Expanding foam

Discussion in 'Materials' started by Saqa, Dec 12, 2014.

  1. Saqa
    Joined: Oct 2013
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    Saqa Senior Member

    Guys, need your assistance here. I am looking for a basic understanding of this material and looking for a quicker primer on the topic of expanding foams that can be used to make a structural plug/former by using a mold, and then be laminated over with epoxy/glass for surface sheathing and structural skinning. The aim is to explore its suitability to make a 20' or longer pontoon type floats, a pair to be used for a catamaran with a rigid full deck. I am reasonably familliar with regular methods like ply or foam flat sheet applications, the intention is to explore the expanding foam material

    I should state, I have zero experience with pourable expanding foam of any sort and also starting with zero knowledge of the material. I want to go about searching on the web armed with the right questions, as it is I may not do a proper search and disregard the material after encountering search results that may not me the foam that I should be looking at subsequently fail to encounter the right foams

    The properties that I am keen on learning about:

    (please excuse the use of metric, I can visualize lengths in feet or inches but anything else is beyond me)

    1 - Feasibility from a weights perspective; a foam plug with a volume of 2000L. The surface area of around 15 square metres laminated with 450gsm+epoxy amounts to best case of 13.5kg sheath weight. The weight of the plug plus sheath will be the total weight of the pontoon, what is the best case weight I can look at using lure grade foam?

    2 - Feasibility from a structural perspective 1; Looking at a pontoon that is 6m long x 50cm wide and 70cm deep. Molded foam plug sheathed in 450gsm biaxial glass and epoxy. How strong is this structure likely to be. How much pounding can it take, opinions wise?

    3 - Feasibility from a structural perspective 2; Same pontoon questioning Friability (from wiki), the condition of being friable, describes the ability of a solid substance to be reduced to smaller pieces with little effort, especially by rubbing. Lets add pounding forces on the sheath and effects on skin to plug adhesion. Lets also add any flex in both the plug and skin induced by torque from wave,load and motion forces as well

    I have no commercial reasons for asking this assistance apart from maybe sometime in the future using my next boat for commercial fishing
  2. gdavis
    Joined: Dec 2014
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    gdavis Junior Member

    plywood web?

    hello Saga, that pourable foam is wicked expensive! How about foam billets or sheets with a plywood web system for added strength and stiffness. Something like a "t" section running full the length of your hulls. The epoxy- glass sheathing would have to be fairly thick to withstand punctures at least below the WL. Perhaps plywood hulls would be better in the long run, easier and faster to build and probably stronger. And if final cost is an issue the wood hulls could be covered with a fiberglass resin instead of epoxy although if you step away from the big names in the epoxy world there are resins that are just as good at cheaper prices. Still good and sticky stuff! Could the hulls be a semi v? The tops could be flat across to make deck and house attachments easy. Okay, bye for now, hope some of this helps............g
  3. Saqa
    Joined: Oct 2013
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    Saqa Senior Member

    Thanks for the input George

    Good quality local marine ply is really cheap here in Fiji, about $60 Australian dollars for a 8'x4' 9mm sheet and 20L epoxy kit is about $150 Australian dollars. The retailers and suppliers work on extremely narrow margins for these kinds of items as otherwise they couldn't sell it. Ply will be my fall back option

    Thing is there are two things I want in this build

    Firstly I dont want anything that will rot if I fail to notice any scrapes and dings, the boat will kept on a mooring and often beached

    Secondly I am a vain ******* who likes to show-off :D All the boats here are either ply or glass pangas. I want to make something that will have the locals scratching their heads on how I managed to build sexy compound curves and flares and such at home :D

    I need to find out what is "that" pourable foam and how expensive is that. The local marine resin supplier has two part expanding foam that is around $150 AUD for a drum kit. I just don't know what specifications I should be asking for and if that will end up being too heavy a float

    Another thought I had after posting the original query was to place an epoxy finished ply box inside the mold with frames and stringers so less foam is needed and the only way water can get to the ply inside the glassed foam would be in a serious damage. Is that lines along which you mentioned?
  4. Saqa
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    Saqa Senior Member

  5. upchurchmr
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    upchurchmr Senior Member

    Foam often seems very light since it is 1-4# / cubic foot. But you need to think carefully about the total volume and thus the total weight.
    Everytime I look at something like this the foam ends up a much larger weight than I want.
    Older expanding foams have not been actually closed cell - allowing huge amounts of water to be trapped over the life of the boat. I know because I have removed some that was more like a full sponge. If you cut or scrape the surface it starts picking up water.

    I have no experience with newer foams - good luck.
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    5 pounds per cubic foot is the minimum for structural applications, with closed cell foam. I too have removed soaked foam that had to be taken out with a shovel, because it was full of water and/or fuel. My favorite is the stuff in a bilge, where the combination of diesel fuel, urine and old vomit can be an enticement.
  7. DennisRB
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    DennisRB Senior Member

  8. Saqa
    Joined: Oct 2013
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    Saqa Senior Member

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