Hardtop methods?

Discussion in 'Boat Design' started by DianneB, Dec 14, 2010.

  1. DianneB
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    DianneB Junior Member

    The fabric and clear plastic on my 24 foot Lonestar is pretty much trash and I am SERIOUSLY thinking of turning it into a hardtop.

    [​IMG]

    When I bought the boat last June the wheelhouse roof was rotten and I made a new one from 1/4" ply over fir 1-by "rafters" and a 2x4 ridgepole and it came out very nice. Now I would like to extend the roof all the way back to the transom and just have canvas (and screened) sides.

    I can weld steel but not aluminium so my first inclination is to use square steel tube and stanchions to frame the outer edges of the roof, either on the same plane as the existing roof (77" above the deck) by replacing the entire roof or to leave the existing roof and step up a few inches over the rear deck. Ply and fir is the easiest build (and very light) but I am a little concerned about longevity of a painted plywood roof.

    What are the thoughts and opinions of those with more experience?
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Cover the ply and edges with a light fabric'n epoxy and paint over..
     
  3. DianneB
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    DianneB Junior Member

    Sounds like a good idea T.D.

    This is what I am thinking of:

    [​IMG]

    Rectangular steel tube for the frame, 1/4" ply over wooden ribs.

    Seem reasonable?
     
  4. PAR
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    PAR Yacht Designer/Builder

    Your idea of a hardtop is certainly doable, but I have issue with a few items, like the steel elements, the 2x4 ridge pole and taking the roof back all the way to the transom.

    A light weight foam cored roof could ease building a bit and also leave the interior beam free. Of course this would be sheathed in 'glass and painted. The perimeter of the roof could be held up with standard stanchion stock, 1" would look nice on your boat, maybe 3 down each side.

    If you carry the roof back to the transom, you'll have a nice, fully covered cockpit, but getting in and out from a dock will be problematic at best, difficult if there's a chop and the dock is fixed. You'll find most prefer to have at least a small portion of the cockpit, not under roof for this reason, so you can step down into the aft portion and not have to "time" you boarding, with the prevailing winds and boat motion.

    Steel is the last choice I'd use for the roof perimeter or beams. As the stanchion tubing, stainless is an option, but I'd go with aluminum just to save weight. Standard stanchion fittings will work, both on the roof and the side decks, leaving only the tubing choice and roof. The roof from plywood over beams or a sandwich of plywood and foam or possibly a composite of foam and 'glass will be all light and effective. Are you looking to putter around Winnipeg with more elements protection?
     
  5. BATAAN
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    BATAAN Senior Member

    Make the roof of 1/4" ply, 2" foam and 1/8" ply on the bottom. Laminate it with epoxy over a simple jig for the camber and put in blocking where the stanchions come. This will be immensely stiff, very light and cheap.
     
  6. DianneB
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    DianneB Junior Member

    I suppose I am just more comfortable building in wood and steel as that is where my experience lies. I have worked only a little with composites and aluminum is expensive and I am not equipped to weld it.

    The existing wheelhouse roof was done with a 2x4 ridgepole and 1x fur ribs and it REALLY looks sharp inside! The look is quite elegant and very befitting a 44 year old cruiser - gives it a touch of class :D

    I thought about that but realized that has never been a problem. I have never had the canvas top off and yet it doesn't get in the way. Nobody has been "banging their head" against the canvas top and it only requires a small amount of duck to enter or depart at the dock. I spend a great deal of time living aboard and I do not tolerate direct sun very well so having as much shade as possible on-deck is important to me.

    I boat on Lake of the Woods and typically spend 4 days to a week at a time living aboard. I don't tolerate direct sun very well (very fair complexion), appreciate the shade in the midday heat, and like to retain use of my deck in the rain. With a hardtop and side curtains, I would always have shade, be able to put the curtains up on only the sunny (or rainy) side, and not fumbling around trying to get zippers to line up in the dark, rain, or wind.

    I always appreciate your opinions Par!

    Bataan: See my comments above on construction methods. Thanks for the suggestions.
     
  7. PAR
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    PAR Yacht Designer/Builder

    I don't have an aversion to 2x4's and steel tubing, but I do the weight. I think the "scale" of the exposed structural pieces should match that of the rest of the boat, if for no other reason then to get the "look" right.

    How is the main cabin roof built? I'd use very similar dimensions and construction techniques on the "addition". My comments about foam and composites are just options.

    Me, I'd laminate a couple layers of really thin plywood, over temporary molds, maybe with bead board on the inside layer facing down, so it looks traditional. This would produce a self supporting roof panel that needs minimal beam requirements. This would be covered with 6 ounce cloth outside, but not have it's weave filled, so it looks much like canvas, but a lot more durable. Of course, it's painted after to protect it and reflect the sun off the roof. Because this type of roof wouldn't need close beam spacing, you could just place them at the stanchion locations, though this would look a bit "sparse", it does offer more headroom. On the other hand you could use an even beam spacing, but make the beams thinner then the main cabin, if headroom is an issue.

    There's lots of ways to do it and it sounds like a fun project. You don't need a steel frame around the edge, a wooden one will do just fine, at a fraction of the weight. Judging by the picture, she may have a weight gain issue as it is, so thinking light is always best.
     
  8. DianneB
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    DianneB Junior Member

    Now we're cooking Par! ;)

    The cabin roof is a molded fiberglass sheet turned down at the edges and supported by aluminum ribs and finished on the under side with a fabric headliner.

