Mixing Foam Brands on Same Laminate??

Discussion in 'Boat Design' started by CatBuilder, Dec 12, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    Is it possible (or advisable) to mix two brands of foam core in the same laminate?

    I am considering making the following laminate:

    *Glass
    *1/2" H100 (6lb) Divinycell
    *Epoxy and microballoon bog to hold foam together
    *1.2" A700 (7lb) Core Cell
    *Glass

    This would be a panel for a bridgedeck, which exceeds the spec on my plans calling for a core of 1.5", H100 (6lb) foam with glass on both sides.

    My reasons for wanting to do this are the following:

    1) I have enough 1.2" Core Cell A700 on hand already to do the whole bridgedeck.

    2) Gurit (the company that makes Core Cell) is just too unprofessional to deal with. Horrible sales people, 6 week lead times, no foam in stock, $9/sqft once you have your boat project underway and need more foam, etc... Not worth the hassle and looking to buy all remaining foam from DIAB instead.
     
  2. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    As a home builder I'd say 'why not?'

    As a general reader I'd say, "Ask your designer"

    As a designer I'd say, "Many people use Airex on the bridgedeck as it's a tougher material"

    But I think better still is to use a slightly Veed bridgedeck, as I have done on my Transit 38 etc. That is a much stiffer arrangement, particularly as you then add a flat top (floor) to the V. And the gap between V and floor allows for cable and piping runs.

    More important though, the slight V dramatically reduces wave slam, much more than you would think from looking at drawings

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. CatBuilder

    CatBuilder Previous Member

    A good response, Richard, but also one that raises a couple more questions...

    As a designer, would you approve your "home builder" response? Ie: Will a sandwich consisting of differing density foam layers not bend at different rates, causing possible strain within the laminate - specifically at that bog layer between the two different densities of foam?

    or... is that not a concern?

    My plans have a camber on the bridgedeck, but I was looking at taking it out to save myself countless hours of building settees and cabinetry on a hill. I planned not to have any extra layer or floor above the bridgedeck panel to keep weight down. I usually stop slamming by altering course. The boat does have a 1 meter (3ft) clearance, so it is not a cat very likely to slam anyway.

    Airex is a possibility, but I'm not sure how it is tougher that Core Cell or Divinycell. A bridgedeck would encounter slams and it is under strain in tension, compression and flexural directions. What benefit would Airex have over Core Cell or Divinycell for those loads and slamming?
     
  4. rberrey
    Joined: Oct 2010
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    Location: AL gulf coast

    rberrey Senior Member

    Maybe put a layer of glass between the cores. A light weight kevlar or S glass might give punture resistance between the two cores and some compression strength. Rick
     
  5. CatBuilder

    CatBuilder Previous Member

    Sorry for the bump, but any designers here know the answer?
     
  6. CatBuilder

    CatBuilder Previous Member

    Rick, it's a bridgedeck. No puncture resistance needed. Mainly, I am wondering if the laminate will self destruct if the core is made from 2 layers of different foam, which flex at different rates.
     
  7. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    Do a test, panel against panel. Like a drop test, or maybe glass the panels face together around their perimeter & pump some water in. 2' or 600mm x 600mm is typical for a test panel. Getting a good consistant bondline between the foam layers will be important.
     
  8. CatBuilder

    CatBuilder Previous Member

    It's actually not breakage strength I'm worried about. My plans call for two layers of foam, my dagger boards are made from two layers of foam, etc... All items like this are bonded under 29" of vacuum and make a perfect join.

    It's if, over 10 years of constant flexing at sea, there will be a problem because one part of the laminate will flex more easily than the other.

    I am uploading a picture, because I'm not sure my question is clear:

    [​IMG]

    I am not concerned with the quality of or method of construction. I know how to make the panel (the foam join will be vacuum bagged, then the glass will be vacuum infused). I am concerned with the long term health of the panel if it flexes over a million cycles (as pictured flexing). Does anyone know what would happen in this case? Would the laminate destroy itself at the bog or glass bond lines due to differing foam densities or modulus?

    Any designers or engineers here that can confirm what will happen to the panel? :confused:
     

    Attached Files:

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  9. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    What do your suppliers say?? Apart from "throw away my competitors foam and buy more of mine as its better"

    More seriously, I don't think any one would commit themselves to an answer and I certainly wouldn't believe any that were made.

    The Volvo race boats are probably the most carefully designed boats around, yet look what has happened to half the fleet already.

    And we don't need to mention the Space Shuttle do we?

    Basically you are asking a question that is impossible to answer honestly, sorry

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  10. CatBuilder

    CatBuilder Previous Member

    Thanks, Richard.

    I know you are a good designer, but mathematically, how can this be a complete unknown?

    After a million cycles on a laminate we can predict how:

    *Various cores behave
    *Glass skins behave
    *Bond lines behave

    Isn't there a way to (mathematically) look at the internal stresses in a laminate that is comprised of all the same core vs. a laminate that is comprised of two different cores?

    I'd hate to have to research this and do all the math just to find out if it can be done.

    Maybe I need to take this question to a mechanical engineering board or materials science board? I have to assume someone, at some point has actually looked into this...

