Help with layup schedule for a custom hardtop, also door and window choices

Discussion in 'Fiberglass and Composite Boat Building' started by s2dm, Jan 28, 2018.

  1. s2dm
    Joined: Jan 2018
    Posts: 1
    Likes: 0, Points: 1
    Location: California

    s2dm New Member

    Hi All,

    First post on this site. We recently bought a Grandbanks eastbay 38 with a soft-top, and I'm planning on building a custom hardtop with a few neat features like integrated surfboard storage above, solar panel pockets and a fold up and in rear window to keep the open feel of the soft top.

    I've done quite a bit of fiberglass work, I built this camper myself with a lifting roof completely out of a combo of 1708 and carbon, with divinycell core (pic attached below). [​IMG]

    I've got some constraints in my workplace regarding working with poly, so I was planning on building this out of epoxy and coosa but debating between doing a biaxial mat approach with 1208 or 1708, or a carbon and cloth approach, since the top is mostly windows and there isn't that much total surface area.

    I was planning on modeling my top after something similar to this: I'm drawing it up in solidworks first and cutting the coosa on my CNC, I'm planning on keeping it a little simplet than this and building it in two parts, the uprights/windows and then a removable roof with drip rails.


    I'm debating about building a simple melamine mold for this vs buidling the structure out of coosa and then doing a wet layup.

    So, questions

    1) Layup schedule - Biaxial or carbon and cloth, and what oz would be sufficient. The roof will primarily be surfboard storage, but will occasionally have a person up on it.
    2) Coosa thickness and density - debating between 3/4 an d 1" and the 20 vs 26 lb density.
    2) Standard epoxy ok, or should I do anything special?
    3) Mold or wet lay up? I'm incorporating some radiused edges, but planning on keeping it a little simpler than the above image. I'd also contemplated building it all with flatpanels, a skins then core with corebond approach, and then putting it together with a structural epoxy like proset and some carbon and cloth secondarys. I usually do my secondarys a little different and will layup a cloth/carbon/cloth sandwich in an aluminum profile to get a finished surface, cure it, radius it on the router table, then apply with proset. So it creates a nice finished look but does sit proud of the surrounding area.
    4) Suppliers for really nice rear door and windows? I'm anticipating dropping some $ into this top so don't mind some higher end recs.

    Attached Files:

  2. gonzo
    Joined: Aug 2002
    Posts: 16,645
    Likes: 1,609, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    If you are using epoxy, there is no need for mat like any of the XX08 have. Can you post a sketch of your idea? If you are making pockets, there will be some rather sharp edges, which may require a lighter cloth. Also, the structure under the top will affect the laminate schedule.
    fallguy likes this.
  3. fallguy
    Joined: Dec 2016
    Posts: 7,457
    Likes: 1,612, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Gonzo is right-no gelcoat no csm.

    I would use vac for sure. Either bag or infusion. Too hard to get done without bubbles, repair, and inferior work.

    I’m a little confused about using carbon and 28# inch thick board. Seems like your percentage weight savings will be very low for the cost. Unless it is done for aesthetics...

    To get more folks to respond; you need to add details as Gonzo also suggests in his last point.
  4. fallguy
    Joined: Dec 2016
    Posts: 7,457
    Likes: 1,612, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    by the way, the top is really nice, but I’ve never been a fan of full glass on the back. A double door with windows on each side not only seems more practical, but looks better to me.

    I haven’t hired them yet, but am considering zarcor for my doors. See if they would be interested...
  5. jorgepease
    Joined: Feb 2012
    Posts: 1,620
    Likes: 51, Points: 48, Legacy Rep: 75
    Location: Florida

    jorgepease Senior Member

    I would go with a much lighter, thick, pvc foam instead of Coosa. You can substitute coosa for wherever you need to screw fasteners etc...

    What is the framing like, is it clear span, a thicker core with thinner skins would be my aim.

    You have CNC so it would take you no time time to cut some stations and sheath it. I would go with laminate over thin bendable ply instead of trying to melamine which you might mar in the fitting process. Also with laminate you can vacuum proof by leaving space between seams, bogging and then cover with clear packing tape. Then infuse the thing for a perfect part... Might as well use an in-mold primer while you are at it.
    fallguy likes this.

  6. PAR
    Joined: Nov 2003
    Posts: 19,128
    Likes: 497, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Agreed, I'd use a cored structure (foam, balsa, etc.), though gel coat is an option now. A Coosa perimeter frame, maybe a few athwart beams, hard points and all else foam, would be my approuch. Unless you think you need a very light weight top, save the money and use more traditional fabrics. Building a mold can work, though maybe more effort than necessary. A simple transverse building jig of station molds and lay some foam over it. Apply the fabrics to the exterior, to an appropriate thickness for the method, than pop it off, apply the inside sheathings and fair you brains out, until satisfied. Vacuum bagging can help with resin content and laminate conformity, though I'd suggest infusion is much more than you'd need for this project.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.