I'm Stuck. Need help and advice.

Discussion in 'Boatbuilding' started by CatBuilder, Feb 28, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    Hey Everyone.

    Sorry I always have so many questions. I'm building full time, so I run into things pretty quickly compared to part time builders.

    I'm putting the next row of foam on to make up my topsides. This is what I currently have done, bogged, faired and ready to glass:


    Now, in addition to the bilge area I have already foamed I have decided to continue putting up foam all the way to the hull/deck curve before I start laying glass down.

    I'm running into a problem though. I saved a lot on my foam. It was nearly half price! But, you get what you pay for. The foam is in tiny sheets. The bilge that's already foamed in is how long my sheets are at their longest. The bilge is made up of those sheets, cut in half to make thermoforming easier. Also, my foam is 1" (25mm) thick, which is well over spec. Spec is 3/4".

    So what's happening is that the new foam I'm trying to put up is not making a good, fair curve to meet the bilge foam that's already up. I was warned about this, but it was too late, as my foam was already up. The really bad news is this isn't the underside of the boat or something. This is the topsides, which will be all glossy, shiny and painted nice. Any imperfection will show badly here and this is where my least fair foam is, currently.

    Here's a picture of the overall, as well as some closeups of the miss. The foam misses by less than 1/4", which makes me wonder if I could just leave it where it lies, fill the inside in with some extra bog, then sand the foam down outside to make a nice, fair curve before glassing. :idea: Maybe? :confused:

    Overall Shot of work area
    Closeup of the miss (1/4" or less - this is the worst spot)
    Closeup of me using clamps to get a piece of foam to line up better.

    Any ideas on how to get that foam (the large pieces in the picture) to meet the edge of the other foam and still have a fair curve?

    Maybe next time, I'll pre-join the foam into longer strips. This time, though... I need to find a solution. Ideas?

    Attached Files:

  2. TeddyDiver
    Joined: Dec 2007
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    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Add some more pieces of wood strips on the sides of the closest strips (or sideways btw them) Then staple some cartboard or ply (whatever) on them until the foam meets the right level..

    ps easier thou is to cut the excisting foam along the last batten it meets. Downside is more wasted foam..
  3. CatBuilder

    CatBuilder Previous Member

    Thank you.

    I think the foam cutting at the last batten is the best idea. There are a lot of gaps to fill anyway, so I need some scraps of foam. Many of them do end nicely on a batten. It is only a few areas that are trouble.

    I'll go take a look to see if this can be done. Good advice!
  4. CatBuilder

    CatBuilder Previous Member

    I went to try this out and it wasn't ideal.

    First, the existing bilge foam is in a complex curve, the shape of the keel line. Unfortunately, so is the last batten it lies on.

    This means I'd end up with a curve matching the bilge as my start point for the new foam. I have a set of straight battens from the bridgedeck join area on the topsides to the hull/deck radius. My hull deck radius is a straight line forward of amidships, but creeps closer and closer to the bilge aft.

    Nothing is straight.

    I'd like to minimize my effort as well as the waste of very VERY expensive Corecell.

    Any math majors here? I believe I am needing help in 3d boundary problems, specifically, tiling. :)

    Any other ideas from a practical sense? I need to get back to work, but I'm stuck trying to figure out how to do this without wasting foam. Even to go from the bilge curve to the deck curve is difficult without wasting foam as they are two curves that face each other like this: ()

    Teddy: Could you rephrase that first option you suggested with cardboard or wood pieces to level that parts? I am not sure I understand 100%.
  5. Submarine Tom

    Submarine Tom Previous Member

    How about getting a large disk grinder involved with farely fine grit paper, collecting what you grind down and using it in a bogg to fill the "vertical" gaps while fairing down the "horizontal" gaps?

  6. CatBuilder

    CatBuilder Previous Member

    That would work, if it wasn't in a mold already. I can't grind the outside of the hull before bogging in the inside part and removing it from the mold.

    Or... did you meant to just proceed and leave the outside piece sticking out, to grind down later, once the hull is glassed and removed from the mold?

    This hull is laid up with the foam in the mold first, then glassed inside, then pulled from the mold, then glassed outside.

