Catamaran Bridgedeck Help

Discussion in 'Fiberglass and Composite Boat Building' started by conceptcat, Sep 29, 2017.

  1. conceptcat
    Joined: Oct 2014
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    conceptcat Junior Member

    I've bought a 29ft Conser Warrior open Bridgedeck catamaran, basically a slightly larger Seawind 24 if your not familiar with the design and have opted for a solid rear deck.
    The area is 12'x10' and I have 5/8 Divinycell h80 foam as a core using epoxy resin (and maybe vacuum).
    Can anyone who's done anything similar recommend,
    1, what glass to use top and bottom, from what I've read the bottom is the more critical as the top is in compression and only needs to withstand impacts ( someone said a lady in stilletto heels ).
    2, what amount of "joists" or secondary beams need to be used underneath on such a large unsupported area, the deck is supported on all sides with aluminium angle.
    3, would you suggest glassing individual 4x8 panels then joining them together or laying up the whole deck in one go with slow hardener?
    4, will I gain much by vacuuming?
    I've searched repeatedly for information on how to build a deck like this but have found nothing as if it's never being done before! which of course it has.
    Cheers.
     
  2. luff tension
    Joined: Aug 2010
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    luff tension Junior Member

    I made a similar deck panel 3.6m wide x 2.4m long as it was limited by the size of the sheets of material I used.
    This has a H80 25mm core with 4mm ply in the top face and a 3mm ply on the bottom face. The top is glassed with Eglass DB460 and the bottom skin is an Eglass 0/90 of 680Gsm. The floor was made in 3 segments 1.2 x 2.4 and there is a fore/aft stringer 50mm wide x 25mm deep at each panel join. This stringer has 3 layers 450g uni carbon on the under face covered in a 450gsm carbon Double bias which overlaps 50mm onto each panel. It turned out much stiffer and lighter than planned.
    In hindsight I could have left off the bottom layer of ply and added extra glass. The top skin of ply help immensely with impact resistance.
     
  3. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I recently posted a similar question without much luck. I am building a cockpit that is removable. It basically will be 2 4'x8' sheets of 12mm?? core with aluminum angle on the 8' sides to join the panels side by side with ss bolts, and to each cat hull. I was really hoping to make the 'stringers' or stiffeners hollow to allow for hydraulic steering and perhaps another for electronics from the helm to pass through, so I had planned to put two box type stringers down each panel the 8' way, for a total of 4 stringers, plus the middle angles for a total of 5 which is 16" o.c., construction was tbd, but I had expected to make a mold and use my scrap 22 ounce triax for the stringers, and use 18 ounce biaxial for the cockpit itself.. I would bag the 48" panels and do the rest by hand. I am a little worried about the thing being bouncy so had been asking, and a little worried about needing to use high density foam where the angle attaches to avoid crushing. And I'm a little worried about it weighing a ton because I have to handle it so 3/4 plywood is out. My cockpit is even a bigger challenge because I have a helm and lift and table and bench to place on it as well.

    I wanted to add flexiteek to it as well. Perhaps if I follow the route of the plywood on the topside, I could put 6mm ply wherever the flexiteek wasn't...It was all going to get painted with kiwigrip, so it doesn't really matter, but I wouldn't want it to delam, so might prefer 6mm more core, but that won't stiffen it.... Would the plywood at 6mm be enough to keep me from needing high density foam, or is overboring and refilling enough to avoid crushing? I'm a little worried the 12mm is too thin.

    For your project, the main thing will be to keep the panel joins flat because you are going beyond core sizes, so you are kind of stuck bagging it. I think you could bag the bottom with a large piece of plastic and avoid the need to make a fancy vac table surface. For the size of cockpit, you almost need to make a table a foot bigger all around, unless you had a really nice and perfectly flat floor. In any case, I think vacuum would be the best way to avoid having high edges and variation at the joins.
     
  4. conceptcat
    Joined: Oct 2014
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    conceptcat Junior Member

    For your project, the main thing will be to keep the panel joins flat because you are going beyond core sizes, so you are kind of stuck bagging it. I think you could bag the bottom with a large piece of plastic and avoid the need to make a fancy vac table surface. For the size of cockpit, you almost need to make a table a foot bigger all around, unless you had a really nice and perfectly flat floor. In any case, I think vacuum would be the best way to avoid having high edges and variation at the joins.[/QUOTE]

    Thanks for the reply.
    Thinking of a way to avoid bagging the deck would be to make 8x4 panels individually then alighn the 4 preglassed panels on a frame to keep level then edge glue and glass.
    I like your idea of putting stringers along the joins.
    And carbon Uni would be a must for the extra cost.
     
  5. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    I have a seawind 24 with hard decks between mast beam & aft beam- about 3 meters... it's poorly illustrated here in my gallery https://www.boatdesign.net/gallery/seawind_port_ha
    Here's a pic of the quick & dirty tooling for the cockpit.. nancys_party_164 | Boat Design Net https://www.boatdesign.net/gallery/nancys_party_164.18352/
    The decks at side are 15mm Klegecell with 450 stitched fabric plus 225chop plus gelcoat to top.
    You definitely need longitudinal stringers. I'd be making in three longitudinal sections for ease of handling.
    Jeff
     
  6. conceptcat
    Joined: Oct 2014
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    conceptcat Junior Member

    Ahh the legendary Seawind 24, in 2000 I converted one to axe bows added a meter to the stern then sailed it without a motor from Whitsundays to Broome. (3000 NM). It had a ply rear harddeck but was so heavy. Just wondering why you put chop strand into the laminate? From what I understand it absorbs 150% it's weight in resin opposed to cloth 100% so extra weight, also chop adds little strength comparatively.
    PS like the retro wave paint job.
     
  7. fallguy
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    fallguy Senior Member

    In my limited experience, I have found the only good way to keep the panel joins stationary and flat is to use 1/4" raptor staples, but the gun is so costly for a one off job... You could do it with some sheets of glass or some cruder weights, or you could staple with metal and then try to remove, but gluing before laminating for me resulted in high and low spots and I was gluing on the 4' edge, so the 8' would be trickier. I glued on my cutting table which is not flat enough. It is just a 3/4" table on horses. Start out real flat and that'll help tons.

    I do not support the idea of laminating the panels individually. I'd much rather get my fabric to cross the joins; that's me. Build the table good and flat and find a way to raptor or connect and weigh the joints down. Some guys use toothpicks between the panels, I tried and gave up on it as my core was too dense and they broke (M80). If you laminate ahead of time and the panels are flat; they wouldn't move the way core can move up and down as easily, that is true, but you still need a flat as heck table, and I like the idea of running glass over the seams better.

    I think the other poster meant 225 chopped strand mat to avoid printthough.
     

  8. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    The choppy is there as the laminate is in polyester resin with gelcoat, to not use the chop would be poor practice. Different for epoxy, yes I could save weight but I use what I have, the deck I replaced was 20mm hdpe sheet- already saving lots Kg from the change:) I like to mold with gelcoat & don't like to fill & sand so much as do the small amount of tooling work & demolding... mind you here is a pic from today- fill & sand 100m2 per side.. upload_2017-10-6_0-4-20.png

    Jeff.
     
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