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Thread: Deck Camber?

  1. #36

    Default Re: Deck Camber?

    Quote Originally Posted by Jim Ledger View Post
    Theoretically you shouldn't be able to compound plywood, but in practice it's done all the time.

    Jim


    I was wondering about how this would work out. Thanks for posting the photo. I want to use 3/8" marine plywood with a layer of 1/4" teak glued over it. The camber in the boat I'm building (Nordic Folkboat) is constant (approximately 3/8" per foot) but because of the way the sheer creates a wider span, and because of the way the sheer rises up at the ends, it will be just like in your photo above. I'd planned to soak my plywood decking before installing it. Would that be a good idea or not? The beams are 10" apart. I just don't want it to end up with dips/humps between the beams.

  2. #37
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    Default Re: Deck Camber?

    Quote Originally Posted by George Ferguson View Post
    I was wondering about how this would work out. Thanks for posting the photo. I want to use 3/8" marine plywood with a layer of 1/4" teak glued over it. The camber in the boat I'm building (Nordic Folkboat) is constant (approximately 3/8" per foot) but because of the way the sheer creates a wider span, and because of the way the sheer rises up at the ends, it will be just like in your photo above. I'd planned to soak my plywood decking before installing it. Would that be a good idea or not? The beams are 10" apart. I just don't want it to end up with dips/humps between the beams.
    I wouldn't soak the plywood if it were me. The ply in the photo conformed to the shape of the deck frame without much coaxing. I wouldn't attempt applying teak to such a thin backer, though. Solid wood applied over plywood has a generally poor track record, judging from some of the threads posted here. A 5/8" thick deck will probably flex underfoot and eventually compromise the teak/ply joint.

    Jim

  3. #38
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    Default Re: Deck Camber?

    This is not too much camber to torture mildly. Use two layers of 1/4" and go a bit lighter on the teak.

  4. #39
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    Default Re: Deck Camber?

    Just throwing this out here, this is from Elco, when they made themboats of WWII

    DFD95FC1-9D09-4E2D-A9FD-5F370538A31B.jpg
    Steve Martinsen

  5. #40
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    Default Re: Deck Camber?

    Quote Originally Posted by Ian McColgin View Post
    I can't find it but there was an interesting article in WoodenBoat a decade or so back. The problem is that to get the deck to fit smoothly to each deck beam, the actual curve of each deck beam is different. Some boats have small enough differences that a little plane work will solve. Others not.

    A method that allows you to loft the upper curve of each deck beam is to draw the stations. Start with the center station where the height of the camber is the most. You mark a line one side to the other and mark the camber elevation at the center. Two long battens are then joined essentially making the upper sides of a shallow triangle.

    If you slide this structure bringing the apex to each beam end, the apex will describe the arc you need for the camber at that spot. Use the same joined battens at each station to get the arc for those deck beams. If you make the intervening deck beams from the station closer to the center station, they will be close enough to plane the fit.
    Never seen it done any other way. I thought that was standard practice; simple and basically fool proof.

  6. #41
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    Default Re: Deck Camber?

    There's a way for people who actually build boats.

    There's a way for people who theorize about building boats.

    And there's a few thousand ways that don't work.

  7. #42
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    Default Re: Deck Camber?

    Quote Originally Posted by ian mccolgin View Post
    there's a way for people who actually build boats.
    There's a way for people who theorize about building boats.
    And there's a few thousand ways that don't work.
    __

    Dreaming a schooner since 1988:

  8. #43
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    Default Re: Deck Camber?

    Here is a section from the Gougeon Bros book. Unfortunately, the Figures didn't come through. If you want to see the figures, you can download the book for free . . .



    Developing Deck Camber
    All decks are curved, or have camber, so that rain or boarding seas will easily run off. Usually, this camber is given in the plans as so many inches of height for the widest deck beam. Using only these two dimensions, we usually make up a deck tram to lay out the deck curvature mechanically for the largest deck beam and then each succeeding smaller beam. Figure 27-3 shows this process in detail.


    Figure 27-3 Laying out deck camber with a tram. Lay out the length of the largest deck beam (points A and B) on the lofting board or other suitable surface, such as a sheet of plywood. Draw a baseline between the two points for reference. Measured up from center of this baseline, mark the maximum deck height (point C). Typically this is 3" to 6" (75mm to 150mm) on a 10' (3m) wide boat. Drive a nail into the board at Points A and B. Make two straight-edged battens, each at least 12" (300mm) longer than the widest deck beam. Lay the battens on the layout with their ends meeting at Point C and their middles resting against the nails at Points A and B. Join the two battens at the center with a plywood gusset, leaving a small gap at the apex for use as a pencil guide. Holding a pencil in the gap, slide the tram from side to side against the nails drawing an arc the full width of the beam. As the beam widths (nail spacing) get smaller, the tram will always draw arcs in exact proportion to each other.


    Point C represents the lofted or projected deck centerline

    The battens should be long enough that each batten will reach from A to B
    Pencil
    Hold both battens tight against the nails at A and B

    A semicircle with its radius A equal
    to the maximum camber at the

    CL of deck.
    Divide a 90 arc into equal spacings.











    Figure 27-4 Geometric layout for deck camber.

    Divide the base line into the same number of sections as the arc 2 then join the corresponding points (as B, C, D) from the C
    L out.
    On the deck beam stock lay out the true
    width of the deck (half is shown for clarity). Erect the camber height A as a perpendicular at the CL. Then mark each half of the baseline, from the centerline to sheer, into the same number of sections as 2 . At these sections mark off the corresponding dimensions B, C, D perpendicular to the baseline. Finely fair a batten through your marks on both sides of the CL to obtain your deck camber curve.



    When you have to lay out only a few deck cambers, such as the bulkheads, you can lay out the camber geometrically. This procedure is explained in Figure 27-4.
    On narrow hulls, typical of multihull craft, you can shape all deck beams from a master pattern; all deck beams, no matter what their width, will simply be pieces of this one master arc. It is usual to use the geometric method to lay out the master pattern for the deck camber desired at the widest deck beam. Mark the master pattern with a centerline dividing the maximum deck width into two parts. Then match up this center with the intended centerline of any smaller beams, which you can then lay out.
    Some deck designs might have unusual shapes that will require full lofting to develop. This lofting usually does not have to be as extensive as that done on a hull because the curves will not be as complex. Also, the dimensional accuracy will not be so critical. (This is not to imply that it will not end up being as fair as the hull.) Good examples of some modern designs that need lofting are those that incorporate a “blister” in the middle of the deck that acts as a cabin-type device to give headroom down below.



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