Is this right? (foam)

Discussion in 'Boatbuilding' started by CatBuilder, Feb 16, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    Today, I worked 7 hours. Here's what I got done:

    1) Applied packaging tape to 1/3 of a 45' mold.
    2) Put down 2 (!!) pieces of 1" (25mm) A600 foam... possibly not well!

    Shouldn't I be getting more done than that? I only took a break for 20 mins to get some fast food and ate it at the boat shed fast. My first fast food in many years. The transmission went in my RV that is at the boat shed, so I had some odd living situations going on and fast food was the only thing.

    Back on topic, putting packaging tape on 1/3 of the mold and getting 2 foam pieces down seems a bit lacking. The foam was much more difficult to work with than I had anticipated.

    Here are some pictures of what I got done. To me, this looks very bad, considering how much effort I made making a perfect mold. The foam is not sitting down all the way on the mold battens and I toasted both sheets.


    [​IMG]
    Sharpest curve of the bilge... the transom area of the hull. This took hours to get in place, but it does look good. There are a few very small warps, like the next picture.

    [​IMG]
    Here is a bad warp in the next panel up from the stern. It just doesn't want to sit down. I broke some 3mm plywood washers trying to force it and the screw went right though the foam.


    [​IMG]
    Here is what they look like in place. Toasted like a mutant toxic marshmallow... both of them. Do I worry?


    What do I do about the toasted part? Sand it off and put bog there to even it out?

    How do I get my foam more fair?!?

    I see the Ian Farrier sites and they all seem to have no problem. Neither does the guy from fram.nl. Granted they all use 3/4" and I'm using 1", but it seems everyone is doing a better job... :(

    Do I just not worry about all the waves and burnt foam? Do I just bog it all out later? :confused: I can't keep blowing through foam sheets practicing. I need to use them in the real boat.

    On the positive side, I no longer feel the effects of hydrogen cyanide gas when burning core cell. I am wearing a hazmat spacesuit with forced air into the full hooded head enclosure. It pulls air along a hose from outside the building, which is fantastic. It even came with a HEPA filter inline! :)

    Any advice for me on the foam?

    Also, how do you use the screws with plywood washers and the screws that go in from the back of the mold? Do I not touch the screws in the back of the mold until after I shape the panel with the plywood washer screws that go in from the front? I tried pulling the foam down with the screws in the back and they just strip the foam. How do people usually work these two types of screws together?
     

    Attached Files:

  2. rberrey
    Joined: Oct 2010
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    Location: AL gulf coast

    rberrey Senior Member

    Cat for my own sake i hope you can do more than 2 sheets in 7 hours. What if you epoxyed some small tabs where your warps are on the batter board side, maybe the screws would pull the foam up a little tighter. I,m sure someone will post some solutions. rick
     
  3. CatBuilder

    CatBuilder Previous Member

    The battens (batter boards?) are already pre-drilled with screw holes in them. The screws were stripping the foam when I tried pulling them down from behind. That's why you see all the screws on the front side. The front side screws were to assist the foam in lying properly.

    I'm not sure if I'm supposed to use the front screws with plywood washers to get the foam to the right shape and *then* screw the back ones in, or what... :confused:

    Wrestling with this foam is a lot harder than I had thought. I may have to go back to getting the hot box running, but I'm waiting on some input.
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    You can use drywall screws with the head sunk in the foam. You simply rip them off when you take the battens out later.
     
  5. CatBuilder

    CatBuilder Previous Member

    The kerf cuts worked really well as an option.

    In my female batten mold, do I lay them with the kerfs in toward the interior of the boat, or with the kerfs facing outward toward the exterior of the boat?

    They laid up very nicely with the kerfs facing in... but there will be tiny little air gaps inside the core if I do that because the kerfs close up completely and can't be bogged inside.
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The kerfs are always on the outside of the curve unless you lay the foam wet with resin.
     
  7. CatBuilder

    CatBuilder Previous Member


    I'm getting conflicting info on this. Some other builders said it was fine for the kerfs to go inside. Hmmm... a few more votes? :)
     
  8. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Check with the designer, that is the only vote that counts.
     
  9. CatBuilder

    CatBuilder Previous Member

    That's a good point.

    Look at how great it came out with the kerfs though.

    I was able to put this up in a total of 15 mins today, including cutting the foam piece from a scrap foam panel, cutting the 1/2" deep kerfs and screwing it all into place. Since it is the absolute transom, it required a tiny bit (30 seconds?) of heat just to be sure the remaining 1/2" of Core Cell below the kerfs didn't break.

    What a process though! Hope I can use it. I suppose I can since the kerfs are a little wider on this one thanks to the larger saw blade I used. I can fill them in with bog, no problem.

    [​IMG]

    [​IMG]

    [​IMG]
     

    Attached Files:

  10. rberrey
    Joined: Oct 2010
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    Location: AL gulf coast

    rberrey Senior Member

    Cat , looks good, are you using a heat gun? rick
     
  11. CatBuilder

    CatBuilder Previous Member

    No, I am using one of these:

    [​IMG]

    The heat gun puts out too narrow of a path of heat and scorches the foam. Also, one part will cool before you heat the next part with the heat gun.

    It literally took between 30 seconds and a minute to heat the un-kerfed side of the foam enough to do the bend in the picture. Sure beats the 15 mins+ it took to burn the foam last time. ;)
     
  12. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Those kerfs are huge. Is that the usual method for those boats? It will take a lot of resin and increase the weight. The kerfs on most boats are knife cut.
     
  13. CatBuilder

    CatBuilder Previous Member

    No, not the usual method at all. Normally, it's bead and cove strip planking or thermoforming the foam.

    I was experimenting to try to find something that would work with this 1", A600 (25mm, 116kg) foam. It is very difficult to bend.
     
  14. fg1inc

    fg1inc Guest

    As Gonzo said, those kerfs are huge. Not only will they add weight, but the rigidity of the resin or bog will cause multiple stress risers in you panels. In other words, as the panel flexes, the rigid strips cannot flex and will start to push the laminate off the foam.
     

  15. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    It will look like the seams on a planked wooden boat.
     
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