Is this right? (foam)

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

  1. Michelle
    Joined: Feb 2011
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    Michelle Junior Member

    I think you should change the foam.
    How is the boat big? I use 12mm thick 80 kg foam for my 9m trimaran.
    Laying foam for 8,5m lengh half float takes us less than one day in two persons.

    The Wrinkless are not good choice. It will add weight and work.
     
  2. CatBuilder

    CatBuilder Previous Member

    All very good points. Thanks.

    I got a tip from a few people about using narrower strips of foam to help them heat more evenly. They are still not easy to work with, but they do work better than thermoforming the larger pieces.

    Here are some pictures of the success today thermoforming the foam.

    Michelle: I can't change the foam. I own all the foam for the entire boat already. The boat is 13.7 meters.

    [​IMG]

    [​IMG]

    The thermoforming creates less fair foam than the kerfing though. It tends to make "lumpy" transitions from batten to batten, while the kerfed foam makes a perfect arc (literally no fairing needed outside).

    Also, the thermoformed foam gets indents in it from where the plywood washers and screws hold it down while it's still hot. Those all have to be bogged in, as does the "out of round" exterior parts.

    Given all of that, which would you choose? :confused:
     

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  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    What does the designer say in the building instructions?
     
  4. CatBuilder

    CatBuilder Previous Member

    Strip planking foam or thermoforming foam...

    but I understand your question. It is a question that teaches. :)
     
  5. CatBuilder

    CatBuilder Previous Member

    It's working!

    Ok, after some practice and some advice from a few people in various corners of the internet (not here, oddly) I found that using narrower pieces of foam works!

    It keeps the heating more even and I don't need to do anything but use that heating element pictured earlier in the thread.

    I found the secrets are to heat the foam evenly and just barely enough to bend. That keeps it from getting lumpy when making the turns over the battens. Now I have an exterior surface as good as the kerf pieces without any kerfs to fill inside.

    However, it was said in this thread that the bog from the kerfs would cause delam. Well, how about all the bog between every single sheet of foam? Same stress concentrations, same everything, all the way through from outer skin to inner skin. Could you tell me why those don't cause delam? Possibly the kerfs would have been fine, I think... thoughts?

    Anyway, I did go with thermoforming since it worked out.

    Here are a couple pictures of this afternoon's progress on the REAL BOAT now that I have the kinks worked out of thermoforming.

    [​IMG]

    [​IMG]
     

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  6. rberrey
    Joined: Oct 2010
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    rberrey Senior Member

    Dont they sell foam with kerfs? Anyway you look like you have a system that works. I might need to know what kind of heater that is. My foam is only 5/8 so I hope there is not as much dending to do. rick
     
  7. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    While less than optimal those kerfs should not cause print thru problems as they are on the inside and you have 1/2" without scoring on the outside. 1" is quite thick actually, a bit thicker than i would have thought necessary but while it would have been beneficial in the strip build clearly not with the vertical build. As you are probably aware some of the advantages of the vertical strip method come from the weight saving of having a lot less epoxy seam length along with the associated time saving, unfortunatly you will more than make up for it with the scoring and/or narrower planks. If you are cutting the kerfs on a table saw i would look for the thinnest blade you can get away with to reduce the amount of resin the consume. I would probably persue the hot box though and try to eliminate the kerfs. One trick you could try is to screw a batten along the keel line (or deck centerline) that protrudes out say, 7/8", cut that end of the plank to the correct angle as it cant run wild as it does now and then push the plank against it from the opposite end and it may bend in fairly, it works with thinner foam but you may still need the hot box with 1" foam.
    Steve.
     
  8. War Whoop
    Joined: Jun 2003
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    War Whoop Senior Member

    Cat build a oven with some insulation foam from Home Depot and heat with a indirect propane burner, use #14 self tapping screws from the back side (predrill the battens),try long strips of 1x on the Face side for a continues washer with drywall screws to hold the core down FLAT and in place while fastening.
     
  9. CatBuilder

    CatBuilder Previous Member

    No more advice needed on foam techniques at this point. See the pictures? Problem solved. The hulls are already going up. Thanks though.

    War Whoop: You can't see it, but behind each batten on the mold/form has tons of pre-drilled screw holes in it. The front tabs are to help me form the foam and hold it in place. This technique is supposed to only need rear screws entering from the outside of the mold. In addition to those rear screws, I start the pieces off by screwing the front tabs on... to hold the soft foam in place before there is any springback. Later, I go around back and drive the normal screws in from behind.

    I will pop those plywood washers off as soon as that bog is set up... leaving the normal back screws from this procedure to hold the single piece in place. Later, sand the bog and glass.

    Here's today's picture of progress...

    [​IMG]
     

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  10. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    It's looking good, Cat.
     
  11. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The screws alone are supposed to hold the foam in place?
     
  12. rberrey
    Joined: Oct 2010
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    rberrey Senior Member

    I think your about to run with it now Cat, looks good .rick
     
  13. CatBuilder

    CatBuilder Previous Member

    Till you glass it. Then you pull the screws, like this.
    [​IMG]




     
  14. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    I would have terminated your planks on the last straight batten. in fact I would have placed a parallel batten next to it so the foam terminated on this last batten and was held down ( screwed ) on the inboard one.
    If you do not terminate a plank on the batten you run a high risk of having a high spot there.
    Also the straight edge rather than a curve would have made it easier to continue the planking of the topside.

    Your glue edges are also very wide, this means lot more sanding later on and potential delamination if not all gloss is removed. Aim for something more like in the last photo.
     

  15. CatBuilder

    CatBuilder Previous Member

    Ah, there are *no* straight battens. This is the problem.

    I have one, single straight batten and this is the one marked "BD" which signifies the spot where the hull stops and a curve begins to attach the bridgedeck. Nothing else is a straight, square line. They are all various curves.

    Yes, I do see that I have a couple spots that are less than ideal where I terminated in mid air. I figure with my 1" core, I'll sand the foam down if it's not looking right before glassing.

    Yes, those glue (bog) edges were stupid. Very wide. I tried doing them the first time with a putty knife and a squeegee. Later, I went and got a cake decorating kit and they have come out like the picture with the young girl finishing up her Farrier boat. :) ;)

    I have plenty of screw holes and other unfair things to bog in, so there will be a ton of bog on this first hull anyway. I have to sand everything (foam and existing bog) then give it another bogging to make the bog stand proud, then sand that back down again.

    Next hull (and rest of this hull), I'll be trying to keep the foam more smooth so I use much less bog.
     
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