Fixing foam block

Discussion in 'Sunfish Talk' started by mdelaney, Nov 30, 2009.

  1. mdelaney

    mdelaney New Member

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    While I think the 2 part is probably the best, I am still looking for an easier method. I recently found a product called Marine Evercoat Sealant Foam, by Evercoat, which they advertise as waterproof. I called the company to inquire about the density and the Tech I spoke with did not know. They are supposed to be checking with their development people and are to call me back. I will advise once I hear, if I hear. But in the mean time, has anyone tried this product? The negative on the Great Stuff seems to be related to it not being waterproof, this in the other hand is by a marine company and is water proof. I am intersted but still waiting.
     
  2. Wayne

    Wayne Member Emeritus

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    In the real world there's waterproof and then there's waterproof.

    Plastic foam comes in two main structures, open cell (not waterproof)... a sponge for instance, and closed cell (what's called waterproof)... pool pasta, food coolers, and of course, our boat's emergency flotation.

    Of the closed cell variety there are different plastics ... polystyrene and polyurethane are the two formulations we are concerned with. Polystyrene is the stuff the emergency flotation blocks are made from. Polyurethane is the stuff the blocks are bed into to adhere them to the hull.

    Both these types of plastic foam are "waterproof"..., but there are differing degrees of waterproofness.

    Both plastics form an extremely good barrier against water in it's usual liquid form, however, when water changes state from a liquid to a vapor the whole equation get more complex.

    As a barrier against water vapor we need to look closer at the plastic's molecular structure. Under the microscope, all materials are porous and our foam's plastic walls are no exception.

    Like a party balloon resists the passage of air, our foam's cell walls resist the passage of water vapor. How well they resist so they won't become waterlogged over time relies on one main factor, wall thickness.

    Cell wall thickness in a foam is determined by air pocket size in relation to the amount of plastic surrounding the bubble of air. We refer to this ratio of plastic to air as a foam's "density". The denser the foam the more resistance to water vapor penetration it has.

    The other quality foam possesses with relation to density is its ability to hold weight without collapsing. Again the denser, the stronger.

    The issue with Foam-In-An-Aerosol-Can is, being that it's developed primarily for insulating in a dry-ish environment. The quality most valued there is maximum air bubble size. So, even in its "low expansion" version the plastic to air ratio has been found to be less than or just equal to the minimum level desired for marine use. (2 lb/cu ft - as outlined in the USCG boat builder's guide book).

    Since the way our boat also applies the emergency foam as hull stiffening, we are doubly interested in foam density. So far, Great Stuff - Contractor Grade and its counterparts in the marketplace have only been shown to meet minimums.

    The quest is to find a suitable spray foam that will be both easy to apply and rise above the minimum density to meet our needs. I'm hoping to hear you've discovered the grail.
     
  3. pthayn

    pthayn New Member

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    I have a couple of quick questions regarding the foam blocks. Are they there just to support the weight of the top of the boat? I would think that there is never much weight on the deck of a sunfish anterior to the mast tube, but there are three foam blocks. I ask this because I am refurbing a 40 year old sunfish that I am starting to think all the block are loose. I am deciding if I should leave them alone, tear them out, or try to glue them back in with foam. My other option is to make a fiberglass tube, cut it to lenght, and wedge it in as a brace bewteen the deck and hull and then slap some epoxy with filler around the base and top of the tube to glue it in.

    I should also note that the edges of the foam blocks are rounding off, like they have been loose for some time.
     
  4. Webfoot

    Webfoot New Member

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    The foam blocks keep both the deck and the hull rigid, all are needed. Using a single tube as you mentioned would not work. All the stress would be on one small area and the unsupported areas of the hull and deck would flex. Try securing them with expanding foam. Making fiberglass tubes for a 'block to block' wedge might be an option.
     
  5. pthayn

    pthayn New Member

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    has anyone used the waterfall foam or aquascape foam like dow great stuff pond and stone? It seems like if it is designed to be submurged, then it should not absorp so much water. also, it is minimally expanding, so it seems like its density would be pretty high.
     
  6. Wayne

    Wayne Member Emeritus

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    Those new varieties of DOW foam were included in my original inquiry. Judging from the vagueness of the reply, I'm wondering if these foams do hold when surrounded by a high moisture atmosphere, but in their intended use it would make no difference whether they become waterlogged or not. Remaining unsaturated and light weight probably isn't part of a garden pond's functional criteria.

    [​IMG]
     
  7. Wavedancer

    Wavedancer Upside down? Staff Member

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    Such a soothing picture.

    Now, do I go right of the lilly pads, and get inundated by the waterfalls, or do I go left where the green stuff is threatening to slow me down, but where there is more pressure?

    PS: Racing radio-controlled fishes, of course. The starting line is on the right hand side, just outside of the picture. And the frogs agreed to volunteer for RC.
     
  8. Wayne

    Wayne Member Emeritus

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    You are supposed to use paints and solvents in a well ventilated area. :eek:
     
  9. ivy

    ivy New Member

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    It might be. If it became waterlogged, it would fall apart in freezing conditions.
     
  10. Webfoot

    Webfoot New Member

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    Too bad there is not some way to use inflatable air bladders instead of foam. Always wondered why they were not used to save a sinking keel boat. Looks like someone has done it already.

    http://www.turtlepac.com/yachtdetails.htm
     
  11. Wavedancer

    Wavedancer Upside down? Staff Member

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    Think Laser, all 200,000 of them...
     
  12. pthayn

    pthayn New Member

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    Has anyone considered installing the cubitainers from a laser in the hull of the sunfish, instead of trying to pour in expanding foam for the foam blocks. Especially is you added some hull-to-deck support?
     
  13. Wayne

    Wayne Member Emeritus

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    That would be great, but what do you do for reinforcing the hull? The styrofoam blocks act as stiffeners.
     
  14. Webfoot

    Webfoot New Member

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    Would not be legal to race. I think it could be done if...

    1. Foam blocks behind the tub remained in place.
    2. The bladder would expand to provide support between the deck and hull without blowing the deck off.
    3. You could make a bladder that is the right size. I don't have a clue how this could be done.

    The whole thing would be much more complex then simply gluing the blocks in place. It would also be less robust than foam blocks. For those who like a to experment, it would be interesting. Might be able to knock the hull weight down to 100 lbs. Failure would most likely mean looking for a new hull.
     
  15. mdelaney

    mdelaney New Member

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    OK, Looking for some guidance. I have removed all of the old foam that was holding my blocks in place and now getting ready to re-attach them. I think I want to go with the two part pourable expansion foam. Does anyone know approx, how much is needed. I have seen it on a few web sites, but not sure how mch to buy.

    Also, in an effort to make the hull stiffer I am thnking about putting a strip of balsa core down on the inside of the hull. Any thoughts on this from you experts.
     
  16. Webfoot

    Webfoot New Member

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    When you get the foam blocks doing what they should do, the hull will be stiff. Sometimes there is a problem with lack of support between bottom of the tub and hull. I used expanding foam but strips of foam wedged in would work. Anyway, just push on the bottom of the hull to check for Oil-Canning.
     

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