Fiberglass Hardtop

Discussion in 'Fiberglass and Composite Boat Building' started by phyrelin, Aug 23, 2007.

  1. phyrelin
    Joined: Aug 2007
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    Location: What?

    phyrelin New Member

    I want to build a fiberglass Hardtop for my fishing boat. I have little fiberglass exp but am learning more on this forum. It is a walkaround Cuddy 24' . Looking to build something that could be stood on.
  2. OGM
    Joined: Sep 2007
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    Location: Jupiter, FL

    OGM Junior Member

    I am in the process of doing the same thing with minor fiberglass experience. My top will be 8 ft X 9ft. I plan on using 1 inch divincell foam with 1808 cloth with a 3/4 oz cloth on the outside to prevent the pattern of the 1808 from showing through. Originally I was going to use polyester resin, but now I'm going with epoxy due to working time. I'm using a mold for the top surface and plan on extending a 2 to 3 inch lip around the perimeter. This will add stiffness and give me a verticle surface to attach the eisenglass to. I may mold the bottom surface also and then bond it to the foam and glass the edges, or just glass the surface of the foam. I all ready have the splines for making the mold of the bottom surface as they are the reverse side of the top. All I have to do is cover them and I have the mold. I have a radar arch in the back that the top will lay on top of. This will give me stability and I'm not going to build an aluminun tubular structure underneath as you see with a lot of tops. There will be 2 tubular triangulated supports in the front for support along with the radar arch in the back. I plan on being able to stand on mine for repairs and there will be a 4 ft radar antenna mounted in the center, but I won't be up there very often and not when underway. I'll be watching your thread for ideas and alterations to my ideas as I am a novice also and appreciate any suggestions.
  3. Ausiwik
    Joined: May 2007
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    Location: Queensland Australia

    Ausiwik Junior Member

    Hi OGM and phyrelin
    There are several different ways to do this and I can show you a few pictures and give a procedure but cant supply that info till tonight heres my blog site there may be some in the dodgers section If you haven't received any help Ill get back tonight (Australia time)
    Steve Marshall
  4. 31 Silverton
    Joined: Sep 2007
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    Location: Mid Atlantic

    31 Silverton New Member

    Also building hardtop about 6 x 8 feet

    I am also building a top. To cut building time I was thinkin of laminating some thin peices of plywood and with some weights in the center to give a little bow. Then attaching a small 2 inch lip a couple inches in from the edge all the way around the underside to snap the curtains to. Then coveing it in glass and painting. However I am might considering a foam core if it would be much lighter.

    Is it possible to get a rigid foam board (pink insuation board from home depot) and simply glass that or will the resin eat it up?
  5. Ausiwik
    Joined: May 2007
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    Location: Queensland Australia

    Ausiwik Junior Member

    Building a hard top one way

    Hi there fellows (building hard tops)
    I appologise for not getting back as I said I would, but I could not find the post Id written too ??"
    Any how I will try to put some more pictues of a big hard top I did for a 50ft Hatteras which was cored and built so that the owner and is very much aging crew could walk on it (fat chance of that at almost 15ft of the water)
    If you have some glassing experience, Youll probally know that the glassing part is relitivly easy, however the finishing is or can be a bear !!
    this method Ill roughly describe may suit you as it vertually eliminates one side finishing and all considered quite simple .
    Ill explain very basically, as if you were building an 8x4 top
    You just have to expand on that. you'll get it !!

    To do this method you need to make a table at least the size of the job you intend to build.
    This can be assembled from chip board and saw horses but it must be flat and reasonable level and able to bear some weight
    You will also need 1 or 2 sheets ( depending on size of job) shiny white polester ply thats the stuff that has a mirror finish coating on it and its about 3/16 thick
    Its really cheap generally. It actually has a really thin film of polyester gel coat on it. don't get the photo finish stuff as this can react and stick and to the job
    You can also do this job by using white coated chipboard (about 3/4) which then becomes your bench as well. If at all possible get the polyester coated surface as it produces the best results.
    You will start by coating your entiretable table surface with release, then gel coat this surface. You then laminate you desired glass laminate ( 1 x3/4 oz chop strand mat followed by 1x 600 grm double biased stitched cloth
    When these laminates are fully cured you mix some bog using your resin and
    filler and basically glue your core onto the laminates you have created .
    When this is throughly cured (about 1 >2 days ) you can lift the core and glass laminate free of the table surface.
    The whole thing will be still flexy so don't try lifting right off the table and care is needed when parting from the mold surface of your table.