    I was thinking if I left that bump, I could grind it down after I pull the hull and still be well within foam thickness tolerance.
  7. CatBuilder

    CatBuilder Previous Member

    Would plastic dowels work? What about wooden ones?

    There's got to be some way to get this fair.
  8. TeddyDiver
    Joined: Dec 2007
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    Location: Finland/Norway

    TeddyDiver Gollywobbler

    So additional "help" battens maybe some 3'-6' lengths where they are needed..
  9. CatBuilder

    CatBuilder Previous Member

    Thanks, I will try the helping battens.

    I realized I'm also being unclear. There are several problems with tiling a complex curve like this:

    1) The edges of the two sets of foam are not sharing a common batten, which Teddy is suggesting I use some extra helping battens for.

    2) The edge of the existing foam is a complex curve, but is also a jagged, staggered line.

    3) The battens at the join of these two foam sections are a complex curve.

    4) The battens from the bridgedeck height and upward to the hull/deck radius are straight, longitudinal lines.

    5) The hull/deck radius (end of the topsides) is not a straight line either, but a curve in the topsides plane. Put another way, the deck lines are a sort of mirror image of the bilge line. The space I'm trying to tile with square Corecell panels looks like the space between these parenthesis: () The top of the parenthesis is the bow and the bottom is the stern. The left of the parenthesis is the bilge of the boat and the right one is the deck. I am trying to tile the topsides without wasting Corecell.
  10. TeddyDiver
    Joined: Dec 2007
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    Location: Finland/Norway

    TeddyDiver Gollywobbler

    I try to draw a picture..
  11. mark775

    mark775 Guest

    Hot glue as you go where they don't align? The cardboard/shimming idea seems good.
  12. CatBuilder

    CatBuilder Previous Member

    Thanks for the advice, guys. Going out to have another look with these tips in mind.

    Mark: No glue allowed. It's epoxy only, according to the designer.
  13. CatBuilder

    CatBuilder Previous Member

    Ok, if I use the extra battens, Teddy suggests I cut into the existing foam to make straight lines for tiling. Good advice.

    When I went outside to actually do this, I found there were a couple situation to choose from. Here is a picture, so I can properly ask the questions:


    The rightmost batten near the blue line in the picture is a straight line relative to the mold. It curves upward a bit toward the ceiling way down by the bow, so that is the slight curvature you see in it. But, if you looked at it from the ceiling, it's straight.

    I have 2 different situations for the foam, numbered 1 and 2 in the picture. #3 is what happens to the #2 situation as I proceed down the hull.

    Situation for foam #1:

    The foam is pulled in to the existing foam so that the left edge forms a straight line in the existing foam. It's here that I can cut out a straight line form the existing foam. However, I end up with the same problem later on. The right hand side of foam piece #1 missed the last batten and I'll have the alignment problems all over again. :(

    Situation for foam #2 and #3:

    Foam #2 and #3 are pulled to be in alignment with the batten on the far right near the blue line. This means I will be rid of the missed batten problem going forward, but in the middle of the hull, I will have the missed batten problem where the mold is widest. That problem goes away toward the bow and stern, like you see in #3.

    So which is best?

    Panel #1, pulled to the existing foam? Or... Panel #2 and #3, pulled to the straight line batten?

    If #2+#3 are chosen, how would I bridge the large gap in the wider part of the mold? Strip planking?

    Attached Files:

  14. variverrunner
    Joined: Dec 2009
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    Location: New York, USA

    variverrunner Junior Member


    Could you try hot gluing and screwing short battens (station to station)to underside of the installed foam so that the next pieces of foam automatically lay properly?

    Good luck,


  15. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Fishing string . . . use it to pull your short pieces down to the mold. I'd use a "U" at each batten (if necessary to make it conform) and tie it loosely under each batten after passing it through the foam. Use a steep ramp wedge to tighten up the now closed loops of fishing string. This method permits some adjustment. It'll remain in place inside the foam after 'glass and can be simply cut and 'glassed over after the inner skin is applied and cure.

    The unsupported area has no choice but to be supported. You should have had a batten under each expected seam anyway, so now's the time. OR, you could glue some foam onto the short stuff and make it fit the work. Judging by the photos you'll need more battens anyway, so make the battens fall at each direction change and glue your foam into pieces that fit.
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