Airex and any foam based hull materials

Discussion in 'Boat Design' started by tdamico, Aug 6, 2003.

  1. tdamico
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    tdamico Junior Member

    I have heard this:

    The weight difference from Airex to balsa is minimal. The reason for the balsacore is that it is stronger. Airex foam is not a good foam for use on catamarans as if it is heated then the Airex foam tends to get soft and this is not good for the open decks of a cat.

    And I have heard this:

    ...However, some foam cores are expensive, such as Airex. In comparison, some PVC foams say they are almost as good as "Airex", but in the long run, the minimal amount you would save using a inferior foam, would not pay off when the foam crushes under impact and you need to replace the entire foam and fabric section. Why would a production company knowingly install foam that will crumble under impact, or use a balsa-core which is heavy and will rot? They do!

    Any thoughts?
     
  2. Willallison
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    Willallison Senior Member

  3. tdamico
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    tdamico Junior Member

    Thanks for the geat link. I will print out the article and read it this evening.

    :)
     
  4. Roger Marshall
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    Roger Marshall Junior Member

    End grain Balsa core does not rot when the core material is fully encapsulated in fiberglass. Styrene in the core stops any rot. When water gets into the core through a crack, water cannot migrate across the grain, just as it does not migrate across the grain in trees, but goes up and down.
    I don't believe Airex is sold in the US anymore, but a whole bunch of new cores are available from ATC Chemical in Ontario, Canada. ATC is run by Thom Johannsen who used to sell Airex core in the US. You can also get Klegecell and Divinycell foam cores.
    As long as the core materials are greater than about 6 pound density, and the laminate is built properly they should not fracture. A core material typically fractures when the laminate is impacted or if it is poorly mainated.
     
  5. Willallison
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    Willallison Senior Member

    1st up, welcome to the forums Roger - another addition to the list of names on this forum who actually does know what he's talking about:D

    Short term, this is certain to be the case. When water is allowed to soak the core for an extended period, however, I'm not so sure. Until recently I owned a 1993, 27ft Searay. Water had migrated into the core of a side deck, through a base plate for the bow rail. The 1st indication of any damage was when the deck became soft under foot. In repairing the damage, the core was found to be rotten for about 50cm either side of the water's entry point. I would expect a manufacturer like Searay to use styrenated balsa, so I don't think it was a case of poor workmanship on their part. Having said that, there was no indication of a solid 'glass block where the through-deck fitting was either....
     
  6. Roger Marshall
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    Roger Marshall Junior Member

    Ok, Maybe I should have said that water takes a long time to migrate across the core. Whenever you find a crack in a cored fiberglass hull or deck, fill the crack ASAP. Leaving it will allow water into the core, and eventually it will spread. Other than removing the core and allowing the area to dry completely before reglassing, I know of no satisfactory way to repair a wet core.
    To fill small cracks I find the best way is to use a Dremel tool with a vee shaped bit and make a small groove. The groove is filled with epoxy, sanded smooth and repainted with deck paint. (I use Interdeck.) Look for cracks around through bolted gear, corners of cabins, and near window corners.
     
  7. Portager
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    Portager Senior Member

    All this talk about Fiberglass cracks and core damage has me wondering, which type of construction requires the least maintenance? I think most people believe that Fiberglass (or fiber reinforced plastic) is very low maintenance, but I wonder if metal boats would be lower. Also how does steel compare to aluminum for maintenance?

