hand lay up of coracell m foam

The skin is bonded to the foam, if the skin moves, so is the core already... neither one "fails first", they work together...

That said, if you use foam core for a deck, most people usually opt for at least 800gsm glass skin to minimize the possibility of denting like this, some people use much more for durability, as a thin skin is easy to puncture like this (dropping tools, anchors, heavy footed people, stilletttos etc) The thicker skin does help...

 

I thermoformed both my 15 meter hulls.

It gets soft, then you have a few moments to get it into the shape you want, then it locks back into hard again. You can, of course, reheat, but it starts to behave poorly on the 3rd reheat. It's best to get the shape on the first try.

There is some "springback" from the shape you bend it to, so you must screw it into place if thermoforming it, so it holds until completely cool.

You can use an oven or a quartz heater. I never got the oven to work and it was too difficult to keep trying, so I mastered the art of doing it with a quartz heater. It's kind of like cooking food... you have to get it just right - no burning it and you do need it heated up sufficiently to get it to bend.

You'll blow a piece or two first starting out. By the 2nd or 3rd piece, you'll have a feel for thermoforming. Just keep flipping it over and over and over while heating it, so it gets nice and hot but doesn't burn.

 

Here are some pictures from my build. I thermoformed the entire hull. In the first picture on the left, you see the beginning of a hull. Next, you see the whole hull thermoformed from Corecell.

http://www.boatdesign.net/forums/fi...direct-female-molding-41587-2.html#post527109

I guess the last picture on the right shows some strip planking of the really tight area. It could have been thermoformed, but I made my mold in a way that it was necessary to strip plank that sheer curve.

 

ah great burning foam,i see the hdt is 110C.i don't have a quartz heater but i got a heat gun, not sure if i can get it up that high.Maybe it'll just take a little longer.
thx again Cat.

 

Watch yourself when you do this. If you burn the foam, it releases hydrogen cyanide gas. Use respiratory protection or do it outside the first couple times until you can do it without it looking like a toasted marshmallow.

 

One of the first signs of cyanide poisoning is hearing loss.

 

Let me also contribute to that one.

My first sign of cyanide poisoning was an instant, horrible nausea followed by an enormous trip to clean out the old bowels.

From there, some shortness of breath - like cotton in your lungs, various other sick feelings, elevated heart rate and blood pressure, etc...

A trip to the ER revealed pretty severe acidosis (of the blood) as a byproduct of the cyanide. They kept me overnight and watched my vitals until they returned to normal the next morning.

I wear a respirator for pretty much everything now after that.

 

Thanks for the warning,i might have to rethink this.
anyway my test piece has cured so onto some unscinetific tests,



i jumped on this 20 times with one foot(im 240lbs)at one point i was jumping off of a chair and landing on it.no visable damage,i could feel it give a little.

next up 3 lb hammer,4 mighty wacks and.


This side has the 6oz on it,after a couple wacks with a 3lb hammer on the 18 side it cracked.my guess is the crack started because of me jumping on it.Hit it a few more times and the back side 6oz let go,it has 2 layers 6oz.
so after seperating the 2 pieces i set up for another test.This is a 40-50lb side walk block dropped on the 18oz side from about 4'

this is the other side.no cracking here just bent up.



Onto 16oz finishing hammer, one mighty wack on the 18oz side.
hard to see but only a little dent.

the 2 layers of 6oz


some other tests,all with the 16 oz hammer one heavy wack.
1/4"6mm baltic birch ply no glass.

backside

1/4" meranti ply.no glass

back side

. the 18 oz WR side was pretty strong compaired to the ply.
not sure what all this means but i was happy to see the 18oz side stand up pretty good to a hammer blow.

 

A lot of fun - that's all.

It probably gives you a 'feel' for the kind of strength that each weight and method produces.

For any given boat design, the ideal is to have an engineer do a 'layup schedule', to make sure the forces on the hull will stand up to the use.

There are some clever people on this site who can do the calcs - it just depends how serious you are about getting a trustworthy boat built.

 

ah yes - of course that would be the case. The resistance is the sum of both layers. I can 'see' that clearly.

Thanks for the education.

 

one more question,after ripping apart my test piece i could see in some spots the glass didn't stick to the foam as good as others.in most areas the glass came off the foam with a little foam stuck to the glass.

The areas that came off clean had little impressions of the glass weave left on the foam,by digging my thumb nail into these areas it would appear there is epoxy there as its much harder then spots where the foam was ripped off.

What happened?

 

It's an open mold hand layup. Not as good as vacuum bagging, which would compress the cloth down harder onto the foam.

 

This is a minor variation of the problem I had with the very light glass - you might see if using peeply on your next test helps the problem.

By the way, this is why West Systems suggest an initial layup of thickened epoxy - 'raw' epoxy is very viscous, and doesnt 'suck' as hard as thickened epoxy.

 

Ok got the glass ,45 and 0- 90.will try thickened this time.can i just go to wetout right after i smoosh on the mixed goo?

 

Yes. That is the preferred method. Wet on wet makes the best layup. For best adhesion, put the smoothest side of the glass against the foam.