Buoyancy foam - what are the options?

Discussion in 'Materials' started by RSD, Jan 3, 2023.

  1. RSD
    Joined: Nov 2022
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    RSD Senior Member

    My knowledge on foams for boats is very limited - all I know is that some foams are suitable but some aren't as they absorb water or induce electrolysis in aluminium boats. Are there any spray expanding foams that are suitable? Ideally ones with good insulation values too!
     
  2. dustman
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    dustman Senior Member

  3. fallguy
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    fallguy Senior Member

    Trapped corrosive water is very bad for aluminum.

    If you are still considering a catamaran; the better way to go is watertight compartments with waterproof venting. Foam can also be used for buoyancy, but one must respect the problems of getting saltwater between foam and hull/framing. This can be managed, at least in smaller vessels, by putting foam in places seawater is unlikely to get to...like underseats or in compartments not directly laying foam on hull.

    Other forum members and professionals have much better knowledge than me, I only know some basics. Aluminum yachts are being made around the world, so someone here will answer better than me.
     
  4. Rumars
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    Rumars Senior Member

    You need what is called a closed cell foam. There are several types available, polystyrene, polyurethane, polyethylene, rubber. Only PU is sprayable, the rest come as rigid or flexible sheets.
    There are several threads here detailing metal boat insulation. For buoyancy only, a few blocks of PS foam strapped to the hull are enough.
     
  5. kapnD
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    kapnD Senior Member

    Brainstorming here, or possibly brain farts!
    Sometimes I get parts shipped in that are in a plastic lined cardboard box with foam blown in to secure/protect the parts.
    This has got me thinking about blowing foam into boat compartments using a plastic bag inside said compartments to isolate it from adhering to the interior. There are corrugated plastic drainage membranes that could be installed against hull surfaces to facilitate some breathing and drainage of condensate.
    Thoughts?
     
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  6. fallguy
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    fallguy Senior Member

    Done all the time in monocoque builds..guys use 4-6 mill plastic. They still limber the boat, sometimes even a bilge pump or just an inspection well.
     
    Last edited: Jan 4, 2023
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  7. ondarvr
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    ondarvr Senior Member

    Yes, the bagged or wrapped foam has many benefits.
     
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  8. Ike
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    Ike Senior Member

    If you bag the foam you can use almost any type of closed cell foam, preferably 2 lb density (that is one cubic foot of foam weighs two pounds). Bagging keeps the water out so, no problem with water absorption. Also it keeps corrosive fluids, gasoline, bilge cleaners, oils, etc away from the foam. However, if you pick polystyrene, do not use styrofoam. It does not stand up well to shock ad vibration and breaks down into little pieces. There are other polystyrene foams that are mostly used for insulation, that make excellent flotation foam. But if you want two part foams, they are usually polyurethane. As mentioned above, lots of choices.
     
  9. fallguy
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    fallguy Senior Member

    2nd to no expanded foam (beaded foams)

    it will absorb water
     
    Last edited: Jan 5, 2023
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  10. rwatson
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    rwatson Senior Member

    For an "after" analysis of expanded foam in aluminium, try this video at about 12:50


    I've found expanded foam is very heavy.
    One fall-back option is Pool Noodles.
     
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  11. fallguy
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    fallguy Senior Member

    One of my vendors did some testing on closed cell marine buoyancy foam and what he tested is actually not as waterproof as the industry lets on. If the applicator is able to finish it with epoxy or bag it; it is best.
     
  12. tane
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    tane Senior Member

    "...However, if you pick polystyrene, do not use styrofoam...."
    please elaborate which polysterene foams are ok?
     
  13. fallguy
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    fallguy Senior Member

    He means to not use expanded polystyrene (beaded foams). The word choice is problematic because many of us grew up thinking all beaded foam was styrofoam, but afaik modern styrofoam is extruded.

    Beaded or expanded foams have intercellular spaces that will allow ingress and overtime water enters beaded foams and becomes trapped forever.
     
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  14. fallguy
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    fallguy Senior Member


  15. Andrew Kirk
    Joined: Jul 2021
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    Andrew Kirk Pedal boater.

    What about PIR foam? Polyisocyanurate is available in sheets of various thicknesses from 10 mm to 200 mm. It is closed cell and claims to be totally water resistant. It is widely used fir home insulation. Does anyone have any experience or further knowledge?
     
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