Core TDS sheets

[fallguy1000]

Gurit Corecell M vs Gurit PVC tds is very strange. The ratings for almost everything on the pvc TDS are better than the M, with the exception of the thermal conductivity.

However, when I do a simple bending test on the pvc; it is like a sponge and the corecell M is much stiffer. What is the measure of stiffness in the panel and why isn't it on the TDS sheets? Is it flexural strength?

What am I missing? The PVC even cuts easier with a knife, and when I put weight on the pvc sheet it bends easier, but it has a higher tensile rating. Is it just that I am that clueless about the engineering attributes?

[Evan_Gatehouse]

Corcell's best attribute is its impact resistance. PVC will have slightly higher shear strength, which is the most important factor for a sandwich core - but for a high speed boat subject to wave impact, Corecell is the gold standard. Nothing wrong with PVC foams, especially for decks, interior parts, etc. but all the high speed round the world racing sailboats (that spend hundreds of hours hitting 20-30 knots in big seas) use Corecell. Your call

Here is the link to the Gurit brochure comparing the differnet cores. Might be interesting to see what each is best for:
http://www.gurit.com/-/media/Gurit/Data ... chure.ashx

[fallguy1000]

Thanks for the link. I saw that sheet at least once before, but that was before working with the pvc. It is very odd how the pvc wins on some stuff, but when you handle it; it seems far 'spongier'. I see that is only has two of the check marks for outgassing vs M. Will I have any trouble with outgassing if I am running full vac? The PVC I have has no perforations, so I was considering doing one side at a time and I would probably laminate the top side of the panel because they are coming out so flat on the topside anyhow. So, for the pvc, maybe I should run at lower vac pressures to avoid outgassing problems.

I'm not sure I like the way they did the comparison, but it is readable if you are careful.

Full vac has resulted in the finest panels with 22 oz triax and 2" perforated Corecell M. They are air free; void free; fully wetted matrix; no white marks; just really nice with resin calculations on my last 3 bulkheads of 33, 35, and 38% resin to resin+glass.

But if outgassing is worse under full vac, I might need to treat the PVC differently?

[fallguy1000]

btw, Evan, I am using corecell M for all water impact areas and the hull panel one up from the WL, but have been considering using the PVC in other places; like my decks or the cabin base even. I have 11 sheets of it; they are smaller by 10" each way from 4x8; so too short for a single panel for the cockpits.

My boat will top out around 20 knots, 25k would be light ship, and I kind of doubt it, but would be pleasantly surprised if it'd do it on flat water or with a slight tailwind. If I can only make 18 lightship, I will be a little disappointed, but can live with it. 16 will be a disappointment, but also tolerable....I digress

[Evan_Gatehouse]

I *think* outgassing is strictly an issue with cooking (post curing) PVC. PVC would tend to "blow off" the glass/carbon on a surface when you post cure at say 50-60C. Room temp vac bagging shouldn't be an issue.

And yes, it's fine for non-impact areas. Before Corecell, PVC was all there was!

[Tungsten]

I have both A and M,I believe Corcell A was first on the seen,pricey stuff.M came after the A the price was a little less.When doing some destructive testing i found the A foam had better peel strength when pulling or ripping the glass from the foam.wondering
how the PVC does when peeling the glass off?
At 5lb density they all dent quite easily,You need around 1/8" outside skin thickness for it to be tough enough.
This is why hull bottoms that will take some abuse are single skin.

[fallguy1000]

I *think* outgassing is strictly an issue with cooking (post curing) PVC. PVC would tend to "blow off" the glass/carbon on a surface when you post cure at say 50-60C. Room temp vac bagging shouldn't be an issue.

And yes, it's fine for non-impact areas. Before Corecell, PVC was all there was!

I am post curing at 155F max. Now you've got me worried.

[fallguy1000]

I called Gurit and they said not to worry about outgassing of pvc during a post cure bake and that the hdt is all that matters. They did tell me that Corecell M wins the impact game despite the differences in the tds where pvc looks like the winner.

The rep said he had one yachtbuilder go by the book and use A/M, pvc, and balsa in the places where they won on the tds; and the guy eventually moved to only the A/M foam.

I think I will save the pvc for the cabin; avoid using xslow on the cabin and laminate only with the slow. Much of the cabin will be handwork. The pvc is not perf'd and would be easier to laminate by hand as such.

Then I am only baking the hulls and M foam. M foam 'grows' above its HDT per the rep; so going to have to limit/avoid the bullet heaters.

[Fuzz]

HDT and TDS What do the acronyms stand for

[Evan_Gatehouse]

HDT = heat distortion temperature

I do know of some high end racing yacht builders using very thin prepreg carbon skins who will not post cure PVC foams.

Where did you get 155F/68C from? Most epoxies are getting pretty rubbery by that temp unless specifically designed for post curing (like Gougeon Pro Set range for example). What epoxy are you using?