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Old 09-02-2015, 11:16 AM   #41
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You can probably get away with using Gflex and cloth, but at 15,000 cps, its not ideal for wetting out laminate...the 655 version is even thicker. It does have similar properties to Plexus in strength/modulus but elongates less, 150% for P vs 32% GF...but the stuff is made to stick to a lot of different components including plastic, which most epoxies don't do.
Thank you, I'm not very knowledgeable of the epoxy products, I tend to avoid them as much as I can.
I'd be worried about getting good wet out of even cloth was something that viscous.

I have four or five tubes of plexus that's nearing its shelf life and looking for a project, if I can't come up with something soon I may need to offer it to anyone on the board that could use it soon. I think it was produced in March and suggested shelf life is seven months.
Any ideas?
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Old 09-02-2015, 11:53 AM   #42
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Thank you, I'm not very knowledgeable of the epoxy products, I tend to avoid them as much as I can.
I'd be worried about getting good wet out of even cloth was something that viscous.

I have four or five tubes of plexus that's nearing its shelf life and looking for a project, if I can't come up with something soon I may need to offer it to anyone on the board that could use it soon. I think it was produced in March and suggested shelf life is seven months.
Any ideas?
Gerald
Those tubes would be great for someone doing a cap off restoration...most older boat rehabs are tabbed in stringers, but to place the liner back in and bond the cap to the hull, that would be perfect. I'm surprised its shelf life is only 7 months, being that its in a closed tube...that's not a cheap adhesive to just throw away....
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Old 09-02-2015, 12:04 PM   #43
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Building boats is a lot of fun but I haven't figured out how to make money at it yet, the type of work that pays my bills
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Last edited by commuter boats; 09-12-2015 at 02:10 PM.
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Old 09-02-2015, 01:55 PM   #44
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Those tubes would be great for someone doing a cap off restoration...most older boat rehabs are tabbed in stringers, but to place the liner back in and bond the cap to the hull, that would be perfect. I'm surprised its shelf life is only 7 months, being that its in a closed tube...that's not a cheap adhesive to just throw away....
Yeah seven months, if somebody's got a project that really needs a special adhesive....
if I can't come up a suitable project in the next couple weeks maybe somebody would be willing to pay shipping. I think it's strong suit is in bonding dissimilar materials.
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Old 09-10-2015, 09:00 PM   #45
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Default Bonding two layers of Corecell in hull bottoms

OK, here is a question related to composite boat building that has me stumped. I recently read an article about Spencer Yachts where they say the hull bottom of their 100% composite hulls are two layers of Corecell bonded together and covered with skins of glass/kevlar. The first layer of Corecell is laid over a male jig and then the second layer is vacuum bagged and bonded to the first using epoxy which is infused via some sort of "flow media". I am wondering how this is done. How would you be able to set up the first layer so that it is air tight and thus be able to pull vacuum on it? What type of flow media could you use to spread resin between the two layers, and how would you do it so that you had a tight, void free core structure. I have been perusing several naval architecture websites that have boats that call for a double layer of corecell in the bottoms of the boats, so I guess there must be a way to do it, and I'd like to know what that is. Any ideas?
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Old 09-11-2015, 08:37 AM   #46
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Modern- I'm not sure of Spencer's exact process but it is possible to pull a vacuum on closed cell foams like corecell. You have to pay attention that there are no screw holes put in the core and that all seams are completely sealed. There are a couple company's that make a unidirectional flow media that can be placed between the layers to promote resin flow. ( I believe Owens Corning makes a material called "flow-tex" for example) Or it could be used around the perimeter to introduce the resin In between the layers when a perforated coring is used that will allow resin to flow.
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Old 09-11-2015, 08:45 AM   #47
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There are several types of flow media available that will provide a path for the resin to go, from bulky weaves to tubular knits. Scoring in the cores is also a popular method. Core Cell (or other foams like Divinycell) are actually pretty easy to bag to, the yellow mastic tape used to seal the vacuum bag even sticks to them fairly well, only big problem would be seams, they have to be meticulously filled first. You can use angle brackets on the jig frames and screws (or sticky tape) from the backside to hold the first layer of foam in place as long as it isn't under too much strain to conform to shape. Then you don't have additional holes to worry about air flow during bagging.

Gluing two layers of foam together is of dubious benefit though and relying on infusion for the bond would worry the heck out of me. There's no way to visibly verify you have full coverage and foams don't do thermal imaging well at all. Most builders (including Paul) are now using a single layer of foam instead of multiples.
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Old 09-11-2015, 09:20 AM   #48
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Hey bills, our DIAB rep. Was here a couple days ago and told us that corcell was either not being manufactured anymore or was going to stop being manufactured. DIAB is offering a High strength modulus of divinycell much like corecell.
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Old 09-11-2015, 09:28 AM   #49
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Hey bills, our DIAB rep. Was here a couple days ago and told us that corcell was either not being manufactured anymore or was going to stop being manufactured. DIAB is offering a High strength modulus of divinycell much like corecell.
And you believed a sales rep?

I've heard that too from other sources. I would think Steve should know a definitive answer to that. Doesn't really affect me though, I've been using Divinycell for a long time and many others have switched to it as well with excellent results.
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Old 09-11-2015, 10:00 AM   #50
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Default A very easily answered question.

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OK, here is a question related to composite boat building that has me stumped. I recently read an article about Spencer Yachts where they say the hull bottom of their 100% composite hulls are two layers of Corecell bonded together and covered with skins of glass/kevlar. The first layer of Corecell is laid over a male jig and then the second layer is vacuum bagged and bonded to the first using epoxy which is infused via some sort of "flow media". I am wondering how this is done. How would you be able to set up the first layer so that it is air tight and thus be able to pull vacuum on it? What type of flow media could you use to spread resin between the two layers, and how would you do it so that you had a tight, void free core structure. I have been perusing several naval architecture websites that have boats that call for a double layer of corecell in the bottoms of the boats, so I guess there must be a way to do it, and I'd like to know what that is. Any ideas?