    It can't be impossible - it's a rather simple problem that I didn't want to have to do and do the math on if someone knew it off the top of their head.
     
  11. tunnels

    tunnels Previous Member

    what ??

    Why does a simple job like laminating and laying glass and rolling bubbles have to be made into a mathimatical night mare ???
    Its simple job , its easy to do so lets keep it that way !!

    We been mixing and matching materials since dinosaurs laid eggs !.
    Cores , glass, even resins and catalysts , Designers i know usually know stuff all if they have never done the hard yards on the floor and got there hands dirty a few times . Looking at a computer screen and punching figures all day the practical and know how and common sense are all missing . We keep trying to get more from less and wonder why it eventuall all turns turtle or even to custard !! Stupidity prevails and things like the lack of logical thinking has no place any more it seems !! A computer does not have a brain and is not able to think for itself !,You are the driver and you feed it information !!if you dont give it all the information it just sorts it and gives you answers!!. Right or wrong you get want you ask for !!,!! The part thats always missing is the know how !! Thats the bits that computer dosent have , because you the drive has never given it know how !!
    Computers cant even make a decent cup of coffee!!, so how does it know what right from wrong ??
    Think!! why does a car have an accident ??
    Is it the cars that has tha accident or is it the fault of the driver? .The car cant drive its self it is only doing what the drive tells it to do, if the driver dosent understand what the cars capabilities are then there is communication breakdown so ?????
    Same applys with glassing!! Know the products capabilities you will be working with Know the best method that should be used and if you think they are wrong say something and tell the designer hes is a nerd and to get his hat on straight He will love for that !!. You are protecting his reputation because of the boat breaks he is the one that gets pointed at !!
    Most times these days the designer or his assistant is to busy watching the office girl walk by and not concentrating on what he is meant to be doing . !!! Designer are only people they do and have made mistakes and will keep making mistakes till they learn Know how !!

    I remember looking at the Young America boat that broke in half and plucking scraps and samples of the damaged hull and thinking to myself How could such a well know and exsperianced designer and a build make such a silly mistake? first with the design and then with the maker of ! one wasnt questioning the others logic for wanting to make a deck in such a way it had a weak place right in the middle so the right hand wasnt looking to see what was practical and questioning the logics behind the designers choice of sillyness .
    I was working in the company where the boat went to be repaired by the maker !!

    Why do you live in the world of, if its simple theres something wrong with it ?? :eek:

    With foam cores if in any indoubt always use a higher densty foam than what specified . Core shere is a major problem when using foam !
     
  12. CatBuilder

    CatBuilder Previous Member

    Thank you sir, can I have another? (Taking a beating)

    So... will the panel survive a million cycles at sea with two different density foams as a core? :?:

    I wouldn't ask the question if I already knew the answer.

    I am assuming you are saying I can throw whatever I want into the area between the glass sheets and "she'll be right?" Is that what you are saying?

     
  13. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    If you converted this equation to 2 different densitys of wood such as Doug Fir and say
    Teak, using epoxy, I would tell you to glue it up and forget about it. I feel the same holds true here. Now if you were building an airplane I would search further for an answer. A boat, NO, do it and move on as you can keep an eye on it for the next 25 years. Relax and get a good nights sleep. We see steel and aluminum bonded to plywood all the time with epoxy. Nothing will happen. It will not turn to mush in a Force 9 Storm. The epoxy has a strength greater then the movement of the unequal cores............................Your not using white glue are you?????????? Paste?????????????
     
  14. rberrey
    Joined: Oct 2010
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    Location: AL gulf coast

    rberrey Senior Member

    The 1.5" H100 requirement should have a safty factor added to it . As you are building a boat designed for home builders I would think it would have a large safety factor. You will be .3" over in thickness overall and 1 lb over with your A700. With your A700 being about 71% of the core,and totaling about 81% of the required core thickness, the core cell alone might meet the needed design strength without the H100. The H100 may only occupy the % of core that is there for the safety factor with .22" of core thickness added.If you are afraid of seperation then add mat or a layer of glass between the two core,s. Rick
     

  15. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    Catbuilder, I like your pictures, I think we'll call that HCT or Hybrid Core Technology, you could ask a similar question of the case of using a core bedding putty in contact molding of composite parts, with that you effectively get a higher density "crust" in the core to laminate interface. I still say make it & brake it to check the failure mode. Another similar question might arise if(as commonly done) you applied an overlay timber deck to the upper side of that laminate & made it stiffer(I know it's different but...), you might ask also what happens with double "kerfed" foam which effectivly gives different core densities, also the result of partially filled core kerfs is well discussed in Pro Boat etc.. Again I'd stress that the quality of your "blind" bondline between the different foams is the key to success(I know you'll be careful etc etc) but for others, the resin priming of the foam is important as the cut cells of the foam will "scavenge" resin from the bonding/bedding microbubbleputtymix, I only say this 'cos I've seen the results of wasted core material with "dry" bondlines, also vent holes in the foam assist in ensuring more complete bedding of plain sheet core bondlines esp at low vac levels.....not everything needs max vac!.

    All the best in your endeavours from Jeff
     
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