Sailing plywood and epoxy cabin roof - compound curves

Discussion in 'Boat Design' started by TomBlake, Aug 24, 2018.

  1. fallguy
    Joined: Dec 2016
    Posts: 1,328
    Likes: 53, Points: 48, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    The OP was really struggling with the basic idea.

    He was originally planning a production quality mould that was driving cost.

    And to be honest, not too many good responses here early.

    I am building a much smaller top with scrim foam.

    The idea of plascore is interesting. I don't quite understand how it is held in place unless you glass over and cut out the fastenings.
     
  2. fallguy
    Joined: Dec 2016
    Posts: 1,328
    Likes: 53, Points: 48, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

  3. TomBlake
    Joined: Aug 2018
    Posts: 25
    Likes: 0, Points: 1
    Location: Qld Australia

    TomBlake Junior Member

    leaning towards what fallguy has recommended. Just need to decide on scrim/foam/polycore. I need to test for compound curving. Technical person selling polycore recommended two layers of 10mm polycore($70 per m2 with thermo-lite being $100). Seems confident that it will handle the compound curves. She says to glass over the polycore and not filling it. Insulation will be better and no difference in strength. Thinking about using strips of thermo-lite for the mainsheet traveller/winch/jibsheet areas.
    Vacuum baggin for 18m2 of roof? For once off job?
    Comes down to how to lay the core, what to use, cut into strips to cater for compound curves? How does this affect strength of roof? Groper says my compound curve is minimal. So maybe over-thinking that.
     
  4. Mike Inman
    Joined: Oct 2018
    Posts: 55
    Likes: 5, Points: 8
    Location: Jacksonville, Florida

    Mike Inman Junior Member

    I've never heard anyone who actually used peel ply or did vacuum bagging say a bad thing about either, both seem to be worth the extra cost / effort in terms of superior results and reduced fairing effort.
     
  5. fallguy
    Joined: Dec 2016
    Posts: 1,328
    Likes: 53, Points: 48, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    The other thing to consider is rebates for overlaps on the exterior. This would reduce fairing later.

    I don't know if I agree with no fill, but honeycomb is the same...
     
  6. fallguy
    Joined: Dec 2016
    Posts: 1,328
    Likes: 53, Points: 48, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    The peelply is one thing, but vac bagging this beast is altogether something else. Maybe with an experienced crew of three. The peelply might actually help in the case of not doing it all same day.
     
  7. Mike Inman
    Joined: Oct 2018
    Posts: 55
    Likes: 5, Points: 8
    Location: Jacksonville, Florida

    Mike Inman Junior Member

    So, that could be the trick, if it's so big that you can't get it all "wet and set" before the cure time, then vacuum bagging might not be for your project.
     
  8. groper
    Joined: Jun 2011
    Posts: 2,453
    Likes: 104, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    i would not attempt vac bagging this if you have not done it before.
    For the polycore - did you look at the link to DIY yachts and did you see my friends polycore compound curve roof?
    How its done;
    Make a frame and batten former which is like a male mold in the form of a stick frame.
    Lay the polycore down and pull it down into the curve using wire ties which go thru the polycore over the top and back down underneath the battens on the mold, twist the ties underneath to hold in place.
    Laminate by hand the top layer of glass and let it cure.
    Cut the wire ties underneath and then pull them out - they will take a little pressure but will come out.
    Flip the whole thing over the then glass the underside.
    Fair and paint.

    Its only requires a small investment in some ply or MDF frames and some cheap pine battens.
    If the roof is large - you can do it in multiple sections so you dont have to work too hard laminating like crazy. My friend did his in 3 sections - middle section first, then stb side, then pt side. Overlap the glass by 50mm when you start the next section.
    Lay peel ply over eveything so you dont have to sand anything before applying bog for fairing.
     
    fallguy likes this.
  9. TomBlake
    Joined: Aug 2018
    Posts: 25
    Likes: 0, Points: 1
    Location: Qld Australia

    TomBlake Junior Member

    yes I saw the site. Spoke to the polycore people. I love the idea of doing it in 3 sections. Especially with my level of expertise (low) and lack of people to do it in the one go. Alot less pressure. I have the mould ready to go. will look at the peel ply.
    Looking at the curve on your friend's roof; I'm sure the polycore will bend to the compound curve I have.
    Thanks everyone. solution is being fine-tuned really well. I'm waiting until winter (May) before starting. Too hot and humid at the moment and I have another house building project on the go for the next few months
     
  10. fallguy
    Joined: Dec 2016
    Posts: 1,328
    Likes: 53, Points: 48, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    4201DD38-2BAE-476D-9E22-34A272F972E8.jpeg If you do it with a foam; you can rebate all the glass overlaps. It might be hard to do on the mould; so you might mark it up on the mould and take it back to a table to rebate.

    Just buy a cheap electric planer with say a 2 1/2" head and run it down then end of the glass roll so the glass lays into the seam. I hand sand with floor paper 36 grit rolled into a radius to break the edge to reduce air pockets in the layup. I would probably only rebate the outside and fair the inside, or you can just fair the entire thing or stagger rebates if you think you can get the tool to work on the inside after flip. Groper might also advise if he didn't already and I just forgot.
     
  11. groper
    Joined: Jun 2011
    Posts: 2,453
    Likes: 104, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    Well the cost is much lower with polycore conpared to foam. whilst you cant rebate the polycore to reduce the fairing of the glass overlaps as there is a bonding scrim on the polycore which cant be removed- you will be filling and sanding the whole thing anyway in prep for paint so the time and effort saved is not as significant as you might think.
    Use a long metal blade like a piece of 50x50x2mm aluminium angle when filling. It can bend slightly to conform to a slight curve but not too much so you get a flat even smear of bog over the surface. It will fair over the glass overlaps nicely provided you sand or grind down any rough bumps directly on the glass overlap itself before you begin... same applies to any other odd bumps as they will really throw off the blade and make things difficult to fill evenly which saves you heaps of time sanding.
    Remember the topside can have nonskid deck paint and this hides small imperfections so you dont have to be overly anal about getting it perfect...
     
    fallguy likes this.
  12. TomBlake
    Joined: Aug 2018
    Posts: 25
    Likes: 0, Points: 1
    Location: Qld Australia

    TomBlake Junior Member

    The maority o f the top will be non-skid paint as we will be walking on it to manage the sails
     
  13. TomBlake
    Joined: Aug 2018
    Posts: 25
    Likes: 0, Points: 1
    Location: Qld Australia

    TomBlake Junior Member

    I'm looking at a grid system where there will be borders of glossy gel coat. Could I locate these borders on the overlaps.Eg. slightly raised borders for the glossy gel coat and the rest for rectangles of non-skid??
     
  14. fallguy
    Joined: Dec 2016
    Posts: 1,328
    Likes: 53, Points: 48, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    for what purpose?
     

  15. TomBlake
    Joined: Aug 2018
    Posts: 25
    Likes: 0, Points: 1
    Location: Qld Australia

    TomBlake Junior Member

    the grid system for asthetic purposes. the positioning so that the slightly raised areas on the sheet joining don't need to be faired as much? maybe talking through my hat??
     
Loading...
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.