I have thrown this out there in the past. A layer of Fiberglass between two thin cores is better then one thicker core. A fact explained to me years ago by a builder who has more historic IGFA record breaking boats then any other custom boat builder. The fiberglass inner layer seems to multiply the cores ability.
This is proven hands on fact. Not some engineering double talk.
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Old 09-11-2015, 10:03 AM   #51
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And you believed a sales rep?

I've heard that too from other sources. I would think Steve should know a definitive answer to that. Doesn't really affect me though, I've been using Divinycell for a long time and many others have switched to it as well with excellent results.
I would agree anyways. I think working with corecell is a PITA!
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Old 09-11-2015, 12:00 PM   #52
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Hey bills, our DIAB rep. Was here a couple days ago and told us that corcell was either not being manufactured anymore or was going to stop being manufactured. DIAB is offering a High strength modulus of divinycell much like corecell.
You can confirm if they still make it next week...maybe its just bad press from a competitor?
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Old 09-11-2015, 02:07 PM   #53
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You can confirm if they still make it next week...maybe its just bad press from a competitor?


Looking forward to talking to you next week.
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Old 09-12-2015, 02:12 PM   #54
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Building boats is a lot of fun but I haven't figured out how to make money at it yet, the type of work that pays my bills
The rest of that job...
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Old 09-13-2015, 11:12 PM   #55
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I have thrown this out there in the past. A layer of Fiberglass between two thin cores is better then one thicker core. A fact explained to me years ago by a builder who has more historic IGFA record breaking boats then any other custom boat builder. The fiberglass inner layer seems to multiply the cores ability.
This is proven hands on fact. Not some engineering double talk.
In simple beam and panel evaluations the skin at the neutral axis of the core should add nothing but thickness but when things aren't simple some interesting and surprising results can be had.
I've done some projects where I was able to justify two different cores ( density and material ) with a skin in between them and have had very good results particularly in damage tolerance.
It would be interesting to know what the builder you mentioned was pursuing, it had to have been more than just stiffness.

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I would agree anyways. I think working with corecell is a PITA!
I haven't done much with corecell but liked the way it sanded, what was it you don't like?
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Old 09-14-2015, 06:38 AM   #56
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For me it seems like corecell is more difficult to work with in all facets. It is more difficult to do things like run it through a table saw for instance. I like the ductility of divinycell. We do a lot of compound curves where it is necessary to do a lot of shaping of the core itself and divinycell really sands and shapes so much easier. Corecell likes to turn into hot melted plastic balls when you are cutting or shaping it which I could do without.

Corecell also uses a bit more resin in the layups due to filling the larger surface cells as opposed to divinycell. Slightly higher resin consumption leads to a slightly heavier panel.

As far as where I would or have used corecell would be in actual hull bottoms. At this point though I would probably opt for divinycell HD over corecell for that application also.
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Old 09-14-2015, 07:29 AM   #57
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The elasticity of corecell can be nice at times, but I'll agree that all in all Divinycell is the superior product.
Corecell is rarely used in our shop anymore.
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Old 09-14-2015, 05:39 PM   #58
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Kln and Composite Rob thank you for participating, I've been missing out on both of your projects. A link from here would be appreciated as well as anyone else that is doing anything cool. Maybe Roger could post some windmill blade shots.

My current build project has corecell in the topsides in the hopes of absorbing docking loads, balsa and Divinycell on the bottom, and the house is Divinycell.

Almost 25 years ago I did a 36' over a pine birdcage. I draped the birdcage with plastic and then with cotton string sewed on three-quarter inch Clark Foam. Did a little fairing than did a laminate with mat and DB 400. Putty bedded a layer of one half inch balsa and did an outside laminate of three-quarter ounce mat and two layers of DB 600, faired and laid a single layer of 10 ounce in vinyl ester resin. The rest of the laminate was a good quality iso. The boat has worked all its life with a few significant events and has held up well. I'll attach a photo of it taken shortly after it covered more than 50 feet of dry boulder patch, its course was more parallel to the ocean but it hit that big rock that's forward on the starboard side of the bow and went to the port, the stern to the starboard. The picture doesn't show it but the bow is so high above the waterline that it will flood by the engine room vents before the bow gets wet on the incoming tide. They had to jerk it off the beach right before it sank with a 50 foot steel boat. Two weeks after this event I got two days to put Band-Aids on and then it finished out the season. The following winter when I repaired it there was only damage into the foam in a couple places, no stress cracks inside the boat and the balsa did not wick water outside the damaged areas. When the boat when a ground it was carrying more than 3000 pounds of cargo and prior to that photo being taken she was stretched to 40.
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Old 09-14-2015, 05:41 PM   #59
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I have seen some research on ballistics with laminates, and having a middle skin separated by foam has been used to minimize damage. the theory is that the bullet will tumble when penetrating the first composite layer into the layer of foam, and the middle laminate stops or severely limits the damage to the inner core and skin... I could see it as a way to make sure you got home...
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Old 09-14-2015, 08:31 PM   #60
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That's pretty impressive Gerald. Most of the groundings I've dealt with the salvage master wouldn't even bother trying to re float if the vessel was on anything but sand or marsh. I've seen a few production rec boats on the jetty with the hull caved in and stringers cracked nearly the whole length. Had one glass over wood sport fisher that was salvaged after a hard landing on the rocks, I imagine the wood core helped keep it relatively intact. Luckily there ain't too many hard surfaces down here, because a lot of folks can't seem to keep it in the channel.
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