EPOXY Honeycomb Vs fiberglass

Discussion in 'Fiberglass and Composite Boat Building' started by phmadeira, Aug 13, 2014.

  1. phmadeira
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    phmadeira Junior Member

    Last edited: Aug 13, 2014
  2. upchurchmr
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    upchurchmr Senior Member

    Honeycomb construction - Stiffer, lighter, can be stronger if designed correctly but will be significantly harder to repair. Stable? if moisture gets in the honeycomb all bets are off and it usually will at least in some areas over the years.

    Plastic honeycomb - personally I doubt it, but I have no data.
     
  3. gonzo
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    gonzo Senior Member

    First, you need to define "Fiberglass standard commercial charter sailboat " so there is something concrete to compare honeycomb to. Secondly, what application is this? For example, a bulkhead would require only cutting a panel to shape. By contrast, doing a hull or deck will require a much more complex procedure.
     
  4. Tungsten
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    Tungsten Senior Member

    I have a small piece here with the vail attached.Hit it hard enough and you crush the cells in that area.How do you fix that?With solid fiber glass you simply grind and add.
     
  5. upchurchmr
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    upchurchmr Senior Member

    Hit anything hard enough and it will be damaged.

    Your suppose to have glass on each side before you try that.

    How hard did you hit it? If you want to do honeycomb you need to get pretty sophisticated with what you expect and how you build it.

    You fix honeycomb basically just like you do solid glass. Grind out the damage, replace the core, replace the skin or skins.
     
  6. Tungsten
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    Tungsten Senior Member

    Sorry I thought it was obvious there was glass on both sides but that's besides the point.How do you grind out the plastic cells and what do you fill them with since nothing sticks to it?

    I have little experience with sort of core but having to cut out the whole core to replace sounds a lot more involved then just grinding down solid glass.

    My backyard tests showed that with enough glass it was pretty strong,some have even used it for drift boat bottoms and have good luck with it.
     
  7. upchurchmr
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    upchurchmr Senior Member

    When you grind out the core, you replace it with the same core.
    I assume it would have the same veil to get it to stick.

    Earlier I did say core was harder to replace.

    Sorry about assuming you did not have glass skins, but I have had similar situations at work where people miss represented a material and how it is actually used.

    With enough glass you don't need the core. ;) Do you know if any weight was actually saved on the drift boat? Core doesn't help at all with abrasion of course.
     
  8. Tungsten
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    Tungsten Senior Member

    I think the main advantage is that if it gets nicked theres no rot issues.Weight savings would be minimal as with any core it requires a thick skin to take the abuse.
     
  9. upchurchmr
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    upchurchmr Senior Member

    The savings is in the skin you don't have to use compared to a solid skin.
    If you didn't save any weight you just made a very expensive, hard to repair skin for no reason.

    Honeycomb that fills with water is also a waste of time. It can even happen with no apparent damage.

    If the honeycomb rots - wait - are you talking about honeycomb or balsa core?
     
  10. Tungsten
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    Tungsten Senior Member

    I should be more clear I guess,rot,compared to plywood.I was talking about drift boat bottoms is where I've seen the honeycomb being used.Hence plywood,rot.

    I haven't used any only tests on the honeycomb.thinking it needs at least an 1/8" outer skin perhaps more to be able to float shallow waters.Hence not a big weight savings.

    again no real experience ,how about you upchurch? Tell us what it can do or where its best used.
     
  11. upchurchmr
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    upchurchmr Senior Member

    My experience is from Aerospace and an engineering background.
    Honeycomb is great stuff.
    A greatly high price, generally.
    Most of the time the focus is on lower weight.
    That takes knowing what your loads are and spending lots of time analysing the structure to see if it works.
    Aircraft can do that because we spend unreasonable amounts of money, we can control what is done with the aircraft (most of the time) and we spend lots of money to inspect, refurbish and repair damage before it gets too big.

    Boats typically have not had that much money (small boats), and are not as easily restricted to known predicted conditions. Rocks in a river is a good example.

    Honeycomb can make structure stiffer for a given weight. However, they suffer due to the thin skins necessary to make lite weight in impact situations.
    Aircraft honeycomb no matter how well sealed and built tends to accumulate water in the core - eliminating the benefit of light weight. In fact I've found that trying to design honeycomb structures gets to be a very difficult thing to make lighter structure using real world requirements
    Those two reasons are why most military aircraft have very little cored structure now days.

    For boats I am more familiar with Polyurethane cores for sandwich construction. Same problems with designing for light weight if you try to insure it lasts a long time. Same problems with repair. It does adhere to glass well, but its strength typically is low enough that its easy to damage the core itself, ruining the structure.
    It is possible to make a sandwich skin that will be more resistant to certain kinds of impact than a solid skin, but there will not be any real weight savings.

    I personally would not use it in the hull for shallow waters, probably the deck or possibly interior structure. But you are going to pay $. Remember I have no information about the plastic core, except plastic is generally quite low strength for its weight. Not a good start.

    Enough of my opinions, I already told you my experience is not with boats.
     
  12. Tungsten
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    Tungsten Senior Member

    Thanks for your input upchurch,the only core that is available to me is the Corecell line.Once winter rolls around I'll try some more testing.
     
  13. upchurchmr
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    upchurchmr Senior Member

    I'd like to know what you get. Are you actually looking for building a river boat?
     
  14. Tungsten
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    Tungsten Senior Member

    More like an all boat. Rivers and lakes. Modified V Car topper no more then 13' long with a floor about 52" wide and about 72" at oarlocks
    The foam I have are M80 in 1/2" T800 in 1/4" and A 1200 in1/2"
     

  15. SukiSolo
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    SukiSolo Senior Member

    There is a similar thread somewhere on here (can't find now or I'd link) but the upshot was for larger more comercial fishing boats, a solid glass bottom was better. Reason was damage from scuffing on rocks etc and ease of repair. The sides and topsides were better cored as lighter but not prone to the same type of (ab)use...

    Despite the weight penalty, it is most likely the most durable solution. Cutting out saturated cores and replacing is not anywhere near as easy as scarfing in new solid glass. Worse in a polyester system with expanded polystyrene as the core ie one type of Coremat. Other 'difficult' core systems are Nomex and aluminium honeycombs - avoid these on the bottom.

    My personal instinct would be do it solid, but if you must have a core, I'd be tempted to use butt jointed WR cedar heavily glassed on the outside. Not the lightest but not to hard to repair either in the worst case.

    In the end, only you can judge the gouging and damage you expect and build accordingly. Definitely take into account the repairability factor.

    You can appreciate that the 'tin fish' type of (aluminium) boat takes a lot of punishment in this scenario prior to any failure.

    BTW upchurchmr, you do not have to replace a damaged core with identical material, merely something similar. I often use solid timber, ply, foam, epoxy microballoon mix etc as replacement core material for repairs. Sometimes you can actually solve a stress problem too with diligent selection. At least on boats....I suspect this practice would not pass aviation standards....;)
     
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