    You then slide a selection of different height timbers under this laminate/ core combination with the thickest or highest in the center to create a gentle chamber in your top ( in the 4ft span with the timber running for and aft you would need about 5 lengths at 8 ft
    when the curved shape (chamber) you desire is set you can proceed with the top laminates.
    This time using only double bias stitched cloth and may be 2x layers of 600 gm

    When these upper laminates are cured completely you will have a ridged curved surface that will need finishing on the out side upper surface only and of course the edge.
    This is generally an easy surface to finish and if your intention is to walk on the top, you'll use a non skid paint (no gloss except border) so this even lessens the the required standard of surface finish.
    Your under side surface (shiny table side ) should be good or at least just need a sand and a spray paint.
    There are many things I have omitted telling that don't actually take any longer but are just what I consider the way to do it !!

    Building this way you can also add a really neat downturn rim or flange for curtains, also mounting and other attachment points can be attended to during the process
    This method works equally well with a laminate of ply, nida core and then another top layer of ply then followed by a final surface layer of glass.
    As you will see on my Blog, (hard dodgers) I offer a design service for this type of thing, so I can, if you wish, supply a totally complete step by step process with diagrams for a fee.
    Any how whilst this may sound like a bit of mucking around you will be able to create a really beaut top.
    Hope this is a help.
    Steve Marshall
  6. KnottyBuoyz
    Joined: Jul 2006
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    Location: Iroquois, Ontario

    KnottyBuoyz Provocateur & Raconteur

    Don't. The foam will fail as a core. This is a cut out from a panel I made using that kind of foam and infused. First time the jig saw blade hit it, the core failed, not the bond to the glass, the foam itself failed. It has virtually NO ability to resist any shearing forces.

    Attached Files:

  7. The Vig
    Joined: Sep 2007
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    Location: Chicago

    The Vig New Member


    What if you used the pink insulation but used contact cement to sandwich it between 2 pieces of 1/4" Ply? Would that bond be strong enough? I would think you would need some kind of wood in areas where the op would mount to the verticle mounting posts.

    Just a thought
  8. FibrSupplyDepot
    Joined: Sep 2013
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    Location: Fort Pierce

    FibrSupplyDepot Fiberglass Supply Depot

    What about using Celtek pvc board. It is lighter then plywood and you can screw to it, glass sticks very well.
  9. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    There are foams that will work and of course ones that don't. Typically the ones that don't, are the least costly (figures). For this application (structural panel) you'll need a higher density then is common in the low cost foams. The minimum would be a 5 pound foam, but I'd be inclined to use a heavier (say 8 pound or better) if much foot traffic was expected.

    There are about a dozen choices in this regard, so find a density foam you can live with (the Lowe's/Depot stuff is 1/2 to 1 pound foam) and accept the costs associated with this method.
  10. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    I am contemplating building a 12' wide 3/4" foam sandwich roof panel, to be supported by aluminum tubing framework. My question is whether it is necessary to lay it up with camber built in? Would it take a 6" curve over the 12' span?
    Maybe lay up one side and flip it over, then bend it over spacers before glassing the other?
    I have a flat table, and would like to not have to build a new one for this project.
  11. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If you'd expect it to keep it's shape and not continuously attempt to "relax" from the bent position, bend it first, then sheath it. The only exception to this would be if you bent it while it was still wet with goo.

    If you make the panel flat, the outer skin will try to stretch and the inner skin will attempt to compress, meaning the inner skin will likely wrinkle or pucker, while the outer skin cracks.

    I make roofs like this fairly regularly and I just use a plywood form, on edge. I cut the radius as needed in plywood or MDF, spacing them out to keep the foam from sagging (24" works with 3/4"). I also use the off cut plywood pieces, but subtract the foam thickness from the radius.

    I bend the foam over and do the outside of the curve sheathing first. When cured, I remove it and place it into the off cuts, as an female mold and then do the inside. The idea being, it's forced to the curve I want, not what I can get, trying to "wing it".

    Don't get me wrong, a 6" crown on a 12' panel isn't much and you could certainly do it flat and bend it over your framework, but the sheathings will be "pre-loaded" once you do that, which reduces strength and load carrying capacity, especially if you want to walk on it someday.

  12. Charly
    Joined: Dec 2009
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    Location: st simons island ga

    Charly Senior Member

    Hey KnottyBuoyz, just curious-how did you prep the blueboard before the infusion? I have done it as a hand layup with 4mm okume as a sandwich for non structural furniture, and so far it is working out OK.
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