that tells me it must be stretchy... Another plus is it is made from recycled milk jugs.



Anyway, was wondering if anyone has boat building experience with it? The price is hard to pass up.

How is your boat being built? Male plug? Female mold? Hard chine or round?

These are the most important parts of choosing the core now that you are at the proper marine cores.

Also, how big is the boat again?

Once you settle on a material, buy the whole boat’s core at one time. I saved a fortune by using 1” thick corecell and buying it all at once from Gurit, the manufacturer. I had cases and cases arrive on a tractor trailer truck. It was overstock they wanted to get rid of. My plans called for 3/4”, but the 1” is awesome! More insulation (heat and sound), an unsinkable boat with all that extra built in flotation and best of all?? The boat is a rock. So stiff it’s crazy. It doesn’t flex or bend in any way at all. Feels great in wave action.

So shop around carefully. Don’t just buy list prices if you are on a budget.

I used a Nidacore product in my build as well. Balsalite. Top grade stuff. Also 1” thick. You can drop a cannonball on my deck and no deflection. Again, plans called for 3/4”. I used 1”. It’s been fantastic for its superior compression strength over normal foam. I used it where I mounted things like cleats and stuff to make that job easier.