    I LIKE the idea of a arched roof without a central beam! That is a process I have done before. It could easily be done over curved wooden ribs in a wooden frame and would look pretty nice! A couple layers of very light ply, glassed over top, and painted would look like canvas. The under-side, finished in stained wood would be real classy!

    Having the roof as a pre-made piece (in the shop) simplifies the stanchions which I could either weld myself in stainless or having someone weld them up for me.

    I KNEW I asked the right people! :D
     
  9. DianneB
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    DianneB Junior Member

    Hummmm .... since the hardtop is wider than a sheet of plywood and plywood arcs easily only in the cross-grain direction, I need THREE sheets wide to span the beam and that means I need two latitudinal seams. At least with a ridepole, I can use two sheet joined at the ridge. That complicates things!
     
  10. Easy Rider
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    Easy Rider Senior Member

    Hi Di,
    What I would like to use for a light cabin on my OB is honeycomb board that's used in bulkheads and flooring in aircraft. Hard to find and it dos'nt bend AT ALL. Here is a cabin on a small'ish ob that looks ok, is light (not feather light) and easy to fabricate. You could laminate thin plywood (door skins) over a form and have a cabin top sheet curved in one dimension any curve you wanted. Use scrap door skin material for gussets on a wood framed structure to attach your laminated roof top. I'll leave the hard part up to you ...attaching the whole top to your boat.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Plywood will easily conform to the very big radius of your roof, so this isn't as big an issue as you might think, especially with thin plywood.

    Here's what I would do for a traditional looking roof. I'd make up a simple roof curve jig with a common crown, say 6" or what ever you choose that looks good. Some cheap particle board, OSB or whatever is what I'd cut up for the roof jig/mold. I'd use some 1/4" bead board (exterior rated) and lay this over the mold, with the beads facing down and aligned fore and aft. Yep, there will be a couple of seams, so you'll have two ridge poles, dividing the roof into three sections, the center and two outboard areas. This will hide the seams pretty good. If it was me, I'd notch these ridge poles so the roof beams would pass through from side to side without having to be cut.

    In fact, the ridge poles could be just pieced in-between the beams, for little more then seam (and wiring) hiding. The way these bead boards are made the seams are almost self hiding anyway, so you may be able to get away with no ridge poles. Over this I'd epoxy an 1/8" or 1/4" layer of plywood and I'd stagger the seams, which means more material waste, but a stronger, self supporting, curved roof. Lastly, I'd use a 2x2 around the edge just as a trim piece and to have something the beams can butt into. For the beams I'd probably laminate two different color woods, like white pine and dark cedar. The contrasting pieces in the laminated beams always looks nice.

    The easy way would be to make an angle iron perimeter frame, toss in some square tube cross braces, screw down some plywood, set it on some stanchion tubes, paint it and call it a day. This would be heavy, boring and likely able to hold rain and snow in the center, where it'll eventually sag.

    Actually, when you think about it, you could do it several ways. One way is to just strip plank the whole darn thing. You can rip the edge off of a 2x6 and use .75"x1.5" strips. Ease the bottom edges on each and it'll look a lot like bead board. Edge nail and glue to their neighbors (over a mold) and bingo and solid wooden roof, with some natural insulating properties, pre-shaped to the desired curve and ready to mount on stanchions.

    It's assumed you'll 'glass the outside for weather and environmental protection, on these wooden roof options.

    You could also double plank it with plywood ripped into say 3" or 4" strips. Again, 1/8" or 1/4" plywood laid on a mold in fore and aft strips (or diagonally), each butted to the next and carefully edge glued if desired. The outer layer glues down, of course would have it's seams offset by half the width of the first layer. The offset seams makes it water tight and the double layer of thin plywood would hold it's shape once the epoxy cured.

    You have lots of possible building methods, I'm just tossing a few out to see what spanks your sweet spot.
     
  12. Carteret
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    Carteret Senior Member

    The boat builders down my way use the 1/2" thick blue tongue and groove foam found at bldg supply houses and insert small diameter dowels in between the foam sheets to strengthen the panels connections. They then cut the foam sheets to the desired shape. To achieve a crown for the top or surface radius they palce the foam top on a set of sawhorses on top of 2x4's placing weights (concrete blocks) tied by strings with the strings transversing the top going past the edges with the weights hanging off the sides. The amount of crown for the top is adjustable by how much weight is placed etc. They then place fiberglass cloth with epoxy over the top and strings and when the epoxy has cured they cut the strings. They then flip the top over and glass the underside of the top. If hardware mounting is needed (hard spots for mounting, electronic boxes, etc.) they install aluminum sheetmetal plates in the surface in selected areas before glassing. They finish and fair the top before painting.
     
  13. DianneB
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    DianneB Junior Member

    Just to complicate matters, the forward 64" of the roof is a cylindrical section and the aft 78" tapes in width which requires a conical profile to maintain the ridge line and the eves as visually parallel. That will necessitate a longitudinal seam (through all layers) to make the transition from cylindrical to conical.

    I like the idea of finished wood on the underside but I guess I am going to have to frame it up to get a good idea how I want to sheet it.
     
  14. PAR
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    PAR Yacht Designer/Builder

    I'm not completely sure I follow you, but you can "tweak" thin plywood into shapes that would be possible with thicker sheets. It's difficult to picture without some more images, but I suspect you can have you cake and eat it too in regard to the shapes on this roof.
     

  15. BATAAN
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    BATAAN Senior Member

    Smart Fellers!! A+ for practical.
     
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