    Thanks;
    Mike Schooley
     
  8. Roger Marshall
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    Roger Marshall Junior Member

    Ooh boy! what a subject! replying to this one will open up a huge can of worms, but we'll give it a go.
    First, fiberglass is low maintenance, but as I said, you need to be careful of cracks in a cored hull. Other than that, polish once a season and you are home pretty free. Older boats need more work, of course.
    In my opinion, metal hulls are relatively low maintenance, given that the finish is applied properly to start with. A steel hull must be sandblasted and primed and faired BEFORE there is any possibility of corrosion starting. Given that most builders are close to the ocean, this usually means sandblasting a strip and coating same within an hour. The faster the better. Steel also needs to be designed so that there is no possibility of standing water anywhere in the structure. Having said that a good finish will last about five to eight years, before it should be repainted.
    Aluminum alloy hulls are also low maintenance if they are coated properly. Again the secret is in the coating. Alloy oxide quickly in air and prevent corrosion. An alloy hull needs to be etched, then primed and faired and painted. If you can find a boatyard to do the job properly and you don't have electrolysis problems, you shouldn't have problems with alloy hulls.
    Note too, that any paint barrier, I don't care who makes it will break down after eight to ten years, so you will see corrosion if you don't keep after it. All in all, you don't need to keep after fiberglass quite as aggressively as you do steel or alloy, but with any finish it will deteriorate if you assume that it will last for ever.
    Part of the problem is that many steel boats are built by amateurs who have little idea about complete corrosion protection and the boat starts to rust quickly. If you look at a steel hull built by a company such as Jongert in Holland the boat lasts for years.
     
  9. Timm
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    Timm Senior Member

    Regarding the availability of Airex, I believe it is now being marketed in the US by Baltec. The biggest problem with cores is the poor workmanship. For instance. . . bow rails, cleats and other deck hardware should NEVER be fastened through core materials, only solid glass or some type of solid blocking such as plywood, plastics or metal. When I worked for Carver, we used to glass aluminum plates into the deck everywhere a stanchion would land. This plate was then drilled and tapped to accept the fasteners. At other companies I have thru-bolted through plywood cores and on some walkarounds with very narrow covering boards up forward, the core was eliminated and replaced by a few layers of 2415 Fabmat. This was easy to install and made for a very strong installation.
     
  10. Portager
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    Portager Senior Member

    Thanks for the information Roger.

    I agree with your assessment, although I have found that fiberglass is more prone to blisters in warn water which increases their maintenance cost. In addition, fiberglass boats are more difficult to protect against lightning and most production boats have no lightning protection to speak of. It seams most manufacturers believe their liability is lower to provide no lightning protection than to provide inadequate lightning protection. I do not understand why people in the lightning capital and warm water do not prefer metal boats over fiberglass.

    In my case, Portager will be a one-off design, so the cost trade favors metal. In addition, I believe that a metal boat will tolerate the vibration of highway transit better than a fiberglass hull.

    Regards;
    Mike Schooley
     
  11. Icomps
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    Icomps Junior Member

    Roger

    I have pulled out very rotten balsa in a number of boats including some well known ones, think that foam cores are better against this, any views




     
  12. BigCat
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    BigCat Junior Member

    Balsa issues

    I don't think placing balsa in female hull molds is a very good idea, because you end up with about 15% voids between the balsa and the outer skin. Water can travel through the voids, if it penetrates the skin, and create a lot of problems. No voids = no balsa problems. So, high quality workmanship in relatively flat panels, or resin infusion, should eliminate this potential. With no voids, balsa is great. Also, only precoated balsa should be used so that there is no excess weight due to resin absorbtion or resin starved laminate from the same cause.
     
  13. jeanke
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    jeanke Junior Member

    Something Strange

    first of all my answers will always be strange :)

    for my aluminium hulls: :idea:

    im trying to melt the rubber of old tires and use that under pressure to fill in voids. Making two weldinglines extra (don't know how to put that in technical ways)inside the hulls i'll use I'm hoping that once hardened this might even work. Cooldown while still under pressure with a removable valve that I can close.

    resolving some weight problems and corrosion that would occure with pu

    I'm not sure what i can use to ensure durability of tirerubber although remelting of the rubber can solve possible cracks being an aluminium boat i could easily cook the boat :D

    :idea: maybe you could even make very small rubberpeaces and combine it with some sort of silicone to put it in the hull

    :idea: you could even just fill her up with silicone or isn't there silicone that has a large lifeexpectancy?

    again I'm being serious but I do have strange ideas. I hope some people will reply :eek:
     
  14. apex1

    apex1 Guest

    Ähhhh..... BigCat and jeanke... you naturally have noticed that this thread died in 2004!
    And jeanke, sorry no offend, but how old are you?

    Regards
    Richard
     

  15. jeanke
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    jeanke Junior Member

    age

    omg I'm just brainstorming

    i will design a new kind of boat ya know

    june 2009 my design will be done atm I'm here:

    [​IMG]
     
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