Hard Chine composite, preglass panals before or glass in place?

Discussion in 'Fiberglass and Composite Boat Building' started by Jetboy, Mar 15, 2012.

  1. Jetboy
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    Jetboy Senior Member

    This may be a elementary question, but I'm not sure what the answer is. If you're building a composite cored boat with hard chines in a stitch and glue type construction over a male mold, is it best to take your sheets of core and put the fiberglass on them before cutting out the patterns, or are you better off to just glue the joints together and cut out the panals, fill and tape the seams, then put your fiberglass over the entire hull at once?


    Why is it better to do one over the other?

    Also if you do put the fiberglass on the sheets before cutting the panels, do you then only need fiberglass tape on the seems and you're ready to fair the bottom? Or is it always necessary to put a full continuous layer of glass on the entire bottom?

    Thanks.
     
  2. hoytedow
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    hoytedow Carbon Based Life Form

    It is best to fiberglass after cutting and assembly because once glassed it will be difficult to cut and wreck your ordinary cutting tools.
     
  3. Jetboy
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    Jetboy Senior Member

    If you do vacuum bag the flat sheets before cutting panels, how do you know whether they will be too stiff to curve onto the forms?
     
  4. CatBuilder

    CatBuilder Previous Member

    Hoyte's answer is a good one and a viable option.

    If I were making a hard chine boat out of glass panels, I'd probably pre-glass everything on a flat surface first.

    The way to avoid wrecking your tools in that case, would be to pre-cut all of your core material pieces to the shape and size you need for the hull.

    Then, cut your dry glass to fit the shape of those panels.

    Now, laminate.

    At the end, you will have a huge stack of all the right panels to tape together - no cutting of glass required, though some grinding will still be in order unless you are really good! :)

    Downside is that you will have to run a wire wheel type thing down all of the edges you are taping to make sure they are properly abraded for taping. Upside is the glassing job will be a lot more simple on a flat surface.

    Nearly all boats are taped together at some point, even round chine ones, as it's hard to make the full hull shape and deck in one go no matter what method you are using.

    Taping is perfectly valid for all boats. Just look at all of the Bob Oram boats built from Duflex. They are all taped and are just fine. No problems, structurally, with taping.

    That's my 2 cents.
     
  5. hoytedow
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    hoytedow Carbon Based Life Form

    That would be a good way to go if the above conditions can be met, but if builder is an amateur and lacks experience and the more sophisticated tools, glassing after assembly would be far less troublesome.
     
  6. Jetboy
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    Jetboy Senior Member

    So by ruining the cutting tools, does that mean a knife blade or do you mean it will ruin saw blades? I was hoping to cut with either a jig saw or possibly table saw. The table saw will be trickier to do the curves with, but none are very small radius and could probably be done just as easily on the table saw.

    Will the fiberglass ruin those blades?
     
  7. CatBuilder

    CatBuilder Previous Member

    It'll go through blades quickly, if that's what you mean. Big teeth and cheap blades are the way to go in that case if you are cutting glass. But... no need to cut cured glass if you cut core first, then cut dry glass to fit that core before doing your lamination.
     
  8. CatBuilder

    CatBuilder Previous Member


    If you need to curve one, you must curve it before you glass it. There are really no other options (there are some, but far too much work).

    If you plan to glass a piece of core and you need a curve in it, you have to bend that core first, then put the glass on.

    For instance, I am going to be building a bridgedeck for a catamaran in a month or two. It has a camber or slight curve to it.

    I will cut out plywood strips to put below the core, between the core and a flat glassing table surface. Those plywood strips will have a nice, rounded curve cut in them that will allow the bridgedeck core to bend to the desired shape.

    I will then glass it while bent, making the correct part.

    In your case, if you have a lot of panels to bend, I would go with Hoyt's idea. If you have very few to bend (just 2?) you can go either way.

    Kind of depends on the boat's design...
     
  9. Jetboy
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    Jetboy Senior Member

    It seems like it will be really difficult to get all the pieces lined up that way. I assume that if I went that route I would be putting fiberglass on both sides prior to putting the panel on the frame? Would you need to do each side separately or would you be able to glass both sides of each panel at once?

    Also the core I'll be using is honeycomb, and I'm concerned that if I vacuum bag it, it will "sag" for lack of a better word all around the edges whereas if I did it flat, I would be discarding the outer edges and cutting from the center of the sheet. Maybe not? Or should I just skip the bagging? It's only an 18 foot boat, maybe the weight savings isn't worth it?
     
  10. Jetboy
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    Jetboy Senior Member

    [​IMG][​IMG]

    Here's a picture of the general shape of the hull.
     
  11. CatBuilder

    CatBuilder Previous Member

    Looking at that hull, every single panel has a curve, so I'd fix the core in place on the forms first, then glass.

    You don't want to do a boat like that flat panel the way I was describing.

    Much less work putting the core up on the form and then glassing in your case. Thanks for the picture. That made a huge difference.
     
  12. Jetboy
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    Jetboy Senior Member

    Thanks for the advice! I'm still about 3 weeks away from getting my core material delivered, so I'm trying to sort out the process as much as I can ahead of time.

    One other concern I have is how to deal with the joints (butt joints in the sheets). I assume the glued joints are going to mean that there are points that don't bend in a nice radius like continuous material would. How do you handle that?
     
  13. CatBuilder

    CatBuilder Previous Member

    I sure hear that. Sorting out the process is probably the hardest part. It was for me, anyway.

    The joint (plans should show this), will likely butted pieces of core with a big gap from the different angles the pieces of core are at. You can stick a wedge of core in there to help fill some space and bog in the rest. Basically, that's what the bog is for - making the core more uniform and filling in any gaps or voids in the core.

    You will also want to make sure your hard chine corners are somewhat rounded and not 100% hard and pointy. Laminating glass over a very tight turn like a perfectly hard point will cause the glass to lift from the core. You want to round off everything you can so the glass can bend over it easily. No hard ridges.
     
  14. Jetboy
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    Jetboy Senior Member

    To fill in the gaps, I see a lot of filler materials. Is there one that is considered the "best" choice for this or do they all work about the same?
     

  15. CatBuilder

    CatBuilder Previous Member

    Here you go. Take a look at the chart to understand the fillers.

    http://www.westsystem.com/ss/filler-selection-guide
     
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